“Man, when I hit 40, it’s like my metabolism just bottomed-out!”
“I just can’t seem to lose weight because my metabolism is soooo slow!!”
“She’s so lucky, she’s got such a fast metabolism, she can eat whatever she wants!!!”
Do these statements sound familiar to you? I’m sure they do. They sound familiar to me; in fact I hear them all the time. The question is what exactly do those statements mean? Is there any physiological truth to a slow (or for that matter, a fast) metabolism?
Now, I’m going to preface all of this by saying metabolism and the biological ability to provide fuel to our working body is a very complex process, and by no means is this going to be a lesson on bioenergetics; mainly because it doesn’t have to be. The above statements (as well as the seemingly infinite variations of these statements I’ve heard over time) tend to be used as a “crutch” for why someone can’t seem to lose weight, or why they’ve gained weight. Well guess what, I’ve got news for you – if your metabolism is slow, YOU’VE MADE IT THAT WAY!!!!
Wait, wait, what did I just say? I didn’t just say this was your fault, did I? This is slow metabolism; it’s a biological side-effect of aging (like losing your hair or getting wrinkles)?!?! How can it be your fault? Well, guess what…this one’s on you!
Now I’ll grant you, most physiological capacities will decline by 1-2% per year starting at the age of 30-ish. But what’s 1-2% per year in metabolic terms? It’s about 15-20 calories max per day. Yup, it’s about 1/200th of ONE pound of fat, so it seems pretty unlikely that you’ve gained 30lbs (or can’t lose 30lbs) because your metabolism has slowed down due to aging.
Before I completely kick that crutch out from underneath you, I need to explain a little more about what metabolism really is, or what contributes to the total amount of calories burned on a given day.
When someone refers to their “metabolism” they are really referring to the total number of calories the body needs in a 24-hour period. This number is referred to as total daily energy expenditure or TDEE. TDEE is actually the sum of four different types of metabolism the body undergoes during a given day:
- Resting (or Basal) Metabolic Rate (RMR): this is your body’s true “natural” metabolism, as this is the energy expenditure associated with all basic biological functions that keep the body alive in a resting, or non-moving state (breathing, heart beating, digestion, etc). RMR, in most cases accounts for the greatest proportion of TDEE, as it can be between 40-60% of the calories burned in a day.
- Physical Activity of Daily Life (PADL): this is the energy expenditure associated with the activities you perform during the course of your day that aren’t exercise-related. Showering, eating, working, cleaning the house, and all other non-exercise activities you perform during the day fall under this category. This number is largely consistent day-to-day, as our daily life activities don’t vary all that much. This is generally expressed as a multiple of RMR, and for most people reading right now (who don’t have incredibly labor-intensive jobs) PADL-associated metabolic cost is about 15-20% of RMR (meaning if your RMR is 1000 calories PADL will be 150-200 calories), so on a whole this represents a fairly small component of metabolism, on the order of 10-20% of TDEE.
- Dietary-Induced Thermogenesis (DIT): this is the metabolism associated with digestion and absorption of nutrients from food and beverages we consume. In short, it costs calories to get calories from the foods we eat, not a lot of calories, but there’s work that needs to be done to turn nutrients into energy and that has a metabolic cost to it. Since our diets are fairly consistent day-to-day, so will be this number. For most people this represents about 5% of their total calories consumed (i.e. DIT for a 2000 calorie diet DIT is about 100 calories), here again we’re taking about a fairly small number relative to overall TDEE.
- Exercise Energy Expenditure (ExEE): this, as the name would suggest, is the amount of calories we burn from exercise. This is obviously the most variable day-to-day; with non-exercising days resulting in zero ExEE and heavy exercising days resulting 500-1000 calories burned. So depending on the type, volume, and intensity of exercise performed, ExEE can obviously have a HUGE impact on metabolism with ExEE accounting for upwards of 30-50% of TDEE on any given exercising day.
What this quick lesson in metabolism should have conveyed is HOW you can influence your metabolism for the positive and the negative.
Let’s review quickly. We’ve got RMR (calories associated with basic biological functions), and although this will decline during the course of your life it is largely consistent, and its decrement certainly can’t account for the inability to lose weight (or gain it, for that matter). Unless your lifestyle varies widely day-to-day PADL and DIT aren’t going to vary tremendously, and although we lead fairly sedentary lives and eat a lot of refined foods (both of which limit PADL and DIT, respectively) this probably isn’t the reason your metabolism is “slow.” That leaves us with… you guessed it: Exercise Energy Expenditure!
The fastest, most time-tested, fail-proof method for raising your metabolism is via exercise (crazy concept, right?). The reality is we are an inactive population. Nearly two-thirds of Americans don’t meet the recommended daily physical activity requirement of 60 (cumulative or consecutive) minutes of ANY kind of physical activity, let alone exercise. Our metabolisms are getting slower because we’re making them that way. Think about it, we go to health food stores spending billions of dollars per year on so-called “weight loss” supplements that supposedly help “boost” metabolism (although not one of them actually does anything close to that), when we have the scientifically proven method for doing it every time, without fail – exercise!
If I told you I could give you a prescription for something that would “boost” your “slow” metabolism by 500-600 calories per day, you’d jump at it, right? I mean who wouldn’t? I should be a zillionaire with access to something like that??!? Well, unfortunately people aren’t nearly as excited when they find out that prescription is exercise.
The harsh reality is this; our metabolism’s decline is a product of our own inability to maintain a high metabolism. It’s not a disease, it’s not a genetic predisposition, and it’s certainly not something that’s just supposed to happen with age.
As a society we need to stop enabling each other by trying to convince ourselves that being overweight and unable to lose it, is because our natural biology is somehow malfunctioning. It’s not, never has been, never will be. Here’s the most exciting part about this whole concept; if you’ve made your metabolism slow, you have the ability to make it fast! That’s the real take-home message here. Now you just have to decide how fast (or slow) you want your metabolism to be! Get moving!