What it is, Can you improve it, and much more!

In it’s most simple definition, metabolism is converting what you eat and drink into energy.

Our metabolism is complex, this is an oversimplification, but metabolism is your body converting energy (calories) from what you eat and drink + oxygen to release the energy your body needs to function.

If you exercise, there are 4 parts to your metabolism. If you do not exercise, you don’t have the EAT portion of your metabolism.
BMR (~60%) – Basal Metabolic Rate
NEAT (~20%) – Non Exercise Activity Thermogenesis
TEF (~10%) – Thermic Effect of Food
EAT (~10%) – Exercise Activity Thermogenesis

Your BMR is your “survival energy”, the energy needed at rest. About 60% of total metabolism.

BMR is determined by many factors, being mostly genetic. You can alter it somewhat, but it’s largely unchangeable. Even at rest, you’re using energy: breathing, blood circulation, hormone levels, cell repair and growth, digestion, heartbeat, even blinking. Some things that determine BMR are:

Body size
Larger bodies proportionally burn more calories. I’m not talking leanness here, I mean that bigger bodies burn more energy. For example, a shorter person will proportionally burn less calories than a taller person, simply due to their size. More mass needs more energy.
Body composition
If you have more muscle in you frame you burn more calories at rest.
Due to naturally having more muscle mass, plus influences from hormonal differences, men tend to burn more calories at rest than women.
With age we start losing muscle mass. If you don’t actively maintain that your body composition changes and you slow down calorie burn.

This is a really cool way of saying “move more”, or more specifically, movement that isn’t really intentional. This accounts for about 20% of total metabolism.

This percentage depends on lifestyle factors, and is highly influenceable. Fidgeting, walking, ANY movement that’s not structured exercise. This is where you have a big impact. You can increase your NEAT by doing some simple things:

At home
Walk or play with dogs
Clean house
Pace while watching commercials or on the phone
Have a dance party
Play with your kids or grandkids

At work
Walk at lunch
Take the stairs
Pace while on the phone
Walk to speak to colleagues instead of calling

When out
Take a walk after dinner
Park far away from entrance
Take stairs instead of elevator or escalator

Thermic effect of food = amount of calories from food that are used to digest, absorb, metabolize, store remaining food and burn as heat. About 10% of total metabolism.

This percentage depends on different factors, mainly the composition of your food (carbs, fat and protein).

Fat has 9 calories per gram, and the TEF is 0-3%.
For instance, if you eat 100 calories of fat, which is about 1 tablespoon of butter, less than 3 calories are used to digest and metabolize that fat. For fat this isn’t great news. Most of the fat we eat gets used as energy or stored, it doesn’t take much, if any, energy from fat to metabolize fat.

Carbs have 4 calories per gram, and the TEF is 5-10%.
If you eat 100 calories of carbs you eat, which is about 1 slice of bread, 5-10 calories are used to digest and metabolize those carbs. This is pretty good.

Protein, like carbs, have 4 calories per gram, and the TEF is 20-30%.
That means that if you eat 100 calories of protein, which is about 2 ounces or 55g or lean chicken, 20-30 calories are used to digest and metabolize that protein. That is… well, that’s outstanding.

All that being said, increasing your protein intake and curbing your fat intake will have an effect on calorie burn and body composition, HOWEVER, all this is still a very small part of your metabolism. So the takeaway here is NOT that you should try to boost this. This is a consequence of your food selection, not something to try to manipulate.

Exercise activity thermogenesis = your formal exercise. This is about 5-10% of your metabolism.

This is that 30-60 minutes of your day that you engage in formal workouts. Depending on the intensity and type of exercise that percentage shifts from 0 to up to about 10%. We’ve talked about this before, and as you’ve learned exercise burns less calories than we would like to believe. However, when you exercise in a way that promotes muscle build, you are improving your metabolism as a side benefit.

The takeaway here is that while this improves your metabolism, the biggest reason to exercise is not to burn calories, it’s to improve your health and positively influence your basal metabolic rate.

Image from PMID: 34385400 (Daily energy expenditure through the human life course)

To round this off I will mention a fascinating database study that was done on metabolism and published last year. The study looked at 6,421 subjects, from 8 days to 95 years of age, both male and female, from 29 countries. There were different data setts, mathematical models and adjustments made to account for differences in body size, age, and reproductive status.

Contrary to popular belief, our metabolism doesn’t suddenly drop when we turn 30. This study found that metabolism accelerates rapidly in the first year of life to about 50% over adult values, declines steadily to adult levels by 20 years of age, and stays stable in adulthood, from 20-60 years of age, and then declines in older adults. For subjects 90 years and older the total expenditure was around 26% below that of middle-aged adults.

Listen, this is GREAT news. This means that we have more control over our energy expenditure than we’ve been led to believe. This means that you don’t, in fact, need that detox, or that supplement to boost your metabolism.

On the flip side, this means that you need to own your metabolism. If you want to increase your energy expenditure, meaning, if you want to increase how much energy your body uses to function, YOU need to do something.

Simple. Learn how much energy your body actually uses.

Increase your daily movement in ways that have nothing to do with exercise.

Exercise in a way that maintains and builds muscle mass.

Eat a full range of macronutrients, and prioritize your protein.

I made a reference sheet about this for you and here it is. Download it to see exactly how these metabolism puzzle pieces fit together, and get tips on how to work on what you can, and to improve what you’ve been given.