The Effect of Protein Intake on Muscle Maintenance during Weight Loss

What muscle mass is and how much we lose

Muscle mass, lean body mass and fat-free mass are often used as synonyms, although they have differences. Muscle mass usually refers to skeletal muscle mass and is included in lean body mass, which instead comprises the total body weight minus fat mass. Thus, internal organs and bone marrow, containing some essential fat, are included in lean body mass. However, fat-free mass is what it sounds like – body mass free from fat. To assess fat-free mass, the essential fat in organs and bone marrow is estimated and subtracted from total body weight. In this article, the term muscle mass will be used. Regardless of used term, muscle mass, lean body mass and fat-free mass are all linked with healthy outcomes, such as lower risk of overweight, type 2 diabetes and cardiovascular disease. 

However, having enough fat mass is extremely important for our health as well, for example for storing energy and vital hormones, protecting our organs and helping us to keep warm. Healthy body fat percentages range from approximately 20-35 % in women aged 20-59 years and 8-22 % in men aged 20-59 years. Body fat percentages below these ranges are not recommended. 

When losing weight from eating a calorie-reduced diet, fat mass as well as muscle mass are lost. In overweight people, 20-30 % of total weight loss is muscle mass. However, in normal weight people, the loss of muscle mass is often as much as 35 % or more of the total weight loss. Also, normal weight people who regain weight after weight loss gain more fat mass than overweight people. Due to the health benefits linked with muscle mass, it is valuable to limit the loss of muscle mass when following a calorie-reduced diet.

How to limit muscle loss

During negative energy balance, muscle mass is willingly transformed to be used for energy production. Periods of reduced calorie intake are therefore problematic for muscle maintenance. Even though some muscle mass unavoidably will be lost during weight loss, there are approaches to limit muscle loss. 

Protein intake plays an important role in maintaining muscle mass. Following a high-protein diet with a protein intake above the requirement level helps preserving muscle mass and increasing fat loss. In addition, diets with a protein intake below the requirement level appears to increase the risk of regaining weight. However, a protein intake above 35 % of the total calorie intake has not been shown to give any additional muscle-sparing effects. Remember to always try to eat well-balanced meals containing fat, carbohydrates and protein. An additional approach to limit loss of muscle mass is strength training. Combining strength training with an increased protein intake during weight loss is advantageous for minimizing muscle loss. It also has the positive effect of improving muscle strength. However, the muscle-sparing effect of combining a high-protein diet with strength training appears to be weakened if the total calorie intake is extremely low in comparison to the energy requirements. In those cases, dietary protein mainly becomes a source of energy for meeting the energy requirements, instead of preserving muscle mass. In order to minimize possible health disadvantages from an inadequate calorie intake, it is important to get professional help when aiming to lose weight.

Additional effects of high-protein diets

Another positive aspect with a high-protein diet is its beneficial effect on resting energy expenditure, which actually is linked with muscle mass. Resting energy expenditure, also called basal metabolic rate, is the amount of energy required for bodily functions when lying down without performing any type of movement. It is directly related to the amount of muscle mass, since muscles are more energy-demanding than fat mass. Thus, eating according to a high-protein diet during calorie restriction is associated with muscle maintenance, consequently keeping up the resting energy expenditure.

However, despite greater weight loss, fat mass loss, satiety and less muscle loss during high-protein diets, the long-term effects on weight status is unclear. This uncertainty is due to difficulties in conducting long-term studies on this area, because of problems of adhering to a high-protein diet for periods longer than one year. Eating a protein-rich food source in each meal is one way to make it easier to adhere to a high-protein diet. Examples of healthy protein sources are fish, chicken, lean meat, vegetarian meat substitutes, eggs, tofu, beans and lentils.

Summary

Muscle mass is evidently linked with health benefits, such as lower risk of cardiovascular disease and type 2 diabetes. Following a high-protein diet during weight loss preserves muscle mass, and the best result is obtained when combined with strength training. A higher protein intake also increases the energy consumption, probably due to the muscle-sparing effect, since muscle mass utilizes more energy than fat mass. However, it is important to remember that dietary carbohydrates and fat have essential functions in our body and should constitute an appropriate part of our diet. 

Written by Ellinor Nilsson

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