Most people who want to change their body are interested in fat loss. At first glance, this makes sense: Excess body fat is unsightly. It makes it hard to move around. It is associated with the development of diseases including cancer and diabetes. It negatively impacts function of other systems in the body, such as reproduction and mental health.
However, human metabolism is far from simple, and any time you lose weight, you lose muscle.
Losing muscle is a big problem because muscle mass is a key indicator of health and a predictor of longevity. The more muscle you have, the longer you will live and the greater your chance of survival if you experience a serious disease or injury.
There is also the fact that muscle defends against getting fat since it is the engine for your metabolism. People who lose a lot of muscle during weight loss skyrocket the likelihood that they will experience rebound weight gain.
In light of these enormous benefits of maximizing muscle mass, it raises the question, is it more important to lose fat or gain muscle?
The answer will depend on the individual. This article will discuss the role of muscle in metabolic function and look at the pros and cons of gaining muscle versus losing fat in different situations. We’ll finish with recommendations for getting the best of both worlds with tips for losing fat, while maximizing muscle mass.
The Benefits of Muscle
A big concern for anyone who cares about the future is maintaining muscle. Any time you lose weight, a portion of that weight is body fat and the rest is lean tissue, mostly muscle. For the average overweight dieter, 70 percent of the weight lost is from fat and 30 percent is from muscle.
Why is muscle so important?
Muscle has a protective effect on the body, allowing people to survive illness and live longer, more vigorous lives. The older you are the more important muscle mass becomes to you. Your muscle mass is your bank account for healing from an illness or injury. The more muscle you have in the bank, the longer you can hold out when things go wrong in your body.
Why is this? Muscle modulates immune function, serving as an active repository for proteins and other components necessary for a robust immune system. Additionally, it may offset inflammation that is associated with the progression of diseases like cancer, diabetes, and heart disease.
Of course, muscle also plays a role in body composition. The loss of lean muscle mass is one reason that so many people have difficulty maintaining fat loss. You might be surprised to hear that less than 10 percent of people who lose weight are able to maintain weight loss over the longer term. One study of 911 volunteers found that only 6 percent maintained weight loss of at least 5 percent after 6 years. How does muscle play a role?
Muscle mass is metabolically costly, requiring calories to sustain it. As you lose muscle, your calorie needs go down. Few people reduce their food intake, experience a weight loss plateau and eventually end up gaining back any fat that they had lost.
Another problem with losing muscle is that people lose strength and become weaker. When this happens, they decrease their physical activity, moving less and burning fewer calories throughout the day.
Muscle also impacts blood sugar and insulin health. Even when you’re not working out, muscle consumes 70 to 90 percent of the glucose in the blood. Exercise increases this demand. Additionally, muscle contractions sensitize muscle cells so that insulin can more easily bind with them.
There’s also the fact that when muscles grow in size, you increase the number of insulin receptor sites, allowing your body to handle more glucose. For all practical purposes, this means your carb requirements go up and you can eat more sweet potatoes, fruit salad, pizza or other delectable carbohydrate-rich food.
What Factors Impact Muscle Loss?
Several factors impact the degree of muscle that is lost during fat loss:
#1: Baseline Body Composition
Baseline body composition plays a large role in how much muscle you are likely to lose. When overweight individuals lose weight, about 70 percent of the weight loss is from fat and 30 percent is muscle. Leaner individuals are not so lucky. Studies show that in men with body fat below 10 percent, as much as 50 or 60 percent of the weight lost during a diet will be from muscle and only 40 to 50 percent will be from body fat.
Scientists call this phenomenon the “protein sparing effect of adiposity” (adiposity means having excess body fat). The theory goes that due to chemical messengers released from fat cells, the human brain is able to sense how much fat is stored on the body. This allows for the brain to regulate whether fat or muscle are being used for energy. When the obese go on a diet, the brain doesn’t feel as threatened and a greater proportion of the weight loss is from fat.
Take Away: Although muscle is always a priority, for obese people, especially for those whose obesity is impacting quality of life, it’s probably safe to say that losing body fat is more important. Doing it efficiently while teaching sustainable eating and exercise habits will yield the best long-term results. For leaner individuals who want to drop body fat, maintaining muscle becomes a priority by maximizing protein intake, using a gradual rate of fat loss, and performing strength training (all strategies that will be discussed in depth below).
