Filling up on protein to build muscle or slim your waistline may cause adverse effects, including increased body fat. As with all calories -- whether they come from carbohydrates, protein or fats -- your body converts what you don't need for energy into stored fat, which will remain until you burn it off.
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The key to preventing fat accumulation is to eat as many or fewer calories as you burn for energy. At a low to moderate activity level, the average woman burns 1,800 to 2,200 calories per day and the average man burns 2,400 to 2,800 calories per day, with older adults burning fewer calories than their younger counterparts. For good nutrition, the "2010 Dietary Guidelines for Americans" recommends getting 10 to 35 percent of those calories from protein.
Exceeding your calorie needs with excess protein may lead to weight gain and can compromise your health. According to the American Council on Exercise, protein metabolism uses extra water, so high protein intake may lead to dehydration. ACE also notes that eating large amounts of protein can make you expel too much calcium in your urine, potentially contributing to weaker bones over time.