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Functional Foods in Health and Disease 2017; 7(9);702-715 Page 702 of 715
Review Open Access
Functional Foods in fad diets: A review
Daniela Abigail Navaro1; Olga Raz1; Sharon Gabriel1; Vered Kaufman Shriqui1;
Esther Gonen1, Mona Boaz1,2.
1Department of Nutrition Sciences, Ariel University, (Ariel), Israel; 2Epidemiology and Research
Unit, E. Wolfson Medical Center, (Holon), Israel
Corresponding Author: Mona Boaz, PhD, Professor, Chair, Department of Nutrition Sciences,
Ariel University, Kvish 36, Ariel, 40700, Israel
Submission Date: March 18th, 2017, Acceptance Date September 27th:, 2017, Publication Date:
September 30th, 2017
Citation: Navaro D.A., Raz O., Gabriel S., Shriqui V.K., Boaz M., Functional Foods in Fad Diets:
A Review. Functional Foods in Health and Disease 2017; 7(9); 702-715
ABSTRACT
Fad diets can be defined as any diet making claims that are unrealistic and not supported by
evidence-based data. Having been developed since the early 19th century, fad diets promise drastic
weight loss and/or other unsubstantiated health claims, often omitting entire food groups. Their
popularity with the public makes them an important topic for nutritionists and clinicians, especially
in the framework of the obesity epidemic. Additionally, it is conceivable that components of fad
diets can indeed facilitate weight loss, even if the diet overall is without merit. The grapefruit diet,
the cabbage soup diet, and the human chorionic gonadotropin (hCG) diet are among the most
popular fad diets and are reviewed within this study not only in terms of the diet plan itself, but
also in terms of possible and known weight loss and health benefits provided by the foods on which
the diets are based. Bioflavonoids in grapefruit, including naringin, hesperidin, and bergamottin,
may benefit glucose homeostasis. Cabbage contains lutein, zeaxanthin, kaempferol, quercetin, and
apigenin, which have anti-inflammatory properties and improve both glucose homeostasis and fat
metabolism. The hCG diet is frequently supplemented with non-hCG preparations, which often
contains African mango, which has been shown to enhance weight loss by an unspecified
mechanism; astragalus root, which has antioxidant, anti-inflammatory, and peroxisome
proliferator-activated receptor-gamma receptor agonistic properties; arginine, which stimulates
lipolysis; glutamine, which has been shown to enhance weight loss, perhaps by altering the gut
microbiome; carnitine, which appears to facilitate weight loss; B12, which improves insulin
resistance; and niacin, which improves the dyslipidemia associated with overweight/obesity.
Presently, high quality clinical trials suggest that fad diets reduce weight in the short term due to
drastic caloric restriction rather than functional food properties. However, the proof of principle
has been demonstrated, and clinical trials of the functional foods utilized in fad diets are much
needed.
Keywords: functional foods, Fad diet, weight loss, naringin, hesperidin, and bergamottin
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 703 of 715
INTRODUCTION
Globally, obesity prevalence has risen steeply between the years 1980 to 2000, in both adults and
children [1-5]. Today, obesity prevalence remains unacceptably high: almost 70% of US adults are
overweight or obese, defined as a body mass index (BMI) ≥ 25 kg/m2 [6]. Of these, more than
30% are considered obese (BMI ≥ 30 kg/m2) and more than 6% are extremely obese (BMI ≥ 40
kg/m2). Just as distressing is the high prevalence of obesity (defined as BMI above the age and
sex-specific 85th percentile of the Centers for Disease Control and Prevention or World Health
Organization growth charts) among children aged 2-19 years, which is as high as 30% in some
countries [7]. Almost 17% of U.S. children are obese, defined as BMI above the age and sex-
specific 95th percentile of the same growth charts [3].
Being overweight or obese are conditions not exclusive to developed nations; in fact,
overweight and obesity prevalence has soared in developing countries, creating the double
healthcare burden of non-communicable diseases associated with obesity on the one hand, and
infectious diseases and under-nutrition on the other [4]. In developed countries, a massive diet
industry has been spawned by the increase in overweight/obesity prevalence, and was estimated
to have reached $61 billion in the US alone in 2014 [8].
Weight reduction interventions within the consensus of medical professions range from
lifestyle interventions, the most efficacious of which include caloric restriction, increased physical
activity, and behavioral changes [9], to pharmaceutical interventions [10] to bariatric surgery [11].
Additionally, a parallel "fad diet" industry has arisen.
