A Review of the Science of Colorful, Plant-Based Food and Practical Strategies for “Eating the Rainbow”

Abstract

Over the past decades, thousands of published studies have amassed supporting recommendations to consume fruits and vegetables for physiological and psychological health. Newer research has emerged to suggest that these plant-based foods contain a plethora of not only vitamins and minerals, but perhaps, most importantly, phytonutrients. These phytonutrients have known pleiotropic effects on cellular structure and function, ultimately resulting in the modulation of protein kinases and subsequent epigenetic modification in a manner that leads to improved outcomes. Even though eating fruits and vegetables is a well-known feature of a healthy dietary pattern, population intakes continue to be below federal recommendations. To encourage consumers to include fruits and vegetables into their diet, an “eat by color” approach is proposed in this review. Although each individual food may have numerous effects based on its constituents, the goal of this simplified approach was to identify general patterns of benefits based on the preponderance of scientific data and known mechanisms of food-based constituents. It is suggested that such a consumer-oriented categorization of these plant-based foods may lead to greater recognition of their importance in the daily diet throughout the lifespan. Other adjunctive strategies to heighten awareness of fruits and vegetables are discussed.

Full text

Review Article
A Review of the Science of Colorful, Plant-Based Food and
Practical Strategies for “Eating the Rainbow”
Deanna M. Minich
1
,
2
1
University of Western States, 2900 NE 132nd Ave, Portland, OR 97230, USA
2
Institute for Functional Medicine, 505 S 336th St #600, Federal Way, WA 98003, USA
Correspondence should be addressed to Deanna M. Minich; deannaminich@hotmail.com
Received 27 September 2018; Revised 27 March 2019; Accepted 17 April 2019; Published 2 June 2019
Academic Editor: Stan Kubow
Copyright ©2019 Deanna M. Minich. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Over the past decades, thousands of published studies have amassed supporting recommendations to consume fruits and
vegetables for physiological and psychological health. Newer research has emerged to suggest that these plant-based foods contain
a plethora of not only vitamins and minerals, but perhaps, most importantly, phytonutrients. ese phytonutrients have known
pleiotropic effects on cellular structure and function, ultimately resulting in the modulation of protein kinases and subsequent
epigenetic modification in a manner that leads to improved outcomes. Even though eating fruits and vegetables is a well-known
feature of a healthy dietary pattern, population intakes continue to be below federal recommendations. To encourage consumers
to include fruits and vegetables into their diet, an “eat by color” approach is proposed in this review. Although each individual food
may have numerous effects based on its constituents, the goal of this simplified approach was to identify general patterns of
benefits based on the preponderance of scientific data and known mechanisms of food-based constituents. It is suggested that such
a consumer-oriented categorization of these plant-based foods may lead to greater recognition of their importance in the daily diet
throughout the lifespan. Other adjunctive strategies to heighten awareness of fruits and vegetables are discussed.
1. Introduction
While there continues to be debate about the inclusion of
meat, dairy, grains, and legumes in a healthy diet, there would
seem to be little disagreement in the scientific community that
eating fruits and vegetables is beneficial for one’s health.
Eating plant-based foods is part of many diverse dietary
patterns, including the well-studied Mediterranean diet [1],
vegan and vegetarian approaches, the hunter-gatherer (Pa-
leolithic) diet [2], and even the less well-studied, ketogenic
diet [3]. e quantity and quality of in vitro, animal, and
clinical data over several decades suggest that intake of fruits
and vegetables is associated with reducing chronic disease
risk, such as cardiovascular disease, diabetes, cataracts, cancer,
dementia, obesity, and others [4–7].
e search strategy for this review article was to start
with a scientific literature review of the health benefits of
fruits and vegetables, along with the predominant issues
surrounding deficiencies in intake. Secondly, the goal was to
organize the findings into a categorical system for ease of
understanding and application.
1.1. Phytonutrient Gap. Despite the widely known health
benefits of consuming fruits and vegetables, low intakes are
historically consistent, with recent data from the 2015 Be-
havioral Risk Factor Surveillance System indicating that
most adults (particularly men, young adults, and those living
in poverty) consume insufficient amounts [8]. Only nine
percent and twelve percent of American adults met the
recommendations for vegetables and fruits, respectively [8].
Moreover, a report [9] based on food consumption data
from the National Health and Nutrition Examination Survey
(NHANES) conducted in 2003-2004 and 2005-2006 found
that eight out of ten Americans fall short in every color of
phytonutrients (referred to as a “phytonutrient gap”), es-
pecially in the color category of purple/blue foods (88% of
people neglected to meet their daily serving).
Hindawi
Journal of Nutrition and Metabolism
Volume 2019, Article ID 2125070, 19 pages
https://doi.org/10.1155/2019/2125070

