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Food Science & Nutrition Technology
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Pinto Beans and Green Beans Result in Comparable Glycemic Control in Adults with Type 2 Diabetes:
A Randomized Pilot Trial
Food Sci & Nutri Tech
Pinto Beans and Green Beans Result in Comparable Glycemic
Control in Adults with Type 2 Diabetes: A Randomized Pilot Trial
Hutchins AM*1 and Winham DM2
1Department of Health Sciences, University of Colorado, Colorado Springs, USA
2Department of Food Science & Human Nutrition, Iowa State University, USA
*Corresponding author: Andrea Hutchins, Department of Health Sciences, University of
Colorado Colorado Springs, Colorado Springs, CO, USA, Tel: +01-719-510-1395; Email: Andrea.
Hutchins@uccs.edu
Research Article
Volume 5 Issue 1
Received Date: February 25, 2019
Published Date: March 04, 2020
DOI: 10.23880/fsnt-16000211
Abstract
Aims: Glucose control is essential to slow disease progression in people with type 2 diabetes mellitus (T2DM). The acute
effects of dry bean consumption on glucose control are well established, but their long-term effects in daily diets are less
known.
Methods: The effect of daily consumption of ½ cup pinto beans, compared to ½ cup green beans, on fasting glucose, postprandial
glucose and hemoglobin A1c (HbA1c) in adults with T2DM was examined. After a 2-week wash-in period, 13 participants
were randomized to two 12-week long treatments: pinto beans and green beans. Before and after each intervention period,
a fasted venous blood sample for glucose and HbA1c analyses was drawn. On 28 non-consecutive days, including the wash-
in, participants kept diet records and measured capillary glucose using a glucometer 1 hour after the meal during which the
treatments were consumed.
Results:
fasting glucose, HbA1c or average postprandial glucose values between the two interventions.
Conclusions: Pinto beans and green beans result in comparable glycemic control when incorporated into the normal diet of
adults with T2DM even though pinto beans have more available carbohydrate per serving.
Keywords: Legumes; Pulses; Phaseolus vulgaris; Diabetes; Glycemic Response; Available Carbohydrate
Abbreviations: DASH: Dietary Approaches to
Stop Hypertension; HbA1c: Hemoglobin A1c Blood
Concentrations; T2DM: Diabetes Mellitus; MANOVA: Multiple
analysis of variance; GI: Glycemic Index; GL: Glycemic Load.
Introduction
Over 27 million people in the United States (US) have type
2 diabetes mellitus (T2DM) [1,2]. Long-term complications
associated with T2DM, especially when blood glucose
concentrations are not well controlled, include increased
risks for cardiovascular disease, peripheral vascular disease,
nephropathy, neuropathy, and retinopathy among others
[3,4]. First-line therapy for controlling T2DM is lifestyle
in combination with metformin [5]. As a component of
the Mediterranean diet, and to a lesser extent the Dietary
Approaches to Stop Hypertension (DASH) diet, dry bean (P.
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
that has been associated with a reduced incidence of T2DM
in adults [6,7] and promoted for improved glycemic control
by decreasing insulin resistance [8].
Several single meal glycemic response studies have
demonstrated that consumption of dry beans, a low glycemic
index food, in combination with high glycemic index foods
such as white rice or white bread lower the postprandial
glycemic response in people with prediabetes or T2DM
compared to consumption of the high glycemic index food
metabolized differently than other foods that fall under the
‘carbohydrate’ umbrella in diabetes education materials. The
difference in metabolism may be due, in part, to the lower
found in dry beans compared to other types of carbohydrates
[11]. The American Diabetes Association, in their 2019
standards of medical care, state “Carbohydrate intake should
emphasize nutrient-dense carbohydrate sources that are high
well as dairy products,” and also emphasize the importance
American Diabetes Association’s view, beans are grouped
with other starches in many diabetes nutrition education
materials. Subsequently, these information tools teach
people with T2DM to view dry beans as equivalent to rice,
pastas, breads and other starchy vegetables such as potatoes
and corn [12,13].
