The importance of maintaining/improving lean body mass.

in health •  last year

If you are on Facebook, Twitter or Google+ chances are you will see some before/after picture pop up at least once a day in your stream. People showing off how amazing they look after a few month on diet X. Most of the time it’s pretty easy to see these people lost a whole lot of weight and a whole lot of body fat. What the photo’s mostly won’t show, at least not to the untrained eye is what happened to this persons lean body mass. Sometimes the second photo shows sharp and impressive muscle definition, and one would be easily fooled to jump to the conclusion that the person became more muscular while dropping body fat. More often than not however, quick weight loss by whatever means will lead to a significant drop in lean body mass (LBM). Typically weight loss programs that have you losing more than one or two kg per month without both significant resistance training and a protein rich diet, will result in lean body mass loss somewhere between 25% and 50% of the total body mass reduction. When combined with a high protein diet and resistance training or when limited to a short time period, the LBM loss can be a bit less dramatic, but even under the best professional supervision, less than 15% LBM loss seems incompatible with the idea of quick weight loss.

A possible central cause

So why worry about lean body mass at all? Losing body fat it what is important for (medical) risk reduction, right? Well, yes and no. If we look at body composition components and how they correlate with clinical endpoints, the picture becomes a bit more nuanced. For those who have read my previous blog post, looking for causal factors in nutritional science is a daunting task and looking for a central cause (not rout cause) in a field of science dominated by starry-sky scatter plots seems to be the most promising road towards assessing risk and possible risk attenuation strategies. At this point in time, visceral fat appears to be a good first candidate. Do we have enough evidence to justify a causality claim? Well, no, but the evidence is significantly stronger than that for any of the main surrogate endpoints used in nutritional science. So what can we say about body composition with respect to clinical endpoints?

  • A: We can’t currently reject the hypothesis that there exists a (non-linear, possibly causal, relatively strong) relationship between visceral fat and multiple clinical endpoints.
  • B: We can’t currently reject the hypothesis that there exists a (non-linear, relatively strong) attenuative relationship between lean body mass and the risk metric defined by A.
  • C: We can’t currently reject the hypothesis that given A and B, there is neither risk nor attenuation of risk associated to the presence of subcutaneous fat.

Or in short, it seems visceral fat might be an important risk factor that is attenuated by muscle mass, while the role of subcutaneous fat should probably be assumed to be neutral.

Metabolic rate

If for the sake of argument we assume the ‘initial’ risk profile of someone who loses 20 kg of body fat at a price of 10 kg of lean body mass to be positively affected, we must also conclude that the positive effect will be significantly less than what the before/after pictures would suggest to many. If we look at the potential long-term effect of a diet accomplishing such weight loss, the picture becomes a bit more grim. The first thing we should realize about the lean body mass delta is that it is metabolically active body mass. Losing lean body mass will reduce your total daily energy expenditure and do so in a relatively decently quantifiable manner.

The Katch-McArdle formula tells us that our Basal Metabolic Rate (BMR), the energy expenditure we would have if we did absolutely nothing to actively burn energy, changes linearly with our body mass at a rate of 21.6 calories per kg of lean body mass. Katch-Mcardle also gives us the concept of an activity multiplier. If we apply the standard multiplier to the per kg LBM basal metabolic rate, we get the following daily expenditures:

  • Moderate activity: 33.5 calories / kg LBM
  • High activity: 37.5 calories / kg LBM

Or if we expand it to a whole year, between 12000 and 14000 calories per year per kg of lean body mass. The equivalent of 1.3 to 1.5 kg of body fat. Yes, that is right, a single kg of lean body mass will burn the equivalent of up to 1.5 kg of body fat each year. Or to say it differently, losing a kg of lean body mass will slow down the metabolism of a highly active individual enough to gain (or not lose) an extra 1,5 kg a year, each year. That would be 3 kg in two years, or for our person who lost 30 kg body mass at 10 kg of LBM, the total amount of body mass loss would be represented by two years of metabolism reduction. And if this metabolic reduction was to lead to weight gain, without high protein and resistance training that weight gain most likely won’t include much of an increase in LBM. So not only do many people who lose weight quickly gain it back, at the end of the cycle when their weight is back where it started, their visceral fat tissue will be higher and their LBM would be lower than where they started out.

