How to Gain Muscle Mass Without Gaining Excess Fat

There are many diets available that purport to build lean muscle and get rid of excess body fat. While there may be some truth to most of them, there are a few that are simply unhealthful fad diets. Others are backed by multiple studies from universities and hospitals. Many contain moderate to high levels of protein, and some contain moderate to high levels of fats. However, most contain low to moderate carbohydrates.

Popular diets that are high in fat and protein have come under attack from the American Heart Association and others as being unhealthy for long term use. The fact that people continue to follow them speaks to their reliability for quick weight loss.

Bodybuilders and other figure athletes follow many of the tenets of Atkins. A study by the Stanford University School of Medicine found support for low-carbohydrate diets.
Women who were on it did significantly better than those on the Ornish diet, a high-carb, low-fat diet.

A high-protein diet offers good results for several reasons. For one, protein takes longer to digest than carbohydrates, resulting in a slower release of nutrients and steadier blood sugar. That means protein results in feelings of satiety, which curbs overeating.

In one study, eating protein before a meal decreased the amount of hunger perceived by participants, which resulted in fewer calories being consumed during the meal.

The body has a minimum amount of calories it takes just to function every day. This is your basal metabolic rate (BMR). When you greatly restrict calories you will get an initial rapid weight loss response, but if you maintain calorie levels that are too low for an extended period of time your body thinks it is starving and lowers your BMR. This means you need less calories a day to maintain weight. Also, your body will strip nutrients from your muscles, causing you to lose muscle mass. Since muscle burns approximately 40-50 calories per day to maintain itself, you are doing more harm than good by allowing your body to strip it of nutrients.
The amount of calories needed per day to maintain weight vary from person to person based on age, gender, weight, and lean muscle mass. A rough estimate of minimum calories per day to keep the body from going into starvation mode is 1200 calories.

Sources:
Bodybuilding diet study
Protein satiety
Minimum calorie requirements
Low carb and ketogenic diet information