Despite evidence suggesting that consumption of dry
beans with a high glycemic index food in a single meal will
lower the overall postprandial glycemic response, few
studies exist that investigate the effect of cooked dry beans
eaten as part of a normal diet over several weeks on glycemic
response in persons with T2DM [9,14,15]. Long-term glucose
control, through diet, exercise and, if necessary, medications,
is important for people with T2DM to slow disease
progression. Prolonged elevation of postprandial glucose
concentrations contribute to factors, such as tissue damage
and impaired vascular endothelial function, that result in
increased risk of related diseases such as cardiovascular
disease and, over time, a decline in the normal physiologic
functioning of the pancreas [16,17]. Therefore, this study was
to green beans for glycemic control. The hypothesis stated
that pinto beans and green beans would provide equivalent
glycemic control as indicated by fasting glucose, postprandial
glucose, and hemoglobin A1c (HbA1c) blood concentrations
research regarding the glycemic properties of dry beans in
the diet, particularly for control of T2DM.
Materials and Methods
Study Design and Participants
This study utilized a randomized, pretest-posttest,
crossover (within-group) design that includes two
treatment periods (½ cup green beans each day and ½ cup
pinto beans each day), each 12-weeks in duration with a
4-week wash-out period to determine the effect on fasting
glucose, postprandial glucose and HbA1c concentrations.
Adults aged 20-75 years with T2DM were recruited from
the University of Colorado Colorado Springs campus and
surrounding community between March 2009 and July
2010. Eligibility criteria included (1) diagnosis of T2DM
by a physician; (2) currently attempting control of T2DM
provided lab analysis conducted within last 30 days) and/
participant provided lab analysis conducted within last 30
days); (4) body mass index (BMI) of 22-40 kg/m2; (5) no
unresolved health conditions (i.e., health conditions that
were not controlled by diet, lifestyle and/or medication) and
no diagnosis of gastrointestinal disease; (6) limited history
of dry bean intake; (7) willingness to follow study protocol,
scheduling, and ability to come to the testing location; (8)
no use of medications and/or dietary supplements other
than metformin that affected glucose; (10) women could
not be pregnant or breastfeeding; and (11) habitual alcohol
Individuals who met the eligibility criteria were enrolled by
study personnel and assigned to an intervention sequence
(green bean-pinto bean or pinto bean-green bean) by the
primary investigators using simple randomization technique
[18]. Due to the interventions used, the investigators and
participants were not blinded to intervention or sequence.
The study was conducted in accordance with the
Declaration of Helsinki and was approved by the University of
Colorado Colorado Springs Institutional Review Board (#09-
028). Informed written consent for inclusion was obtained
from all participants. Participants received an incentive in
the form of gift cards for the completion of each intervention
period. The study is registered with ClinicalTrials.gov,
NCT04003194.
Participants completed a 2-week wash-in period to
allow for baseline collection of diet information via four 24-
hour diet records and familiarization with diet recording
Participants were instructed to not eat other dry beans, fresh
or canned string or wax beans during the intervention phases.
Food Science & Nutrition Technology
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
The researchers explained to participants which ‘beans’ they
should not be consuming and provided an information sheet.
During each intervention week, participants completed one
24-hour diet record, providing 12 diet records during each
intervention for a total of 28 diet records, including those
completed during the wash-in period. Diet records were
analyzed to determine macro- and micronutrient intake
during the wash-in period and interventions (The Food
Processor® version 11.4.0; ESHA Research, Salem, OR, USA).
Diet records were also used to determine total carbohydrate
(CHO) and available CHO for the day and for the meal at which
the intervention food was consumed. Each week participants
completed a gastrointestinal symptom questionnaire for
the 7-days preceding. Questions asked about changes in
Those who answered yes, were asked if these changes
interfered with their daily activities or social events [19].
