The study to which he refers:
A Low-Fat Vegan Diet Improves Glycemic Control And Cardiovascular Risk Factors In A Randomized Clinical Trial In Individuals With Type 2 Diabetes, Diabetes Care, August 2006
Here's a discussion of this study from a few years ago: High-Carb, Low-Fat Diet For Diabetes.
Barnard compared his low-fat, vegan diet to the American Diabetes Association's diet. What happened when people with diabetes ate a high-carb, low-fat diet - consuming 70% of their calories as minimally-processed carbohydrates? They lowered their blood glucose. Here's how each group fared (all of the following were statistically significant):
Among participants whose diabetes medications remained unchanged: (A1C is short for hemoglobin A1c or HbA1c, a measure of blood glucose over the last 3 months.)
- A1C fell 1.23 points in the Vegan group
- A1C fell 0.38 points in the ADA group
- 43% of the Vegan group
- 26% of the ADA group
- 6.5 kg [14.3 lbs] in the Vegan group
- 3.1 kg [6.8 lbs] in the ADA group
- LDL cholesterol fell 21.2% in the Vegan group
- LDL cholesterol fell 10.7% in the ADA group
- 15.9 mg/24h in the Vegan group
- 10.9 mg/24 h in the ADA group
Those on a low-fat, vegan diet had lower blood glucose, lower LDL cholesterol, improved kidney function, and over double the weight loss. There were also significantly greater reductions in BMI, waist circumference, and total cholesterol in the low-fat group compared to the ADA group.
Notably, there was no significant difference in exercise between groups, so these changes weren't because vegans were overtly spending more calories. ("Overtly" is key, since, as previously discussed, some diets lead to greater expenditure of calories from digestion and thermogenesis.)
Participants in the low-fat, vegan group were allowed unrestricted consumption. They could eat as many calories and as much carbohydrate as they wanted, as long as they didn't eat from certain food groups. Participants in the conventional diet group had to limit their caloric intake, count calories, and control portion sizes. Even with unrestricted food intake and a higher calorie consumption, the high-carb group lost more than twice as much weight.
It is frustrating for me to hear people say their doctor instructed them to eat fewer carbohydrates since their blood glucose is inching up. I've researched this for years and I can see it's more the fat in the diet, not the carbohydrate, that is a problem. Also, fat is the ideal solvent for many industrial pollutants, chemicals which have been implicated in the development of diabetes, obesity, and other metabolic disorders. And these chemicals bioaccumulate, making the fat of animals - cheese, butter, lard, marbled steak - likely to contain the highest amounts.