Both high protein and high dairy intakes have been shown to be beneficial for weight loss. Protein is beneficial because it can increase satiety and may be less efficiently metabolised compared to fat or carbohydrate. Dairy is possibly beneficial because of the high calcium content which may increase satiety and alter cellular signalling. Because of the potential benefits, one group of researchers1 has investigated the effects of varying protein and dairy intakes on weight loss in premenopausal women. One group of subjects was fed a high protein (30% energy) high dairy (15% energy) diet, another group was fed an adequate protein (15% energy) medium dairy (7.5% energy) diet, whilst another was fed an adequate protein (15% energy) low dairy diet (<2% energy). Body composition was measured using dual energy x-ray absorptiomometry (DXA) and visceral adipose tissue was measured using magnetic resonance imaging (NMR).
All groups were subjected to regular exercise that involved 7d/wk supervised and unsupervised aerobic exercise, as well as 2d/week resistance training. Energy deficit from training was estimated to be 250kcal, while a reduced calorie diet cause a further deficit of 500kcal/d. All subjects lost weight and body fat, but there was a significantly greater loss in the high protein high dairy group during weeks 8 to 16. This group also gained significantly more lean mass during weeks 8 to 16 than the adequate protein medium dairy group, whereas the adequate protein low dairy group lost lean mass. The high protein and high dairy diet was also shown to cause a significant reduction in visceral fat (as assessed by NMR) and abdominal fat (as assessed by DXA). The reduction in visceral fat was associated positively with the intakes of calcium, which supports previous epidemiological and clinical evidence.
These results support existing data demonstrating the benefits of high protein and high calcium (dairy) intakes on weight loss. This study lacked an exercise control group, that could have been used to determine if the exercise was beneficial to weight loss. While weight loss has been shown to occur following exercise in overweight subjects, the long-term benefits of exercise are not proven, with many studies showing inconclusive results. However, the overweight subjects in this study did benefit from exercise in terms of aerobic fitness, with heart rate reducing by 15 beats per minute at the same absolute workload, over the 16 week training period. Significant blood lipid changes were seen in the high protein high dairy and adequate protein medium dairy groups, with plasma levels of with triglycerides, total and low density lipoprotein cholesterol decreasing. This was likely in response to the weight loss and carbohydrate restriction.