Your body won’t take your muscles away instead of your fat

I’m currently on a weight loss journey—I’ll tell more about that in a future post. But I just heard a statement once again that confused me for a long time:

When you’re losing weight, you need to be careful that your body doesn’t burn your muscles instead of your fat.

This is very misleading and oversimplified. It can sound as though you’ll stay fat while your body consumes only your muscles. It sounds daunting and makes it seem more difficult. In reality, your body does not choose exclusively between burning fat and losing muscle.

Weight loss usually consists of body fat together with some fat-free mass (water, glycogen, muscle, etc). A frequently cited rule of thumb is that roughly 75% of weight loss is fat and 25% is this other fat-free mass. This is only a very rough average because the actual proportions vary between people and diets.

Another common rule says that saving 7,700 calories means losing roughly 1 kg of body fat. In reality, if you have a deficit of 1,100 calories per day, you’ll not lose exactly 1 kg after a week, and you won’t see this progress happening linear, day to day, on your scale. Weight loss is not linear, and short-term changes in body water can change what you see on your scale. However over many weeks and months, I found this to be a reliable estimate, even if it’s not an exact prediction. It’s very rewarding to see this relation between cause (calorie deficit) and effect (losing weight that closely matches the calorie deficit), so I keep doing it.

Over weeks and months, for people with excess body fat, a sustained healthy calorie deficit will cause weight loss largely from body fat. It’s true that there’s also some weight loss from fat-free mass, but it will not cause losing drastically less fat and instead lose too much muscle mass.

Whenever I started dieting, I was told that I had to do strength training or else I would lose muscle instead of fat. So I always tried to combine my diet with strength training, but doing both was too much for me. It’s exhausting, was difficult to fit into my daily life, and often caused me to abandon the diet altogether.

That rough 75/25 ratio can change slightly depending on what you’re doing. Strength training can have a positive effect, and even just having more protein without strength training can have a positive effect, but both are not required for fat loss. A sustained calorie deficit without strength training will still result in substantial fat loss.¹

In my current diet, I’m not doing strength training. Instead, I have reduced my overall calorie intake while making protein a larger part of my diet. I do this partly because protein may help me to retain more fat-free mass, but mostly because it helps me feeling full for longer. I also continue walking 8,000-10,000 steps each day. That’s sustainable for me and results in losing 3-4 kg per month, and I’ve lost 18.6 kg so far.