Lean body mass (LBM) seem to be correlated with long term health. As in, the more muscle you have as you age, the less prone you are to injury.
As you grow older, muscle becomes proportionally more expensive to maintain. Your metabolism slows as you grow and (without external stimulus) decides that the effort in maintaining muscle is more than it's worth. So your body sheds muscle. Some blogs I've read say something like 5% lean body mass per year over the age of 30 (presuming you are doing no exercise to maintain lean body mass).
Anyway this is a long winded explanation for saying that I think it's really important to build muscle when your young and maintain as you grow older. No surprise there.
To build muscle you need to eat. A lot. More than your body expends on a daily basis so there are extra nutrients and calories to actually develop and build additional muscle mass.
However, our metabolisms do not convert 100% of the excess calories to building muscle. Some portion of those extra calories goes into storing fat. I don't understand the exact reasons why.
If I had to guess, it's because evolutionary storing fat during times of plenty was a good safeguard against starvation during times of famine. I also suspect that converting excess calories to fat is a more efficient process than converting excess calories to muscle. Muscle takes more calories to maintain and is less calorically dense (i.e. a gram of muscle is ~4 kilocalories, a gram of fat is ~9 kilocalories). So, it's a sound survival strategy to turn excess calories into some mix of muscle and fat.
In a country like the USA, calories are aplenty. And so sound survival strategies in paleolithic America are not so sound today. In America at least, more people suffer from obesity than undernourishment.
Anyway, I wanted to know what the most efficient way to shed body fat would be. When losing weight, not 100% of the weight loss is fat. Similar to gaining weight, some portion of the shedded weight will be fat and some of it will be muscle. How do we minimize muscle loss while losing weight then?
The really rough heuristic is the "quarter fat-free mass (FFM) rule" which says that a quarter of the weight you lose will be LBM. It turns out that this heuristic is really rough.
Lots of factors affect the ratio of LBM to fat loss when losing weight. This includes: how many calories you're eating (i.e. how aggressive you're dieting), the composition of your diet, sex, whether you're doing cardio, whether you're strength training, and you're unique hormonal and body composition.
That's a lot.
And so, depending on all these factors, the ratio of LBM/fat loss can be anywhere from ~.4 to ~.2. Meaning, for the blessed and strong amongst us, for every lb they lose, only .2 of that lb is LBM.
Having a lower LBM/fat loss ratio is helpful when losing weight. As mentioned before, more LBM just seems to be generally correlated with better longevity, quality of life, and health. And, being totally vain here, being lower weight looks a lot better. I want that Dorito-shaped body (broad shoulder, thin waist, like a triangle).
From my understanding of the survey, there are some guidelines to incorporate into a weight loss program to minimize muscle loss.
- Don't be too aggressive with the amount of calories you reduce your diet by.
- Start or maintain strength training during the program.
- Start or maintain cardio during the program.
- Don't be too aggressive with exercise during the period of caloric deficit.
- Make protein ~35% of your diet.
That's pretty much it. Everything else is genetics or sex or pretty much things out of your control. Sticking to these rough guidelines should, for most people, suffice in minimizing muscle loss during weight loss programs.