New research suggests a higher-protein, lower-carbohydrate energy-restricted diet has a major positive impact on body composition, trimming belly fat and increasing lean muscle, particularly when the proteins come from dairy products.
The study, published in the September issue of the Journal of Nutrition, compared three groups of overweight and obese, but otherwise healthy, premenopausal women. Each consumed either low, medium or high amounts of dairy foods coupled with higher or lower amounts of protein and carbohydrates.
The women exercised seven days per week for four months, a routine that included five days of aerobic exercise and two days of circuit weightlifting.
According to the researchers, there were identical total weight losses among the groups, but the higher-protein, high-dairy group experienced greater whole-body fat and abdomen fat losses, greater lean mass gains and greater increases in strength.
The tissue composition, exclusively fat, of the weight the women lost has profound implications for longer-term health, say the researchers.
"One hundred per cent of the weight lost in the higher-protein, high-dairy group was fat. And the participants gained muscle mass, which is a major change in body composition," says Andrea Josse, lead author of the study and a graduate student in the Department of Kinesiology at McMaster University. "The preservation or even gain of muscle is very important for maintaining metabolic rate and preventing weight regain, which can be major problem for many seeking to lose weight."
Researchers found the lower-protein, low-dairy group lost about a pound and half of muscle whereas the lower-protein, medium dairy group lost almost no muscle. In marked contrast, the higher-protein, high-dairy group actually gained a pound and half of muscle, representing a three-pound difference between the low- and high-dairy groups.
On top of the muscle mass differences, the higher-protein, high-dairy group lost twice as much belly fat than the lower-protein, low-dairy group.
"Fat in the abdomen is thought to be especially bad for cardiovascular and metabolic health, and it seems—according to what we found in this study—increasing calcium and protein in the diet may help to further promote loss of fat from the worst storage area in the body," says Josse.
"A very important point is that these changes were not captured by simple measures of body weight or body mass index, which are the most commonly used measures of dietary 'success'" adds Stuart Phillips, a professor in the Department of Kinesiology. "These women also got fitter and stronger, which greatly reduces their risk of disease."
The I.D.E.A.L. (Improving Diet Exercise and Lifestyle) for Women study was funded by Dairy Farmers of Canada, the US Dairy Research Institute and Canadian Institutes of Health Research. Agropur Incorporated provided the dairy products used in the study.
Attention editors: Video clips of Stuart Phillips and Andrea Josse discussing the findings can be found at: http://www.youtube.com/watch?v=G4B-35-lwCc
A copy of the study can be found on the Journal of Nutrition's website at http://jn.nutrition.org/content/141/9/1626.full
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Journal of Nutrition