Introduction.
A new study finds more support for the idea that low-carb diets can be especially effective, as long as they don’t lead people to eat more fat or avoid exercise.
In nutritional parlance, carbohydrates refer to sugar and starches. Among dieters, carbohydrates have become foods that are especially rich in these food constituents, namely potatoes, rice, cereals, loaves of bread, sweets, fruits and vegetables.
Cutting carbs to lose weight, often under the rubric of the Atkins diet or the Zone diet plan, has become popular in recent years. Several major studies have added to the appeal of these regimens showing that compared to equal-calorie high-carb diets, low-carb diets help people lose weight more quickly, yet experience less hunger while doing so .
However, many people who have eliminated carbohydrates from their diets have replaced sweet, starchy foods with fatty foods. The fact that many low-carb diets are, in fact, high in fat may explain some potentially detrimental cholesterol trends in a substantial subset of low-carb dieters.
1. High-carbohydrate diets help people lose weight faster.
The new study explored what would happen if the proportion of fat in the diet were held constant and reduced carbohydrates were replaced, gram for gram and calorie for calorie, with protein. This four-month trial, conducted on 48 obese women ages 40 to 56, also assigned half of the volunteers from each diet to a low-intensity exercise regimen.
The findings, published in the Journal of Nutrition, showed not only that the dieters lost more weight on the low-carb, high-protein diet, but also that they lost more body fat than muscle. In addition, the women on the high-protein diet who exercised lost 20 percent more weight than the more sedentary women on this diet. That’s a bit surprising, says 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 noticeable weight loss. In fact, the exercise regimen did not provide any additional weight loss for women on the high-carbohydrate diet.
What this means, she told Science News Online, is that the extra protein some women ate somehow helped exercise to reduce weight.
“This is really surprising and quite frankly quite important,” Layman says, as the observation goes against 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 instructions on how to prepare the recipes. Participants were instructed to weigh portions to ensure they did not eat more than the recommended amounts. Each woman’s energy intake was expected to be about 1,700 calories per day. In fact, based on weight losses and records, it became clear that most women ate even fewer calories, in the range of 1,400 to 1,600 per day.
Every woman eats the same foods, regardless of her diet. What differentiated the two diet groups were the portions allowed. For example, the high-carbohydrate group was instructed to eat eight servings of starchy foods per day, which included loaves of bread, cereal, rice and potatoes.
“The high-protein group also ate bread and other starchy foods, only half as many,” says Layman. Similarly, while the high-protein group was instructed to eat nine ounces of meat and eggs per day, the high-carb eaters were restricted to just 5 ounces.
In the end, the women on a high-carbohydrate diet ate about the same proportion of macronutrients as they had before participating in the study: 55% of their calories were sugars and starches, 30% were fats, and 15% were from foods. protein. It was the other group that made significant changes in the proportion of these macronutrients. The high-protein group ate just 40 percent carbohydrates, 30 percent fat and 30 percent protein.
Furthermore, the proteins included in each day’s menus were dominated by what Layman calls “high-quality” protein, the kind especially rich in muscle-building amino acids. Some of these amino acids, such as leucine, are not produced by the body and must be obtained from the diet, primarily from foods such as meats, dairy, eggs, and soybeans.
Ensuring that each diet provided adequate leucine was a focus of menu planning. says the layman. 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 helped keep the body’s metabolism revved up for longer.
Adding a little exercise to the diet regimen helped keep the woman’s metabolism revved up longer and her muscles conditioned. The two groups prescribed exercise were required to participate in a 30-minute supervised walk five days a week and do 30 minutes of stretching and resistance exercises twice a week, using marked gym machines with minimal weights. Even the two most sedentary groups were advised to walk 30 minutes a day, five days a week. Layman says, although their compliance was not monitored.
The focus on protein appears to have paid big dividends, says Layman, as women who followed the protein-enriched diets retained more muscle than those who ate high carbohydrates. That means protein and exercise combined to reduce women’s weight by burning body fat.
Both diet groups lost more body fat when they got some extra exercise. Sedentary women on the protein diet lost 15 percent of their body fat during the trial, and those who added extra exercise lost 21.5 percent of their body fat. By contrast, those who exercised and ate the high-carb fare lost 15 percent of their body fat, while their sedentary counterparts on that diet shed just 12.3 percent of their fat.
Preserving muscle is important, Layman emphasizes, because, unlike fat, it burns a substantial amount of energy when the body is at rest. The greater the proportion of the body that is lean muscle, the greater its energy demand, and the more likely a person is to burn most of the calories they eat, not store them as fat.
The encouraging news, he says, is that the short-term advantages seen in the protein-rich portion of this trial may hold. Some of the women were recruited to stay on their regimens for an additional year, she notes, “and we found that basically the same results continued” for each group.
In a couple of articles he co-authored over the last 2 years, Layman reported that a key feature of the protein diet benefits may be leucine. Although it’s a building block of protein, it may have additional metabolic activities, such as being a signaling agent that helps regulate the rate of muscle development and the body’s use of blood sugar, he notes. For these functions, leucine may have to be present in higher concentrations than is needed just to build protein.
Conclusion.
In fact, Layman says that leucine-rich diets may even help stabilize blood sugar levels before and after meals, a boon for 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 future studies.