Participants were provided with and trained to use
OneTouch® Ultra glucometers (LifeScan, Inc. Malvern,
PA). Testing supplies, including glucometer test strips
(OneTouch® Ultra test strips; LifeScan, Inc. Malvern, PA), were
also provided. During the wash-in period and interventions,
on the days during which the participants kept a diet record,
participants measured their glucose concentration one (1)
hour after the meal (postprandial glucose) during which
they consumed the pinto beans or green beans. There were
no changes to the methods once the study commenced.
Diet Interventions
Participants incorporated ½ cup of pinto beans or ½ cup
of green beans into their normal diet during the 12-week
interventions. The beans were consumed as part of one meal
of the participants’ choice each day. Canned pinto beans or
sliced French style green beans each purchased from the
same lot number (both from The Kroger Co. Cincinnati, OH)
were provided every 2 weeks when participants came to the
testing center to be weighed and submit diet records. Each
can contain three ½ cup servings. Instructions regarding
the measurement and proper storage of the pinto bean
or green bean servings once a can was opened were given
verbally and in writing at study start. Participants drained
and rinsed both beans prior to consumption. Measuring cups
and storage containers were provided at the beginning of the
study.
The quantity of ½ cup of pinto beans was chosen because
it conformed with the US Dietary Guideline recommendation
for consumption of dry beans as a vegetable or protein food
that was current at the time the study was conducted [20].
The portion also follows with the serving recommendation
for dry beans as a starchy vegetable for people with
diabetes who are using carbohydrate counting as a means
of controlling blood glucose concentrations [12,13]. The
total carbohydrate, available (or net) carbohydrate, glycemic
index and glycemic load values are found in Table 1.
Green beans were chosen as a comparison food because
commonly consumed and accepted canned vegetable that
provides a low amount of available carbohydrate, has a
low glycemic index and glycemic load (Table 1) and may be
to the serving recommendation for non-starchy vegetables
for people with diabetes who are using carbohydrate counting
as a means of controlling blood glucose concentrations [12].
Amount Carbohydrate
(g)
Dietary
Fiber (g)
Available
carbohydrate1 (g)
Protein
(g)
Fat
(g)
Glycemic
Index2
Glycemic
Load3
Pinto Beans,
canned
½ cup
(128 g) 16 5 11 6 1 39 5
Green Beans,
canned
½ cup
(120 g) 4 2 2 1 0 20 0.4
Table 1: Macronutrient content, glycemic index and glycemic load of pinto beans and green beans [22-26].
Glycemic index presented uses glucose as a comparison [26].
Glycemic Load = GI/100 multiplied by the net grams of planned carbohydrate (net carbohydrate is the total grams of
Anthropometric and Biochemical Evaluations
After an overnight fast (approximately 12 hours) at the
beginning and end of each intervention, participants came
to the test site where they were weighed to the nearest 10th
of a pound on a scale (Tanita TBF300A, Arlington Heights,
Illinois, USA). Participants were weighed every 2 weeks when
they came to the testing site to turn in diet records and pick
up cans of the intervention foods during each intervention
period. Height was measured to the nearest ¼ inch using a
stadiometer at the beginning of the baseline wash-in period.
Body mass index was calculated using the standard formula
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
weight (kg)/height (m)2.
Venous forearm blood samples were taken at the start and
determine fasting glucose and HbA1c. Serum was separated
by centrifugation at 1000g for 10 min and picked up from an
insulated lockbox on the same day it was drawn for analysis
of glucose and HbA1c by a commercial laboratory (Centura
Laboratory, Centura Health, Colorado Springs, CO, USA) using
standard commercial methodologies. There were no changes
to the trial method or primary or secondary outcomes once
the trial commenced.
Data Analysis and Variable Transformation
Data are expressed as means (±SD) change (end value –
beginning value) for each end point during each intervention.
Data were tested for normality via the Kolmogorov-
Smirnov and Shapiro-Wilk tests and no transformations
were necessary for analysis. Multiple analysis of variance
(MANOVA) for repeated measures with time and diet as
factors was used to establish differences between treatments.
tests were performed to determine differences by treatment.
increase were examined by intervention type for each week
using Chi-square. If a person reported that the change was due
to other food or illness, a change was not counted as relevant
to the treatment (n=4). Dietary intake data (macro- and
micro-nutrients) was analyzed using multivariate analysis to
determine if nutrient intake changed during the pinto bean
the meals during which the pinto beans or green beans were
≤ 0.05.
