Demystifying Metabolism (Part 1): Exercise

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. ” [1]

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. [2]

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 [3]). 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 [4]. 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 [5]. 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 [7] 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.

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Comments

  1. I have a question for you….my boyfriend and I have both noticed a metabolic change in how we process alcohol when we’re cycling a lot. When summer comes and the training increases and I get fitter and fitter, it feels like I process the alcohol super fast. For example: I’ll drink a beer and have an immediate buzz (“wow that’s weird, I usually don’t get this drunk on beer”!) and then within 30-60 minutes, it’s gone. It’s as if I never drank the beer. Do you know anything about this in terms of metabolism? I’m just curious.
    Lisa recently posted..Create Your Own Masterpiece + A GiveawayMy Profile

  2. Great concise explanation that will certainly help people understand what metabolism really means!

    People who have more muscle mass than average should consider using the Katch-McArdle formula (there are others too) for resting metabolic rate so their lean mass can be taken into account.
    Mary C. Weaver, CSCS recently posted..Your diet is working . . . so what?My Profile

  3. heyoooo~!
    so if the ‘current’ formula is actually old and grossly inaccurate, is there a newer one, or a more modern way to determine BMR?

    anxiously awaiting part deux!!!!

    woop woop!

    • Hey Gene! Apparently the Katch-McArdle formula is for people with more muscle mass. However, it didn’t make much of a difference for me (I’m kinda small ;)). At any rate, I think you can use the original formula while assuming that’s probably at least 10% higher. Many fitness pros use it.

  4. I use the Harris-Benedict too. Imperfect, but I find adding BF% does help a bit. I recently got a Nike Fuelband and I am curious to see how my burn compares to my predicted daily expenditure from the Harris Benedict Equation.

    • Those “bodybugg” type of tools are supposed to be pretty accurate. Please do let me know what you find out.

      • My husband has been a “guinea pig” of sorts for testing the bands for me. THe fuel band is nice if you want an overall INSTANT look at your activity but it’s far from accurate. The body bugg type are more accurate. For instance: rowing the fuelband hardly said he’d worked at all, when he was working at 70-80% of his max! The bugg was more accurate with higher mets/burn for the exercise. As an overall activity tracker the fuelband is ok, but for a more accurate figures go for the body bugg/media
        Di recently posted..Workouts – interval timer appsMy Profile

  5. Great post Suzanne. I definitely do the hard core workouts with cardio & circuit type training for my weights but my own special Jody type training – lots of years doing this lead me to just find what works best for me & age too! 😉 I know I would have to eat a lot less if I did not have as much muscle nor work at the intensity I do. 🙂

    Can’t wait for part 2!
    Jody – Fit at 54 recently posted..One of My Crazy Workouts – I Break the Rules!My Profile

  6. Also worth noting that whilst the increase in EPOC after exercise is small it CAN and WILL affect weight loss when COMBINED with diet. a 5lb gain over a year is just an extra 50 calories a day consumed! Therefore if you burn 50 calories more a day than you consume you should lose 5lb (eat clean!). Also worth noting that the 50 cals extra a day is 1/2 tablespoon of butter or 1/2 slice of bread! Those little extra’s every day really DO add up!!!
    The best way to get your RMR is to get your body fat measured hydrostatically. That will take into account your lean muscle mass and give you figures for RMR, calorie intake required etc.
    Looking forward to your next installment 🙂
    Di recently posted..BodyPump 83 and CXworx 8 on the way!My Profile

    • True, and I like breaking it down into small quantities of calories like that. Makes it seem much more manageable! Regarding EPOC, in theory someone could lose five pounds doing HIIT every day, but how many people can really exercise at that intensity every day? One study said people were exercising at 90% capacity for an hour! I do see what you’re saying about burning an extra five pounds per year via lean tissue… it’s better than nothing! It’s true that hydrostatic is the most accurate way to measure body fat, but most people don’t have access to it.

  7. Wow, what a great explanation of how metabolism works! I especially appreciated the distinctions about the impact certain kinds of exercises and intensity levels have on it. Makes me want to go pump some iron right now!
    Shira recently posted..Three Tips for Successfully Shifting from Weight Loss into MaintenanceMy Profile

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