Over the years, several opinion leading health organi-
zations such as the American Institute for Cancer Research
[10], the American Heart Association [11], and the USDA
Food and Nutrition Service [12] have advocated eating “the
rainbow” of healthy food-based colors. e 2015–2020
Dietary Guidelines [13] emphasize a healthy eating pattern
across the lifespan that encourages variety and nutrient
density across color categories, especially dark-green and red
and orange vegetables. Dark-green vegetables are cited as
good sources of vitamin K, while the red and orange veg-
etables are recognized for their vitamin A content. Whole
fruits (fresh, canned, frozen, and dried forms) and 100%
fruit juice are also included. Federal government recom-
mendations depend on gender and age for intake but are
generally 1·1/2-2 cup equivalents of fruit and 2·1/2-3 cup
equivalents of vegetables daily [14]. Reduced rates of many
common cancers have been associated with the equivalent of
400–600 grams daily of fruits and vegetables [7].
1.2. Newer Documented Benefits. It has been known for some
time that the ingestion of plant foods is strongly correlated
with reduction of chronic disease [5]. Newer research
suggests that diets high in anti-inflammatory plant com-
pounds such as polyphenols and other phytochemicals may
help to offset pollutant toxicity [15, 16]. us, consuming a
diet rich in plants may help buffer one’s susceptibility to
disease risks associated with exposure to toxic pollutants in
the environment [15, 17].
Another less-recognized aspect to increased fruit and
vegetable consumption is that of psychological benefit.
Eating fruits and vegetables was shown to have a favorable
impact on psychological well-being in 12,385 Australian
adults studied longitudinally over twenty-four months using
a validated questionnaire to assess overall life satisfaction
[18]. Findings revealed that increasing fruit and vegetable
intake (for up to eight portions daily) was positively asso-
ciated with happiness, life satisfaction, and well-being, to the
extent that the improvements were equal in measure to the
psychological impact of transitioning from unemployment
to employment. Similarly, in a large population sample of
60,404 middle- and older-aged adults [19], food intake and
psychological distress assessed over almost three years of
follow-up indicated that baseline fruit and vegetable intake
at a certain threshold was associated with a lower prevalence
of psychological distress.
In addition to reducing psychological distress and en-
hancing psychological well-being, curiosity, happiness, and
creativity appeared to be changed in those eating fruits and
vegetables. In a study of 405 young adults [20], researchers at
the University of Otago in New Zealand found that those
who ate more fruits and vegetables over thirteen consecutive
days reported greater flourishing in daily life as assessed by
higher levels of well-being, intense feelings of curiosity, and
creativity, compared with young adults who ate less fruits
and vegetables. ese effects were not limited to the ex-
tended duration of intake. On days when young adults ate
more fruits and vegetables, there was a corresponding in-
crease in the defined markers of flourishing compared with
days when they ate less fruits and vegetables. Finally, in a
smartphone-based assessment logging, 1,044 completed
eating episodes, and it was found that, of fourteen different
main food categories, vegetable consumption contributed
the largest share to eating happiness measured across eight
days [21].
1.3. Revisiting Mechanisms. Understanding the role of
complex bioactives from foods in chronic disease is difficult,
considering it has been estimated that there are more than
25,000 bioactive food constituents [22]. Additionally, phy-
tonutrients are pleiotropic and have multiple effects on
cellular physiology, especially in the area of inflammation,
insulin sensitization, and stress response [23, 24]. Newer
research now suggests that phytonutrients play significant
roles beyond their protective, antioxidant activity [25]. ey
have been shown to have functional and structural capac-
ities, in addition to being cell signaling agents and mes-
sengers and modifying telomerase activity, as well as
partaking in epigenetic changes through histone modifica-
tion and demethylation [26, 27]. Due to their ability to
address multiple mechanisms simultaneously, phytonu-
trients may be especially helpful in chronic diseases. For
example, polyphenols have been suggested to be a potential
nutraceutical intervention in type 2 diabetes [28], where
there are several dysfunctional processes related to glucose
and lipid metabolism that impact a number of body systems.
1.4. Phytochemical Index (PI). A longstanding challenge has
been quantifying the complex array of phytochemicals in the
diet. While that continues to remain a research hurdle, there
are now other valuable metrics that can be used. e USDA
Nutrient Database [29] now includes food measurements for
flavonoids, proanthocyanidins, isoflavones, and carotenoids,
which cumulatively give a better estimate of a food’s phy-
tochemical content.
Phytochemical index (PI) is a relatively recent term,
introduced in the cited scientific literature by McCarty in
2004 [30], and is defined as “the percent of dietary calories
derived from foods rich in phytochemicals.” As outlined in
the article, those calories would be from several select plant-
based foods, including fruits, vegetables (excluding pota-
toes), fruit/vegetable juices, legumes, whole grains, nuts,
seeds, soy products, wine, beer, and cider, and foods derived
therefrom. Refined oils, sugars, and grains, along with potato
products, hard liquors, and animal products, would be
excluded from the index. While still a general estimate, the
PI could be a helpful marker in epidemiological studies. It
might be reasonable to envision such a marker in a
smartphone application whereby a consumer could input
their food intake to get a corresponding PI value. Moreover,
as the PI concept evolves, it is foreseeable that it could be
correlated directly to the colors of food.
Since PI was introduced in 2004, it has been used as a
research measure in a variety of studies. PI has been shown
to be inversely associated with body mass index, waist
circumference, waist-to-hip ratio, and plasma oxidative
stress [31]. A higher dietary PI was shown to have favorable
2Journal of Nutrition and Metabolism

effects on prevention of weight gain and reduction of body
adiposity in adults [32], along with improved lipids [33, 34],
and lowered risk of hypertension [35] and breast cancer [36].
As the field of personalized nutrition evolves along with
a better understanding of the mechanisms of phytonutrients,
there may be possibilities to do more selective phytoprofiling
or targeting of conditions to certain plant-based agents for
their disease-modulating effects [37].
1.5. Botanical Diversity and Color Density. Botanical di-
versity and food variety are relevant topics in the field of
phytonutrients. In a recent review, Pruimboom and Muskiet
[38] discussed the disparity between the plant diversity of
Homo sapiens’ diet of over 135,00 years ago at over 3000
species compared to the modern-day diet of which 400 plant
species are gathered, but only more than 100 are utilized for
food. Research suggests that greater variety of fruits and
vegetables may have more significant impact on health
markers like blood pressure, oxidative damage, and risk of
falls than a less-varied diet [39–42]. In an excellent review
article making a case for food diversity for the gut micro-
biome, Toribio-Mateas [43] recommends a “50-food chal-
lenge” chart to log intake of fresh fruits, vegetables, herbs,
and spices over a 7-day period. e intended goal is to help
individuals track their eating pattern for the benefit of
providing a wide range of prebiotic compounds, especially
polyphenols [44], from plant-based foods to feed a vast
spectrum of bacteria. Indeed, even small amounts of spices
have been shown to have prebiotic potential for the gut
bacteria, indicating the significance of concentrated sources
of phytonutrients [45].
Most plant-based foods are known to contain more than
one colorful pigment, which typically corresponds to a
phytonutrient or phytonutrient category, e.g., orange/beta-
carotene, green/chlorophyll, and purple/flavonoids. Since a
healthy eating pattern involves both a varied array (“nutrient
diversity”) and dense concentration of nutrients (“nutrient
density”) [46], it might be worthwhile to assess the different
phytonutrient pigments contained in one food as a way of
eating more “color density.” ose foods which have more
than one class of phytonutrient and perhaps more corre-
sponding colors (“greater color density”) would be those
which would be most desirable for inclusion in the diet.
Food listed according to their color density index is pro-
posed in Table 1.
1.6. Taking a Qualitative (“Eat by Color”) Approach to
Increasing Fruit and Vegetable Intake. While consuming
recommended quantities of fruits and vegetables continues
to be difficult for most people, it might be plausible to take a
qualitative color rather than a quantitative servings ap-
proach. e concept of eating the rainbow of healthful foods
would seem to be an effective strategy for assisting people in
improving their diet. It can be implemented by all ages
through a variety of methods. For easy reference and re-
membering, the importance of getting each color may be
associated with some general related health benefits [7].
Preliminary research suggests that there may be rele-
vance to the colors of fruits and vegetables and their effects
in the body. For example, Mirmiran et al. [48] examined
whether the colors of fruits and vegetables were associated
with cardiometabolic risk factors in 1,272 adults over three
years. Based on food frequency questionnaires, de-
mographics, anthropometrics, and biochemical measures, it
was found that higher intake of red/purple fruits and veg-
etables were related to lower weight and abdominal fat gain,
and yellow, green, and white fruits and vegetables were
associated with lipid parameters.
Moreover, in a Dutch prospective study over ten years,
it was found that higher intakes of white fruits and veg-
etables were inversely associated with incident stroke. For
each twenty-five gram per day increase in white fruits and
vegetables (e.g., apples and pears), there was a 9% lower
risk of stroke [49]. Along similar lines, the same research
group found that, with each twenty-five gram per day
increase in the intake of deep orange fruits and vegetables,
there was an inverse association with coronary heart
disease (CHD) [50]. Of these orange foods, carrots were
the largest contributor (60%) with a 32% lower risk of
CHD.
In this article, each of the different colors of foods will
be reviewed for their health properties for specific organ
systems or functions. While there is no exclusive classi-
fication of color for their physiological activities, these are
general patterns based on scientific research for the ease of
establishing a learning system and “art of eating” for the
average consumer. More specifically, each color category,
associated corresponding foods, phytonutrient content,
and conferred benefit(s) were determined based on the
preponderance of research publications. us, for the
purpose of ease in categorization, this review article fol-
lows these criteria:
(i) Red Foods and Inflammation. High in antioxidants
and red-food carotenoids (e.g., astaxanthin and
lycopene), anti-inflammatory properties, and im-
mune system modulation (e.g., vitamin C)
(ii) Orange Foods and Reproductive Health. Abundant
in carotenoids, endocrine-regulating activities, and
role in fertility through support of processes such as
ovulation
(iii) Yellow Foods and Digestion. Rich in fibers to support
a complex microbiome and assist in maintaining
gastrointestinal health through gastric motility and/
or digestive secretions
(iv) Green Foods and Cardiovascular Health. High in a
variety of nutrients for cardiovascular health, such
as vitamin K, folate, magnesium, potassium, and
dietary nitrates
(v) Blue-Purple Foods and Cognition. Polyphenol-rich
foods to assist with learning, memory, and mood
(flavonoids, procyanidins (monomeric and oligo-
meric form), flavonols (i.e., kaempferol, quercetin,
and myricetin), phenolic acids (mainly hydrox-
ycinnamic acids), and derivatives of stilbenes)
Journal of Nutrition and Metabolism 3

Table 1: Color density index (CDI) chart.
# Plant food Red
(lycopene)
Orange
(beta-carotene)
Yellow
(lutein/zeaxanthin)
Green
(folates)
Purple
(flavonoids)
1 Acorn squash X X X N/A
2 Almonds X X X X
3 Amaranth X X X N/A
4 Apricots X X X X
5 Artichokes X X X X
6 Arugula X X X X
7 Asparagus X X X X
8 Avocado (all commercial varieties) X X X X
9 Bananas X X X X
10 Basil (dried) X X X X
11 Beets X X X
12 Black beans X X
13 Blackberries X X X X
14 Blueberries X X X X
15 Broccoli X X X X
16 Brussels sprouts X X X X
17 Butternut squash X X N/A
18 Cabbage X X X X
19 Cantaloupe X X X X
20 Carrots X X X X X
21 Casaba melon X X N/A
22 Cashews X X X
23 Cauliflower X X X
24 Celery X X X X
25 Chinese cabbage (pak choi) X X X X
26 Chinese cabbage (pe-tsai) X X X X
27 Chives X X X X
28 Cilantro (coriander) X X X X
29 Cranberries X X X X
30 Cucumbers X X X X
31 Eggplant X X X X
32 Endive X X X
33 Feijoa X X X X N/A
34 Fennel X X X X
35 Figs X X X X
36 Flaxseed X X N/A
37 Fuji apples X X X X
38 Gala apples X X X X
39 Garlic X X X X
40 Golden delicious apples X X X X
41 Granny smith apples X X X X
42 Grapefruit X X X X X
43 Green and red grapes X X X (especially green) X
44 Green hot chili peppers X X X X
45 Green peas X X X X
46 Green peppers X X X X
47 Green snap beans X X X X
48 Guava X X X X
49 Hazelnuts X X X X
50 Honeydew melon X X X X
51 Iceberg lettuce X X X X
52 Jalapeño peppers X X X X
53 Jicama X X N/A
54 Kale X X X X
55 Kiwi X X X X
56 Kohlrabi X X X
57 Leeks X X X X
58 Lentils X X X
59 Mango X X X X X
60 Medjool dates X X X X (deglet noor)
61 Millet (cooked) X X X N/A
4Journal of Nutrition and Metabolism

Table 1: Continued.
# Plant food Red
(lycopene)
Orange
(beta-carotene)
Yellow
(lutein/zeaxanthin)
Green
(folates)
Purple
(flavonoids)
62 Nectarines X X X X
63 Okra X X X X
64 Onion X X X X
65 Oranges (all commercial varieties) X X X X
66 Oregano (dried) X X X X
67 Papayas X X X X X
68 Parsley X X X X
69 Pear X X X X
70 Pecans X X X X
71 Pine nuts (dried) X X X X
72 Pineapple X X X
73 Pistachios X X X X
74 Plums X X X X
75 Pumpkin X X X X
76 Pumpkin seeds (dried) X X X N/A
77 Quinoa X X X N/A
78 Radishes X X X X
79 Raspberries X X X X
80 Red cabbage X X X X X
81 Red delicious apples X X X X
82 Red hot chili peppers X X X N/A
83 Red lentils N/A X N/A X N/A
84 Red peppers X X X X
85 Red potatoes X X X X
86 Romaine lettuce X X X X
87 Russet (white) potatoes X X X
88 Rutabagas X X X X X
89 Savoy cabbage X X X X
90 Scallions X X X X
91 Sea vegetables (kelp) X X N/A
92 Serrano peppers X X X X
93 Sesame seeds (dried) X X N/A
94 Shallots X X X N/A
95 Snap peas X X X N/A
96 Sour red cherries X X X X
97 Soybeans, mature seeds X X X
98 Spaghetti squash X X N/A
99 Spinach X X X X
100 Spirulina X X N/A
101 Strawberries X X X X
102 Summer squash X X X X
103 Sunflower seeds (dried) X X N/A
104 Sweet cherries X X X X
105 Sweet potato, raw X X X
106 Swiss chard X X X X
107 Tangerines X X X X
108 Tomatoes X X X X X
109 Walnuts (English) X X X X
110 Watercress X X X X
111 Watermelon X X X X X
112 Yellow peaches X X X X
113 Yellow peppers N/A X N/A X X
114 Yellow plantain X X X N/A
115 Zucchini X X X X
e table is in the alphabetical order and contains many of the commonly consumed vegetables, fruits, grains, legumes, and spices. One or two main
phytonutrients were used to represent the colors: lycopene for red, beta-carotene for orange, lutein and zeaxanthin for yellow, folate for green, and flavonoids
for purple. e majority of information comes from the USDA National Nutrient Database [29], with some of the flavonoid information derived from the
USDA Database for Flavonoid Content of Selected Foods 3.1 [47]. e latter database is not as extensive as the former, so some of the foods on this table were
not included in that database. ese foods have an “N/A” listed under the “purple” column. ere were also a few foods for which the USDA National
Nutritional Database did not list the lycopene, beta-carotene, lutein, and/or zeaxanthin content, which corresponds to an N/A listed for those foods. Finally,
the table only designates that there is some quantity of these phytonutrients but does not designate which are highest in the color nor which of the colors is
more dominant for the particular color. Unless designated, the results are for the raw version of the foods.
Journal of Nutrition and Metabolism 5

Summaries of the colors, nutrients, and physiological
effects can be found in Table 2, while specific foods, their
nutrients, and health benefits are in Table 3. Although this
review uses generalized concepts about color, phytonu-
trients, and foods, it is important to remember that there are
thousands of (phyto)nutrients present in food. e in-
teraction between different phytochemicals that can be
found inherently in the whole, plant-based food, and their
interactions, is not accounted for in this overview. Certainly,
there can be interactions within the food itself as well as the
food with the gut microbiome; however, for the purposes of
cultivating improved dietary intake of plant-based foods as
the aim of this paper, these details were not addressed.
2. Red Foods and Inflammation
Red-colored fruits and vegetables are included in Table 2.
Red-colored foods tend to be high in certain (phyto)nu-
trients that may confer antioxidant, anti-inflammatory, and
immune-modulating activities such as ascorbic acid, lyco-
pene, astaxanthin, fisetin, and the wider class of anthocy-
anins. Chronic inflammation is closely associated with a
dysfunctional and dysregulated immune response, ulti-
mately resulting in a wide variety of conditions such as
cancers, neurological abnormalities, cardiovascular diseases,
diabetes, obesity, pulmonary diseases, immunological dis-
eases, and other life-threatening conditions [51].
Red-colored foods such as acerola cherry, rosehips, red
bell pepper, and tomatoes also tend to be some of the highest
vitamin C-containing foods [29]. Vitamin C (ascorbic acid)
is well known for its effects on the immune system, and in
states of increased inflammation, vitamin C levels tend to
decrease in the body [52]. Several studies in cell, animals,
and humans have suggested that red-colored foods and/or
their isolated constituents [53] may assist with reducing
systemic inflammation and bolstering immune status by
reducing infections, including watermelon [54], apples
[55–61], cherries [61–63], cranberries [57, 64, 65] pome-
granate [66–70], and raspberries [71–73].
2.1. Tomatoes. Tomatoes have been widely studied in a
variety of formats, from raw tomatoes to tomato juice, and
even further into isolated tomato-derived phytonutrients
like lycopene. ey are especially known for their abundant
levels of vitamin C, flavonoids (e.g., fisetin), and carotenoids
(e.g., lycopene) [74]. Since they are part of the Solanaceae
botanical family, there is commentary by consumer-directed
websites and organizations that their alkaloid content may
be inflammatory to individuals who are sensitive to those
compounds.
An animal study [75] concluded that both lycopene and
tomato powder supplementation given separately were
equally effective in reducing inflammatory and metabolic
issues that arise with a high-fat diet. Both supplemental
formats helped to reduce inflammatory and lipid markers,
mainly through a reduction in the phosphorylation levels of
IkB and p65. A group of 106 overweight or obese female
students at the Tehran University of Medical Sciences were
randomly assigned either 330 ml of tomato juice or water per
day for twenty days. Compared with the control group and
with baseline, serum concentrations of IL-8 and TNF-α
decreased significantly in overweight and obese female
subjects [76]. Other studies using tomato juice [77] or
tomato-based drinks [78] have shown beneficial effects on
inflammation. In another study with tomato juice, in-
dividuals with metabolic syndrome had a significant im-
provement in inflammation status and endothelial
dysfunction after having tomato juice four times a week over
a period of two months compared with the control group
[79]. Specifically, tomato products consumed with a high-fat
meal were effective at attenuating postprandial lipemia-
induced oxidative stress and associated inflammatory re-
sponse (notably, the rise in IL-6) in healthy individuals [80].
Tomato intake in any form, whether as raw tomatoes,
tomato sauce, or tomato sauce with refined olive oil, de-
creased plasma total cholesterol, triglycerides, and several
cellular and plasma inflammatory biomarkers, and increased
plasma HDL cholesterol and IL-10 concentrations [81].
However, the addition of the oil to the tomato sauce caused
greater changes of plasma IL-6 and vascular cell adhesion
molecule-1 (VCAM-1) and lymphocyte function-associated
antigen-1 (LFA-1) from T-lymphocytes and CD36 from
monocytes than after the other tomato interventions.
Overall, studies would suggest that tomato-based
products, particularly when included with a meal, may
offset inflammatory markers related to cardiometabolic
health and oxidative stress.
2.2. Strawberries. Strawberries, a rich source of anti-
inflammatory polyphenols such as anthocyanins, have
been shown to reduce postprandial meal-induced increases
in inflammation and oxidative stress in fourteen overweight
health adults, particularly when the strawberry drink was
consumed before the meal [82]. Schell et al. [83] found that
obese adults with knee osteoarthritis drank a reconstituted
freeze-dried strawberry beverage (50 grams daily) for twelve
weeks, and it was more effective at reducing serum bio-
markers of inflammation and cartilage degradation, IL-6, IL-
1β, and matrix metalloproteinase-3 (MMP-3), compared
with the control beverage.
Strawberry supplementation also significantly reduced
constant, intermittent, and total pain, which led to the re-
searchers concluding that dietary strawberries have signif-
icant analgesic and anti-inflammatory effects in obese adults
with established knee osteoarthritis. Overweight adults
(n�24) consumed a high-carbohydrate, moderate-fat meal
accompanied by either a strawberry or a placebo beverage in
a crossover design [84]. e strawberry beverage signifi-
cantly lessened meal-evoked postprandial inflammation as
measured by high-sensitivity C-reactive protein (hs-CRP)
and IL-6, in addition to reducing postprandial insulin
response.
irty-six subjects with type 2 diabetes were randomly
divided into two groups [85]. e treatment group con-
sumed two cups of freeze-dried strawberry beverage (50 g of
freeze-dried strawberry is equivalent to 500 g of fresh
6Journal of Nutrition and Metabolism

