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Can a plant-based diet prevent or reverse type-2 diabetes?

Short answer: It clearly lowers your risk of developing it, and can sharply improve blood sugar and weight if you already have it, though most of the benefit comes from the weight loss and better food it brings.

Exhibit A
How often type-2 diabetes turns up, by diet
Vegan 2.9%
Lacto-ovo vegetarian 3.2%
Pesco-vegetarian 4.8%
Semi-vegetarian 6.1%
Non-vegetarian 7.6%

Prevalence in a single large cohort, a near three-fold gap between vegans and meat-eaters. Vegans kept around 49% lower odds even after adjusting for body weight and lifestyle.

Tonstad et al., Adventist Health Study-2, Diabetes Care (2009)

The objection

“Type-2 diabetes runs in my family and it’s basically permanent. A vegan diet isn’t going to fix my blood sugar.”

The answer

Prevention is the strongest part of the case. Pooling 9 prospective cohorts, 307,099 people, 23,544 new cases, found that the people eating the most plant-based had a 23% lower risk of developing type-2 diabetes (RR 0.77). Stick to healthful plant foods, fruit, veg, whole grains, legumes, nuts, and the gap widens to 30% lower (RR 0.70).

It shows up in single cohorts too. In the Adventist Health Study-2, diabetes prevalence climbed steadily from 2.9% in vegans to 7.6% in meat-eaters. Even after adjusting for body weight and lifestyle, vegans had roughly 49% lower odds (OR 0.51).

If you already have it, a randomised trial put a low-fat vegan diet against the standard ADA diet for 22 weeks. The vegan group did better: HbA1c fell 1.23 points versus 0.38 (among those not changing medication), weight dropped 6.5 kg versus 3.1 kg, and 43% cut their diabetes drugs versus 26%.

Now the honest bit, because this site doesn’t oversell. Followed out to 74 weeks, that head-to-head advantage shrank and lost statistical significance (HbA1c −0.34 vs −0.14, P=0.43). And weight change tracked blood-sugar change closely (r=0.50). So most of the gain rides on how much weight you lose and how good your food is. A well-built plant-based diet earns its place here precisely because it makes both of those easier.

Sources

  1. Qian et al., Plant-Based Dietary Patterns and Risk of Type 2 Diabetes, systematic review and meta-analysis, JAMA Internal Medicine (2019)
  2. Tonstad et al., Type of Vegetarian Diet, Body Weight and Prevalence of Type 2 Diabetes (Adventist Health Study-2), Diabetes Care (2009)
  3. Barnard et al., A Low-Fat Vegan Diet Improves Glycemic Control in Type 2 Diabetes, 22-week RCT, Diabetes Care (2006)
  4. Barnard et al., A low-fat vegan diet and conventional diabetes diet, 74-week RCT, American Journal of Clinical Nutrition (2009)