Diet dilemmas: When you lose fat, you also lose muscle. How can you prevent that?

When you go on a diet, you don’t just lose fat – you lose muscle too. This can have many repercussions – not only on your fitness and strength, but on your metabolism.

To lose weight (body fat), you need to be in a calorie deficit. This means consuming fewer calories than your body uses, or exercising to burn more calories than you consume.

During the first few days in a calorie deficit, the body uses up its small reservoir of glycogen stores for energy. Glycogen is a string of glucose (sugar) that comes from the carbohydrates you eat. Since carbs are the body’s main energy source, this is why any glucose the body doesn’t immediately use is stored to use for energy later.

Given you only have days’ worth of glycogen stores, this is why the body uses fat to store extra calories for when you need it. Once the glycogen stores are used up, the body shifts to metabolising fat to get the energy it needs to function.

But not all tissues can use fat for energy – such as the brain. This is why the body needs to metabolise your muscles when you’re in a calorie deficit.

Protein (from the food you eat) is stored in your muscles. The...

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