= Full article availableJust as the air is going out of the “low-carb” diet craze, scientists may be figuring out why they seem to work for some people. As it turns out, the secret isn’t cutting carbohydrates—it’s the added protein in the foods used to replace the “carbs.” A new study suggests protein suppresses the appetite.
In a small test that varied the diets of 19 volunteers, researchers found that people felt less hungry when their calorie intake from protein was increased from 15% to 30%. At the same time, calories from fat were cut from 35% to 20%. But carbohydrate calories were kept constant—unlike in plans such as the Atkins Diet, which emphasizes reducing carbohydrate intake.
Evidently people have gotten tired of cutting carbohydrates, anyway. Atkins Nutritionals, the company founded by Robert C. Atkins, MD, filed for Chapter 11 bankruptcy protection on July 31. Dr. Atkins, who died in 2003, originally started the company in 1989 to sell vitamins and other supplements. But in 1997 Atkins Nutritionals began to ramp up to market low-carb versions of everything from candy bars to frozen dinners, zooming to 175 different products by the end of last year. As the numbers of low-carb dieters declined, however, the company sank into $300 million of debt.
The latest research, published in the American Journal of Clinical Nutrition, implies that dieters may have been wasting their money on all those low-carb products and focusing on the wrong part of the equation. Like the Atkins Diet, other popular plans such as the South Beach Diet and the Zone result in an increase in the percentage of protein in your meals to 30–40%. Until recently, most national dietary guidelines have recommended keeping your calories from protein at only 10–20%, notes Arne Astrup, MD, PhD, head of the Institute of Human Nutrition at the Royal Veterinary and Agricultural University in Copenhagen, in an accompanying editorial in the journal.
It’s important to figure out how to make people feel full with fewer calories, Dr. Astrup writes, because “just telling people that they should eat less and exercise more” isn’t working: “This simplistic strategy assumes that humans have conscious control over appetite and body-weight regulation, which is certainly not the case for most people; if it were true, there would be no overweight or obese people. I have never met an obese patient who has worked hard to become obese and to maintain an excessive body size.”
In the new study, lead author David S. Weigle, MD, of the University of Washington School of Medicine and his colleagues put volunteers on three different eating regimens. First, for two weeks, subjects ate a weight-maintaining diet with 15% of calories from protein, 35% from fat and 50% from carbohydrates. Next, for two weeks they tried a high-protein plan with exactly the same number of calories: 30% from protein, 20% from fat and still 50% from carbohydrates. Participants reported feeling less hungry on this high-protein diet.
Finally, for the next 12 weeks the scientists unleashed the volunteers to eat as many calories as they liked—as long as their intake stuck to that high-protein, low-fat ratio. Even though there was no ceiling on their calories, during this period the subjects actually reduced their eating by an average 441 calories a day. They lost an average of 10.8 pounds in body weight and 8.2 pounds in fat mass.
The results “clearly showed that protein is more satiating than is fat, and previous studies have shown that protein is more satiating than is carbohydrate,” according to Dr. Astrup. So it may be that increasing consumption of lean meat and low-fat dairy products will encourage people to eat fewer calories overall and thus lose weight, he says.
What about cutting carbs? Go ahead and cut sugary soft drinks and possibly processed pasta and white bread, Dr. Astrup suggests. But don’t reduce your intake of fruits, vegetables and whole grains.
Scientists don’t yet understand why protein makes you feel fuller than other foods. A recently funded European trial, the DiOGenes (Diet, Obesity and Genes) project, will investigate the effect of high-protein diets for a much longer time, one year, on a far larger group, 1,500–3,000 subjects, than the University of Washington study. It may provide some answers, as well testing concerns about any potential adverse health effects of a high-protein diet.
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