It is estimated that one out of every three people in the United States is overweight, and two out of every three is obese. This trend toward overweight and obesity is not confined to America, and the world in general has seen an increase in the problem. Obesity increases the risk of type 2 diabetes, high blood pressure, heart disease, and stroke. Weight loss by following a low fat, high carbohydrate diet has been recommended in the past by both the American Heart Association and the National Institutes of Health. Recently, low carbohydrate diets have gained in popularity as a method for weight loss. Low carbohydrate diets have higher percentages of fat and cholesterol, and some have raised concern that these diets may be associated with increases in metabolic risk factors.
Researchers, led by Dr. Lydia A. Bazzano from Tulane University, have found that low carbohydrate diets are equally as effective as low fat diets for weight loss and improvement in cholesterol and lipid profiles. The results of their research were published online in the American Journal of Epidemiology. The researchers conducted a meta-analysis of 23 trials with a total of 2,788 participants to evaluate the effects of low carbohydrate diets (<45% carbs) versus low fat diets (<30% fat) on metabolic risk factors. The researchers found that both diets lowered weight and improved metabolic risk factors. When compared to study participants on the low fat diets, persons on low carbohydrate diets has slightly lower reductions in total cholesterol, and LDL cholesterol, but greater increase in HDL cholesterol, and greater decrease in triglycerides.
The authors wrote, “In the present meta-analysis of randomized controlled trials comparing low-carbohydrate diets with low-fat diets, we found that both diets were equally effective at reducing body weight and waist circumference. Both diets reduced participants’ blood pressures, total to HDL cholestero lratios, and total cholesterol, LDL cholesterol, triglycerides, blood glucose, and serum insulin levels and raised HDL cholesterol; however, participants on low-carbohydrate diets had greater increases in HDL cholesterol and greater decreases in triglycerides but experienced less reduction in total and LDL cholesterol compared with persons on low fat diets”.
The authors also wrote, “Our findings suggest that low-carbohydrate diets are at least as effective as low-fat diets for weight loss, regardless of gender, age, length of intervention, diabetes status, and level of carbohydrate restriction… Low-carbohydrate diets resulted in reductions in total cholesterol, LDL cholesterol, the ratio of total to HDL cholesterol, and triglycerides, and an increase in HDL cholesterol from baseline to at least 6 months of follow-up”
The authors concluded, “Because metabolic risk factors are important determinants of cardiovascular disease morbidity and mortality, recommending a diet in clinical practice that can improve these factors is vital to curbing the epidemics of obesity and cardiovascular diseases in the general population. Low carbohydrate diets had beneficial effects on weight loss and metabolic risk factors, and these effects were comparable to those seen on low-fat diets”
This study adds to the growing body of evidence that supports the finding that low carbohydrate diets are safe and effective for weight loss, and provide for improvements in cholesterol and lipid parameters. The concern with the increased fat and cholesterol in low carbohydrate diets is reasonable. As this and other studies have shown, metabolic risk factors for heart disease and stroke are in fact improved with low carbohydrate diets. Future studies should evaluate the effect of low carbohydrate diets on long term outcomes such as impact on the incidence of heart attack, stroke, and overall mortality. This study provides additional support for the notion that low carbohydrate diets are not only successful for weight loss but also safe for their effects on cholesterol and lipid profiles.
Tian Hu et al. “Effects of Low-Carbohydrate Diets Versus Low-Fat Diets on Metabolic Risk Factors: A Meta-Analysis of Randomized Controlled Clinical Trials” Am. J. Epidemiol. (2012) 176 (suppl 7): S44-S54. doi: 10.1093/aje/kws264