What is a healthy body composition?

We have a lot of fancy terms for it: getting “shredded”, “hench”, “lean” or “toned” but when it comes to body recomposition we can only really impact 2 factors: muscle mass and fat mass. 

Muscle mass is not the same as lean mass, as lean mass also comprises bone mass, water and organ weight. Aside from the practical benefits of having muscle mass such as being able to perform physical daily tasks easily, having muscle mass makes you burn more calories which means you can eat more without gaining fat and it keeps your bones and joints strong. 

Losing muscle is one of the main factors that causes the negative effects of aging. Age-induced sarcopenia is the loss of muscle mass due to age. This occurs from as early as 25 years old (3) and reduces your skeletal muscle mass gradually to about 70% by the time you’re 80. It can’t be avoided, but the process can be slowed down by doing resistance training and ensuring an adequate protein intake (4).

Body fat often has a very negative association, but we need some fat to remain healthy, women more so than men. A healthy body fat percentage for men is up to 25% and for women up to 30%. This is a very rough measure and it can vary widely between individuals, Asians typically have more body fat than Europeans for example and store more fat around their abdomen (5). 

You might know that fat serves as a storage for excess energy, but it’s involved in a lot more processes. Unlike what you might think, fat is not some passive fat storage unit. It is actually an organ that produces hormones and is involved in healthy immune function and reproductive health. As a consequence having a lot of it can cause problems in all these areas. We know that having a lot of fat causes low grade inflammation and fertility problems. 

Furthermore, fat serves as a physical barrier to protect the vulnerable tissues in our body such as organs and capillaries such as the capillaries around the heart. Fat is far from useless.

What does the number on the scale mean then?

The problem with taking your weight as your only measure of progress is that it cannot tell you what the weight is made of. Some factors, such as water weight can fluctuate on a day to day basis depending on how long it has been since you last trained, how stressed and how hydrated you are. For women, the time of the month can affect how much water you are holding on to (1). For example, if you are holding on to water because you are very stressed, this can mask fat loss and make you think you are not on the right track, when you are actually doing really well, which can be very demotivating. 

Conversely, if you go on a very low carbohydrate diet you will initially lose a lot of weight simply because you lose a lot of water. This is because water is needed to store carbohydrates. This may falsely be perceived as fat loss while actually, you are not in a calorie deficit at all and you need to revise your diet. 

However, these are relatively short term changes. Eventually fat loss will catch up with the water retention and water loss can only account for weight loss to some extent. 

When is weight loss not a good thing?

If your focus is losing weight, rather than losing fat you might embark on methods such as very aggressive and unsustainable calorie deficits, that waste a lot of muscle in the process. If half of the weight you have lost is muscle tissue this can be negative in the long run, especially if the weight loss is then followed by weight regain, which is the case for many dieters (2,6). 

Even if you end up back at your old weight after your crash diet, your body composition has changed towards a higher fat and lower muscle mass. As muscle burns more calories than fat, this means you need to eat less calories than before to avoid gaining more weight. If this is taken to extremes by losing and gaining weight, in other words, by yo-yo-ing, you can develop what is called sarcopenic obesity: when you have low muscle mass combined with a high body fat percentage (4). This phenomena is more popularly referred to as being “skinny fat” and it is possible to have a healthy weight with this condition.

A focus on weight loss rather than fat loss can also mask positive results in the long run. For example if an adequate calorie deficit, combined with resistance training leads to muscle gain and fat loss at the same time. Muscle weighs more per volume than fat so it is possible to gain muscle and lose fat at the same time while your weight stays the same. Your body composition has shifted to a lower fat percentage but because you only see your weight hasn’t shifted you think you haven’t made progress, and this is not the case!

How should I track my progress then?

I’m not saying keeping track of your weight is completely useless because for most people overall it tends to be a good indicator of how well you match your calorie intake to your needs. Measuring your weight can be a good tool to see trends over a long period of time, but don’t use it as the only measure of progress. When you have a fat loss goal, use other measures too, such as:

• Hip to waist ratio

• Progress Pictures

• Assess how well your clothes fit

• Girth Measures

But don’t get too caught up in numbers all together – what matters most for achieving and more importantly, maintaining fat loss is building healthy habits. 

• Maintain a healthy diet

• Exercise Regularly

• Prioritise your sleep

• Manage your stress

As long as you are focussing on improving these habits, successful fat loss will only be a matter of time.  

References

1. Bunt, J.C, Lohman, T.G. and Boileau, R.A. (1989). Impact of total body water fluctuations on estimation of body fat from body density. Medicine and Science in Sport and Exercise, 21(1), 96-100.

2. Curioni, C.C. and Lourenco, P.M., 2005. Long-term weight loss after diet and exercise: a systematic review. International journal of obesity, 29(10), p.1168.

3. Lexell, J., Taylor, C.C., Sjöström, M. (1988). What is the cause of the ageing atrophy? Total number, size and proportion of different fiber types studied in whole vastus lateralis muscle from 15- to 83-year-old men. Journal of Neurological Science, 84(2-3), 275-294.

4. Lee, D. C., Shook, R. P., Drenowatz, C., & Blair, S. N. (2016). Physical activity and sarcopenic obesity: definition, assessment, prevalence and mechanism. Future science OA, 2(3), FSO127. 

5. Sun, G., French, C.R., Martin, G.R., Younghusband, B., Green, R.C., Xie, Y., Matthews, M., Barron, J.R., Fitzpatrick, D.G., Gulliver, W., Zhang, H. (2005). Comparison of multifrequency bioelectrical impedance analysis with dual-energy X-ray absorptiometry for assessment of percentage body fat in a large, healthy population, The American Journal of Clinical Nutrition, 81(1), 74–78.

6. Wing, R.R. and Phelan, S., (2005). Long-term weight loss maintenance, The American Journal of Clinical Nutrition, Volume 82, Issue 1, July 2005, Pages 222S–225S