Table 2: Color of fruits and vegetables, select phytochemicals, and physiological effects.
Color Fruits Vegetables Select
phytochemicals Physiological effects
Red
Apples
Blood oranges
Cherries
Cranberries
Lingonberries
Nectarines
Pink grapefruit
Pomegranate
Raspberries
Red currants
Red pears
Red plums
Strawberries
Watermelon
Radicchio
Radishes
Red beets
Red bell peppers
Red cabbage
Red chard
Red jalapeño pepper
Red onion
Red potatoes
Tomatoes
Anthocyanins
Carotenoids
Ellagic acid
Ellagitannins
Fisetin
Flavones
Lycopene
Phloretin
Quercetin
(i) Anti-inflammatory
(ii) General antioxidant activity
(iii) Immune modulation
Orange
Apricots
Blood oranges
Cantaloupe
Kumquat
Mandarins
Mangoes
Nectarines
Oranges
Papaya
Passion fruit
Peaches
Persimmons
Tangerines
Carrots
Orange bell peppers
Pumpkin
Sweet potatoes
Turmeric
Yams
Alpha-carotene
Beta-carotene
Beta-
cryptoxanthin
Bioflavonoids
Carotenoids
Curcuminoids
(i) Antioxidant for fat-soluble tissues
(ii) Endocrine modulation
(iii) Role in ovulation and fertility
processes
Yellow
Apples (golden
delicious)
Asian pears
Bananas
Lemons
Pineapple
Star fruit
Corn
Ginger
Potatoes (Yukon)
Squash (acorn, buttercup, butternut,
summer, winter)
Yellow bell peppers
Yellow onions
Bioflavonoids
Bromelain
Gingerol
Lutein
Nobiletin
Prebiotic fibers
Rutin
Zeaxanthin
(i) Antioxidant
(ii) Enzymatic activity
(iii) Gastric motility and regulation
(iv) Reduce glycemic impact
(v) Role in fostering a healthy gut
microbiome
Green
Avocado
Brussels sprouts
Green tea
Green apples
Limes
Olives
Pears
Artichokes
Asparagus
Bamboo sprouts
Bean sprouts
Bell peppers
Bitter melon
Bok choy
Broccoli
Broccolini
Cabbage
Celery
Cucumbers
Edamame
Green beans
Green peas
Greens (beet, chard, collards, dandelion,
kale, lettuce, mustard, spinach, turnip)
Okra
Rosemary and other herbs
Snow peas
Watercress
Catechins
Chlorogenic acid
Chlorophyll
Epigallocatechin
gallate
Flavonoids
Folates
Glucosinolates
Isoflavones
Isothiocyanates
L-theanine
Nitrates
Oleocanthal
Oleuropein
Phytosterols
Silymarin
Sulforaphane
Tannins
eaflavins
Tyrosol
Vitexin
(i) Antioxidant
(ii) Blood vessel support
(iii) Role in healthy circulation and
methylation
Journal of Nutrition and Metabolism 7

strawberries) or macronutrient-matched placebo powder
with strawberry flavor daily for six weeks in a randomized
double-blind controlled trial. Freeze-dried strawberry sup-
plementation significantly decreased CRP and malondial-
dehyde at six weeks compared to the baseline.
In a crossover design, fourteen women and ten men were
randomized to a six-week strawberry or placebo beverage
followed by a high-carbohydrate/fat meal with assessments
for six hours postprandially [86]. High-carbohydrate/fat meal
responses after six weeks of the strawberry beverage showed
significantly attenuated inflammatory markers compared
with placebo. Specifically, consumption of the strawberry
beverage resulted in lower postprandial PAI-1 concentrations,
especially at six hours. IL-1 βwas also decreased in the
strawberry group, and IL-6 increased significantly from
baseline to six hours after the meal, following the placebo but
remained relatively flat following the strawberry beverage
from fasting to six hours. To summarize, strawberries, pri-
marily as a freeze-dried beverage, appears to mitigate the
inflammatory response over time and postprandially.
2.3. Beets. Beets provide a complex array of nutrients, but
the beetroot itself is especially rich in a class of compounds
known as betalains [87]. Betalains have been heralded as
important considerations in chronic diseases involving in-
flammation, oxidative stress, and dyslipidemia [87]. A small
clinical trial demonstrates the efficacy of the beet, prepared
as either a juice or cooked, for reducing inflammation in
hypertensive individuals. Specifically, hypertensive subjects
who took either raw beet juice or cooked beet in a crossover
design demonstrated that both forms of beetroot were ef-
fective in reducing systemic inflammation as assessed by
intracellular adhesion molecule-1 (ICAM-1), VCAM-1, hs-
CRP, IL-6, E-selectin, and TNF-α(P<0.05) [88].
3. Orange Foods and Reproductive Health
Orange-colored fruits and vegetables are listed in Table 2.
Orange-colored plant foods share common properties with
the red-colored ones with respect to their antioxidant ca-
pacity. e primary difference is the carotenoids associated
with this color class of foods, such as beta-carotene and beta-
cryptoxanthin. Carotenoid compounds are fat-soluble an-
tioxidants, stored in subcutaneous fat and in adipose tissue.
While carotenoids can be ubiquitously found throughout the
body due to the widespread occurrence of adipose tissue,
they can be allocated to different parts of the body for
particular functions [89].
ere appears to be localization of specific carotenoids in
certain parts of the body related to hormones and re-
productive health, most likely due to their antioxidant na-
ture [90, 91]. Oxidative stress is associated with infertility for
both men and women [92]. Carotenoids may be especially
important in ovaries [93]. Czeczuga-Semeniuk and Wolc-
zynski [94] found the presence of up to fourteen different
carotenoids (e.g., beta-carotene, beta-cryptoxanthin, echi-
nenone, and hydroxyechinenone) in the ovarian tissue of
100 women operated on for ovarian tumors.
Although it has not been confirmed in humans, animal
research in goats [95–98] suggests that even short-term
beta-carotene can enhance or modulate ovarian function
and progesterone synthesis. Furthermore, beta-carotene
may have endocrine-stimulating or modulating effects as
shown in prepubertal goats [99–101], given beta-carotene
supplementation compared with a control group: positive
changes in blood biomarkers such as total protein [99],
cholesterol [99], glucose [99], insulin [100], and tri-
iodothyronine [101] were noted. In support of the concept
emerging from studies in goats that beta-carotene may
influence the endocrine system, a longitudinal study [102]
in 1106 men and women followed for three years showed
that greater intake of dietary carotenoids, particularly those
found in orange foods, such as beta-carotene and beta-
cryptoxanthin, was associated with a reduced risk of insulin
resistance.
In cattle, the highest beta-carotene levels in the
plasma, corpus luteum, and follicular fluid were found
during pregnancy when there is maximal luteal function,
and the beta-carotene level of the corpus luteum was
significantly correlated with the weight and diameter of
corpus luteum [103]. While there is a paucity of human
data, previous studies have indicated that women with
endometriosis have lower intake of vitamin A than women
without endometriosis [104]. Certain carotenoids, such as
beta-carotene, are provitamin A compounds, and there-
fore, may be of use. Supplementation with beta-carotene
and other antioxidants in women has shown to reduce
time to pregnancy in couples treated for unexplained
fertility [105].
Carotenoids are also important for male fertility. Sperm
is susceptible to oxidative damage from the reactive oxygen
species they generate, together with the fact that they have a
high polyunsaturated fat content and a reduced capacity to
Table 2: Continued.
Color Fruits Vegetables Select
phytochemicals Physiological effects
Blue-
purple
Blackberries
Blueberries
Boysenberries
Figs
Huckleberries
Prunes
Purple grapes
Raisins
Eggplant
Plums
Purple bell peppers
Purple cabbage
Purple carrots
Purple cauliflower
Purple kale
Purple potatoes
Anthocyanidins
Flavonoids
Phenolic acids
Proanthocyanidins
Pterostilbene
Resveratrol
Stilbenes
(i) Antioxidant
(ii) Cognitive support
(iii) Healthy mood balance
(iv) Role in neuronal health
8Journal of Nutrition and Metabolism

