We don’t know yet because they’ve never been compared head-to-head.
What we do have is a specific vegan diet (Ma-Pi 2) compared to a low-fat diet in a study published by Nutrition & Metabolism. Carbsane Evelyn dove into the study at her blog (recommended reading), or you can read the original research report yourself. Study subjects had fairly well-controlled type 2 diabetes and were elderly (66) and overweight (84 kg or 185 lb). The vegan diet was mostly whole grains, vegetables, legumes, and green tea. The low-fat and vegan diets both probably supplied 200-300 calories/day fewer than what the subjects were used to: 1900 cals for men, 1700 for women. The study lasted only three weeks.
The vegan group ate 335 grams/day of carbohydrate compared to 235 grams in the low-fat group. In contrast, the Paleobetic Diet provides 60-80 grams/day of digestible carb and the Ketogenic Mediterranean Diet allows a max of 20-30 grams.
The vegans in the study at hand ate 15-20 more grams/day of fiber. High fiber intake is linked to better blood sugar control.
From the study abstract:
After correcting for age, gender, BMI at baseline, and physical activity, there was a significantly greater reduction in the primary outcomes fasting blood glucose and post-prandial blood glucose in those patients receiving the Ma-Pi 2 diet compared with those receiving the control diet. Statistically significantly greater reductions in the secondary outcomes, HbA1c, insulin resistance, total cholesterol, LDL cholesterol and LDL/HDL ratio, BMI, body weight, waist and hip circumference were also found in the Ma-Pi 2 diet group compared with the control diet group. The latter group had a significantly greater reduction of triglycerides compared with the Ma-Pi 2 diet group.
The take-home point for me is that overweight T2 diabetics can improve short-term diabetes numbers despite a high carbohydrate consumption if they restrict calories and eat the “right” carbs. Restrict calories enough—600/day?—and T2 diabetes might be curable.
I’ve written before about vegetarian/vegan diets for diabetes. My patients are more resistant to vegan diets than they are to low-carb.
I scanned the original report and don’t see any problems with Evelyn’s summary.
Steve Parker, M.D.