Can You Build Muscle in a Calorie Deficit?

muscular-backWhen I heard about a study supposedly showing 16 pounds of fat lost and 10 pounds of muscle gained — all at the same time — my BS detector started working overtime.

Either somebody was telling me “porkies” or they had just made an honest mistake.

But when I looked at the research myself, there was no mistake. A group of eight men had lost 16.3 pounds of fat and gained 9.5 pounds of lean mass in just 14 weeks.

Is it really possible to build so much muscle while you’re in a calorie deficit?

The results I’m talking about come from a United States Sports Academy study looking at the effects of strength training and aerobic exercise on body composition in a group of overweight (27% body fat) men.

The men were assigned to one of two groups and trained three days per week for 14 weeks.

  • An endurance-only group performed both cycling and walking (30 minutes each at 60-70% heart rate reserve for a total of 60 minutes).
  • A cross-training group performed both cardiovascular and resistance exercise (8 exercises, 4 sets per exercise, 8-12 repetitions per set, 60 seconds of rest between sets) in a single session. Exercises included the bench press, lat pulldown, military press, barbell curl, triceps extension, leg press, leg curl, and calf raise.

The results are shown in the table below, which I scanned in from the research paper.
Can you build muscle in a calorie deficit?As you can see, the group that combined cardiovascular with resistance exercise were able to lose fat (7.4 kilograms or 16.3 pounds) while gaining muscle (4.3 kilograms or 9.5 pounds) at the same time.

That’s pretty impressive.

Truth is, losing 16 pounds of fat and gaining almost 10 pounds of muscle in 14 weeks is a result that most people (and that includes me) would be very happy with.

But as I mentioned earlier, not everyone is going to make such rapid progress.

Firstly, the men taking part in the study were beginners, who tend to make rapid gains in muscle mass when they start training with weights.

They were also overweight (bordering on obese) with a lot of fat to lose. Take someone who is untrained AND extremely overweight (which these men were) and they’ll often drop relatively large amounts of fat while gaining muscle at the same time.

Why do overweight beginners have such an easy time gaining muscle while losing fat?

People who are very overweight are usually insulin resistant to some degree. Insulin resistance tends to develop as you gain fat. It appears to represent an attempt by your body to stop you gaining more, or to help you lose fat once the excess calories are removed from your diet.

Insulin is primarily a storage hormone. It helps to drive nutrients, such as glucose, from your blood into the cells of your body. High levels of insulin also inhibit the rate at which stored fat is mobilized (i.e. broken down and prepared to be burned off).

But when fat cells are insulin resistant, insulin doesn’t have the same effect. Which means that even in the presence of high insulin levels, fat can still be mobilized for fuel. The overall effect is as though fat cells are “full up” and resisting further fat storage.

When an overweight beginner starts exercising and dieting, nutrients are diverted away from fat cells (which are still insulin resistant) and towards muscle, which has become more insulin sensitive as a result of the training. The uptake of glucose in insulin resistant muscle is also reduced. Because there’s less glucose available, muscle cells will burn more fat.

While I’m on the subject of hormones, it’s also worth pointing out that a restrictive diet combined with a lot of exercise can lead to a large rise in cortisol levels, which in turn can cause water retention. This may have accounted for at least some of the gains in fat-free mass.

Second, the researchers used underwater weighing to measure changes in body composition.

Underwater weighingAlthough underwater weighing is still considered by many as the “gold standard” when it comes to estimating body composition, there’s still a surprisingly large margin of error, which can skew the results.

As Weightology founder James Krieger points out in his excellent series of articles on the subject, “body fat testing is not a measurement; rather, it is a prediction.”

Researchers have compared underwater weighing with something called the 4-compartment (4C) model for assessing body fat change in individuals.

The 4C model is an expensive method of measuring body composition that divides the body into four components (mineral, water, fat, and protein) and measures each one independently.

Short of killing someone, stripping off their fat and weighing it, the 4C model is currently the best method available to predict body composition.

The results, as James puts it, “aren’t pretty.”

For example, one person showed a 10% loss of body fat using something called the 4-compartment model. But underwater weighing showed a change that was near 0%.

Another person showed a loss of 10% body fat in the 4-compartment model, but a loss of nearly 20% body fat with underwater weighing.

“This means that underwater weighing could tell you that you had very little change in body fat, when you actually had a large change,” adds James.

“On the other hand, underwater weighing could tell you that you lost a huge amount of body fat, when in fact you didn’t lose much.”

Of course, this doesn’t mean that we should ignore the results of this study. But the accuracy of body fat testing is something to keep in mind when you see results that seem a little too good to be true.

Third, the average gain in muscle tells you nothing about the individual results for each subject, which can often vary widely.

Let’s say that you take a group of six men and get them to lift weights for 12 weeks.

Two of the men might make reasonable progress and gain five pounds of muscle. Another two might make slower progress and gain only two pounds.

If we take the results of these four men, the average gain in muscle is 3.5 pounds (5 + 5 + 2 + 2 = 14/4 = 3.5)

But if the other two guys have an easy time putting on muscle (let’s say they gain 12 pounds of muscle), they’re going to skew the results of the group. Adding their results to those of the other four men takes the average muscle gain up from 3.5 to 6.3 pounds (12 + 12 + 5 + 5 + 2 + 2 = 38/6 = 7.3). In other words, two high responders have had a disproportionate influence on the results of the study.

It’s possible that a few of the men in the United States Sports Academy study got outstanding results, which would have boosted the average. The large standard error shown in the results table would suggest as much. But without seeing the individual results for each subject, it’s hard to say for sure.

In summary, some people can and do build a decent amount of muscle while they’re in a calorie deficit.

But it’s a phenomenon that’s generally limited to people who are very overweight and have never lifted weights before, or those who are returning to exercise after a layoff, where muscle memory comes into play.

Once you’ve move past the “overweight beginner” stage, building a significant amount of muscle while losing fat is a goal that becomes progressively more difficult.


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Christian FinnChristian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.