Plant-based diet may curb T2D risk
Individuals who adhere to a plant-based diet, particularly one consisting of healthy plant-based foods, may reduce their risk of developing type 2 diabetes (T2D), according to a recent meta-analysis.
“[W]e found that greater adherence to a plant-based dietary pattern was inversely associated with the risk of T2D,” said study author Frank Qian from the Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, US, and co-authors. This association was strengthened when the analysis was limited to only healthy plant-based foods, they added.
“[O]ur study provides important supporting evidence … to suggest a possible protective role of these dietary patterns against the development of T2D,” they said.
The results showed that individuals with a greater adherence to a plant-based diet had a 23 percent reduced likelihood of developing T2D compared with individuals with a lower adherence to a plant-based diet (relative risk [RR], 0.77, 95 percent confidence interval [CI], 0.71–0.84; pheterogeneity=0.07). [JAMA Intern Med 2019;doi:10.1001/jamainternmed.2019.2195]
The inverse association was strengthened when the analysis was confined to a “healthful plant-based dietary index” in four studies, which comprised healthy plant-based foods such as fruits, vegetables, whole grains, nuts, and legumes, instead of refined grains, starches, and sugars that were included in the overall plant-based diet (RR, 0.70, 95 percent CI, 0.62–0.79).
“This finding is consistent with prior observations that not all plant foods are equally beneficial and that the quality and food matrix … play an important role in determining their health effects,” said the researchers.
An analysis of five of the studies (82.4 percent of participants, 93.5 percent of T2D cases) showed that the greater the adherence to a plant-based diet (based on diet index), the lower the risk of T2D (p<0.001 for linearity).
The results did not widely differ after accounting for potential publication bias (RR, 0.81, 95 percent CI, 0.77–0.85), or after excluding one study which did not sufficiently adjust for confounding factors and had a >20 percent loss to follow-up (RR, 0.77, 95 percent CI, 0.70–0.85; pheterogeneity=0.05).
The results were based on a systematic review and meta-analysis of nine prospective observational studies comprising 307,099 individuals (mean age 36.0–64.6 years) that evaluated if a plant-based diet had an impact on the risk of T2D in adults. From this, 23,544 cases of T2D were identified. Duration of follow-up ranged from 2 to 28 years.
According to the researchers, diets that comprise healthy plant-based foods are rich in vitamins, minerals, fibre, antioxidants, phenolic compounds, and unsaturated fatty acids, elements that have been shown to among others, improve insulin sensitivity, and prevent weight gain and inflammation, all of which have been implicated in T2D. [Nutrients 2018;10:189; Diabet Med 2011;28:549-559; Public Health Nutr 2017;20:2713-2721] Furthermore, individuals on plant-based diets may be inclined to eschew animal-based foods such as processed and unprocessed meat that could contribute to T2D. [Curr Atheroscler Rep 2012;14:515-524]
“Overall, these data highlighted the importance of adhering to plant-based diets to achieve or maintain good health, and people should choose fresh fruits and vegetables, whole grains, tofu, and other healthy plant foods as the cornerstone of such diets,” said study senior author Associate Professor Qi Sun also from the Department of Nutrition, Harvard T. H. Chan School of Public Health.
The researchers suggested that the effect of plant-based diets on T2D risk may be underestimated as all studies adjusted for BMI, and plant-based diets may have an impact on reducing the risk of weight gain. Even in the present meta-analysis, adjusting for BMI in six of the studies affected the findings (RR, 0.53 and 0.79 before and after BMI adjustment, respectively; p<0.001).
“[I]t is likely that a considerable proportion of the protective association between plant-based diets and risk of T2D can be attributable to weight control,” said the researchers. However, the improvement in glycaemic control with a plant-based diet as demonstrated in certain studies implies that “the health benefits extend beyond weight control,” they said, advocating for further research to identify the mechanisms behind the plant-based diet-T2D association. [Nutrients 2018;10:189; Cardiovasc Diagn Ther 2014;4:373-382]