repair DNA damage [106]. Beta-carotene was found to be
associated with sperm concentration in healthy, non-
smoking men [107]. In another study [108], beta-carotene
was one of the three antioxidants that significantly decreased
in seminal plasma of immunoinfertile men as compared to
levels in fertile men.
3.1. Wild Yam (Dioscorea). In traditional medicine, wild
yam is widely used to treat menopausal symptoms, most
likely due to its phytoestrogen content and corresponding
ability to stimulate ovarian estradiol synthesis [109–111]. In
one study [112], twenty-four healthy postmenopausal
women replaced their staple food of rice with 390 grams of
Table 3: Select foods, their (phyto)nutrient profile, and health benefits.
Color Food Some food formats researched Basic (phyto)nutrient profile Researched health benefits
Red Tomatoes Juice, powder, raw, sauce (prepared
with and without oil)
Carotenoids (e.g., lycopene),
flavonoids, vitamin C
(i) Reduction in inflammatory
markers
(ii) Reduction in postprandial
inflammation
(iii) Improvement in lipid markers
Red Strawberries Freeze-dried as beverage Polyphenols (flavonoids, phenolic
acids, tannins), vitamin C
(i) Reduction in postprandial
inflammation
(ii) Reduction in pain due to
osteoarthritis
Red Beets Cooked, raw juice Betalains (i) Reduction in inflammatory
markers
Orange Wild yam Cooked Phytoestrogens
(i) Increase in estrogen and
estrogen metabolites
(ii) Phytoestrogenic activity
Orange Carrots Not specified Alpha- and beta-carotene
(i) Decrease in rate of breast and
prostate cancer
(ii) Phytoestrogenic activity
(iii) Association with estrogen
metabolism
Orange Orange fruits Not specified Bioflavonoids, beta-carotene, beta-
cryptoxanthin
(i) Delay in ovarian senescence
(ii) Lower risk for endometriosis
Yellow Ginger Standardized extract Gingerols, shogaols (i) Decrease in nausea
(ii) Increase in gastric emptying
Yellow Citrus
(lemons) Juice, raw Hesperidin, nobiletin, rutin,
vitamin C
(i) Protective against gastric ulcer
(ii) Antidiabetic
(iii) Reduction in glycemic impact
Yellow Pineapple Juice Bromelain, serotonin (i) Enzymatic activity
Yellow Bananas Raw Prebiotic fiber, serotonin (i) Increase in bifidobacteria
(ii) Reduction in bloating
Green Leafy greens Raw, spinach Chlorophyll, folate, nitrates,
phylloquinone
(i) Reduction in blood pressure
(ii) Increase in nitric oxide
(iii) Increase in blood flow
Green Cruciferous
vegetables Not specified Glucosinolates, isothiocyanates,
sulforaphane
(i) Antioxidant action
(ii) Reduction in platelet
aggregation
(iii) Reduction in thrombus
formation
Blue-
purple
Concord grape
juice Juice Phenolic acids, stilbenes,
anthocyanins, proanthocyanins
(i) Improvement in spatial memory
and performance
(ii) Improvement in reaction time
on attention
(iii) Increase in calm ratings
Blue-
purple Blueberries Beverage, freeze-dried, raw
Flavonoids, procyanidins
(monomeric and oligomeric form),
flavonols (i.e., kaempferol,
quercetin, myricetin), phenolic
acids (mainly hydroxycinnamic
acids), derivatives of stilbenes
(i) Improvement in measures of
cognition
(ii) Benefit to mood
(iii) Improvement in
neuroplasticity
is table provides a summary of certain foods and accompanying animal and/or clinical research studies as discussed in this review article. Details on the
studies can be found in the respective color section in the text.
Journal of Nutrition and Metabolism 9

yam or sweet potato (control) in two of the three meals per
day for thirty days. Yam ingestion led to increases of 26% in
serum concentrations of estrone, while urinary concentra-
tions of the genotoxic estrogen, 16alpha-hydroxyestrone,
decreased by 37%. Along similar lines, a variety of Chi-
nese yam (Dioscorea opposite unb.) was shown to have
estrogenic effects in vitro and in vivo [113]. Although studies
are limited in food form, wild yam products are commonly
used in the dietary supplement industry for enhancing
progesterone levels.
3.2. Carrots (Daucus carota). Carrots (Daucus carota)
contain alpha- and beta-carotene [114], and extracts may
have (phyto)estrogenic activity [115, 116] or be associated
with estrogen metabolism [117]. While the mechanism(s)
remain(s) unknown, epidemiological studies suggest that
dietary carrot intake is associated with lower rates of breast
[118, 119] and prostate cancer [120]. While these are pre-
liminary findings, it would seem that, based on their ca-
rotenoid (especially beta-carotene) content, there could be
an implied association with ovarian health based on the
animal studies listed above, perhaps related to the con-
centration of carotenoids in the ovary.
3.3. Orange Fruits. Orange fruits include the citrus family
(e.g., mandarins, oranges, and tangerines) in addition to the
tropical orange fruits such as papaya, peaches, and persim-
mons. ere is a host of nutrients to be found in the different
classes, ranging from vitamin C and bioflavonoids to carot-
enoids such as beta-carotene and beta-cryptoxanthin.
Alarge study [104] of 70,835 premenopausal women as
part of Nurses’ Health Study II demonstrated a nonlinear
inverse association between higher fruit consumption,
particularly for citrus fruits, and risk of endometriosis.
Women who had ≥1 servings of citrus fruits/day had a 22%
lower endometriosis risk compared to those consuming <1
serving/week. Beta-cryptoxanthin, a carotenoid commonly
found in orange-colored fruits, was the only nutrient ex-
amined that correlated with the lower risk of endometri-
osis. Furthermore, Pearce and Tremellen [121] investigated
the influence of diet on the onset of natural menopause in
1146 premenopausal women followed for an average of
12.5 years. ey found that the age of natural menopause is
closely associated with dietary intake of beta-cryptoxanthin
and fruit. It was suggested that a diet containing ∼400 mcg
of β-cryptoxanthin per day from orange-colored fruits such
as mandarins, oranges, and peaches may have the potential
to delay ovarian senescence by 1.3 years. Overall, there is
good emerging data to suggest that orange fruits may
contain the essential carotenoids for healthy reproductive
function.
4. Yellow Foods and Digestion
Yellow foods are found in Table 2. ese foods may contain a
wide array of actives that benefit the gastrointestinal tract
and digestion, including bioflavonoid constituents that may
modify gastric microbial activity, such as H. pylori and the
propensity towards ulcers, or even the activity of cytochrome
P450 enzymes which can ultimately modify the intestinal
and/or hepatic detoxification of toxic compounds. Various
soluble, insoluble, and prebiotic fibers are used to impede the
release of simple carbohydrates into the bloodstream,
thereby lowering glycemic index. ey may also provide the
raw materials required as an energy substrate to be used by
the gut microbiome.
4.1. Ginger. Ginger is a long-recognized rhizome that
contains over 400 different chemical compounds, of which
gingerols and shogaols are widely discussed [122]. An ex-
tensive review of the literature suggests that ginger is helpful
for a variety of gastrointestinal disorders, ranging from
vomiting to dyspepsia to irritable bowel syndrome [122].
Most notably, ginger has been used traditionally for nausea
[123]. A study in healthy volunteers using a standardized
extract of ginger and artichoke promoted gastric emptying
in healthy volunteers without adverse effects [124]. Ginger
stimulated gastric emptying in healthy adults [125] and
gastric emptying and antral contractions in patients with
functional dyspepsia, with no impact on gastrointestinal
symptoms or gut peptides [126].
4.2. Citrus Fruits (Lemons). One of the distinctive features of
citrus fruits is that they are acidic, mostly due to their high
ascorbic acid content. is low pH may be helpful for di-
gestive health. Several studies have reported that the gly-
cemic response to starch-rich meals can be reduced by
20–50% with acidic drinks or foods [127]. Using an in vitro
model [127], it was shown that lemon juice consumed with
starch-rich foods resulted in a two-time lower breakdown of
starch compared with water, suggesting a strategy to reduce
the glycemic impact of high-starch meals.
Furthermore, consumption of citrus fruits has been
shown to be associated with reduced risk of esophageal and
gastric cancers [128, 129]. Various phytonutrients within
citrus fruits such as hesperidin [130], nobiletin [131], and
rutin [132] have been demonstrated to be protective against
gastric ulcer, suggesting that, either alone or in combination
with other agents, they could be useful therapeutics for
common gastrointestinal complaints [133]. Naringenin, a
flavonoid found in high concentrations in yellow citrus
fruits, has been reported to have several beneficial effects,
one of which involves antidiabetic activity. From a mech-
anistic point of view, naringenin has been shown to inhibit
gluconeogenesis by upregulating AMPK [134], in addition to
its influence on improving metabolic disturbances as shown
in ovariectomized mice [135].
4.3. Pineapple. Bromelain, a proteolytic enzyme found in
pineapple juice, may be helpful in metabolizing undigested
food remnants in the stomach [136, 137]. In one study,
drinking one liter of pineapple juice daily for three days was
found to be a useful strategy for dissolving food remnants in
patients undergoing endoscopic procedure for removal of
intragastric balloon [138]. Similarly, adding pineapple juice
10 Journal of Nutrition and Metabolism

