Until recently, it was thought that a low-fat, low-protein diet paved the way to weight loss, kept cholesterol levels in check and prevented heart disease. Then came the ultra high-protein diets, and as soon as we went back to a higher-calorie, higher- carbohydrate diet, the weight came back.
New research suggests something in between might best help maintain desirable body weight and overall health.
For 30 years, the government has touted a diet based on 60% carbohydrates, 30% fat and 10% protein.
“Yet, obesity rates are higher, diabetes is on the rise, and the rates of heart disease are the same as they were in 1970,” says Donald Layman, professor of food science and human nutrition at the University of Illinois-Urbana. “And now we have a new disease, known as Syndrome X, associated with insulin insensitivity.”
One thing wrong with the carbohydrate-based diets is that people are always hungry. Also, as people look for alternatives, they often turn to fad diets that go to extremes and may be unhealthy or hard to maintain.
“In fact,” Layman says, “losing weight and lowering cholesterol are not just about reducing fat intake. Carbohydrates are just as guilty because they cause us to eat too much and lead our bodies to make fats.”
In two research studies, Layman reports, women who ate a diet with increased protein (124 g./day) and lower carbohydrates (40% of energy) for 10-16 weeks lost more weight than women on a low-protein (68 g./day), high-carbohydrate diet (55% of energy).
Likewise, women who ate higher amounts of protein lost significantly more body fat and less muscle mass than women on a high-carbohydrate diet.
And women on the high-protein diet had minimal variations in blood glucose and insulin and were less hungry. Meanwhile, women on the carbohydrate diet exhibited reduced blood sugar, elevated blood insulin and experienced increased hunger.
“In these studies, both groups ate a diet with 1,700 calories/day, but the higher protein group lost more body weight and more body fat and maintained muscle mass,” says Layman.
Carbos, Insulin And More
Layman's interest in the high-protein diet sprang from his research in defining the roles of amino acids in metabolic regulation and muscle development. He sees leucine, an essential amino acid found in protein, along with insulin, as critical factors in glucose management and, therefore, weight maintenance.
Leucine is an important part of the mechanism by which the body regulates muscle synthesis of protein. The amount present in the body's cells, and presumably the amount in the diet, helps regulate insulin's role in metabolic processes. These findings may have implications for people who are diabetic or overweight.
“Carbohydrates, such as bread, rice, pasta and potatoes, have a very high glycemic index,” explains Layman. “On a high-carbohydrate diet, the body's levels of glucose and insulin swing dramatically.”
After a meal, blood glucose increases rapidly and insulin is released. Insulin helps to lower the level of blood glucose, but it also reduces the body's ability to burn fat. In fact, when insulin levels are high, the body is in the mode of storing not burning fat.
What's more, adds Layman, in the insulin-controlled environment that a high-carbohydrate diet fosters, insulin insensitivity can result. So, the body needs higher amounts of insulin to have any effect on glucose levels.
“On a high-protein diet, blood sugar levels tend to be more constant because amino acids trigger the body to make its own glucose. The body makes carbohydrates from protein to use as energy, but it does it slowly throughout the day. It's a continuous process. The demands on insulin are much less after a meal with a lower ratio of carbohydrate to protein.
Layman sees moderation as important to weight loss success. “The average American consumes 300-400 g. of carbohydrates, although 100 g. are necessary. Our 1,700-calorie diet includes 170 g.,” he says. “Americans interested in losing weight should reduce their consumption of bread, cereals, rice and pasta from nine servings/day to four, double protein intake and increase physical activity.”
For weight loss, Layman advises keeping calories in the 1,700 range daily, eating about 120 g. of protein/day and limiting carbohydrates to 100-175 g./day. He advises eating more green vegetables, which have a low glycemic index, and drinking only water between meals. For snacks, he recommends eating cheese sticks, a few nuts or low-fat lunchmeat. Eat fruits only at lunch or dinnertime.
There's more than a decade of proof that basing a diet on carbohydrates hasn't worked, he says. “The focus has been on reducing fat, so it's been suggested to limit protein intake. These recommendations have been a miserable failure.”