Squatting Can Make Your Liver Bigger
Maybe.
Metabolism is weird. In my post about body composition I talked about how losing 30 pounds of fat and gaining 30 pounds of muscle would improve your Resting Metabolic Rate (RMR). Pound for pound muscle burns twice as many Calories as fat, so a 30 pound recomp would leave you at the same weight and a higher RMR. Analytically the effect is pretty small, burning an 100-200 Calories per day, but I said that the effect can compound over days and weeks to help you keep the fat off easier than just losing 30 pounds of fat. I’m told by coaches that the observed effects on keeping weight off is higher than I would assume for that level of difference. That seemed weird, but it matched my personal observations.
It looks like their might be more going on when people put on muscle than just putting on muscle. You might be growing your liver, kidneys, and all other organs1 along with your muscle tissue. This is a big deal, since while muscle is more metabolically active than fat, it’s less metabolically active than basically everything else in your body. 2
The chart above isn’t a very happy one for the idea you can grow muscle to increase your daily Caloric spend. It says you need to put on 30 pounds of muscle to burn enough fat to lose a pound a week, putting on that much muscle can take years for an adult male and longer for other genders. But a more modest increase in the size of your kidneys, liver, heart, and brain would do wonders
Can you get your Organs to be bigger?
Maybe. No one has been done a proper trial. What we do know is that bigger athletes have bigger organs. Mostly larger livers, but also somewhat larger kidneys and hearts.3
What’s the causality? No one’s investigated this enough to be sure. It’s possible that people with larger livers are more inclined to larger and more muscular physiques. But this suggests that for every pound of fat free mass you gain, at least 3.7% is healthy organ tissue4 that increases your RMR 20 times5 as much as muscle.
Under the old theory if you gained 1kg of fat free mass by lifting weights, you’d increase your RMR by 13 Calories per day. If gaining fat free mass increases the size of your organs, gaining 1kg of fat free mass increases your RMR by 12.48 from the extra muscle tissue and by 9.62 from those three organs for a total of 22.1. If other organs are also getting larger (they haven’t been looked at), the effect can be even larger.
The value of 22.1 is pretty close to what people find when they measure the relationship between resting energy expenditure and fat free mass directly678. When looked at directly, increasing fat free mass seems to increase RMR by somewhere between 23 and 33, which is a lot better than the 13 for pure muscle tissue.
Problems
Causality. None of these studies observed people’s RMR or fat free mass changing due to new resistance training. Without checking that, we don’t know if an individual adding muscle will increase their daily Caloric burn by 20-30, or if they’re stuck at 13 from pure muscle change. We can’t know that without more research.
Going Forward
Reading these papers and writing this post convinced me to get a body scan9 to determine the size of my various organs, see how I fit on those graphs. I’m not an athlete, and I came to muscle growth pretty late in life (i.e. after high school). Maybe I missed my shot to have a huge liver burning Calories while I sleep.
I recommend anyone who can easily afford it and is planning on a recomposition fitness plan to try something similar, getting new scans after you estimate you’ve gained a few kilograms of fat free mass. Let me know what you find, I’ll try and write a follow up post.
besides your brain
Milo says it so it must be true.
The graph is on page 4 of this paper. https://www.jstage.jst.go.jp/article/jnsv/59/3/59_224/_pdf/-char/en
The sum of the slopes of the heart, kidneys, and liver. Other organs might also grow.
The ratio of the weighted average of the RMR of a kg of liver, kidney, and heart, and muscle tissue.
https://www.jstage.jst.go.jp/article/jnsv/57/6/57_6_394/_pdf/-char/en
https://www.jstage.jst.go.jp/article/jnsv/57/1/57_1_22/_pdf/-char/en
https://pubmed.ncbi.nlm.nih.gov/17414807/
Still looking into which one I can get, it looks like it needs to be a CT, MRI, or ultrasound.
The liver is storage for all the glycogen the body needs so it would seem like athletes who burn a lot of glycogens would have large livers.