Metabolic syndrome is not a disease, but rather a set of symptoms that frequently appear together in patients as they grow older. Typically these symptoms include obesity, low HDL cholesterol levels, high triglyceride levels, high glucose and insulin levels, and high blood pressure. As these symptoms worsen, patients with metabolic syndrome frequently progress to type 2 diabetes and cardiovascular disease. If we could somehow prevent or reverse the symptoms of metabolic syndrome, it seems logical that we could correspondingly decrease the incidence of type 2 diabetes and cardiovascular disease.
Obesity is one of the characteristics of metabolic syndrome. Because obesity is easy to observe, it is commonly assumed that metabolic syndrome is caused by obesity. However, a careful inspection of the markers associated with metabolic syndrome reveals that they are all related to insulin resistance.
While weight loss will relieve some of the symptoms of metabolic syndrome, weight loss is notoriously difficult to accomplish and even harder to maintain. The good news is that carbohydrate restriction, even in the absence of dramatic weight loss, is effective in alleviating all of the aspects of metabolic syndrome.
In a study published in the New England Journal of Medicine, 63 obese patients were assigned to a low-carb/high-fat/high-protein diet or to a high-carb/low-fat/low-calorie conventional diet. They were given little follow-up to mimic typical dieting conditions. The graph above summarizes the findings. Light blue bars represent low-carbers at 6 months and dark blue bars represent low-carbers at 12 months. Light red bars represent high-carbers at 6 months and dark red bars represent high-carbers at 12 months.
Although the low-carb group lost more weight than the high-carb group, at 12 months the difference was not significant. The low-carb group experienced a slight decline in systolic blood pressure while the high-carb group experienced a slight increase. HDL cholesterol was significantly higher and triglycerides were significantly lower and in the low-carb group at 12 months. Finally, there was less insulin released in the low-carb group at 6 months, though the difference was no longer significant at 12 months.
Jeff Volek and Richard Feinman have compiled a review of over 30 dietary studies, tabulating the effects of carbohydrate restriction on the markers associated with metabolic syndrome. As we might expect, some studies show great differences and other show little or none. However, taken together, the studies show that while both low-carb diets and conventional diets are associated with an overall decrease in weight, low-carb diets also typically produce the following
- an increase in HDL cholesterol
- a decrease in triglycerides
- a decrease in glucose levels
- a decrease in insulin levels
- a decrease in blood pressure
In other words, a review of the scientific literature shows that dietary carbohydrate restriction is a reproducible way to improve the features of metabolic syndrome.