The truth behind ... exercise & weight loss - Part 3

By Dr Janet Aylott BSc (Hons) PhD RNutr

We all know that exercise helps weight loss and our general health, but we're left scratching our heads when the scales don't reflect our good work.

I asked members what frustrated them about their dieting and weight loss efforts, and not surprisingly a number of questions came up about exercise.

Does muscle weigh more than fat?

A very good question and the answer is quite simple. Muscle is denser than fat, so it means that for the same amount (or volume), muscle does weigh more than fat. The simplest way that this is often put is that gram for gram, muscle is heavier than fat. Not strictly true in the law of physics but roughly right!

How can the inches be going down, but the pounds stay the same? Surely if you are getting smaller you are losing body fat and so therefore weight?

If you are someone who exercises quite a lot, you will be changing the composition of your body internally by losing fat and gaining muscle. Muscle is denser than fat (so heavier for the same volume), but tends to be found more 'internally' in your body. So you may be losing inches off your arms, stomach, thighs etc because this is where we tend to store fat, but you will be gaining muscle in your legs, abdominals, chest etc.

Because muscle is denser than fat, it will show up on the scales that you're not losing weight but what you're actually doing is changing your body composition to become much healthier and smaller!

I understand that you will gain weight through exercise because muscle weighs more, but surely you should still lose weight as exercise speeds up your metabolism and you're burning calories?

Yes you are right in many aspects - you do burn more calories as you exercise, and you will build muscle stores, which in turn leads to more calories being burned. Exercise itself doesn't speed up your metabolism, but it's the muscle you build which can make burning calories more efficient.

Everyone is individual and for some people exercising won't lead to weight gain, whilst for others there can be quite a big change in muscle stores. What is important is that you are eating the right level of calories for the amount of exercise you're doing. It's no good setting your activity levels at very active, if you only go for a walk a couple of times a week. In the same way, if you're at the gym every night but have your settings at light / inactive, this isn't right either. Make sure you're being honest about what you're eating and the exercise you're doing to get the maximum benefit from dieting and exercising.

Still have some unanswered questions? Check out Part 1 and 2 for Food Myths and Calorie Claims