Why you need to add muscle (and don’t need to lose fat) for better metabolic balance.
TL;DR: How much our muscles weigh - and not our total body weight - has the biggest impact on how “fast” or “slow” our metabolism is. We can maintain better metabolic balance by moving our muscles than by trying to lose fat. (about 6 min read)
Metabolic tips for increasing metabolic balance:
Add some resistance training to your routine to build muscle mass and burn more calories at rest.
Move around for 5-15min after eating so that more blood glucose gets stored in your muscles. This helps stabilize BGLs and reduces metabolic stress.
Focus on moving throughout the day and building muscle, instead of losing fat. Movement + muscle mass will have a much bigger impact on your health than obsessing over body fat or total weight.
The weight of your muscles is the biggest factor in how much food your burn for energy. Now we’re going to actually break down why you can eat more (and worry less about how much you’re eating) when you have more muscle mass. Your “resting metabolism” - the number of calories your body needs at rest to stay alive - is mostly determined by the weight of your muscles. So having more muscle mass means you actually can burn calories for energy without even moving.
Let’s say two people both have 150 lbs of total body weight (BW). Their skeleton is going to weigh about 85 lbs. The 85 lb skeleton + non-muscle needs about 1200 cal/day. The rest of their body (muscle + fat) will weigh 65 lbs. Your fat cells store energy; they don’t use that much energy and their calories are part of the 1200 cal/day that your skeleton + non-muscle needs. Your muscles need about 11 cal/lb/day. Let’s estimate how many calories these two people use when they aren’t moving around.
Example 1: 150 lb person with 15% body fat needs a minimum of ~1650 cal/day. Their total BW is 150 lbs, so their fat weighs about 22.5 lbs. This means their muscle mass is about 42.5 lbs. (85lb skeleton + 22.5 lbs fat + 42.5 muscle = 150 total lbs). If the muscle is going to use ~11 cal/lb, then this person needs to eat about 1650 cal/day to maintain their weight if they aren’t moving around. (11* 42.5 = 467 cal for the muscle + 1200 cal for the skeleton + non-muscle = ~1650 cal/day when doing nothing).
If this person does some movement throughout the day, their muscles will burn some of their body fat and they’ll lose weight OR they will need to eat more to stay the same weight. Some movement throughout the day will bring their calorie needs up from ~11 cal/lb BW to about 11.5-12 cal/lb BW (depending on the person and their movement patterns) and they will burn about 1700-1800 cal/day.
Example 2: 150 lb person with 25% body fat needs a minimum of ~1500 cal/day. This person’s body weight is still a total 150 lbs, their skeleton will still weigh about 85 lbs, and their skeleton + non-muscle still needs about 1200 cal/day.
However, with 25% body fat, this person’s muscle mass will only be 37.5 lbs and their fat will be 27.5 lbs. Now, 37.5 lbs of muscle will burn 302 cal/day if this person isn’t moving, and their total cal needs/day go down to 1500 cal (11 * 37.5 = 302 cal for the muscle + 1200 cal for the skeleton + non-muscle). Having 25% body fat drops this person’s “metabolic rate” from 11 cal/lb to 10 cal/lb.
If this person does some movement throughout the day, their calorie needs will go from ~10 cal/lb BW up to about 10.5-11.5 cal/lb BW and they will burn about 1575-1700 cal/day.
Having a “slower” metabolism can be due to having less muscle than another person who weighs the same. You can see that the person with 15% body fat may burn 1700 cal/day (the lower end of their estimated calorie needs) and the person with 25% body fat may also burn 1700 cal/day (the higher end of their estimated calories needs) when both people are moving throughout the day. However, at rest, the person with more muscle mass (and it’s the muscle mass that’s important! not the lower body fat!!!) will consistently need more calories than a person with less muscle.
Our muscles will burn fat for energy first. Our muscles will rely on burning fat for energy when we are moving enough to increase our heart rates but not too much - you can carry on a decent conversation while doing this (I mean, you could do a decent job of talking and breathing when you’re moving. Whether or not the conversation itself is decent depends on who you decided to hang out with). This amount of movement has gotten the flashy title “fat-burning zone” which is kind of inaccurate bc all zones are fat-burning up until you move faster than your blood can get fat to your muscles fast enough (and then your muscles switch to burning glucose). The switch from fat to blood glucose doesn’t happen until you start going fast**.
How much do we need to be moving our muscles to help our metabolism? You may have heard of “heart rate zones” or “perceived exertion” as other ways to know if your muscles are burning fat or have switched to glucose. Heart rate and perceived exertion are helpful metrics if you have a heart rate monitor or think about your exertion level when you have nothing better to think about on the treadmill. For people who don’t have heart rate monitors - or have better things to think about than exertion on a treadmill - here’s a table I put together to help people find their estimated cal/day based on activity level.
Losing fat does not “speed up” your metabolism. Reducing metabolic stress and increasing muscle mass does. Actually, nothing really “speed up” your metabolism. A more accurate way to describe what’s happening is “metabolic stress slows down your metabolism”. You can still increase the rate you burn calories by reducing metabolic stress and lowering the amount of growth factors and inflammation signals that tell your body to store fat. And by increasing muscle mass so you burn more calories at rest. “Speeding up” your metabolism is really just maintaining metabolic balance.
Losing body fat without increasing muscle mass just decreases body fat. This may or may not be healthy for you - like, if you have extra weight putting pressure on your joints, losing fat can be good. If a lot of your body fat is stored around your internal organs and is pushing on them, losing fat can be good. But if your joints aren’t stressed, your blood pressure is good, and your internal organs aren’t packed with fat, you probably don’t need to focus on losing body fat for health reasons.
Metabolic tips for increasing metabolic balance:
Add some resistance training to your routine to build muscle mass and burn more calories at rest.
Move around for 5-15min after eating so that more blood glucose gets stored in your muscles. This helps stabilize BGLs and reduces metabolic stress.
Focus on moving throughout the day and building muscle, instead of losing fat. Movement + muscle mass will have a much bigger impact on your health than obsessing over body fat or total weight.
**Fast for you. This is where things get nuanced because “fast for you” is going to depend on how trained your muscles are (basically, how much muscle fibers you have), what type of training you’re doing (weights vs endurance exercises), and how well you actually fuel your movement and recovery (not enough fuel = not enough glycogen + fat stored in the muscle itself and more reliance on blood glucose levels and fuel stored in your liver and fat cells). Feed your movement so you can heal your bones, grow your muscles, and move faster.
*Heavy resistance and/or vigorous cardio should be done no more than 3-5 days/wk (depending on goals) so that bones and muscles have time to recover properly to prevent injuries. Moderate exercise can be done 6-7 days/wk but exercise plans should alternate muscle groups to allow tired muscles time to rest & properly recover to prevent injury. Light exercise can be done every day.
Jenson, J. et al., (2011) The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise. Frontiers in Physiology.
Pontzer, H. et al., (2021) Daily energy expenditure through the human life course. Nature.