A "fad diet" can be described as any diet making claims that are unrealistic and not supported
by evidence based data [12]. Other frequent characteristics of fad diets include emphasis on a
certain food or food group; omission of certain foods or food groups; claims of drastic weight loss
(> 1.5 kg/week); and other health claims [13].
Fad diets are not a new phenomenon. The market for weight loss diets arose with
industrialization, a time during which food became a market commodity [14]. In the early 19th
century, poet Lord Byron advocated vinegar as a remedy for obesity, claiming it reduced his
appetite; however, it has been suggested that the romantic author suffered from anorexia [15]. An
early version of a fad diet can be seen in the writings of Jean Brillat-Savarin, who blamed refined
flour and starch for obesity and in 1825 recommended a low carbohydrate, high protein diet for
weight loss [15]. In 1863, William Banting published "Letter on Corpulence Addressed to the
Public". In this treatise, Banting counseled the overweight to omit sugar, starch, fat, and beer from
their diets [16]. Perhaps the most dangerous fad diet was the "smoking diet" which was made
famous in the early 20th century, in which at least one tobacco company marketed cigarettes to
women as a means of controlling body weight [15].
Neither the safety nor the long-term efficacy of fad diets is supported in scientific evidence.
However, scientific and clinical communities should not ignore this phenomenon. The public
continues to utilize these diets in an attempt to control body weight, oblivious to the potential
health damage they may incur through these diets. In fact, these diets do result in short term weight
loss, as any calorie restriction would do. It is reasonable for nutritionists, biochemists, physicians,
and food scientists to familiarize themselves with some of the more popular of these fad diets in
order to understand their basis and to properly advise the public.
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 704 of 715
The Grapefruit Diet: Description of the diet
The Grapefruit Diet has been present in the United States since the early 20th century. At the time,
proponents of the diet claimed that enzymes or some other component in grapefruit possessed a
"fat burning" property. However, this enzyme was not identified [17].
A typical meal plan for this diet includes the following [15]:
• Breakfast: half of a grapefruit or 200 ml unsweetened grapefruit juice; a cup of tea or black
coffee, 2 eggs and 2 slices of bacon
• Lunch and dinner: half of a grapefruit or 200 ml unsweetened grapefruit juice; 200 g meat,
poultry or fish cooked as desired; unlimited "non-starchy" vegetables, black coffee or tea
Some versions of the diet allow for an additional 200 ml vegetable juice and/or skim milk to
be consumed during the day.
This is a very low calorie, low carbohydrate diet. Depending on the version of the diet
followed, it may provide as few as 800 kcal/day.
Bioactive Qualities of Grapefruit
Grapefruit (citrus paradise) is a natural hybridization of pomelo and orange belonging to the large
Rutaceae family of citrus [19].
Grapefruit is relatively low in calories (less than 50 kcal/100 g), being high in pectin, an
insoluble fiber that, in large amounts, is capable of laxative qualities [20]. These qualities may
explain the weight loss properties attributed to grapefruit. Additionally, grapefruit provides large
amounts of vitamin C, vitamin A, and antioxidants lycopene in pink grapefruit, beta carotene,
xanthin, and lutein. Grapefruit, together with other citrus fruits, has been shown to possess highly
active antioxidant activity on several assays [21].
Additional bioactive compounds in grapefruit include flavonoids - especially naringin and
hesperidin, furanocoumarins, in addition to bergamottin and 6'7'-dihydroxybergamottin [22-24].
Citrus-derived flavonoid supplementation has been shown to improve insulin sensitivity and
to prevent hepatic steatosis and dyslipidemia, apparently via inhibition of hepatic fatty acid
synthesis together with increased fatty acid oxidation [25]. Furthermore, citrus flavonoids have
been shown to attenuate the inflammatory response in adipose tissue and in the liver, thereby
having the potential benefit to treat and prevent obesity, diabetes, hypertension, and metabolic
syndrome [26, 27].
One of the most important citrus bioflavonoids is naringenin, which occurs in both an
aglycone and glycoside form. Naringenin has been shown to participate in carbohydrate
metabolism; specifically, naringenin has been shown to inhibit gluconeogenesis from lactate plus
pyruvate, alanine, and dihydroxyacetone [28]. In vitro studies have demonstrated that naringenin
participates in the induction of peroxisome proliferator-activated receptors (PPAR)-regulated fatty
acid oxidation genes, including Cytochrome P450 4A11 (CYP4A11) and uncoupling protein 1
(UCP1) while inhibiting liver X receptor (LXR) alpha–regulated lipogenesis genes, such as the
first apoptosis signal (FAS) gene. The net result of this effect is the increased cholesterol
production coupled with increased fatty acid oxidation [29].
