The Bottom Line: In this small study, the low-carb vegan group did better on many measures than the high-carb vegeatarian group, including a substantial reduction in LDL cholesterol ("bad cholesterol"). Weight loss was similar (both diets were low in calories). Although the study had some problems that make it difficult to give advice based on the results, it is an interesting addition to our knowledge about limiting carbohydrates in the diet.
The Study: The study had 47 overweight participants with elevated cholesterol. They were assigned one of two diets to eat for four weeks. All food was provided, which makes it much more likely that people followed the diets as directed. The diets were both calculated to provide about 60% of the calories a person would need to maintain their weight. So, for example, a person who's weight is stable on 2000 calories per day would be given a diet with 1200 calories in it. This pretty much guarantees that there will be a weight loss.
The diets had several differences between them:
Diet A: Low in carbohydrate (130 grams, but with fiber subtracted probably about 100 grams and 27% of calories), vegan, protein mainly from wheat gluten (55%) and soy (23%), 31% protein, 43% fat. This diet was also higher in fiber than the other group, and had supplementation of several vitamins and minerals.
Diet B: Higher in carbohydrate (58% of calories), vegetarian, protein from egg white and low-fat or fat-free dairy products (16% total protein), 25% fat. Less fiber, and no vitamin/mineral supplements.
Both diets were low in saturated fats.
Note that the low-carb diet was high in soy, wheat, and fiber while the high-carb diet was high in dairy products and egg protein. It should be noted that processed foods such as veggie bacon and high protein bread were included, and were probably a substantial part of the low-carb vegan diet.
Results: Both groups lost about the same amount of weight over the course of the month: about 9 pounds. This is an expected result on a low-calorie diet. Interestingly, satiety ratings were higher in the low-carb group, which won't surprise the readers of this site. It would be very helpful if more diet studies tracked satiety, as it is essential to the long-term effectiveness of any diet.
In most of the measures of blood lipids, the low-carb group improved more than the high-carb group. This included LDL cholesterol, which the researchers were particularly interested in, as the response to low-carb diets in regards to LDL as a whole has been mixed in various studies. They did not specifically test LDL particle size, which was too bad, as almost every time particle size is tested in low-carb diets, it proves to change to a less dangerous pattern. Curiously, HDL cholesterol did not change among the participants of the study, which is an unusual result in a test of low-carb diets. One possible explanation is that the level of saturated fat was kept very low.
Commentary: The paper starts out with a now-tired myth about low-carb eating: that a lot of animal protein, particularly beef and pork, is "advocated" as part of a low-carb diet. Nonetheless, we should certainly be interested in finding out the effects of variations in the components of a healthy low-carb diet, and this issue has not been studied very much.
What is surprising is that the study did not control the variables better. For example, they could have compared a regular mixed low-carb diet to a vegan or vegetarian low-carb diet. Or compare a high-carb vegan diet to a low-carb vegan diet, where the food sources for the various macronutrients were similar, and only the proportions varied. As it is, the reasons for the results are already being questioned in various media ("It's the soy!" "No, it's the fiber!") as well as in the conclusions written by the authors themselves.
The researchers' note in their introduction that we now have ample evidence that low-carb diets produce improvements in triglyerides, insulin resistance, and HDL cholesterol relative to high-carb/low-fat diets. These changes have now been replicated many many times, but still so often the results are seen as "surprising". It is refreshing that this group of researchers used these findings as a starting point. I take that as a positive sign, and will welcome more research along these lines, with more subjects and better controls.
In Robert Atkins' last book, Atkins for Life, he talked about the importance of monounsaturated fats, from sources such as olive oil, as well as ample omega-3 fats. He also advocated a mixture of healthy, natural fats, warning people away from refined oils high in polyunsaturates (such as corn and soy oils) as well as trans fats. Could this mix of fats in a low-carb diet consistently produce both lowered LDL cholesterol as well as a higher HDL? It would be interesting to see.Source:
Jenkins, David, Wong, Julia, et al. "The Effect of a Plant-Based Low-Carbohydrate ("Eco-Atkins") Diet on Body Weight and Blood Lipid Concentrations in Hyperlipidemic Subjects." Archives of Internal Medicine 169.11 (2009):1046-1054.
Photo Of Tofu and Vegetables © Nicola Stratford