to a polyethylene glycol-based solution for a colonoscopic
procedure improved the quality of colon cleaning [139].
While food studies are sparse, bromelain derived from
pineapple is often isolated for application in dietary sup-
plements marketed for enzymatic activity.
4.4. Bananas and Plantains. Depending on their degree of
ripeness, bananas contain considerable amounts of in-
digestible carbohydrates, which could serve as prebiotic
sources for the gut microflora. In one study [140], healthy
women without history of gastrointestinal disease were asked
to maintain their usual dietary habits for sixty days. ey were
randomly assigned to consume twice a day a premeal snack,
either one medium banana or one cup of banana-flavored
drink or one cup of water (control group). Stool samples were
collected, and gastrointestinal symptoms were also recorded.
Mean bifidobacteria levels were increased only in the banana
group both at thirty and sixty days of intervention, although it
did not reach a statistical significance. Analysis of the gas-
trointestinal symptoms records revealed significantly lower
bloating levels in the banana group, compared to controls, at
26–35 days (p�0.009) and 51–60 days (p�0.010).
In addition to providing a source of prebiotic fiber, both
plantains and bananas (and even pineapples) were highest in
the serotonin content of 80 different foods tested [141]. With
many neurotransmitters being formed in the gastrointestinal
tract, the implications of interaction with dietary neuroac-
tive substances remain unknown, yet an area of research that
provides promise.
5. Green Foods and Cardiovascular Health
Green foods are listed in Table 2. Green leafy vegetables are
particularly abundant in nutrients that may be beneficial for
heart health, including vitamin K (phylloquinone), mag-
nesium, potassium, naturally occurring nitrates, and folates
[142, 143]. Based on findings from a meta-analysis, Pollock
[144] indicated that 15.8% of cardiovascular disease (CVD)
risk could be reduced by “almost every day” consumption of
green leafy vegetables, which included those in the crucif-
erous variety. Convincing evidence from studies exists to
suggest that increasing daily consumption of vegetables and
fruits can reduce risk for hypertension, coronary heart
disease, and stroke [145]. Green leafy diets can be high in
polyphenol concentration and provide a variety in poly-
phenol subclasses, which may differentially affect car-
diometabolic risk factors [146, 147]. Flavonoid antioxidants
such as vitexin and others have cardioprotective effects and
can be found in green leafy vegetables like Swiss chard
[148–150].
5.1. Leafy Greens (Spinach). Leafy greens provide copious
nutrients for cardiovascular health, most notably, dietary
nitrates.
Short-term and even long-term (14 year) trials indicate
inorganic nitrate and nitrate-rich vegetables may have
vascular health benefits and lead to lowered CVD mortality
[151–153]. e consumption of nitrate-rich vegetables, such
as several of the leafy greens like spinach, has been shown to
promote nitric oxide bioavailability, reduce systemic blood
pressure, enhance tissue blood flow, modulate muscle ox-
ygen utilization, and improve exercise tolerance, thereby
potentially attenuating complications associated with lim-
ited oxygen availability or transport, hypertension, and the
metabolic syndrome [154, 155]. Some of the highest nitrate
containing green foods include celery, cress, chervil, lettuce,
spinach, and rocket [156].
Spinach contains phytochemicals that may help with its
cardiovascular benefits [157], especially nitrates. In one
study [158], twenty-seven healthy participants were ran-
domly assigned to receive either a high-nitrate (spinach;
845 mg nitrate/day) or low-nitrate soup (asparagus; 0.6 mg
nitrate/day) for seven days with a one-week washout period.
High- vs. low-nitrate intervention reduced central systolic
and diastolic blood pressure and brachial systolic blood
pressure.
5.2. Cruciferous Vegetables. While vegetables and fruits have
consistently shown benefit for reducing CVD risk, crucif-
erous vegetables specifically have been shown to be asso-
ciated with cardiovascular health [159]. Cruciferous
vegetable intake was inversely associated with reduced
cardiovascular mortality [159] and subclinical atheroscle-
rosis [160] and 15-year atherosclerotic vascular disease
deaths [161] in older adult women. Cruciferous vegetables
are identified by their high concentration of organosulfur
compounds such as isothiocyanates and glucosinolates
[160]. Sulforaphane is an isothiocyanate with recent data
indicating that its favorable effects in CVD are due to its
antioxidant and anti-inflammatory properties [162, 163] as
well as its ability to prevent platelet aggregation and reduce
thrombus formation in flow conditions [164].
6. Blue-Purple Foods and Cognition
Blue-purple foods are listed in Table 2. Studies indicate that
blue-purple foods are helpful for cognition and mood.
Favorable studies for blue-purple foods have been docu-
mented for blueberries and grapes, both of which contain
health-related phytonutrients, mainly polyphenols [165–
167]. In blueberries, polyphenols include flavonoids,
procyanidins (monomeric and oligomeric form), flavonols
(i.e., kaempferol, quercetin, and myricetin), phenolic acids
(mainly hydroxycinnamic acids), and derivatives of stil-
benes [165]. Grapes possess strong antioxidant activity due
to the variety of phytochemicals they contain, such as
phenolic acids, stilbenes, anthocyanins, and proantho-
cyanins (amounts vary based on the variety). ey have
been shown in vitro and in vivo to inhibit cancer cell
proliferation, reduce platelet aggregation, and lower cho-
lesterol [167].
6.1. Concord Grape Juice. Daily intake of Concord grape
juice over three to four months has been shown to improve
memory function in adults with mild cognitive impairment
[168]. Healthy mothers who consumed twelve ounces of
Journal of Nutrition and Metabolism 11

