Introduction.

A new study finds further support for the idea that low-carbohydrate diets can be especially effective, as long as they do not lead people to eat extra fat or avoid exercise.

In the nutritional parlance, carbohydrates refer to sugar and starches. Among dieters, carbohydrates have come to refer to foods especially rich in these food constituents, namely potatoes, rice, grains, loaves of bread, candy, fruits, and vegetables.

Cutting carbohydrates to trim weight-often under the rubric of the Atkins Diet or the Zone Diet plan- has grown popular in recent years. Boosting these regimens’ appeal have been several major studies showing that compared with equal-caloric diets rich in carbohydrates, low-carbohydrates ones help people shed the pounds more quickly and yet experience less hunger while doing so.

However, many people who have pulled carbohydrates from their diets have replaced sweet and starchy foods with fatty ones. The fact that many low-carbohydrate diets are, in fact, high in fat may explain some potentially detrimental cholesterol trends in a substantial subset of low-carbohydrate dieters.

1. Diets rich in low carbohydrates help people shed the pounds more quickly.

The new study explored what would happen if the ratio of fats in the diet were held constant and the pared carbohydrates were replaced, gram-for-gram and calorie-for-calorie, with protein. This four-month trial, conducted in 48 obese women between the ages of 40 and 56, also assigned half of the volunteers on each diet to a low-intensity exercises regime.

The findings, reported in one of the Journal of Nutrition, showed not only that the dieters lost more weight on the low-carbohydrate, protein-rich fare, but also that they lost more body fat than muscle. Moreover, women on the protein-rich diet who exercised lost 20 percent more weight than did the more-sedentary women on this diet. That is a bit surprising, notes study leader Donald K. Layman of the University of Illinois at Urbana- Champaign because the prescribed exercise shouldn’t have been enough extra activity to translate into any discernible weight loss. Indeed, the exercise regimen did not provide any extra weight loss to the women eating the carbohydrate-rich diet.

What this means, he told Science News Online, is that the extra protein some women were eating somehow collaborated with exercise to reduce weight.

“This is really surprising, and, frankly, pretty important,” Layman says since the observation flies in the face of most nutrition guidelines, which advise dieters and everyone else in the United States to eat less protein, not more.

For their new trial, Layman and his colleagues gave their volunteers two-week menus and directions on how to prepare the recipes. Participants were instructed to weight portions to ensure she didn’t eat more than the recommended amounts. Each woman’s energy intake was expected to run about 1,700 calories per day. In fact, based on weight losses and records, it became clear that most women consumed even fewer calories, in the range of 1,400 to 1,600 per day.

Each woman ate the same foods, regardless of her diet. What differentiated the two diet groups were the allowed portions. For instance, the high-carbohydrate group was instructed to eat eight servings of starchy foods per day, which included loaves of bread, cereals, rice, and potatoes.

“The high-protein group also ate bread and other starchy foods, just half as much,” Layman says. Similarly, while the high-protein group was instructed to eat nine ounces of meat and eggs per day, the high-carbohydrate eaters were restricted to just 5 ounces.

In the end, women on the high-carbohydrate diet ate about the same proportion of macro-nutrients as they had been downing before taking part in the study: 55 percent of their calories as sugars and starches, 30 percent as fat, and 15 percent as protein. It was the other group that made major changes in the ratio of these macronutrients. The high-protein group consumed only 40 percent carbohydrates, 30 percent fat and 30 percent protein.

Moreover, the proteins included in each day’s menus were dominated by what Layman terms “high-quality” protein- the type especially rich in the amino acids that build muscle. Some of these amino acids, such as leucine, aren’t made by the body and must be obtained from the diet- primarily from foods such as meats, dairy, eggs, and soya beans.

Ensuring that each diet provided adequate leucine was a focus of the menu planning. Layman says. He explains that this amino acid is valued for “regulating one of the first steps in turning on the machinery for protein synthesis.” That’s important since muscle is almost all protein.

2. Adding a little exercise to the diet regime helped keep a body metabolism revved up longer.

Adding a little exercise to the diet regime helped keep a woman’s metabolism revved up longer and her muscles conditioned. The two groups that were prescribed exercise were required to take part in a supervised 30-minute walk five days a week and to do 30 minutes of stretching and resistance exercise twice a week, using gym machines dialled to minimal weights. Even the two more-sedentary groups were advised to walk 30 minutes a day five days a week. Layman says, although their compliance was not monitored.

The protein focus seems to have paid rich dividends, Layman says, since women on the protein-enriched diets preserved more of their muscle than the high-carbohydrate diners did. That means that protein and exercise combined to reduce the women’s weight by burning body fat.

Both dieting groups trimmed more body fat when they undertook some extra exercise. Sedentary women on the protein diet dropped 15 percent of their body fat during the trial, and those who added in extra exercise lost 21.5 percent of their body fat. By contrast, those who exercised and ate the high-carbohydrate fare lost 15 percent of their body fat, while their sedentary counterparts on that diet shed only 12.3 percent of their fat.

Preserving muscle is important, Layman stresses, since-unlike fat- it burns substantial energy when the bodies at rest. The higher the proportion of the body that is lean muscle, the higher its energy demands and the more likely that an individual will burn most of the calories she eats-not store them as fat.

The encouraging news, he says, is that the short-term advantages seen in the high-protein part of this trial can be maintained. Some of the women were recruited to stay on their regimens for another year, he notes, “and we find that basically, the same results continued” for each group.

In a pair of papers he co-authored during the past 2 years, Layman has reported that a key feature of the protein diet’s advantages may be leucine. Although a building block of protein, it may have additional metabolic activities, such as being a signalling agent that helps regulate the rate of muscle building and the body’s use of blood sugar, he notes. For these functions, leucine may have to be present in concentrations higher than those needed just to build protein.

Conclusion.

In fact, Layman says that leucine-rich diets might even help stabilize blood-sugar concentrations before and after meals- a boon to anyone with type 2 diabetes or a constellation of related heart-disease risk factors known as Syndrome X. He plans to investigate leucine’s potential value for such individuals in upcoming studies.