Losing Fat Without Losing Muscle

When people diet, the goal is to lose fat. The body does not always cooperate. In a calorie deficit it draws energy from fat, but it can also break down muscle, and without the right inputs a meaningful part of the weight you lose can be lean tissue.

Why muscle goes too

Muscle is expensive to maintain. When food is short and there is no reason to keep it, the body lets some go. In diet studies without strength training, roughly a quarter of the weight lost often comes from lean mass. Losing weight quickly and eating little protein both push that share higher.

That matters because muscle is what carries your strength, stores glucose and protects you from falls later in life. A hypothetical 50 year old man who loses 20 pounds, 5 of them lean mass, has improved his weight and given back some strength he will want at 70.

How to protect it

Three things do most of the work:

• Give muscle a reason to stay. Strength training two to three days a week tells the body the muscle is still in use. This is the most important signal.
• Supply the materials. Protein at about 1 gram per pound of lean body mass per day, spread across 3 to 4 meals of 30 to 50 grams.
• Keep the pace moderate. Losing about 0.5 to 1% of body weight per week gives the body less reason to break down lean tissue than a crash diet does.

Sleep helps as well. In one well known study, people who slept about 5.5 hours during a diet lost more lean mass and less fat than when they slept about 8.5 hours.

How you would know

The scale cannot answer this. It drops whether you lose fat or muscle. An InBody scan reports fat mass and lean mass separately, so you can see which one moved.

One caution when reading the results. In the first week or two of a diet, especially one lower in carbohydrates, the body uses stored glycogen. Each gram of glycogen is stored with about 3 grams of water, and that water counts as lean mass on the scan. Early lean mass loss is often mostly water, not muscle.

That is why we look at the trend over several monthly scans, taken under the same conditions each time: same time of day, before eating and before exercise. If fat mass falls and lean mass holds steady over two or three scans, the plan is doing what it should. If lean mass keeps dropping, we adjust protein or training before more is lost. Strength in the gym is a useful second check.

That's the kind of thing we measure.

Book an InBody scan at HYBRD Health ($39)

This article is educational and is not medical advice.