Every so often in the 5:2 group someone posts a photograph purportedly showing the difference between lean tissue and fat. Fat is indeed less dense than muscle – the so-called “Muscle weighs heavier than fat” but from many of the photographs you’d think the difference was huge. It’s not.
The reason the internet abounds with these misleading photographs is to give a crumb of comfort to people whose weight has remained static. The conversation generally goes like this:-
Distressed dieter – “I haven’t lost any weight for a month. I go to the gym three times a week and run five miles twice a week. I don’t understand it.”
Worried gym instructor (worried because client may take custom elsewhere) – “Ah, well. you’ve been building up muscle, and muscle weighs heavier than fat. See this photograph.” Flourishes graphic photo of masses of yucky yellow fat and a lot smaller piece of red muscle.
Distressed dieter – “Oh well, that’s all right then. I’ll carry on doing what I have been doing (inadvertently cheating and massively overestimating exercise levels) and carry on paying your gym subscription.”
So how much of a difference between muscle and fat is there?
To show this I bought some beef suet from my local friendly butcher and compared it with steak. The first photos show the weight is approximately the same (78 g and 79 g). Then compare the two side by side. The fat is indeed bigger, but not twice as big as some photos would have us believe. Because the fat is all knobbly and the meat is nicely trimmed, it’s not easy to see exactly how similar or different they are. The knobbles of fat make it appear to take up more room than it does.
So I filled a jug up to the 900ml mark, then looked to see how much water was displaced by the fat (I don’t have a suitable measuring cylinder). I then compared that with the water displaced by the meat. The fat floated because it’s less dense than water and had to be held down.
There is a difference of about 10%, though the jug just isn’t accurate enough to measure it precisely.
Although we should bear in mind that the bathroom scales don’t tell the whole story, we have to beware of fooling ourselves by assuming that weight gain or lack of weight loss is due to lean tissue. Building muscle, especially for females, is hard work. It requires stimulation of a subset of muscle fibres called the fast twitch fibres, and these are not stimulated by long distance running nor aerobic gym work. look at the physical difference between a sprinter and a marathon runner, especially the men. This illustrates it very well. So if we’re not losing weight, chances are we’re eating more than we think and not exercising as much as we think we are.
Gaining/protecting muscle during weight loss is good because it burns calories, quite apart from being needed for doing every day activities.