Low Carb Diets Beat Low Fat Diets in Weight Loss and Improvement in Lipid Profiles

by Dr Sam Girgis on September 6, 2012

As a result of the obesity epidemic occurring throughout the world, weight loss and fitness has become a multibillion dollar industry.  There have been numerous diets that have been recommended for weight loss and traditionally, a low fat high carbohydrate diet has been recommended.  The erroneous nature of this recommendation has been increasingly recognized.  High carbohydrate foods cause the pancreas to secrete large amounts of insulin in an effort to lower blood glucose levels.  In addition, insulin causes excess energy from carbohydrates to be converted into fatty acids and stored in fat cells.  The end result of a low fat high carbohydrate diet is to cause more fat accumulation and weight gain… the exact opposite of the goal of the diet.  Low carbohydrate high fat diets have become increasingly popular, and have been shown to accomplish the intended outcome of weight loss.  Low carb diets are intended to cause a state of ketosis which causes the body to switch from using glucose as the primary energy source to using ketones as the primary energy source.  When carbohydrate ingestion is low and the body is in a state of ketosis, fatty acids in fat cells are mobilized and converted to ketones for energy requirements.  The end result of low carbohydrate high fat diets is weight loss through fatty acid catabolism.

Researchers, led by Dr. William Yancy from Duke University Medical Center, have compared a low carbohydrate ketogenic diet to a low fat, low cholesterol, reduced calorie diet.  The results of their study were published in the Annals of Internal Medicine.  The researchers performed a randomized controlled trial that included 120 obese hyperlipidemic individuals who were randomized to either a low carbohydrate ketogenic diet or to a low fat, low cholesterol, reduced calorie diet.  The study participants were followed for a 24 week period on the diets and were given exercise recommendations while they participated in group meetings.  The researchers found that the study participants in the low carbohydrate ketogenic diet lost more weight, had greater decrease in triglyceride levels and had greater increase in HDL cholesterol levels.  Changes in LDL cholesterol levels did not vary significantly between the two groups.

The authors wrote, “Over 24 weeks, a low-carbohydrate diet program led to greater weight loss, reduction in serum triglyceride level, and increase in HDL cholesterol level compared with a low-fat diet… The changes in body weight, blood pressure, and serum lipid levels that we observed suggest that research may be warranted on the effects of the low-carbohydrate diet in patients with the metabolic syndrome, which is characterized by increased blood pressure, hypertriglyceridemia, low HDL cholesterol levels, abdominal adiposity, and insulin resistance. We did not measure insulin sensitivity, but previous studies of the low-carbohydrate diet have shown that serum glucose and insulin levels decrease”.

The authors concluded, “In summary, over 24 weeks, healthy hyperlipidemic persons who followed a low-carbohydrate diet lost more body weight and body fat than did those who followed a low-fat diet. Serum lipid profiles improved in both groups, but monitoring remains important because a small percentage of persons may experience adverse changes. Further research is needed in other groups and for longer periods to determine the safety of this dietary approach”.

This study is one of the first to show that low carbohydrate ketogenic diets cause weight loss and improve lipid profile parameters, including decreasing triglyceride levels and increasing HDL cholesterol levels.  In addition, low carb ketogenic diets were shown to cause more weight loss than low fat low cholesterol reduced calorie diets.  From a theoretical standpoint, a low carb ketogenic diet should be superior for weight loss.  This study provides scientific evidence that backs the theory behind ketogenic diets and the principle of ketosis for weight loss.

In future posts, we will discuss the mechanism behind ketosis and weight loss and also discuss the safety of ketogenic diets.



William S. Yancy et al. “A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet To Treat Obesity and Hyperlipidemia: A Randomized Controlled TrialAnnals of Internal Medicine. 2004 May;140(10):769-777.

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