I can’t believe how often I’m seeing “a pound of muscle weighs a pound of fat” to try and prove that muscle and fat weigh the same. I think this actually needs its own topic to address this bizarre fallacy.

A pound of anything weighs the same as a pound of anything. This is true, but it is also utterly meaningless.

This is why humans tend to compare weights per volume or per unit.

It makes no sense to say that a grape weighs the same as a cauliflower. This is an example of comparing weight by unit. A single grape (one unit) weighs less than a single cauliflower. It is true to say that a pound of grapes weighs the same as a pound of cauliflowers, but it does not impart any useful information.

A 100 litre crate of carrots will weigh significantly more than a 100 litre crate of broccoli. So, in this instance it makes sense to say that carrots weigh more than broccoli. This is an example of comparing weight per volume.

You don’t tend to have units of fat and muscle, so the weight per volume makes most sense in comparisons. As it happens, a pound of fat takes up approximately four times the space taken by a pound of muscle. Therefore, by common convention of English language communication – muscle does indeed weigh more than fat.

That old thing of “which weighs more, a pound of feathers of a pound of bricks?”, that is a trick question. Your brain automatically assumes that you’re talking weight per volume because that’s a question that makes sense. Bricks clearly weigh more per volume (shipping container of bricks weighs more than shipping container of feathers), so you say “BRICKS!” and the person who asked you the question laughs at you. That’s because your brain just assumes the question is what makes sense, when the trick is that it’s actually asking something meaningless – there is use for comparing weight per weight, it’s total nonsense.

Of course, regarding muscle and fat, you’re kind of comparing apples with oranges. Removing fat doesn’t necessarily imply gaining muscle and vice versa. But I think it is encouraging to know that if you lose a pound of fat and gain a pound of muscle, you will be slimmer. That is what is meaningful when people talk about muscle weighing more than fat.