I bet you've heard this before:
"Muscles are like the engine of your car. The bigger the engine the more fuel you burn. So having more muscle will burn a lot more calories."
This is essentially true, but overrated. In reality, gaining a pound of muscle will increase daily energy expenditure by 15-25 calories, which is really not that much. It's equivalent to about one-third of an apple.
Arguably, if you gain 10 pounds of muscle it can lead to a greater caloric expenditure of around 200 calories per day. But it's still not anywhere close to what people would believe.
And honestly, most people do not add 10 pounds of muscle in a year of training once they're past the beginner stage. (They might gain 10 pounds of body weight, but not muscle.) The average male has the potential to add 30-40 pounds of muscle over his normal adult weight over his training career.
The point is that while adding muscle will increase energy expenditure, it's not as much as what people think and certainly doesn't justify eating like an ogre "because I have the muscle to burn it."
Adding more muscle WILL make it easier to get leaner and harder to gain fat. But burning extra calories isn't the only (or even most important) reason.
It's also due to an increase in storage room. If you gain one pound of muscle you can store an extra 15-20g of glycogen in the muscles. So if you gain 5 pounds of muscle you'll be able to store 75-100g of glycogen more. This means you can eat more carbs before storing them as fat – the body will fill up glycogen stores before converting carbs to fat.
So, strictly from a mechanical standpoint, bigger muscles = more room for glycogen which means that I can have more carbs daily without storing them as fat.
Being able to consume more carbs daily will help you keep your metabolic rate elevated because the conversion of T4 into T3 is dependent on carb intake and cortisol levels. Higher carbs normally means lower cortisol because the function of cortisol is to mobilize glycogen to elevate blood sugar levels. There's less need for that when eating carbs.
So, more muscle allows you to eat more carbs which helps keep your metabolic rate humming and also makes you more anabolic via a higher level of insulin and IGF-1.
Having more muscle also makes the muscles more insulin sensitive. This is good for two reasons:
- If you're more insulin sensitive it means you need to produce less insulin to get the job done. If insulin is elevated less, it means that it gets back down quickly. As long as insulin is significantly elevated, fat mobilization is less efficient. So the quicker insulin comes down, the more time you'll be spending mobilizing fat for fuel.
- If your muscles are more insulin sensitive, you'll be better at storing nutrients in the muscle instead of as body fat. By the way, that's why Indigo-3G® is so effective: it specifically increase muscle insulin sensitivity.
So the car engine analogy isn't terrible, but there's a little more to it than most people know. And you actually don't "burn" that much more fuel when you build muscle. At least not compared to the calories you stuffed down your throat last weekend.