Obese cats were fed a diet supplemented with a combination of naringenin and hesperidin in
one arm of a crossover study. Reductions in plasma acute phase protein and peripheral blood
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 705 of 715
mononuclear cell interferon (INF)-gamma levels suggest that these polyphenols could ameliorate
the inflammatory state associated with obesity [30].
Because dietary polyphenols including bergamot have been shown to reduce nonalcoholic
fatty liver disease (NAFLD), its use was studied in a rat model of pediatric metabolic syndrome
and NAFLD. Indeed, drinking water supplemented with bergamot curtailed obesity and blunted
increased blood glucose and triglyceride levels in these cafeteria diet fed rats. Significantly,
NAFLD was prevented, apparently by stimulating lipophagy [31]. In a small study with human
subjects, supplementation with a combination of polyphenols including bergamot was associated
with improved lipid profile and reduced oxidative stress; however, a decline in body weight was
not observed [32].
In a study designed to investigate interventions for insulin resistance, male Wistar rats fed a
high fat and sucrose diet were assigned to supplementation with helichrysum extract,
grapefruit extract or no supplementation (controls). Rats supplemented with either grapefruit or
helichrysum extract exhibited less insulin resistance, oxidative stress, and inflammation, in
addition to gaining less body weight than controls [33].
Human Studies
In a randomized clinical trial, obese adults with no comorbidities were instructed to consume a
calorie restricted diet and either ½ grapefruit, one glass of unsweetened grapefruit juice, or bottled
water 20 minutes before each meal. Weight loss did not differ significantly between groups at the
end of follow-up, nor did any anthropometric measures [17]. All three groups lost approximately
7% of the baseline body weight, indicating that pre-meal satiating strategies can be an effective
weight loss strategy.
In contrast, a clinical trial conducted in 91 obese adults found greater weight loss among
subjects exposed to grapefruit or grapefruit products than placebo [34]. The study randomized
participants to one of four interventions: 1) 207 ml of apple juice plus placebo capsules (control);
2) grapefruit capsule plus 207 ml apple juice; 3) 237 ml grapefruit juice plus placebo capsule; 4)
1/2 fresh grapefruit with a placebo capsule. Interventions were consumed prior to every meal. At
the end of the 12-week follow-up, subjects with the metabolic syndrome exposed to grapefruit in
any format (capsules, juice or fresh fruit) lost significantly more weight than participants in the
control condition.
Consistent with these results, citrus polyphenolic extract including grapefruit extract was
found to increase fat loss in a 12-week, randomized, placebo-controlled clinical trial in overweight
adults [35].
The Cabbage Soup Diet: Description of the diet
As the name suggests, the cabbage soup diet permits an unlimited intake of cabbage soup. A
number of variations on the cabbage soup recipe have been publicized, but most of these recipes
include, in addition to cabbage: onions, tomatoes or tomato juice, celery, and carrots.
The 7-day meal plan for the cabbage soup diet permits unrestricted cabbage soup intake
together with combinations of foods that are claimed to facilitate and maximize weight loss [36]:
• Day 1: cabbage soup and raw fruit but not bananas
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 706 of 715
• Day 2: cabbage soup and raw or cooked vegetables but not potatoes
• Day 3: cabbage soup and raw fruit and vegetables but not bananas or potatoes
• Day 4: cabbage soup, skim milk, and as many as eight bananas
• Day 5: cabbage soup, six tomatoes and 565g beef.
• Day 6: cabbage soup, unlimited beef, and unlimited vegetables (excluding potatoes)
• Day 7: cabbage soup, brown rice, and sugar-free fruit juice
The diet provides much less than 1000 kcal/day on Days 1-3, about 1000 or slightly more on
Days 4 and 7, and more than 1200 kcal on Days 5 and 6. Though exercise is discouraged on this
diet, a weight loss of 4.5 kg/week or more is promised [36].
Bioactive Qualities of Cabbage
The cabbage soup recipes used in this diet plan are based on white (rather than red) cabbage.
According to the United States Department of Agriculture (USDA) National Nutrient Database
[37], 100 g shredded white cabbage provides 23 kcal, 1.9 g fiber, and 1.3 g protein. Cabbage is
rich in vitamin C, providing 38 mg, or 41-50% percent of the Recommended Dietary Allowance
(RDA); and vitamin K, providing 110 mcg, which or 60-67% of the RDA. A 100 g serving of
white cabbage also contains lutein and zeaxanthin (27 mcg) in addition to flavonoids kaempferol
(1.2 mg), quercetin (3.9 mg), and apigenin (0.04 mg) [38].
