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What diet is better -- low carbohydrate or low fat?


I would like to lose weight and am confused by the dietary advice from different sources. Some books and magazine articles recommend a low carbohydrate diet while others stress the importance of a diet low in fat.

What kind of diet promotes weight loss?

A study reported last year found that weight loss was the same with low carbohydrate (high fat) or high carbohydrate (low fat) diets containing equal amounts of calories.

In this study 43 severely obese individuals (9 men and 34 women) were randomly assigned to either a low carbohydrate (15 percent carbohydrate, 53 percent fat) or high carbohydrate (45 percent carbohydrate, 26 percent fat) diet, each containing 1,000 calories daily during a six-week period of hospitalization. Both diets were rich in protein (about 30 percent). The two groups exercised for two hours each day. Weight loss on the low carbohydrate (high fat) diet (19.5 pounds) was not significantly different than the weight loss on the high carbohydrate (low fat) diet (16.5 pounds).

Both groups had similar reductions in their waist circumference and in the ratio of waist to hip circumference (a high ratio of waist to hip circumference is a measure of abdominal obesity which is associated with insulin resistance, abnormal blood lip values, high blood pressure and a predisposition to the development of diabetes).

Individuals on the low carbohydrate (high fat) diet, but not the high carbohydrate (low fat) diet, had a significant fall in plasma insulin and triglyceride levels.

This trial was carried out in a controlled environment where the subjects had no choice in their selection of foods. Under more usual circumstances, people's ability to follow a weight-reducing diet depends partly on whether the diet satisfies their hunger.

An interesting study from Australia examined the satiety index (the ability to satisfy hunger) of a number of common foods. They fed individuals 240 calories of a single test food early in the morning. Two hours later, the subjects were asked whether they felt hungry and were given free access to a range of standard foods and drinks.

The satiety index of the test food was determined by how hungry subjects felt and how much they ate two hours after eating the test food. The satiety index of a test food was considered high if the subjects were not hungry and ate little, even two hours later.

In general, fruits had the highest satiety index, while snacks, confectioneries and bakery products had the lowest.

Satiety was increased with a larger bulk of food intake. A higher fat content of a food was associated with a lower satiety index; higher amounts of protein, fiber and water in a food increased its satiety score. Thus, larger portions were needed to provide 240 calories from foods with lower caloric density -- because of their low content of fat and high content of fiber and water -- than for foods with a high caloric density, mainly due to a high fat content. For example, boiled potatoes satisfied hunger seven times better than croissants. The satiety index decreased progressively from boiled potatoes to french fries to potato chips.

Although weight loss may not depend on whether a diet is high or low in carbohydrates, provided that the two diets contain equal calories, the second study described above strongly suggests that a high carbohydrate diet may be easier to continue over the long haul because it does a better job of satisfying hunger.

Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.

Pub Date: 2/04/97

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