(dailyRx News) If you eat 1000 calories of donuts, or 1000 calories of steak, or 1000 calories of broccoli, does your body treat them differently when it comes to keeping weight off?
This question has plagued researchers for decades as they have sought to find out whether restricting fat or restricting carbohydrates does a body more good.
Recently, the research scales have tipped in favor of reducing carbohydrates, although not restricting them to such a level that the diet can increase other health risks, such as heart disease.
A recent study challenges the notion that simply cutting calories to a specified amount - regardless of what those calories include - means the same thing to your body when you're trying to maintain weight loss.
Instead, researchers found that diets which lead to a lower post-meal increase in blood sugar by restricting carbohydrates may help you keep the weight off better than simply sticking to a low-fat diet that includes more carbohydrates.
Associate Director Cara Ebbeling, PhD, and Director David Ludwig, MD, PhD, of the New Balance Foundation Obesity Prevention Center, joined five other researchers in exploring the impact of three different diets on maintaining weight loss.
The study involved 21 overweight and obese young adults, aged 18 to 40, from June 2006 to June 2010. Each participant lost about 10 to 15 percent of their weight and was then put on one of three different diet types for four weeks.
One type was low-fat, with 60 percent of the calories from carbohydrates, 20 percent from fat and 20 percent from protein.
Another diet was low-glycemic, which means it caused lower levels of blood sugar in the dieter because there were fewer carbohydrates, which raise the blood sugar in a person's body. This diet included 40 percent carbohydrates, 40 percent fat and 20 percent protein.
The third diet was very low-carbohydrate, including only 10 percent of calories from carbs, 60 percent from fat and 30 percent from protein. This diet would also keep the body's blood sugar lower.
At the end of the first four weeks, the participants were put on one of the other three diets for four weeks, followed by four weeks on the third diet. Each participant spent equal time using each diet, and the order was randomly distributed.
The researchers measured how many calories each person burned while at rest, how many calories their bodies burned throughout an entire day and the participants' hormone levels. They also looked at measurements related to symptoms of metabolic syndrome, a collection of health conditions that together increase a person's risk of coronary artery disease, stroke, and type 2 diabetes.
The researchers discovered that the number of calories a person burned while at rest was lowest while participants ate the low-fat diet, second lowest during the low-glycemic diet and highest with the very low-carb diet.
While on the low-fat diet, participants were burning about 205 fewer calories on average while they were at rest than they had before they lost weight. They were burning an average 166 fewer calories at rest on the low-glycemic and an average of 138 fewer with the very low-carbohydrate.
In other words, the participants' bodies were burning more calories more efficiently while at rest during the month they were eating the very low-carbohydrate diet compared to the other two diets.
The researchers saw a similar pattern with the total number of calories the body spent in a day with larger differences between the three diets. On low-fat, the participants burned an average 423 fewer total calories; on low-glycemic, an average 297 fewer total calories were burned; on very low-carbohydrate, they burned only an average 97 fewer calories.
The factors related to metabolic syndrome that were studied included their insulin sensitivity, their cholesterol levels and their triglycerides. These measurements and the levels of the participants' cortisol (stress hormone) and leptin (hunger hormone) also varied by diet, but the researchers found no consistent patterns.
After losing weight, the body's metabolism can slow down a bit more, and the person doesn't burn as many calories. But the researchers found that the diets influenced how much less energy the participants' bodies were spending.
The very low-carbohydrate diet led them to continue burning more calories, both at rest and total throughout the day, than the other two diets, so the participants had the most improvement in their metabolism during this diet.
However, this diet also had higher levels of inflammation and stress as measured by their cortisol levels than the low-glycemic diet, which had similar benefits for the body's metabolism without the extra stress. Higher cortisol levels is linked to insulin resistance (which can lead to diabetes) and heart disease.
Meanwhile, during the low-fat diet, the participants burned calories least efficiently and had more insulin resistance and unhealthy levels of lipids.
"We've found that, contrary to nutritional dogma, all calories are not created equal," Dr. Ludwig said. "Total calories burned plummeted by 300 calories on the low-fat diet compared to the low-carbohydrate diet, which would equal the number of calories typically burned in an hour of moderate-intensity physical activity."
Naheed Ali, MD, whose book "The Obesity Reality" was published this year, told dailyRx, however, that while the study's results somewhat contradict conventional wisdom regarding weight loss, it should not alter the way people view calories.
"Overall, the study is surprising since it opposes the standard notion that low-fat diets result in weight-loss, not weight gain," he said. "Our perception of a calorie should remain unchanged since the study agrees with the standard idea that calories are correlated with energy expenditure."
Dr. Ali said it was not surprising that people have difficulty keeping weight off long-term. The study's background information cited that only one in six people will maintain a 10 percent weight loss for at least a year.
"Keeping the weight off for the long run can undoubtedly prove difficult in the absence of motivation and other provisions, not only the energy-related factors investigated as part of the study," Dr. Ali said. "We are definitely seeing a shift, traversing from full-scale mental and social approaches for keeping the weight off to biological methods (adaptions)."
Lead author Dr. Ebbeling pointed out that the middle-ground diet, the low-glycemic one that reduced carbohydrates but not dramatically so and which showed a better efficiency of calorie-burning than the low-fat diet, was likely also the easiest for people to follow because it's less restrictive than the very low-carb or the low-fat ones.
The study was published June 26 online in the Journal of the American Medical Association. The research was funded by grants from the National Institute of Diabetes and Digestive and Kidney Diseases, the National Center for Research Resources at the National Institutes of Health and the New Balance Foundation.
Dr. Ludwig reported that he receives royalties from a book about childhood obesity, and he and Dr. Ebbeling both have received NIH grants to study obesity. No other disclosures were reported.