People Will Lose More Weight with a Modified Low-carbohydrate Diet than a Low-fat diet

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Aude YW, Agatston AS, Lopez-Jimenez F, et al.: The national cholesterol education program diet vs a diet lower in carbohydrates and higher in protein and monounsaturated fat: A randomized trial. Arch Intern Med 164:2141-2146, 2004.

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

Obesity is a big problem in the U.S. Being overweight causes diabetes, high blood pressure, and problems with the amount of fat (cholesterol) in the blood. These problems can lead to even bigger problems with a person's heart and blood vessels.

Even losing just a little bit of weight (5% to 10% of total body weight) can help a person's blood pressure, blood lipid levels (fat in the blood), and blood glucose levels. Yet even though there are a lot of diets for people to choose from, many people are still overweight and the problem of obesity continues to grow.

Why did the researchers do this particular study?

A low-calorie diet that is low in fat is generally accepted as a good way to lose weight. The researchers wanted to learn if a different diet is better. The other diet they looked at was low in total carbohydrates and replaced saturated fat with protein and monounsaturated fat.

Who was studied?

The study included 60 people (29 women and 31 men) between the ages of 27 and 71. The people each had a body mass index (BMI, a measure of weight in relation to height) greater than 27. The study did not include people with thyroid disease or diabetes patients that used insulin, pregnant women, or people who were using weight-loss medications.

How was the study done?

The participants were asked to follow one of two diets for 12 weeks. The diets differed in the amounts and kinds of fats, carbohydrates, and proteins they contained. Every person received written guidelines and lessons from a diet expert or a nurse to learn about the diet he or she agreed to follow.

People in the U.S. National Cholesterol Education Program diet, called the “NCEP diet,” got their calories from fat (30%) carbohydrates (55%), and protein (15%). Saturated fat made up less than 7% of the total fat they were allowed to eat, and monounsaturated fat was between 10% and 15% of the total fat they were allowed to eat.

The modified low-carbohydrate diet, called the "MLC diet," was lower in total carbohydrates but higher in complex carbohydrates, protein and monounsaturated fat. People on the MLC diet went through three different phases. In the first phase, calories came from more fat (62%), carbohydrates (10%), and protein (28%). In the second phase, fat was decreased to 43%, while carbohydrates increased to 27% and protein increased to 30%. In the third phase, 39% of calories came from fat, 28% from carbohydrates, and 33% from protein.

Calories from monounsaturated fats were 13% in Phase 1 and 8% in Phases 2 and 3. Recommended foods in the MLC diet included lean meats like chicken; olive, canola, and sunflower oils; and peanuts, almonds, pecans, avocados, and other foods.

Blood tests and body measurements were done for all the participants at the beginning of the study. These measurements were compared with measurements that were taken at the end of the study.

What did the researchers find?

People on the MLC diet lost more weight than the people on the NCEP diet.

After 12 weeks, the people on the MLC diet lost 13.6 pounds and the people in the NCEP diet lost 7.5 pounds. People on the MLC diet also had healthier lipid levels.

A low-fat diet that is high in carbohydrates may increase the level of fat in a person's blood, but lower the person's HDL cholesterol.

What were the limitations of the study?

While people on both diets ate a similar number of calories, some people may not have calculated the number of calories they should eat as well as others. This may have caused some people to eat more calories than they should have.

The 12-week study was a short time period. The weight loss and benefits found in the people on the MLC diet might not be the same if they were followed for a longer period.

What are the implications of the study?

The kinds of fat eaten in a low-carbohydrate diet are important.

Although people on the MLC diet ate a lot of fat, they were mostly monounsaturated fats (like the fat found in nuts, avocados, and olive oil). Diets high in monounsaturated fat lower cholesterol. The benefits of a diet high in unsaturated fats could also keep people's heart and blood vessels healthy.