People lose weight when they cut kilojoules, but a diet with some extra protein may be especially effective at trimming body fat and improving blood fats, a new study suggests.
Researchers found that over one year, a moderate-protein diet was better than a standard high-carbohydrate, low-fat diet at helping overweight adults shed body fat. What's more, it had greater benefits when it came to boosting "good" HDL cholesterol and lowering triglycerides, a type of blood fat that contributes to clogged arteries.
The findings, reported in the Journal of Nutrition, suggest that trading in some carbs for protein may do dieters good.
For the study, 130 overweight adults were randomly assigned to one of two calorie-restricted diets: the commonly recommended higher-carb diet, with about 15% of kilojoules coming from protein, 55% from carbohydrates and 30% from fats; or a moderate-protein diet where 30% of kilojoules came from protein - including lean meat, low-fat dairy and nuts - while 40% came from carbs, and 30% from fats.
How the study was done
All participants were given menu plans and attended weekly meetings with a dietitian to help them stick with their new lifestyle. After one year, the average weight loss was similar in the two groups – 10,4kgs with the moderate-protein diet, versus roughly 8,6kgs with the high-carb diet.
However, the moderate-protein former group lost more fat mass, and had greater improvements in both HDL and triglyceride levels.
The extra protein at each meal helps dieters preserve "metabolically active" muscle mass, explained lead researcher Dr Donald K. Layman, of the University of Illinois in Urbana. At the same time, he said, the diet's lower carbohydrate content means lower levels of the blood-sugar-regulating hormone insulin.
So the diet encourages the body to shed more stored fat, according to Layman. The greater improvement in triglycerides, he said, is largely the result of cutting carbs, which can raise triglyceride levels.
Forget 'old diet concepts'
A problem with any diet is that people have to do it right to be successful. In this study, dieters in both groups got a lot of help, with planned menus and weekly educational sessions. Whether people would fare as well on their own is unclear.
"One of the problems with moderate protein diets is that people bring old diet concepts to their approach," Layman said. For example, he said, the concept of eating "lots of small meals" throughout the day works when the diet is high-carb, low-fat because people are hungry more often - but it's a bad idea with a moderate-protein diet.
"The important change is three consistent meals with a balance of protein and carbohydrates at each meal," Layman advised. "A higher protein diet is not more protein at dinner, but balanced protein at breakfast and lunch." – (Reuters Health, March 2009)
Low kilojoule diet works best
Body clock regulates metabolism