DM: Effectiveness of MNT Provided by RD/RDN (2015)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To test the hypothesis that, in individuals with type 2 diabetes, a low fat plant-based diet improves glyceic, plasma lipid, and weight control compared with a diet based on current American Diabetes Association guidelines.

Inclusion Criteria:

Individuals with type 2 diabetes defined by a fasting plasma glucose > than 6.9 mmol/l on two occasions or with prior diagnosis of type 2 diabetes with the use of hypoglycemic medications for 6 or more months.

Exclusion Criteria:
  • A1C levels of < 6.5 or > 10.5%,
  • Uses insulin for more than 5 years,
  • Current smoker,
  • Alcohol or drug abuse,
  • Pregnancy,
  • Unstable medical status,
  • Current use of a low-fat vegetarian diet ,
  • Inability to attend scheduled meetings,
  • Failure to keep interview appointment,
  • Reluctance to change diet.
Description of Study Protocol:


Participants were recruited through newspaper advertisements in the Washington DC area in 2003 and 2004 during the months of October through December.


Participants were randomly assigned to follow a low-fat vegan diet or a diet following the 2003 ADA guidelines for 22 weeks (approx. 5.5 months).

Blinding used (if applicable)

Endocronilogists who prepared participants medications as well as laboratory technicians were blinded.

Intervention (if applicable)

Special Diet Prescriptions or Modifications (e.g., low fat, etc)



Diabetes Diet


No restrictions

Energy intake deficit of 500-1,000 kcal/day


15% energy form protein

15-20% energy from protein


75% energy from carbohydrate

Favor low-glycemic index foods

60-70% energy from carbohydrate and monounsaturated fats

Fat/fatty acids

10% energy from fat

Avoiding added fats

< 7% energy from saturated fat



< 200mg cholesterol/day


B12 supplement

B12 supplement

Length of Treatment: 22 weeks

Follow-up: None reported

Behavioral/Educational Interventions:

  • Subsequent nutrition and cooking instruction for an hour weekly

  • Instructions to limit alcoholic beverage consumption

  • Instructions not to alter their exercise habits during study period

Statistical Analysis

  • Power analysis was calculated to achieve 80% chance of detecting between-group differences in A1C.
  • Between-subject t-tests were used to determine if changes associated with the intervention were different among the groups.
  • Within each diet group, paired t-test were used to determine whether changes from baseline to end of study duration (22 weeks) were different from zero.
  • Regresion analyses, among those who did not change their medications, were used to assess diet group effects on A1C and body weight were significant while controlling for baseline glycosylated Hgb and changes in body weight.
  • Statistical significance was set at p<.05, without multiple comparison adjustment.
Data Collection Summary:

Timing of Measurements

Measurements were taken at baseline and 22 weeks unless noted otherwise.

Dependent Variables

  • Hgb A1C (primary end point) - measured in plasma after 12- hour fast by lab technicians blind to group assignment. (taken at baseline, 11 weeks and 22 weeks)
  • 3-day dietary record (taken at baseline, 11 weeks and 22 weeks)
  • Plasma glucose
  • Plasma cholesterol and triglyceride
  • HDL, LDL
  • Urinary albumin
  • Physical activity assessed over a 3-day period by pedometer
  • Body weight (taken at baseline, 11 weeks and 22 weeks)
  • Waist and hip circumference
  • Blood pressure

Independent Variables

  • Diet intervention - Adherence to diet intervention was measured for each group using 24 hour recalls administered by a registered dietitian at weeks 4, 8, 13 and 20.

Other Variables

  • Changes in medication
  • Changes in body weight

Control Variable

  • Exercise
Description of Actual Data Sample:

Initial N:

Screened: n=1,049

Met criteria: n=99 randomized to vegan group n=49 and ADA group n=50

Attrition (final N):

11 participants (8 from ADA group and 3 from vegan group) did not complete measures at week 22. All analysis included total sample except when noted in the results.


Mean age among the vegan group was 56.7 ranging from 35-82 years while ADA group had a mean age of 54.6 ranging from 27-80. DIfferences in mean age were not significant.


Majority of the sample (approx. 44-45%) was non-Hispanic with similar proportion of race among both groups.

Other relevant demographics:

Majority of the sample had a college or partial graduate degree.


At baseline, none of the measures were significantly different among the groups. The majority of participants in both groups had BMI > 30.


Washington DC

Summary of Results:

All Subjects


Vegan, Baseline

Vegan, 22 weeks


Diabetes Diet,


Diabetes Diet

22 Weeks


Statistical Significance of Difference Diets

Blood Lipids






Total cholesterol (mg/dL)

187.0 ±37.4

-27.7 ±28.5*

198.9 ±44.0

-24.2 ±30.5*


HDL (mg/dL)

52.3 ±19.7

-5.0 ±7.1*

49.8 ±14.5

-3.2 ±11.0$


Non-HDL cholesterol (mg/dl)

134.7 ±39.2

-22.7 ±28.2*

149.0 ±44.1

-21.0 ±31.5*



4.0 ±1.6

3.7 ±1.2$

4.3 ±1.7 3.9 ±1.2$ NS

LDL (mg/dL)