either Concord grape juice or an energy-matched placebo
daily for twelve weeks showed significant improvements in
immediate spatial memory and driving performance with
the grape juice compared with placebo [168]. ese effects
are not limited to those who are older in age or after chronic
consumption. Haskell-Ramsay et al. [169] found that 230 mL
purple grape juice improved reaction time on an attention
measure and increased calm ratings in twenty healthy young
adults compared with a sugar-matched control. While there
are many mechanisms postulated for why grape juice may be
helpful for the brain, one interesting mechanism is that it
seems to modulate brain-derived neurotrophic factor
(BDNF) as shown in an animal study [170].
6.2. Blueberries. Studies with animals suggest that blueberry
supplementation of the diet may help with cognitive tasks.
Willis et al. [171] found that supplementing aged animals at
2% of the diet (equivalent to ½ cup per day for humans)
improved performance in the radial arm water maze, the
Morris water maze, a step-down inhibitory avoidance task,
and a footshock-motivated 14-unit T-maze, along with re-
versing cognitive decline in an object recognition test.
In addition to animal studies, there are several clinical
trials demonstrating that blueberry may help cognition in
older adults [172]. In a study with thirteen men and twenty-
four women between the ages of 60 and 75 years, freeze-
dried blueberry (24 g/day, equivalent to one cup of fresh
blueberries) led to significantly fewer repetition errors in the
California Verbal Learning Test and reduced switch cost on a
task-switching test across study visits, relative to controls. A
single dose of a flavonoid-rich blueberry drink produced
significant improvements in the delayed recall of a pre-
viously learned list of words just two hours after con-
sumption in children aged eight to ten years compared with
a matched control [173]. A similar study [174] in seven- to
ten-year-old children found significant wild blueberry-
related improvements in cognition, such as final immedi-
ate recall at 1.15 hours, delayed word recognition sustained
over each period, and accuracy on high-demand cognitive
trials with increased interference at three hours. In a larger
clinical trial with 16,010 participants ≥70 years [175], greater
intakes of blueberries and strawberries were associated with
slower rates of cognitive decline, specifically equivalent to
delay cognitive aging by up to 2.5 years.
Aside from cognitive measures, inclusion of blueberry in
the diet may help with mood, as has been shown in children
and young adults [176]. Similar to the effects found for grape
juice, blueberry supplementation seems to have an effect on
cognition most likely through its effects on hippocampal
BDNF mRNA expression as shown in young rats [177]. In
addition, berries may help to reduce inflammation and
improve cell survival and neuroplasticity [178].
7. Practical Ways to Get More Colorful Fruits
and Vegetables
e concept proposed in this paper of “eating by color”
could be tracked through a questionnaire that allows an
individual to check boxes each time they have fulfilled their
daily requirement of a color corresponding to an acceptable
plant-based food item. is type of tracking method has
been used by the author with a high degree of receptivity by
individuals attempting to eat a healthier diet. Counting
colors rather than calories may be a more effective way to
engage long-term lifestyle change, although that concept has
yet to be tested. Using this simplified approach to food may
also help the category of restrained eaters, who tend to have
low self-esteem [179], higher stress [180], and disordered
eating patterns compared with nonrestrained eaters.
ere have been several methods to help individuals
increase their fruit and vegetable intake (Table 4). One of
them is to encourage greater variety. Ahern et al. [181] found
that vegetable consumption was promoted when variety and
frequency of vegetables were increased for children between
six and twelve months. Furthermore, a lunch study [182]
with students showed that having vegetable options leads to
increased propensity to choose vegetables and results in a
more balanced meal. Other ideas for greater variety could
involve nutrition education in school and implementation of
concepts through school gardens [183, 184].
Variety could also include different formats of foods. e
variations on raw, steamed, or boiled fruits and vegetables
are vast and encompass the use of spices, seasonings, and
herbs, blended fruit and vegetable drinks, herbal teas, fruit-
and-vegetable-infused waters, juices, and whole-food pow-
ders. In one study [185], people who did not often consume a
vegetable with lunch while dining out were 1.59 times more
likely to select the seasoned vegetables over steamed vege-
tables. erefore, given a choice, consumers may opt for a
seasoned vegetable. Furthermore, incorporating vegetable
juices and powders may also be helpful for those having
difficulty in making time to prepare vegetables. Drinking
vegetable juices or adding in juice powders based on tomato,
carrot, or spinach was shown to reduce DNA damage and
strand breaks in lymphocyte DNA in healthy individuals
after several weeks’ intake. e carrot juice intervention led
to significantly reduced oxidative base damage [186].
Another way to emphasize fruit and vegetable intake is to
eat more meals at home versus in a restaurant. Eating home-
cooked meals was associated with increased consumption of
fruits and vegetables and greater adherence to plant-based
diets such as the Mediterranean diet. ose eating from
home more than five times compared with less than three
times weekly consumed 62.3 grams more fruit and
97.8 grams more vegetables daily [187].
Establishing a supportive community may also be pivotal
to behavior change related to fruit and vegetable contact.
Role modeling by parents correlates with fruit and vegetable
intake by children [188]. Social relationships have been
associated with dietary behavior [189]. Conklin et al. [189]
found for both men and women that less contact with
friends was correlated with less variety of fruit and vegetable
intake, although the trend was more significant for men.
Finally, for the younger generation, it has been suggested
that bringing in elements of fruits and vegetables into video
game development could be one possible strategy to increase
receptivity to healthy eating [190].
12 Journal of Nutrition and Metabolism

8. Summary
In conclusion, there are numerous benefits to eating plant-
based foods, especially fruits and vegetables. Since the di-
etary intake continues to be less than what is recommended,
it is important to develop clinical strategies to consume a
greater quantity of these foods. Associating each of the colors
with a health benefit for ease of remembering to eat a variety
of colorful foods in one such approach may help people to
relate to the health properties of fruits and vegetables.
Ensuring the consumption of a variety of foods will enable
the individual to sample from thousands of phytochemicals
that may help to offset an increased risk of chronic disease.
Conflicts of Interest
e author declares no relevant conflicts of interest.
Acknowledgments
e author thanks Kendra Whitmire for compiling the color
density information in Table 1 and Jeffrey Bland, PhD,
Miguel Toribio-Mateas, BSc (Hons) NMed, PgDip, MSc, and
Benjamin Brown, ND, for providing the instrumental
feedback and insights.
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