Does muscle really weigh more than fat?

Question

I recently dropped 30 lbs through diet adjustments. Nothing trendy, just cutting back on prepared and processed foods and most importantly: portion sizes.

5 weeks ago I started a strength training program. Progressive overloading using compound barbell exercises: back squat, press/bench press, and deadlifts. I've never felt stronger!

The thing that's confusing me is that the scale is no longer changing. I feel like I'm eating pretty well, lots of fibre, fruits, and proteins. A lot less carbs than I used to eat.

Is this adage of "muscle weighs more than fat" actually true? And is it keeping my body weight around the same mark because of it? I'm lifting some seriously heavy weights at 5 weeks for a novice -- I'm 5'9" 202lbs and yesterday I squatted 195, benched 175, and deadlifted 215. Today is a rest day and tomorrow I'll be adding 5lbs to each (hence the progressive overloading).

I can't tell if I'm still eating too much since my target weight is definitely under 200 at my height and body type. But I've never done strength training so I don't know how much muscle mass will change my expectation of a target weight because my previous experience was as a lean, aerobically fit twenty-something.

Answer 1

Yes: muscle tissue is denser than adipose tissue:

• Adipose tissue has a density of ~0.9 g/ml
• Skeletal tissue has a density of ~1.06 g/ml

_{Source: Wikipedia; with references to the scientific literature.}

This means that, per volume, skeletal muscles weigh more than fat. However, skeletal muscle (which you gain by exercising) only contributes a fraction to the overall lean body mass. Another substantial contributor is water, and the amount of water in the body varies drastically.

To quote “InBody”:

• Lean Mass gains, when they do occur, are largely increases in body water
• It’s difficult to say with any certainty how much any Lean Body Mass increase is due to Skeletal Muscle Mass without using sophisticated tools

And they have bad news for you:

[Do] not try to use a scale to measure changes in Lean Body Mass or Skeletal Muscle Mass. It’s impossible […]

You should therefore track your exercise progress differently. As for tracking the progress of your diet, it may seem tempting to measure body fat percentage. Unfortunately this also requires sophisticated tools: those home-use scales that give you body fat estimates are unreliable.