104.4 ±32.9

-16.4 ±30.6†

118.5 ±41.5

-15.4 ±25.1*


VLDL (mg/dL)

26.2 ±14.4

-3.2 ±10.0$

26.8 ±13.8

-4.4 ±12.4$


Triacylglycerol (mg/dL)

148.1 ±112.5

-28.5  80.0$

158.1  133.1

-25.1 ±124.7








Weight (kg)

97.0 ±22.9

-5.8 ±4.4*

99.3 ±21.0

-4.3 ±4.4*


BMI (kg/m2)

33.9 ±7.8

-2.1 ±1.5*

35.9 ±7.0

-1.5 ±1.5*


Waist (cm)

110.8 ±18.4

-5.3 ±4.4*

112.3 ±14.9

-2.8 ±4.7*


Hip (cm)

118.4 ±17.8

-3.9 ±3.4*

121.3 ±12.7

-3.8 ±3.9*


Waist-to-hip ratio (cm)

0.94 ±0.08

-0.02 ±0.03‡

0.93 ±0.07

0.01 ±0.04


Diabetes Related Variables






Fasting plasma glucose (mmol/l)

9.08 ±2.95

-1.97 ±2.68*

8.90 ±2.26

1.92 ±2.48*


A1c (%)

8.0 ±1.1

-1.0 ±1.2*

7.9 ±1.0

-0.6 ±1.1†


Blood Pressure







123.8 ±17.1

-3.8 ±12.6$

122.9 ±15.1

-3.6 ±13.7



77.9 ±11.1

-5.1 ±8.3*

80.0 ±10.5

-3.3 ±8.8$


*P <0.0001, †P <0.001, ‡P<0.01, and $P<0.05 for within group changes

Results for Subjects Whose Medications Did Not Change (Diabetes Medications or Lipid Lowering Medications)


Med Stable

Vegan Diet Change

Med Stable

Diabetes Diet Change

Significance of Difference

Blood Lipids




Total cholesterol (mg/dL)

-33.5 ±21.5*

-19.0 ±28.5*


HDL (mg/dL)

-6.0 ±6.8*

-2.8 ±11.6


Non-HDL cholesterol (mg/dl)

-27.6 ±21.1*

-16.3 ±30.1$


LDL (mg/dL)

-22.6 ±22.0*

-10.7 ±23.3$


VLDL (mg/dL)

-3.5 ±10.5

-3.8 ±12.1


Triacylglycerol (mg/dL)

-22.2 ±58.5

-22.8 ±134.3






Weight (kg)

-6.5 ±4.3*

-3.1 ±3.4*


BMI (kg/m2)

-2.3 ±1.5*

-1.1 ±1.2*


Waist (cm)

-5.0 ±3.7*

-2.3 ±4.2‡


Hip (cm)

-4.1 ±2.8*

-3.1 ±3.3*


Waist-to-hip ratio (cm)

-0.01 ±0.03

0.00 ±0.04


Diabetes Related Variables




A1c (%)

-1.23 ±1.38†

-0.38 ±1.11


Fasting plasma glucose (mmol/l)

2.73 ±3.05†

1.57 ±2.50‡


*P <0.0001, †P <0.001, ‡P<0.01, and $P<0.05 for within group changes

Weight Change
  • Vegan group lost 5.8 kg of body weight from baseline (p<.0001)
  • ADA group lost 4.3kg of body weight from baseline (p<.0001)
  • There were no statistically significant differences between the vegan and ADA diet groups in terms of the different measures of adiposity at 22 weeks.

Regression analysis to test effect of diet on A1C taking into account weight change did not indicate significant effect from diet group (p=.23). Weight change was significantly associated with 12% decrease in A1C (r=.51; p<.0001).

Other Findings
  • Total cholesterol from baseline to 22 weeks was significantly lower among the vegan group (156.9mg/dl) than ADA group (175.9mg/dl) p=.01, effect size= -14.5.
  • LDL cholesterol from baseline to 22 weeks was significantly lower among vegan group (84.6mg/dl) than ADA group (104.6mg/dl) p=.02, effect size -11.9.
  • VLDL cholesterol from baseline to 22 weeks was significantly lower (-3.2 ± 10.0, P<0.05) in the vegan group. There was no significant difference between the vegan group and the ADA diet group at 22 weeks.
  • HDL cholesterol from baseline to 22 weeks for vegan group, significantly lower (-5.0 ± 7.1, P<0.0001) HDL. Vegan group not significantly different than ADA diet group at 22 weeks.
  • Diet aherence was better in the vegan group (67% met criteria) than ADA group (44% met criteria).
Author Conclusion:

Individuals with type 2 diabetes participating in a 22 week clinical trial, both a low fat vegan diet and a diet following ADA guidelines improved glycemic control. Changes were greater in the vegan group and these were associated with changes in body weight among those following the low fat vegan diet. Further research is necessary to establish longer term effects and sustainability.

Funding Source:
Government: NIDDK
Foundation associated with industry:
Reviewer Comments:

This was a well executed clinical trial. Statistical analysis is not explained in detail and raises questions with regards to effect size and regression analysis method. From results, it seems weight change was more important than diet in its effect on A1C.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes