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 language, carbohydrates refer to sugar and starches. Among dieters, carbohydrates have become especially rich in these dietary components, namely potatoes, rice, cereals, loaves of bread, sweets, fruits and vegetables.
Cutting carbs to cut 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 and starchy foods with fats. The fact that many low-carb diets are, in fact, high in fat may explain some potentially harmful cholesterol trends in a substantial subset of low-carb dieters.
1. Diets rich in carbohydrates help people lose weight more quickly.
The new study explored what would happen if the proportion of fat in the diet remained constant and reduced carbohydrates were replaced, gram for gram and calorie for calorie, with protein. This four-month trial, conducted on 48 obese women between the ages of 40 and 56, also assigned half of the volunteers on each diet to a low-intensity exercise regimen.
The findings, published in one of the Journal of Nutrition, showed not only that dieters lost more weight on low-carb, high-protein foods, but also that they lost more body fat than muscle. Additionally, women on a high-protein diet who exercised lost 20 percent more weight than more sedentary women on this diet. That’s 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 noticeable weight loss. In fact, the exercise regimen did not provide any additional weight loss for the women on the high-carbohydrate diet.
What this means, she told Science News Online, is that the extra protein that some women were consuming in some way assisted with exercise to reduce weight.
“This is really surprising and 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 test, Layman and his colleagues gave their volunteers two-week menus and instructions on how to prepare the recipes. Participants were instructed to weigh their portions to ensure that they did not eat more than the recommended amounts. Each woman’s energy intake was expected to be around 1,700 calories per day. In fact, based on weight loss and logs, it was clear that most women were consuming even fewer calories, in the range of 1,400 to 1,600 per day.
All the women ate the same foods, regardless of their diet. What differentiated the two diet groups was the allowable portions. For example, 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, only half,” Layman says. Similarly, while the high-protein group was instructed to eat nine ounces of meat and eggs per day, those who ate high-carbohydrates were restricted to just 5 ounces.
In the end, the women on a high-carbohydrate diet ate roughly the same proportion of macronutrients that they had ingested before participating in the study: 55 percent of their calories from sugars and starches, 30 percent from fat, and 15 percent. cent as protein. It was the other group that made important changes in the proportion of these macronutrients. The high-protein group consumed only 40 percent carbohydrates, 30 percent fat, and 30 percent protein.
Additionally, the proteins on each day’s menu were dominated by what Layman calls “high-quality” protein, the kind especially rich in the amino acids that make up muscle. Some of these amino acids, such as leucine, are not produced by the body and must be obtained from the diet, mainly from foods such as meats, dairy products, eggs, and soybeans.
Ensuring that each diet provided adequate leucine was a focus of 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 is important since muscle is almost all protein.
2. Adding a little exercise to the diet helped keep the body’s metabolism revved up longer.
Adding a little exercise to the diet helped keep a woman’s metabolism revved up longer and her muscles conditioned. The two groups prescribed exercise had to participate in a supervised 30-minute walk five days a week and do 30 minutes of stretching and resistance exercises twice a week, using gym machines marked with minimal weights. Even the two most sedentary groups were recommended to walk 30 minutes a day five days a week. Layman says, although its compliance was not monitored.
The focus on protein appears to have paid big dividends, Layman says, as women on protein-enriched diets preserved more muscle than those high-carb. That means protein and exercise combined to reduce women’s weight by burning body fat.
Both dieting groups cut more body fat when they did a little extra exercise. Sedentary women who followed the protein diet lost 15 percent of their body fat during the test, and those who added extra exercise lost 21.5 percent of their body fat. In 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 only 12.3 percent of their fat.
Preserving muscle is important, Layman emphasizes, because, unlike fat, it burns a substantial amount of energy when bodies are at rest. The greater the proportion of the body that is lean muscle, the greater its demand for energy and the more likely that a person will burn most of the calories they eat, not store them as fat.
The encouraging news, he says, is that the short-term benefits seen in the high-protein portion of this trial can be maintained. Some of the women were recruited to stay on their regimens for another year, he notes, “and we found that basically the same results continued” for each group.
In a couple of articles he co-authored over the past 2 years, Layman reported that a key feature of the benefits of the protein diet may be leucine. Although it is 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 proteins.
Conclusion.
In fact, Layman says diets high in leucine could even help stabilize blood sugar levels before and after meals, a boon for anyone with type 2 diabetes or a constellation of risk factors related to heart disease. known as Syndrome X. He plans to investigate the potential value of leucine for these individuals in future studies.