Not all weight loss comes from fat.
While fad diets can sometimes cause you to quickly lose quite a few pounds, this doesn't mean you are actually losing that much fat. Some of this weight loss comes from water weight loss, which will come back once your diet returns to normal, and some of it comes from lost muscle. However, there are steps you can take to ensure you lose as much fat as possible while retaining most of your lean muscle mass.
Weight Loss Versus Fat Loss
When you diet to lose weight without taking any steps to maintain your muscle mass, about 25 percent of what you lose will come from muscle rather than fat, notes the American Council on Exercise. You want to minimize your muscle loss, because muscle takes more calories to maintain than fat. Muscle also takes up less space, so when you replace fat with muscle you sometimes look leaner even if you are still at the same weight.
Effect of Diet Composition
You may be better able to maintain your muscle and lose more fat if you follow a high protein diet. A study published in "The FASEB Journal" in September 2013 found that participants who consumed two to three times the recommended dietary allowance for protein while following a low-calorie diet for 21 days lost more fat and maintained more muscle than those who consumed a low-calorie diet with only the recommended dietary allowance for protein. In a study published in the "Journals of Gerontology, Series A" in 2011, researchers found that participants who followed a high-protein diet also improved the amount of muscle they had per pound of body weight while losing more fat than people who followed a diet higher in carbohydrates.
Strength Training Effects
Adding strength training to a weight loss diet will help you maintain more of your muscle mass while increasing your strength and losing weight compared to dieting alone, according to a study published in "Medicine and Science in Sports and Exercise" in July 2008. The Centers for Disease Control and Prevention recommends adults do at least two strength training workouts per week that work out all of their major muscle groups.
Aerobic Exercise Effects
Strength training isn't the only type of exercise that helps you improve your body composition while losing weight. A study published in "The Journal of Clinical Endocrinology & Metabolism" in September 2008 noted that either aerobic exercise alone or aerobic exercise plus strength training during a reduced-calorie diet resulted in a smaller loss of muscle and a greater loss of fat than following a low-calorie, high-protein diet alone. Aim for at least 75 minutes of high-intensity aerobic exercise or 150 minutes of moderate-intensity aerobic exercise each week, recommends the CDC.