#2: Severity of Diet
A second factor that impacts weight loss is the severity of the diet. A big mistake many people make is to slash calories below 1,200 a day. They want to lose fat quickly, so they figure more of a deficit is better. This backfires because the greater the energy deficit, the more muscle you lose.
This can be offset by using more moderate rates of weight loss. For example, a study of athletes compared what would happen with a 500-calorie a day diet or a 1,000-calorie diet. Results showed that although it took the athletes three weeks longer to lose the weight with the 500-calorie deficit diet, the greater daily energy intake allowed them to gain 2.1 percent muscle mass at the same time.
The group on the 1,000-calorie deficit diet lost 5 percent of body weight in 5 weeks and dropped 0.2 kg of muscle. Both groups ate a higher protein diet and did a heavy weight-training program in conjunction with regular sport training, which is likely the reason the muscle loss in the 1000-calorie deficit group was insignificant.
Take Away: Leaner individuals (including people in the overweight category who are not obese) will benefit from slower rates of weight loss because the experience will be less miserable and it is possible to preserve lean mass.
For the obese who have a lot of weight to lose, faster rates may be warranted because they can boost morale. However, in this situation it’s generally best to “periodize” calorie intake such that you use a larger calorie deficit for roughly 2 weeks alternated with a smaller deficit in order to avoid the slow down in energy expenditure that coincides with weight loss.
Aging automatically leads to muscle loss of about 1.5 kg per decade. For older individuals trying to lose weight, muscle losses increase, nearing 50 percent of weight lost. In one estimate, a senior over 65 losing 5 kg in body weight would lose about 2.15 kg of muscle. The loss of muscle is particularly harmful in this population because they are unlikely to gain it back and it leads to a decline in strength, physical function, and eventually frailty, which is associated with increased mortality risk.
Take Away: The general rule for older adults who are overweight is to focus on increasing muscle through diet and exercise. This will lead to a shift in body composition, increasing lean mass for a lower body fat percentage even if no fat is lost. For severely obese individuals, fat loss may be the focus, however, certain action should be taken to maintain muscle, which we will discuss in the next section.
What Can You Do To Maintain Muscle?
Fortunately, there are two proven strategies to preserve muscle during weight loss: Protein and exercise.
Scientists have tested a couple of different exercise interventions on the maintenance of muscle:
When subjects exercise without going on a diet, lean mass is typically preserved or even increased. A study that had women burn 600 calories a day by running on a treadmill found that the women lost 2.7 kg of fat and increased lean mass by 1.1 kg.
When diet and exercise are combined, preservation of lean mass is not as favorable: One review found that a low-calorie diet combined with aerobic exercise produced muscle loss of about 1.7 kg in both men and women.
Performing strength training may eliminate the loss of muscle, especially if it coincides with a high protein intake. One study from Canada found that doing an intense 6-day a week training program and eating a high-protein diet preserved muscle mass. Subjects who ate 1.2 g/kg of body weight of protein maintained muscle while losing 3.5 kg of body fat. A subset of volunteers who had a higher protein intake actually gained 1.2 kg of muscle while losing 4.8 kg of fat.
Protein and strength training are game changers because they are the only two ways to stimulate protein synthesis in the body. Protein synthesis is the method by which muscle is built and lean tissue is restored.
Strength training does it by overloading the muscle, triggering a protein synthesis pathway known as mTOR, whereas protein foods provide amino acids. Based on the availability of amino acids, the body is constantly in a fluctuating state of muscle loss and gain. Anytime you replenish the pool of amino acid building blocks by eating protein, it’s a good thing, protecting the muscle you’ve got.
Take Away: To blunt muscle loss when dieting, perform strength training and increase protein intake to a minimum of 1.6 g/kg. For someone weighing 165 lbs, this equals 75 kg in body weight, so you need a minimum of 120 grams of protein daily.
There may be a benefit of going as high as 2.4 g/kg of body weight, especially if the program is combined with strength training. Be sure to spread high-quality protein meals out over the day to continually stimulate protein synthesis and avoid muscle breakdown.