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Why Plant-Based Diets for Type 2 Patients?

Jan 28, 2020
 
Editor: Steve Freed, R.PH., CDE

Author: Nadeen Ayad, BCPS, PharmD Candidate, Skaggs School of Pharmacy, University of Colorado

The most extensive evidence on whether or not plant-based diets for type 2 diabetes patients or those at risk of developing type 2 are beneficial.  

Plant-based dietary patterns are widely believed to have potential benefits in preventing or managing several major chronic diseases such as type 2 diabetes, cardiovascular disease, and cancer by improving insulin sensitivity, blood pressure, and reducing long term weight gain.  Plant foods are rich in vitamins, minerals, and antioxidants. In addition to that, consumption of plant foods helps lower the consumption of red and processed meats, which are high in cholesterol and could be harmful if consumed in large amounts. However, certain plant-based foods can have a potentially opposing effect on the risk of type 2 diabetes, such as refined grains, starches, and sugars. Therefore, it is important to recognize the difference between healthy plant-based foods and unhealthy ones.

This systematic review and meta-analysis of prospective observational studies studied the association between plant-based dietary patterns and the risk of type 2 diabetes among adults 18 years or older.  The primary exposure of interest was adherence to the plant-based diet and lower consumption of animal-based foods. The assumption was that higher adherence to plant-based dietary patterns was inversely related to the risk of type 2 diabetes. Healthy plant-based foods included fruits, vegetables, whole grains, legumes, and nuts.

A total of 9 studies were found, totaling 307,099 patients with 23,544 cases of type 2 diabetes with a duration of 2 to 28 years of follow up. The mean age was between 36.0 to 64.6 years, mean BMI from 23.0 to 26.7. Food frequency questionnaire was used to self- assess diet in all the studies. Studies that were identified to be at high risk of bias were excluded. Data analysis was performed between December 2018 and February 2019. Statistical heterogeneity was assessed with the Cochran Q-test (P < .10) and I2 statistic. In addition to that, publication bias was assessed using funnel plots. All P values were from 2-sides tests and the results were deemed statistically significant at P<0.05. Most to all studies were adjusted for risk factors such as age, BMI, smoking status and family history of diabetes.

Results showed that greater adherence to plant-based diets was associated with a lower risk of type 2 diabetes ( RR 0.77 95% CI, 071-0.84). Consistent associations and similar results were obtained when using different models including the forest plot and the fixed-effects model (RR 0.80; 95% CI, 0.75-0.84). When testing for heterogeneity between studies, no potential sources of heterogeneity were identified by age, sex, global region, BMI, sex composition, duration of follow-up or study quality. In addition to that, the funnel plot did not suggest any obvious publication bias.

While this study had several strengths including large population size and cases of type 2 diabetes with consistent and robust findings using several analytic methods, it did come with a lot of limitations as well. The most common limitation among the studies included was the lack of a power or sample size calculation. In addition to that, not all studies used repeated dietary assessments during follow up which might have affected the accuracy of the results. Moreover, all the studies were observational leaving room for potential bias that could not have been accounted for. This meta-analysis included studies from high-income countries, which could suggest that these findings may not be generalizable and applied to low-income countries due to the difference in the quality of food and composition.

In conclusion, greater adherence to plant-based diets is inversely associated with type 2 diabetes. These findings were consistent between all studies and subgroups.

Practice Pearls:

  • Plant-based diets can prevent or manage several major chronic diseases such as type 2 diabetes, cardiovascular diseases, and cancer.
  • This meta-analysis included 9 prospective observational studies to study the association between plant-based dietary patterns and risk of type 2 diabetes among adults 18 years of age and older.
  • Results showed that greater adherence was associated with a lower risk of type 2 diabetes (RR 0.77 95% CI, 0.71-.084).

Qian F, et al. Association between plant-based dietary patterns and risk of type 2 diabetes. JAMA Intern Med. 2019 doi:10.1001/jamainternmed.2019.2195

Nadeen Ayad, BCPS, PharmD Candidate, Skaggs School of Pharmacy, University of Colorado