In an animal model of non-alcoholic fatty liver disease (NAFLD), supplementation with lutein
resulted in a reduction of fat mass but not body weight in rats that were fed a high fat diet. Lipid
profile was improved, perhaps through the increased peroxisome proliferators activated receptor
alpha and sirtuin expression. Insulin sensitivity was also improved with an increased expression
of insulin receptor substrate-2, phosphatidylinositol 3-kinase, and glucose transporter-2 at both
gene and protein levels (39). Zeaxanthin produced anti-inflammatory effects by inhibiting nuclear
factor kappa B (NF-κB) activity and restoring inhibitor kappa B alpha (IκB-α), and while this was
demonstrated in an animal model of alcoholic fatty liver disease, the protein expression of NF-κB
inhibitor IκB-α has been shown to be lower in aorta from obese mice, suggesting a role for
inflammation in the pathogenesis of chronic diseases associated with obesity; furthermore, NF-κB
inhibition has been associated with the reduced expression of several pro-inflammatory proteins,
many of which are elevated in obesity [40-42].
Obesity has been characterized by low grade, chronic inflammation [43]. It is through the
inhibition of several inflammatory pathways that the flavonoid kaempferol, which is abundant in
white cabbage, may be beneficial in treating obesity. Inflammatory mechanisms inhibited by
kaempferol include expression of interleukin (IL)-1 beta and tumor necrosis factor by lowering
messenger RNA (mRNA) transcription of these cytokines [44]; suppression of tumor necrosis
factor (TNF) -induced IL-8 promoter activation and gene expression [42]; and inhibition of the
Janus kinase (JAK)3 signaling pathway, which inhibits IL-4 and IL-2 mediated outcomes [45].
The flavonoid quercetin, which is also abundant in white cabbage, has been shown to improve
insulin resistance and glucose tolerance and to reduce body weight, specifically, body fat, in rats
fed a high fat diet [46]. Quercetin produced weight and visceral fat loss in another animal model,
associated with reduced lipid accumulation in adipocytes together with increased carnitine
palmitoyltransferase 1α mRNA expression but decreased PPAR-γ and CCAAT/enhancer binding
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 707 of 715
protein in adipose tissue [47]. In another model of the high fat diet in mice, intraperitoneal
injections of rutin, the glycoside of quercetin, was shown to inhibit the anticipated increase in
adipocyte size. Weight and fat mass gain was prevented without accompanying changes in lean
body mass or food intake. Additionally, rutin treatment was associated with improved glucose
tolerance and insulin sensitivity together with reduced blood insulin levels [48].
On the other hand, mice fed a high fat diet and supplemented with either 0.05% or 0.1%
quercetin did not exhibit reduction in body weight; however, both dose groups showed an increase
in lean body mass. Only the lower dose group showed reduction in epididymal fat. These changes
were accompanied by reduced markers of inflammation [49]. Similarly, quercetin did not reduce
body weight or fat mass, but did improve serum glucose homeostasis in mice fed a high fat, high
sucrose diet for six weeks [50].
Another bioactive flavonoid found in white cabbage is apigenin, which has been shown to act
as a PPARγ activator and modulator. Apigenin-activated PPARγ decreases NF-κB activation. In
an obese mouse model, apigenin decreases pro-inflammatory cytokines, reducing inflammatory
cell infiltration in both the liver and adipose tissue. This improves glucose tolerance and reduces
the overall inflammatory response associated with obesity [51].
Obese mice were fed a high fat diet with or without apigenin supplementation. Apigenin
supplementation was associated with improved lipid profile and markers of liver function, though
neither food intake nor body composition was changed. Additionally, apigenin was associated with
reduced blood glucose levels, improved glucose balance, and lower levels of pro-inflammatory
markers [52].
Human Studies
No randomized clinical trials of the cabbage soup diet or of cabbage have been reported in medical
literature as of 2017. In a pilot study, participants were randomized to dietary enrichment with a
specially prepared fruit/vegetable drink or a commercially available vegetable juice that included
cabbage extract. The specially prepared fruit/vegetable drink was superior to the commercial
vegetable juice in terms of normalizing the lipid profile; however, subsequent analysis revealed
that superiority had in fact not been shown [53, 54]. Change in body weight or composition was
not reported in this study.
In early work on the satiety index, the Cabbage Soup diet was cited as an example of including
a high satiety, low calorie food source to produce weight reduction [55]. However, the ability of
this diet to produce weight loss compared to an isocaloric alternative has not been demonstrated.
The HCG Diet: Description of the diet
Frohlich's Syndrome, also known as adiposogenital dystrophy, is a rare metabolic disease
associated with hypothalamic tumors, which may increase appetite and depress gonadotropin
secretion. Consequently, this disorder is characterized by obesity and growth retardation, with
impaired development of the genitalia [56]. Endocrinologist ATW Simeons treated patients with
this syndrome with intramuscular injections of human chorionic gonadotropin (hCG). He noted
that this treatment resulted in a reduction in fat mass and a change in fat distribution, even in cases
where weight loss was not achieved. This observation appears to have inspired him to test this
treatment in otherwise healthy obese adults. Using a very low calorie diet (500 kcal/day) together
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 708 of 715
with daily hCG injections (125 IU/day), Simeons reported great success in achieving weight loss
in his subjects, noting that fat mass was reduced without loss of lean body mass [57]. Interestingly,
subsequent studies have not been able to duplicate the hCG-associated weight loss reported by
Simeons [58].
While there are many versions of this diet, menu plans typically divide food intake into two
meals. At lunch the dieter consumes 100 grams of a low fat protein (chicken breast, fish, turkey,
etc.), one serving of a vegetable, one fruit, and a serving of starch. This meal is repeated at dinner
[59].
Legitimately used in assisted fertility, hCG has not been approved by the US Food and Drug
Administration (FDA) for weight loss. In fact, the FDA, together with the Federal Trade
Commission, have issued a warning that over the counter HCG products marketed as weight loss
aids are unproven and illegal. These organizations have jointly issued warning letters to companies
illegally marketing over-the-counter hCG products labeled for weight loss [60]. Despite this, a
variety of hCG preparations, some of which are crude or degraded and some of which actually
contain very little or no hCG, are marketed to the public for weight loss. These preparations can
be administered via intramuscular or subcutaneous injection, but some offer oral or nasal
administration [61].
Some of the non-hCG preparations include the African mango or its extract (Irvingia
gabonensis). This supplement has been identified as a popular supplement for weight loss [62]. In
a systematic review of African mango for weight reduction, three randomized clinical trials were
identified, all of which observed significantly greater weight loss in treated vs. untreated
individuals; however, the study quality was poor, precluding recommendation of this supplement
for the treatment of obesity [63]. The astragalus root is also found in many non-hCG preparations,
and has antioxidant, anti-inflammatory, and PPAR-gamma receptor agonistic properties which
may improve insulin sensitivity and glucose homeostasis [64]. Both animal models and in vitro
studies have shown that astragalus root is associated with improved measures of metabolic control,
including normalized levels of glucose, insulin, and blood lipids. Furthermore, astragalus root has
been shown to attenuate leptin resistance [65].
Arginine and glutamine are amino acids frequently included in some non-hCG preparations.
A stimulator of lipolysis, L-arginine participates in the oxidation of fatty acids to CO2 and water
by increasing PPAR-gamma coactivator-1 alpha (PGC-1 alpha) expression. Lipid metabolism and
energy balance are further acted upon by L-arginine via increased 5' adenosine monophosphate
(AMP)-activated protein kinase (AMPK) expression and activity. Significantly, dietary arginine
supplementation has been shown to reduce white adipose tissue in a number of animal models and
in obese humans with type 2 diabetes. Animal studies have shown that supplementation with L-
arginine is associated with reduced perigonadal fat deposits and improved glucose homeostasis
compared to mice fed an isocaloric diet. This was observed despite the relative hyperphagia
observed in the arginine-supplemented animals, suggesting a significant decrease in feed
efficiency together with increased energy expenditure [66, 67]. Glutamine supplementation has
been shown to enhance weight loss in overweight or obese women, accompanied by a non-
significant 20-% decrease in hyperinsulinemia [68]. It is possible that one mechanism through
which glutamine enhances weight loss is by altering the gut microbiome. In a short-term pilot
study in which overweight or obese adults were randomized to supplementation with glutamine or
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 709 of 715
alanine, subjects in the glutamine group exhibited alterations in the composition of gut microbiota.
Significantly, there was a significant decrease in the Firmicutes:Bacteroidetes ratio, a biomarker
associated with weight loss [69].
Perhaps due to its role in fat metabolism, carnitine is often included in non-hCG preparations.
A large meta-analysis including data for more than 900 human subjects indicates that carnitine can
significantly facilitate weight loss. Compared to controls, carnitine supplemented subjects lost
approximately 1.33 kg and 0.47 kg/m2 BMI from baseline measures [70].
Two B-vitamins, B12 and niacin, are frequently listed as ingredients in non-hCG preparations.
In a large cross-sectional analysis in white British women at the 28th week of pregnancy, inverse
associations between blood levels of vitamin B12 and both BMI and markers of insulin resistance
were observed [71]. However, this association cannot be interpreted as causal because exposure
and outcome were measured simultaneously.
Niacin is also frequently included in no-hCG supplements. While niacin has been shown to
benefit the dyslipidemia often associated with obesity, its role as an anti-obesity intervention is
less clear. Metabolic syndrome patients were assigned to treatment 1500 mg extended-release
niacin or a placebo. Niacin was associated with a 56% increase in adiponectin together with a 27%
increase in leptin, but no changes in measures of inflammation or endothelial function were
observed; in fact, glucose homeostasis deteriorated [72]. Niacin-induced pancreatic islet
dysfunction may be modulated through the activation of the islet beta-cell G-protein-coupled
receptor, (GPR) 109a-induced pathways involving reactive oxygen species, PPAR-gamma and
uncoupling protein (UCP) 2 pathways [73]. Niacin supplementation has been shown to stimulate
the expression of genes involved in carnitine uptake and to replenish depleted carnitine levels in
obese rats, presumably via PPAR-activation [74].
Human Studies
A systematic review of randomized clinical trials comparing the hCG diet identified 12 studies of
good methodological rating. One reported that HCG was a useful adjunct while the remaining 11
did not detect a benefit of hCG treatment beyond the calorie restriction inherent in the diet.
Superior weight loss, fat distribution, hunger, or wellbeing did not differ between hCG-treated
patients and controls [75]. There appears to be little evidence for the efficacy of hCG as treatment
for obesity [76].
Summary and Conclusions
There are a number of mechanisms through which substances in food specific fad diets might
contribute to efficacy. Flavonoids such as naringenin and bergamot in grapefruit, kaempferol in
cabbage and the amino acids arginine and glutamine (frequently included in non-hCG
preparations) improve glucose homeostasis. Quercetin in cabbage and astragalus in non-hCG
preparations have anti-inflammatory properties. Thus, a “proof of principle” has been identified
for a number of these bioactive ingredients. However, long term randomized clinical trials of good
quality are necessary to demonstrate the efficacy of these diets independent of caloric restriction.
Identifying bioactive ingredients with high efficacy in facilitating weight reduction would permit
the use of these products in the framework of safe and adequate dietary patterns. Until such studies
are available, it would be prudent to encourage overweight or obese individuals to consume varied
Functional Foods in Health and Disease 2017; 7(9);702-715 Page 710 of 715
and nutritious diets in accordance with accepted guidelines to facilitate prudent weight loss. In
conclusion, the weight reduction achieved by fad diets is achieved primarily by drastic calorie
restriction rather than the phytochemicals presented in food. Nevertheless, because functional
foods used in these diets are conceivably useful in weight reduction, high quality randomized
clinical trials are needed to examine their efficacy in weight reduction in overweight/obese
humans.
Abbreviations: AMP: 5' adenosine monophosphate; AMPK: AMP-activated protein kinase;
CYP4A11: Cytochrome P450 4A11; FAS: First apoptosis signal; hCG: human chorionic
gonadotropin; IL: Interleukin; INF: Interferon; JAK: Janus kinase; LXR: Liver X receptor; mRNA:
messenger RNA; PGC1-alpha: Peroxisome proliferator-activated receptors (PPAR-gamma)
coactivator-1 alpha; PPAR: Peroxisome proliferator-activated receptors; TNF: Tumor necrosis
factor; UCP1: Uncoupling protein 1; UCP2: Uncoupling protein 2
Authors’ contributions: M. Boaz and A. Navaro conceived of and designed the review. M. Boaz,
O. Raz S. Gabriel, and V. Kaufman-Shriqui participated in drafting the manuscript. E. Gonen
reviewed the manuscript and all authors were engaged in the manuscript work. M. Boaz and A.
Navaro have primary responsibility for the final content. All authors have read and approved the
final manuscript.
Acknowledgements and funding: There is no funding to declare.
Competing interests: None of the authors have competing interests to declare.
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