Losing body fat, or gaining muscle—which do you think is most important?
Most people would say fat loss. At first glance, this makes sense: Excess body fat makes it hard to move around. It leads 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.
The Benefits of Muscle
A big concern for anyone who cares about the future is maintaining 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 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.
How Muscle Protects Body Composition
The loss of lean muscle mass is one reason that so many people have difficulty maintaining fat loss. 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.
Muscle mass is metabolically costly, requiring calories to sustain it. As you lose muscle, your calorie needs go down.
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.
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”. 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 you are gaining muscle or losing body fat. 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.
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.
#2: Severity of Diet
A second factor that impacts weight loss is the severity of the diet. A big mistake is to slash calories below 1,200 a day. A severe deficit 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 not greater.
Leaner individuals (including people in the overweight category who are not obese) should use slower rates of weight loss 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.
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.
The rule for older adults who are interested in losing body fat is to focus on gaining 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, efforts should be taken to maintain muscle.
What Can You Do To Maintain Muscle?
Fortunately, there are two proven strategies for gaining muscle and losing body fat: Protein and exercise.
To maintain muscle when losing weight, perform a total body strength training program. Strength training may eliminate the loss of muscle, especially if it coincides with a high protein intake.
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.