This study used a crossover, repeated measures design
in which each participant served as his or her own control.
Continuous data sample size determinations indicated a
sample size of approximately 10 participants would be
α of 0.05. Therefore, an initial sample size of 13 participants
differences by repeated measures of analysis of variance
intervention periods over the course of the study. SPSS
version 19 (SPSS, Chicago, IL, USA) was used for all analyses.
Results
Thirteen participants began the study and 8 participants
completed both interventions (Figure 1).
Figure 1: CONSORT 2010 Flow Diagram.
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
The reasons for participants dropping out included: moved
out of the area (n=2), unwilling to continue consuming beans
the green bean intervention and two were on the pinto bean
intervention).
Participant characteristics are shown in Table 2. The
average BMI at baseline was 33.7 ± 6.0 kg/m2 (Table 2). Body
the baseline, nor between interventions (data not presented).
The HbA1c and fasting glucose at the beginning of each
intervention were analyzed to determine if there was any
effect of order or carryover effect from the previous period.
noted; therefore, the 4-week washout between intervention
periods was adequate.
Participants who started the
study (n=13)
Participants who completed both
interventions (n=8)
Gender 2 male, 11 female 1 male, 7 female
Age (years) 53 ± 12 54 ± 15
Height (inches) 65.0 ± 2.8 64.7 ± 2.9
Weight (pounds) 209.6 ± 38.8 200.3 ± 37.6
BMI 35.0 ± 5.4 33.7 ± 6.0
6.5 ± 1.0 6.6 ± 1.0
n = 10
n = 3
n = 6
n = 2
Fasting Glucose (mg/dL) 131 ± 27 132 ± 30
Baseline Postprandial Glucose (mg/dL) 143 ± 49 154 ± 49
Table 2: Baseline characteristics of T2DM participants.
Data presented as means ± SD. There were no statistically
study, participants who dropped out (data not presented),
and those who completed both interventions.
Participants reported both the pinto beans and green
beans were palatable. Based on the diet records, both were
consumed as single component of a meal rather than being
combined with other foods (e.g., beans and rice). Diet records
and return of the empty cans every 2 weeks indicated
consumed during interventions). Based on self-administered
observed in mean daily energy, protein, carbohydrate, total
interventions or between the interventions (Table 3).
Baseline Pinto Beans Green Beans
Total kcal 2125 ± 621 2024 ± 534 1889 ± 575
Protein (g) 83 ± 31 88 ± 23 84 ± 28
Carbohydrate (g) 257 ± 85 236 ± 58 216 ± 57
22 ± 10 24 ± 10 21 ± 5
Available Carbohydrate (g) 236 ± 76 212 ± 58 195 ± 54
Total fat (g) 90 ± 35 83 ± 33 80 ± 38
Table 3: Dietary intake across treatment periods.
Data presented as means ± SD. n = 8 for all dietary intake values presented.
interventions in energy or macronutrients consumed (Table
4) or correlations between postprandial glucose and total
carbohydrate or available carbohydrate at the meals at the
meals at which the beans were consumed (Table 5).
Food Science & Nutrition Technology
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
Pinto Beans Green Beans
Total kcal 388 ± 321 461 ± 396
Protein (g) 20 ± 19 34 ± 102
Carbohydrate (g) 49 ± 33 43 ± 37
8 ± 3 6 ± 6
Available Carbohydrate (g) 41 ± 30 37 ± 32
Total fat (g) 22 ± 90 21 ± 26
Table 4: Dietary intake for meals at which pinto beans or green beans were consumed.
Data presented as means ± SD. n = 8 for all dietary intake values presented.
