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The purpose of this study was to analyze the effects of a low-calorie, high-protein diet (using two different protein supplements) and resistance training (weight lifting), versus a low-calorie diet alone, on body composition changes in overweight police officers. The first group of 10 officers was placed on a low-calorie diet alone. The second group of 14 officers was placed on a low-calorie diet and given 1.5 grams per kilogram bodyweight per day of a casein protein supplement. The third group of 14 officers followed an identical regimen to the second but the supplement consumed was whey-based protein. Both groups 2 and 3 engaged in a resistance-training program in conjunction with their diet. Programs were maintained for 12 weeks. All groups lost an average of 5.5 pounds. At 12 weeks, the average percent body fat with diet alone decreased from 27% to 25%, the casein protein group decreased from 26% to 18% and the whey protein group from 27% to 23%. The average fat loss was 5.5, 15.4 and 9.3 pounds in the three groups respectively. Lean muscle mass gains did not occur in the group that was on a low-calorie diet alone. But the casein group had an average lean muscle mass gain of 8.8 pounds and the whey group an average increase of 4.4 pounds. Average increase in strength for chest, shoulder and legs was 59% for the casein group and 29% for the whey group, resulting in a significant difference as compared with the diet-only group. The researchers concluded that differences in body composition and strength are likely due to improved nitrogen retention (being in positive nitrogen balance, allowing for tissue building) and overall anticatabolic effects (prevention of muscle breakdown) caused by the casein proteins’ peptide (chains of amino acids that make up the protein) content.