The hallowed halls of the Academy of Broscience contain untold tomes of knowledge, wisdom, and recipes for “sick” pump stacks. Over the years, their scholars have elucidated the arcane esoterica of muscle confusion, thereby making it palatable for the layman. They discovered that any gram of carbohydrate eaten after dusk turns immediately to fat, and that curling in the squat rack engages more muscle fibers than curling elsewhere. Their field researchers are reportedly close to confirming the existence of spot reduction. But perhaps their greatest contribution to modern physical culture has been the establishment of the unassailable fact that muscle burns fifty times more calories than fat, at fifty calories per pound per day. (Even Dr. Oz says it, so it must be true.) As they have so painstakingly shown, adding twenty pounds of muscle increases your resting metabolic rate by 1000 calories. With that kind of leeway, you could eat a delicious twenty egg-white microwaved omelet with low-fat cheese and a side of plain oats and never worry about body fat accumulation!
This, of course, is complete nonsense. Broscience is not even peer-reviewed and their application for accreditation is still in administrative limbo.
No, but seriously: the idea that muscle significantly boosts resting metabolic rate is pretty much nonsense. Now, don’t get me wrong. I like muscle. Love it, even. Nothing I like more than a bit of lean mass, but I don’t like how this notion of “muscle burning fat at rest” has taken hold in the collective psyche. It leads to lofty expectations that come thundering down to shatter to pieces. It gets people on a single, obsessive fitness track where all they want to do is lift, lift, and lift (and eat, eat, eat) some more to the exclusion of other, perhaps more enjoyable pursuits. And, it can even negatively impact one’s health or progress toward desired body composition, either via overtraining the heavy lifting and undertraining the other stuff, like sprints, walks, hikes, and simple play.
Anyway, I came across an article several months ago detailing the author’s discovery that muscles don’t actually burn that many more calories than body fat. He doesn’t cite any specific studies, but he does cite Claude Bouchard, an obesity researcher from the Pennington Biomedical Research Center, who revealed that a pound of muscle, at rest, burns about six calories per day (and a pound of fat burns about two). That’s a far cry from the 50 calories per day figure “cited” by others. This number isn’t available in the abstract of some specific study. It’s drawn from extensive reading of the “biochemical and metabolic literature”. If you have literature to suggest otherwise I’m all ears. For the purposes of this post, though, I’ll take Claude at his word.
So, straight from the guy that studies this stuff for a living, muscle doesn’t burn a significant number of calories at rest. To illustrate the point let me quote the author of the LA Times article:
The 20 pounds of muscle I’ve gained through years of hard work equate to an added 120 calories to my RMR. Not insignificant, but substantially less than 1,000. However, I also engaged in a lot of aerobic activity and dietary restriction to lose 50 pounds of fat, which means I also lost 100 calories per day of RMR. So, post-physical transformation, my net caloric burn is only 20 calories higher per day, earning me one-third of an Oreo cookie. Bummer.
Or a single macadamia nut as the case may be. But that doesn’t mean having more muscle isn’t good for body composition and overall leanness, because it definitely is. Let’s look at some of the metabolic and other benefits of having more muscle mass.
Recent epidemiology (13,644 participating subjects) reveals that skeletal muscle mass strongly correlates with improved insulin sensitivity. With each 10% increase in skeletal muscle index (a measure of how much muscle is on one’s body), HOMA-IR (a measure of insulin resistance) saw a relative reduction of 11%. Folks with higher insulin sensitivity have better glucose control (carbs don’t destroy them) and lower rates of diabetes. Another study looked at the relationship between sarcopenia, or muscle wastage, and insulin resistance. There was a distinct relationship between sarcopenia and insulin resistance, independent of obesity, which can also exacerbate insulin resistance. So, based on epidemiology, a lack of muscle is linked to increased insulin resistance and poor glucose regulation. This should go without saying, but sarcopenia was also linked to obesity.
How does one get increased muscle mass? Why, by lifting heavy things. And what does lifting heavy things do to insulin sensitivity in addition to its effects on muscle mass? It improves it. To show this, a study placed older Hispanic adults with type 2 diabetes on a 16-week resistance training regimen and measured their baseline and post-treatment muscle mass and markers of insulin sensitivity. Folks in the strength training group got stronger, leaner, built more muscle mass, and developed more type 1 and type 2 muscle fibers. They also became more insulin sensitive. The increase in type 1 fibers, in fact, was strongly associated with the improvements in insulin sensitivity, as this graph shows. Note how the sedentary group didn’t do so hot in either department (increasing muscle mass or decreasing insulin resistance). That looks like a pretty strong link between increased muscle mass and insulin sensitivity to me.
Why is this important? Being insulin sensitive means you handle glucose well, which means less dietary glucose becomes body fat and less insulin is required to handle your business. This is far better than the idea of having a rumbling muscular engine idly burning calories as you watch TV, mostly because while the latter is a fun story to tell your bros at the gym, it’s not really true.
Having greater muscle mass also acts as metabolic reserve in times of trauma. I’m not talking about famine or starvation. I’m talking about car accidents, internal damage to organs, severe burns, cancer, sepsis, and catastrophic injury. A great review article (PDF) from five years ago summarizes the role skeletal muscle plays in recovery from and survival of trauma. In these unfortunate but very real instances, protein requirements shoot up to repair damage, and muscle protein breakdown increases. More muscle mass means you have more reserves to keep the amino acids flowing. When healing from burns, dietary protein needs increase to 3 grams per kg of bodyweight. If you can’t stomach that much or dietary protein isn’t available to you, it comes from existing muscle. And, if you don’t have much muscle to spare, you’re going to recover more slowly from severe burns. Same goes for cancer patients; those who have the greatest muscle mass tend to suffer fewer recurrences and live longer. Think of skeletal muscle mass as a buffer for hard times.
Finally, muscle looks good when attached to a human skeleton by tendons and covered with skin. And don’t we all want to look good naked, ultimately? Heck, I’d say this last one is enough reason to lift heavy things by itself.
Now that you’ve (hopefully) ceded the “idle muscle burns fat” idea, we need to go further. Let’s stop thinking of exercise and weight loss in mechanistic terms. Let’s not think of “burning” calories by subjecting our bodies to punishment. Sure, you could grind away and, with enough volume and intensity, “burn” off calories through sheer force of will. If your only concern is that you maintain low body fat, you could eat a bad diet and run fifteen miles a day. I did, and I was skinny. It “works.” But isn’t it much more freeing to realize that 80% of your body comp will come through proper diet, meaning you don’t have to grind on the treadmill and you can instead explore the joy of movement for its own sake? Isn’t it more elegant to imagine the hormonal cascade that heavy lifting jumpstarts and which gently nudges one’s physiology toward leanness and away from adiposity? Whether you see it as science, art, or a blend of both, the way we do things is more effective and enjoyable than hammering away at your fat stores.
Some may continue to hold their peace of mind ransom for those 500 calories of donut they just ate. That’s not me. While they’re waiting for “500 cal” to pop up on the elliptical’s readout, I’ll be eating real food, lifting heavy things, and appreciating the beauty of a complex physiological system allowed to do its thing. I suggest you do the same.