Pinto Beans Green Beans
Postprandial
Glucose
Total
CHO
Dietary
Fiber
Available
CHO
Postprandial
Glucose
Total
CHO
Dietary
Fiber
Available
CHO
Week 1 141 ± 29 47 ± 31 7 ± 2 40 ± 30 144 ± 42 74 ± 46 11 ± 12 63 ± 38
Week 2 167 ± 65 50 ± 23 10 ± 5 40 ± 20 147 ± 37 41 ± 34 6 ± 4 35 ± 30
Week 3 147 ± 40 51 ± 31 9 ± 4 42 ± 28 147 ± 25 46 ± 48 7 ± 6 39 ± 43
Week 4 166 ± 60 52 ± 35 8 ± 3 45 ± 33 167 ± 41 34 ± 28 5 ± 4 28 ± 24
Week 5 130 ± 32 42 ± 23 7 ± 2 35 ± 21 144 ± 30 37 ± 32 4 ± 4 33 ± 28
Week 6 123 ± 30 51 ± 40 9 ± 5 42 ± 35 144 ± 30 31 ± 30 3 ± 3 27 ± 27
Week 7 136 ± 22 45 ± 24 9 ± 4 36 ± 21 139 ± 28 38 ± 33 4 ± 3 34 ± 31
Week 8 139 ± 35 54 ± 56 8 ± 4 46 ± 53 141 ± 31 27 ± 33 3 ± 3 24 ± 30
Week 9 150 ± 48 40 ± 34 7 ± 3 33 ± 31 138 ± 32 36 ± 25 7 ± 5 29 ± 22
Week 10 150 ± 35 44 ± 33 7 ± 2 37 ± 31 126 ± 38 54 ± 40 6 ± 3 48 ± 38
Week 11 145 ± 30 52 ± 34 8 ± 3 44 ± 31 148 ± 49 63 ± 42 11 ± 10 52 ± 34
Week 12 152 ± 46 55 ± 39 8 ± 3 47 ± 36 137 ± 29 36 ± 42 5 ± 6 31 ± 36
12-week
average 145 ± 29 49 ± 33 8 ± 3 41 ± 30 143 ± 27 43 ± 37 6 ± 6 37 ± 32
Table 5:
at which pinto beans or green beans were consumed (b).
(b)Data presented as means ± SD.
values, ending values or change in values for fasting glucose
and HbA1c with either the pinto bean or green bean
interventions (Table 6).
Pinto Beans Green Beans
Beginning End ΔBeginning End Δ
Fasting Glucose (mg/dL) 144 ± 54 144 ± 48 0.3 ± 19 133 ± 31 151 ± 48 18 ± 20
7 ± 1.5 7 ± 1.5 0.01 ± 0.9 6 ± 1.1 7 ± 1.2 0.3 ± 0.7
Table 6: Fasting glucose and HbA1c values and change measured from the interventions.
Data presented as means ± SD. n = 8 for all values presented.
Data analysis of the gastrointestinal questionnaires
stool change, or bloating increase between the two treatment
phases, or by treatment week (Table 7). Out of a total 185
valid observation weeks, participants were fully compliant
with eating the intervention food daily and no eating of other
Food Science & Nutrition Technology
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
weeks, participants ate the treatment food less than daily
the intervention food was eaten daily, but the participant
also consumed more than a ¼ cup of other beans at least
once. Twelve percent of the weekly reports indicated non-
compliance for both daily treatment consumption and the
exclusion of other dry beans. Two of the 8 participants had
family medical emergencies or travel which affected their
ability to participate fully.
Flatulence Stool Change Bloating
Pinto Beans Green Beans Pinto Beans Green Beans Pinto Beans Green Beans
Week 1 0 0
Week 2
Week 3 0
Week 4
Week 5 0
Week 6 0 0 0
Week 7 0
Week 8 0 0
Week 9 0
Week 10 0 0 0
Week 11 0 0 0
Week 12 0 0 0
Table 7:
bean or green bean intervention.
Data presented as percentage and (n).
