The fast/slow metabolism myth
The truth about our metabolism
How many times have you or someone you know moaned about being unable to lose weight no matter what you or they do? Or that there is someone who, no matter what they eat never gains weight?
The truth of the mattter is, unless you have legitimate endocrine issues, you are very unlikely to have a slow or fast metabolism. Apart from some outliers, everyone’s metabolic rate is almost identical.
Our basal metabolic rate (BMR) is the number of calories needed in a day for the cells of our body to just exist, and the greater the amount of energy-demanding cells (such as weight in fat or muscle), the more energy you need to survive. What this means is that if you take two people, identical in every way, except one is overweight, it’s the overweight person who has a higher metabolic rate than the lighter person.
Its not your metabolism, its NEAT
Will two people of identical weight and body composition always burn the same amount of calories? No, and I’ll explain why. While genetics will play a role, which I’ll go into more detail in a future post, It usually comes down to a little known thing called NEAT, or Non-Exercise Activity Thermogenesis. So what is it? NEAT is a fancy word for a fairly simple concept, any activity you do subconsciously that burns calories is classified as NEAT, so all that figeting you do at your desk, its NEAT. The importance of NEAT is that these seemingly unimportant movements like figeting burn a LOT more calories than one would think, and account almost entirely for differences in calories burnt between individuals.
So what influences NEAT if its subconscious? This is where the most important genetic part comes in. Your body tries to maintain you, if youre in a calorie deficit, its will increase hunger and decrease NEAT. If you’re in a suplus it’ll decrease hunger and increase your NEAT. These compensatory mechanisms are incredibly variable and hard to accurately study, so it’s still early days, but we do know that your body does attempt to regualate your weight through these changes.
An important point is that even though the degree of which your body yells at you to is very variable, it is also easy to ignore its signals. Someone with a ‘fast’ metabolism can keep eating ice cream until they’re overweight, and someone with a ‘slow’ metabolism, can ignore the signals telling them to eat more, and stick to a regimented diet. So maybe that skinny person doesnt have a fast metabolism, they just have better compensatory mechanisms, and listen to them.
Burn calories by eating
One under-appreciated fact about the body is that your basal metabolic rate accounts for a considerable amount of the calories you burn each day. Physical activity, unless you are a professional athlete or work a very physically demanding job, only accounts for 10-30% of your total energy expenditure (TEE) and digesting food, only about 10%.
The digestion of food, also known at the Thermic Effect of Food (TEF) is the amount of energy required to breakdown and absorb different macronutrients.
Protein has the highest TEF with 20-35% of the calories burned through processing
Carbohydrates only have 5-15% of calories burned through processing
Fat has the lowest TEF of all the macronutrients with 0-5% of calories burned through processing
Your total daily energy expenditure, or TDEE, includes all the energy burned through exercise, eating and your BMR. If this is greater than your energy intake, you will lose weight. If its higher, you will gain weight.
Take home message
Do you have a fast or slow metabolism? At the end of the day, probably not, and if you do, it’s unlikely to be that much higher to make a massive difference. By increasing the amount of conscious movement you do in a day you. For those who believe they have a slow metabolism, by prioritising calorie dense foods and tracking calories, you can still gain weight