Gain weight to reduce risk?

So all of this is bad, right. You can’t lose weight quickly without losing lean body mass and you can’t lose lean body mass without reducing your energy expenditure, eventually leading to you consuming an energy surplus that will have you gaining (the wrong kind of) weight again. But how about reversing it? What if we start by actually increasing our weight. Increasing our LBM. Forget about body fat loss for a year or two, maybe three ? Sounds like a bad idea, right? Please hear me out though. Swap your current endurance or aerobic workout, even drop your cardio for a while and instead start focusing on resistance training. Not the sissy fitness type of resistance training, but something halfway between a body building and a power lifting regime. Forget about putting too much focus on the smaller muscles. Forget about the idea that you need to keep your core muscles from growing too big. Forget about looking amazing on your before/after pictures, we are not in it for the aesthetics. Our goal is to gain lean body mass quickly end effectively. Focus on the muscle groups that allow for quick mass gain. Especially legs should play a central role, never ever skip leg day and keep it legs exclusive, it is the pivotal part of your workout week. Hit the big muscles hard, twice a week and stack up on protein rich foods in order to gain lean body mass quickly. Now think what happens if you keep it up for a few years. Depending on your age and gender and your starting LBM you may have put on 10, 15 or maybe even 20 kg of LBM or more. LBM that will be burning calories 24/7. Even if you gained 15kg without losing a single kg of body fat, your personal risk will already have been reduced. But with the slowly increased metabolic rate, chances are you already lost at least a few kg of body fat, most likely ,if your diet has been strict with carb timing, with a large part of that being visceral fat.

Conversely, your net weight change in body weight will probably have been weight gain, your body composition from a risk perspective will have improved at least as much as your quick weight-loss peers, but without the LBM reduction induced metabolic rollercoaster.

Take it slow

While many obese people who have repeatedly lost weight only to regain it will have an LBM so low that gaining lean weight should take precedence over losing fat weight, for those with relatively decent LBM, and for those who have taken the strength first approach outlined above, muscle mass gain could be secondary to visceral fat loss. It is tempted to go on a diet and trade in a bit of LBM for a quick body fat loss. A better solution however is to still limit LBM loss first at the expense of taking a bit more time. If you can lose zero kg LBM while losing only 1.0 or 1.5 kg of fat mass per month, that should be preferable over losing 1 kg LBM against 3 kg of body fat in a singe week.

Finding the proper focus.

If both your visceral fat level and your LBM are high, the slow weight loss at stable or minimally reduced LBM will be the best risk reduction strategy. If however your LBM or visceral fat level is relatively low, then increasing LBM will be more effective for reducing risk.

So while visceral fat reduction is an important tool in risk reduction, the price of LBM loss can quickly make quick weight loss a really bad bargain. Lean body mass increase can be a solid long term geared alternative for risk reduction even if it is accompanied by an increase in total body mass. Wherever you are in terms of visceral fat mass and lean body mass, losing multiples kilos of lean body mass is never a good idea. Losing visceral fat however almost always is. For some combinations of high visceral fat and low LBM, increasing muscle mass at unchanged visceral fat can be a much better risk reduction strategy than a focus on visceral fat reduction at unchanged LBM. A long term strategy should try to both decrease visceral fat while increasing muscle mass. In such a strategy, total body weight is totally irrelevant.

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Thank you for a very interesting and informative article. I'm currently working on losing weight at a rate of about 10% of my weight over the last 6 months. I was thinking of doing anothwr 10% over the next 6 but will think abou mayby trying to add some muscle first.

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