Discussion
This study sought to determine if there was a link
between pinto bean consumption and improved health or
nutritional outcomes in adults with T2DM by exploring the
strength of the relationship between regular pinto bean
ingestion, as part of a ‘normal’ diet, and glycemic control.
Comparing a starchy vegetable, pinto beans, with non-
starchy vegetable, green beans, challenged the conventional
paradigm that all starchy food (grains, vegetables, cereals)
are the same and have equivalent impacts on glycemic
control. Many studies examining glycemic control compare
foods with similar total or available carbohydrate content.
under the current food categorizations utilized for education
of people with diabetes. We chose to compare a starchy and
non-starchy vegetable to demonstrate dry beans provide a
glycemic response that more closely resembles that of foods
Our results from glycemic response trials utilizing beans
indicate that black beans or chickpeas provided as a whole
bean reduced the glycemic response to a rice test meal in non-
diabetic women [27]. Pinto beans, black beans and dark red
kidney beans provided as a whole bean lowered the glycemic
response to a rice test meal in people with T2DM [10]. This
intervention expanded on those single-meal results in people
with T2DM by measuring the response to daily consumption
of whole pinto beans as part of their normal diet over a 12-
week intervention period.
Education on carbohydrates and carbohydrate counting
is part of the diet counseling provided to people diagnosed
with T2DM. Conventional education on carbohydrates
starchy vegetables (including dry beans), milk and fruits,
which are the primary sources of carbohydrate in the diet
of carbohydrate to consume each day, but the amount of
available carbohydrate in the foods is rarely considered
when determining that part of the nutrition prescription.
Expert opinions are mixed on the use of glycemic index
(GI), glycemic load (GL), total carbohydrate and/or available
carbohydrate in the education of people with T2DM to
help them improve glycemic control [28-30]. Although the
the comparison used (white bread vs. glucose), source, etc
[25,26,31], there is consensus that foods can be grouped into
high, medium and low GI categories based on the glucose
Food Science & Nutrition Technology
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
response following their ingestion [31]. The use of GL instead
of GI may be encouraged since it considers the portion size
consumed which is known to impact the postprandial glucose
response as well as the available carbohydrate, instead of
total carbohydrate, in the food [11]. Available carbohydrate
the food, representing the portion of the carbohydrate in the
food that will impact postprandial glucose concentrations
[11].
dietary constituents that slow carbohydrate digestion and
absorption [32]. These dietary constituents result in dry
beans, including pinto beans, to be considered a medium
or low GI food with a low GL [25,26]. They also lower the
available carbohydrate in dry beans compared to many of the
other carbohydrates included in the “Grains, breads, starchy
vegetables” category commonly found in diabetes education
materials [12]. Therefore, we expected the glycemic response
to a meal that includes pinto beans to be no greater than a
meal that includes the green beans. Green beans are included
in the ‘non-starchy vegetable’ list in diabetes education
materials [12] due to their low carbohydrate content. Green
beans also have a low GI, GL and available carbohydrate
[25,26].
This study found that daily consumption of ½ cup pinto
postprandial glucose concentrations compared to ‘non-
starchy’ green bean consumption, even though pinto beans
have a higher GI, GL and amount of available carbohydrate.
Participants’ 1-hour postprandial glucose concentrations
fell within the normal range (60-200 mg/dL) for both
interventions, indicating that the carbohydrate from the
pinto beans did not have a negative impact on glucose control.
is clinically relevant because it challenges the validity of the
categorizations used for diabetes education that are based
on total carbohydrate content.
Participants’ long-term glucose control indicated by
HbA1c values at baseline as well as at the beginning and end
of each intervention, was also equally good when consuming
the pinto beans and the green beans. Even though fasting
mg/dL) at both the beginning and end of the interventions,
neither of the interventions had a statistically relevant impact
on the ending fasting glucose concentrations or change in
concentrations.
Strength of this study was asking the participants to
incorporate the interventions as part of a normal diet,
representing how people will typically use and consume
these foods. Unlike other long-term studies, meals were
not provided. Based on diet records and biweekly face-to-
face interactions with participants, the 12-week duration
was tolerable. Results substantiate that adding the ½ cup of
beans (110 calories pinto beans vs. 20 calories green beans)
did not cause weight gain.
