Is It Harder to Build Muscle When You Have More Body Fat?

Is It Harder to Build Muscle When You Have More Body Fat?

Building muscle, especially for women, isn’t easy. Most females don’t have the hormonal make-up that makes it easy to build muscle tissue. As a result, most women have to use heavy resistance, eat a protein-rich diet and have lots of patience to develop significant muscle definition.

Men have an easier time building muscle because they have higher levels of androgens, hormones like testosterone that are anabolic. Age is a factor too. Muscle development is more challenging for women after menopause. This is due to hormonal factors and the fact that muscle loss speeds up after menopause. Now a new study shows that simply having more body fat works against you when you’re trying to build muscle.

The Challenges of Building Lean Body Mass

To build lean body mass, you have to take in more calories than you burn off. That’s why people who reduce their calorie intake too much and do too many hours of cardio usually can’t develop muscle and may even lose muscle mass even when they resistance train.

Why is excessive cardio a problem? The pathways your body uses to build muscle are different than those activated during resistance training. One of the primary pathways your muscles use for growth is called the mTOR pathway. Resistance training combined with dietary protein turns on the mTOR pathway. When this pathway is active, muscle protein synthesis takes place.

Cardiovascular exercise blocks the muscle-building mTOR pathway by its effects on an enzyme called AMPk, an enzyme active when energy requirements are high, as with long periods of cardio. This is more likely to be a problem if you do long periods of cardiovascular exercise.

Does Having Too Much Body Fat Make It Harder to Build Muscle?

An interesting study carried out by a scientist named Forbes showed a relationship between body fat and the ability to build muscle tissue. According to his research, people who have lower levels of body fat put on muscle more easily than those with higher levels of body fat. Apparently, having higher levels of body fat makes it harder to build lean body mass. According to Forbes, it’s easiest to build lean body mass when your body fat percentage is under 15%.

Muscle Development and Body Fat

Is there an explanation for this finding? For one, higher levels of body fat are linked with insulin resistance. Insulin resistance is a problem where cells, including muscle cells, become less responsive to the insulin your pancreas produces to get glucose into cells. Insulin also ferries amino acids into muscle cells so they can use them to build muscle tissue. When insulin doesn’t work as well due to insulin resistance, it’s harder to get amino acids into the muscles you just worked so they can use them to grow. Plus, insulin resistance makes it harder to shed body fat by blocking its breakdown. In general, people who are lean have greater insulin sensitivity and less insulin resistance.

According to one study, when lean and obese people eat a high-calorie diet to promote weight gain, leaner people gain more lean body mass relative to fat while obese people gain a higher proportion of body fat relative to muscle. In this study, lean individuals put on an average of 65% lean body mass on a high-calorie diet and the remainder was fat. Eating a similar diet, obese people gained an average of 35% lean body mass and 65% fat.

Eating a high-fat diet may also interfere with muscle growth, based on some research. In mice, eating a diet high in fat on a long-term basis interfered with the ability to build muscle even when their muscles were overloaded and given a stimulus to grow. A high-fat diet seems to interfere with the mTOR signaling pathway important for muscle growth.

What Does This Mean?

Having a high body fat percentage could make it more challenging to build lean body mass, probably due to the association of higher levels of body fat with insulin resistance. Fortunately, cardiovascular exercise increases insulin sensitivity. Resistance training does too, to some degree.

If you’re carrying around too much body fat, it’s important to do some form of cardio to burn calories and body fat and to improve your insulin sensitivity. Increasing insulin sensitivity will make it easier to get amino acids into muscle cells to help you build muscle tissue.

The higher your body fat, the more important it is to incorporate some form of cardio into your routine. Long periods of cardio make it harder to build muscle by turning off the mTOR pathway. Shorter periods of high-intensity interval training or circuit training workouts are better.

A combination of resistance and cardio exercises done circuit style is a good way to burn fat and get cardiovascular benefits. This type of training is less likely to interfere with muscle growth. As your body fat percentage falls, you can devote a greater proportion of your time to resistance training and less to cardio.

The Bottom Line?

Building lean body mass may be more challenging if you have a body fat percentage. If your primary goal is to lose body fat, focus on high-intensity interval training and metabolic resistance workouts initially to help your body burn more body fat. As you lose body fat, gradually devote more time to hypertrophy and strength training.

Don’t forget about the importance of good nutrition! It may sound trite but good physiques are built in the kitchen. Make sure you’re eating a clean diet and enough protein to build lean body mass and satisfy your hunger.



Exercise Biology. “Can Gaining Too Much Fat Decrease Muscle Gains?”
J. Physiol. 2009 Dec 1: 587(Pt23): 5753-65.
Ann NY Acad Si. 2000 May: 904: 359-65.


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