This is a two-part series – see Part 2 here.
How many people really understand metabolism? We hear about how “metabolic training” can burn mega calories, so it must be a good thing. But we also hear scary terms like “metabolic syndrome,” so we know it can go wrong. And the term “metabolic health” is thrown about as well – what exactly is that?
Although metabolism is a complex subject that includes everything from one’s lifestyle to their thyroid gland, one of the primary goals of this blog is to sculpt thy body into a lean, healthy machine. So in this two-part series you’ll (1) learn how to increase your metabolism, and (2) understand what isn’t affected by metabolism. We’ll start with the definition:
Metabolism is the biochemical process of combining nutrients with oxygen to release the energy our body needs to function… Total metabolic rate represents the calories needed to maintain body functions, daily activity (occupational and lifestyle) and the energy cost of exercise. ” 
For simplicity’s sake, we can break metabolism into two basic types:
- Resting metabolic rate (RMR): How much energy (calories) your body burns to sustain bodily functions like breathing and heart rate (typically about 70 percent of your energy expenditure). This can include being in a very restful state and we can also include thermogenesis here (how many calories your body burns as it breaks down food). RMR is sometimes used interchangeably with BMR (basal metabolic rate), although BMR uses more precise measurements.
- Lifestyle metabolism: How many calories your body burns in daily activities, such as standing, typing, fidgeting, cooking, and exercising. This is the part of metabolism you can control most easily, obviously, but it has a smaller impact than your RMR. 
Everyone seems to want a higher metabolism because it means higher energy expenditure (which translates into burning calories and being able to eat more). Let’s look at the basics of metabolism and see how exercise affects it… from an evidence-based standpoint, not “truthiness.”
How Do I Measure RMR?
If you’re trying to lose weight, knowing your resting metabolic rate will help you determine how many calories per day you need. You should also not go below your RMR for reasons which I will discuss in Part 2 of this series. There are several ways to measure metabolism, some more scientific (and inaccessible) than others. The most common way is to use an online calculator using the Harris-Benedict Equation, which uses your height, weight, age, and gender. Lifestyle activity level is also factored in.
This calculation was created based on males in 1919, so it’s safe to say it’s outdated and somewhat inaccurate (possibly overestimating RMR by 10 to 15 percent ). However, it’s what most of us have, and unless we want to hire a trainer who uses indirect calorimetry, we’ll have to rely on this formula. I have to believe this formula must be inaccurate for myself; there’s no way my RMR is only 1,200 kcals per day. I eat 2,000 or more kcals a day and certainly do not burn 800 kcals in daily exercise, yet I do not gain weight.
How Does Exercise Affect RMR?
Exercise is one thing to be proven to have an effect on metabolism. But how much? I lift weights four times a week – is that enough to give me a high metabolism? EPOC (elevated post-exercise oxygen consumption) occurs after intense exercise as your body restores itself to a resting state. There’s conflicting evidence about how long this calorie burn lasts; Lyle McDonald analyzed one study which found that working at 90 percent capacity for nearly an hour would raise your energy expenditure (EE) for 14 hours . But EPOC is temporary and for most people, probably not significant enough to affect weight loss. Most people do not/cannot exercise at such an intense all-out effort frequently (and it can lead to overtraining); HIIT (high-intensity interval training) isn’t something you should do every day.
Multiple studies have shown that lower intensity endurance and cardiovascular exercise do not impact RMR or impact it indirectly . Resistance training has been shown to affect fat-free mass and lean tissue, which raises RMR. But unless it’s coupled with appropriate dietary support for growing lean tissue, resistance training may have little effect on RMR. It’s the growth of lean tissue that promotes a higher RMR – but how much?
Does Muscle Increase RMR?
If you’ve heard that lean muscle mass increases your metabolism, you’d be right. However, it has a fairly small impact: the metabolic rate of muscle is about 4.5 to 7.0 kcal/lb per day. That means someone who gains 4.5 lbs of muscle would increase their RMR by about 50 kcals per day  and possibly burn five extra pounds per year. We’ll take it though, right?
Since a pound of fat burns only about two calories per day, so this admittedly small benefit should still motivate you to put on more muscle with resistance training. Check here to estimate how much lean muscle mass you have and see this article for more on this subject. It’s important that you focus on diet and exercise when thinking about your RMR, which I’ll discuss in Part 2.
Does Metabolic Training Lower my RMR?
This type of workout uses intense strength training to raise your heart rate and thus take advantage of EPOC. Often the exercises are performed back-to-back with little to no rest such as circuits, supersets, or timed sets. While the benefits of EPOC might be small, if you’re already in decent condition you can use this type of workout to get a short-term calorie burn benefit in addition to calories burned during your workout (lifestyle metabolism). But as I discussed above, exercise in and of itself doesn’t lower metabolism. See this article for more information about metabolic training.
So now that you have a general idea of what metabolism is and how exercise impacts it, how are diet and weight loss affected? And how do other factors such as age really affect RMR? And is there such a thing as a “slow” metabolism?” I’ll discuss these issues in Part 2 of this series.