It is a pervasive belief among general people that avoiding carbohydrate is the key to controlling diabetes. The notion is understandable, given that, when people have diabetes, their blood glucose levels are high, and glucose comes from carbohydrate. However, several observations have demanded a new way of thinking.
First, countries, like Japan and China, whose traditional diets are very high in carbohydrate (rice, noodles, starchy vegetables), have very little type 2 diabetes. Even sedentary people—barbers and accountants—were generally thin and healthy. Then, with the invasion of western diets, rich in meat and dairy products, type 2 diabetes rates rose sharply. This happened explosively in Japan in the 1980s and is happening currently in China. Rice-based diets have been replaced by meat-based diets, and the result is diabetes, heart disease, and other problems.
Second, in clinical trials, people with type 2 diabetes who eliminate animal products and build their diets from grains, beans, vegetables, and fruits soon find improvements in their weight, blood sugar control, lipids, and blood pressure. In our NIH-funded study, published in Diabetes Care in 2006, we found that the average drop in A1c in individuals with type 2 diabetes who began a low-fat vegan diet while keeping their medications constant was 1.2 absolute percentage points, which is obviously a major improvement.
Scanning studies show that when muscle and liver cells accumulate microscopic fat particles—that is, intracellular lipid—insulin resistance typically worsens. It is not yet clear whether the harm is done by the number of fat particles or—more likely—something about how these particles are metabolized. But it appears that fat inside cells fuels insulin resistance, which ultimately contributes to type 2 diabetes. So suddenly, it makes sense why a meaty diet would lead to diabetes and why a low-fat vegan diet would help prevent it. A plant-based diet has very little fat in it, and presumably it causes the intracellular lipid to dissipate.
Key benefits of plant-based approach to diet:
1. It causes blood glucose to fall, for the reasons we’ve talked about already.
2. It causes weight loss, without counting calories or limiting carbohydrate. The main reason for that is that the diet is high in fiber, which has effectively no calories, so people feel full with fewer calories. Also, most plant-based foods are very low in fats, which are, by far, the most calorie-dense part of the diet.
3.Cholesterol levels fall, which is due to the fact that the diet contains no animal fat or cholesterol, and is high in cholesterol-taming soluble fiber. Fourth, blood pressure falls. In fact, the observation that vegetarian diets reduce blood pressure was the inspiration for the DASH study. And of course there are many other benefits, such as better athletic performance, improved sexual potency, reduced joint pain, and others.
Yet it is still not conclusive that vegetarian diet is the optimal approach for glycemic control among diabetic patients. In a 2014 meta-analysis,the highest quality studies on the use of vegetarian diets for glycemic control in diabetes were analyzed.Unfortunately among included trials, only four were actually randomized-controlled trials (RCTs) (gold standard). RCT's are required to make claims about the how well a proposed diet changes outcomes compared to a control.