Do Low-Carb Diets Affect Fats in the Blood?

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Sharman M, Gomez A, Kraemer W, et al.: Very low-carbohydrate and low-fat diets affect fasting lipids and postprandial lipemia differently in overweight men. J Nutr 134:880-885, 2004.

What is the problem and what is known about it so far?

Diets that limit the amount of carbohydrates a person eats have become very popular in recent years. Carbohydrates are found in bread, pasta, sugar, and other foods.

Low-carbohydrate diets can sometimes be high in fat and cholesterol (fat in the blood). Many studies have shown that a diet high in fat and cholesterol can lead to cardiovascular disease (disease of the heart and blood vessels). These studies usually involve men and women of normal weight.

The researchers in this study wanted to find out the effect a low-carbohydrate diet has on overweight men.

Who was studied?

A total of 15 overweight, but healthy men were studied. None of them smoked, took vitamins or minerals regularly, or were on a special diet. Their weight had been stable for the past month.

How was the study done?

The men each followed two diets for six weeks. One diet was low fat; the other was very low carbohydrate. Blood samples were drawn before the study began and after each 6-week diet phase. Researchers also tested to see how the body reacts to a high-fat meal.

What did the researchers find?

The low-fat diet was more effective at lowering their LDL ("bad") cholesterol level.

The very low-carbohydrate diet was better at improving many of the characteristics that make up metabolic syndrome (like glucose levels and HDL cholesterol -- the "good" cholesterol).

Participants lost more weight on the low-carbohydrate diet than on the low-fat diet.

What were the limitations of the study?

The study was only 6 weeks long with just 15 participants. A similar, longer-term study with more participants is needed to better understand this issue.

What are the implications of the study?

A very low-carbohydrate diet may help lower high levels of fat in the blood and may help people lose weight better than the low-fat diet. More studies are needed to see if a low-carbohydrate diet will harm a person's health in the long term.