Limitations
This study has limitations that effect the ability to
generalize the results to other populations. The study
included people with T2DM, so whether other populations
with impaired glucose and insulin utilization, such as those
with prediabetes or polycystic ovarian syndrome, would
respond in a similar manner is unknown. Documentation of
consumption relied on return of the canned food products
and was not validated by a biomarker. Full compliance with
the protocol for all weeks was met by almost half of the
participants for the two 12-week intervention periods. Due
conclusions to be missed. Glycemic response studies using
beans have noted postprandial glucose differences at 90- and
120-minutes following meal consumption [9,10,27,33-35].
In non-diabetic individuals, the peak postprandial glucose
concentration often occurs at approximately 60 minutes.
However, in people with T2DM, abnormalities in insulin
release and metabolism and glucose uptake and metabolism
result in postprandial glucose concentrations that may peak
later, often at approximately 120 minutes [36]. Although the
current recommendation for postprandial glucose testing for
persons with T2DM is that it is conducted 1-2 hours after the
meal [16], testing the postprandial glucose 1 hour following
the bean meal may have missed postprandial glycemic
differences due to bean consumption.
Conclusions
This study demonstrated that glycemic control when
pinto beans were incorporated into the normal diet of men
and women with T2DM was similar to glycemic control
when a non-starchy vegetable, green beans, was included
as part of the daily diet. Conventional diabetes education
on carbohydrates and controlling carbohydrate intake
emphasizes the difference between ‘starchy’ and ‘non-
starchy’ vegetables, with non-starchy vegetable consumption
encouraged and starchy vegetable intake controlled or
limited. However, this study suggests that some starchy
glucose or long-term glucose control in a manner similar to
non-starchy vegetables, suggesting that their intake should
be encouraged as well.
This study was designed as a short-term trial and,
Food Science & Nutrition Technology
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Hutchins AM and Winham DM. Pinto Beans and Green Beans Result in Comparable Glycemic Control
in Adults with Type 2 Diabetes: A Randomized Pilot Trial. Food Sci & Nutri Tech 2020, 5(1): 000211.
Copyright© Hutchins AM and Winham DM.
based on the results obtained, provides enough preliminary
evidence to support a longer-term trial exploring this
relationship. A longer-term trial should include participants
tracking their fasting and 2-hour postprandial glucose values
daily using a glucometer to better assess the day-to-day
impact of dry bean consumption on glucose concentrations.
In addition, we recommend exploring this relationship in
other populations with compromised glucose and insulin
utilization such as people with prediabetes or those with
polycystic ovarian syndrome.
Study Highlights
• Daily consumption of ½ cup pinto beans as part of a
normal diet results in similar postprandial glucose
concentrations compared to ‘non-starchy’ green bean
consumption, even though pinto beans have a higher GI,
GL and amount of available carbohydrate.
• This study demonstrates the glycemic response to a food
‘non-starchy’, challenging the categorizations based on
total carbohydrate content used for diabetes education.
• Participants’ long-term glucose control, indicated by
HbA1c values at baseline as well as at the beginning
and end of each intervention, was equally good when
consuming the pinto beans and the green beans.
• Consumption of dry beans, like pinto beans, should be
encouraged by people with diabetes due to their positive
impact on glycemic control.
Contributions
The authors contributed the following: conceptualization,
A.M.H. and D.M.W; methodology, A.M.H. and D.M.W; formal
analysis, A.M.H. and D.M.W; investigation, A.M.H.; writing-
original draft preparation, A.M.H.; writing-review and
editing, A.M.H. and D.M.W; project administration, A.M.H.;
funding acquisition, A.M.H.
had no role in the design of the study; in the collection,
analyses, or interpretation of data; in the writing of the
manuscript, or in the decision to publish the results.
Acknowledgements: The authors thank the participants
for their time.
Funding: This research was supported by the U.S. Dry
Bean Council.
References
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