People who cut carbohydrates in order to lose weight do equally well whether they compensate with increased amounts of animal protein or plant-based fats, a new study suggests.

Australian researchers found that a low-fat, high-protein diet and a high-fat, moderate-protein diet were equally successful in helping 57 overweight and obese volunteers shed pounds over three months.

Both regimens, which restricted carbs to a moderate degree, also showed similarly positive effects on the dieters’ levels of cholesterol, blood sugar and insulin, the key hormonal regulator of the body’s blood sugar levels.

The findings, say the researchers, show that people have some choices when it comes to carb-cutting.

The Low fat dietslow-fat, high-protein diet used in the study was based on fairly generous portions of lean meats and fish and low-fat dairy products. The high-fat version was rich in monounsaturated fats from canola oil and nuts, and contained more-moderate amounts of lean meat and dairy.

Both meal plans kept carbohydrates to about one-third of the dieters’ daily calories, and included fruits, vegetables and even a slice of whole-grain bread.

“The implication of these findings,” the study authors report in the American Journal of Clinical Nutrition, “is that protein from meat, poultry and dairy foods or fat from food sources rich in monounsaturated fatty acids are both suitable options to replace some dietary carbohydrate, at least in the short term.”]

A number of studies have suggested that low-carb diets spur weight loss more quickly than low-fat diets do. Proponents of carb-cutting say the diets force the body to switch from using mainly using glucose (sugar) for fuel to burning its stored supplies of fat instead.

However, many questions about low-carb diets remain - including whether the eating plans keep the weight off and whether they might have ill effects on health in the long term.

Some experts worry about the eventual effects on the heart and blood vessels, particularly when people follow diets that are heavy in saturated fats from meat and dairy products. In addition, the metabolic effects of high-protein, high-fat diets may deplete minerals in the bones or stress the kidneys.

Another question has been whether it’s best - as far as weight loss and overall health - to replace some of the lost carbohydrates with protein or fat. In the current study, it did not matter, Dr. Peter M. Clifton of the University of Adelaide told Reuters Health.

He and his colleagues found that after 12 weeks on either diet, men and women lost a similar amount of weight - more than 20 pounds, on average. They did not, however, shed any weight during an additional four-week period where they replaced carbs with protein or fat but did not cut their calorie intake.

In addition to the weight loss, dieters’ levels of blood cholesterol and insulin fell with either plan, and there were no signs of short-term harm to participants’ bones or kidney function from either diet.

However, as Clifton pointed out, neither diet was “radical,” with each being relatively low in the saturated fat and balanced in nutrient content. “Either diet would be sustainable in the long term,” he said.

There was, though, one subtle difference potentially in favor of the high-protein tactic, at least in terms of weight loss. Men and women on that diet showed a smaller decrease in a measure called the “thermic effect of feeding.” This means that they used more calories simply metabolizing their food than their peers on the high-fat diet did.

It’s possible, Clifton said, that over one to two years, the high-protein diet could end up spurring greater weight loss.

SOURCE: American Journal of Clinical Nutrition, April 2005.