Now that I’ve covered protein very thoroughly in this series, we need to talk about fat and carbs. But to do that we first need to understand metabolism.
Otherwise it would be like learning about the fuel and the engine of a car without understanding the concept and need of driving a car.
What is life?
Why do we say a plant and an animal are alive while a brick and a glass of water are not? What is the definition of a living creature?
This question is actually not that easy to answer and has been the source of a lot of heated discussion both among scientists and religious people.
If the answer is “having a soul” then are all the cells in the creature alive or is the creature itself alive? A dead organ is different from a dead person. Also how do we conclude the presence of a soul? Using “If it’s alive then it has a soul” to say “having a soul means life” is circular logic.
If the answer is “being able to multiply”, then does fire have life? What about crystals? Or biological viruses?
As you can see, “what is life” looks like a simple question but is very hard to answer.
The most commonly accepted definition comes from the physicist Erwin Schrödinger (who won a Nobel Prize for his work in quantum mechanics but is famous among the masses for a “cat in a box” experiment).
In his book What is life? he identified something all living things have in common: Living matter evades the decay to equilibrium (“it feeds on negative entropy” in his words).
Take a glass of cold water and put it in a room. Eventually the water will warm up to meet the temperature of the room (equilibrium). Then all the molecules of the water will eventually evaporate and spread evenly across the room (another equilibrium). Then they will eventually end up outside the room and be spread evenly across the earth by becoming a part of the water system.
Take a brick and it will eventually wither away into dust and the dust molecules will fly into the air and spread across the ground evenly.
This progression towards uniformity is called entropy.
Living matter is different because it tries to fight this progression towards uniformity (negative entropy).
When you are in a cold room, your body produces heat (and when you are in a hot room, it tries to get rid of it) to keep your body temperature in a certain range.
You have a protective layer of skin that insulates you from the outside world and prevents foreign substances from damaging your organs and other internal machinery.
Your cells are constantly working to fight against entropy. Damaged cells are repaired when possible or they are killed and replaced. Your body has an immune system to fight foreign microbes and to maintain a state of health.
Your body tries to keep its own entropy as low as possible. It tries to get rid of some of the entropy it generates as waste products (poop, pee, pus, and other waste products)
The mechanisms are not perfect so eventually enough entropy (cell damage, toxins, clogged arteries, etc.) accumulates and kills the organism. In other words, life is a fight against entropy.
What powers life?
Now that you understand that living matter is matter that is trying to fight against entropy, it should pop the next question – how does living matter do this?
There are various processes that are the result of millions of years of evolution:
- Thermoregulation
- Immune systems
- Protective barriers (skin, fur, feathers, cell walls, etc.)
- Redundancy in your DNA
- etc.
All of these activities require one common thing: ENERGY.
At the very basic level, everything comes down to cells. From simple bacteria to complicated organisms like yourself – all living matter are made of some number of things called cells.
The evolution of the cell was the start of life as we know it. There are no non-cellular living beings.
Every cell, whether it is a part of a complex organism like a human being, or is alone like a bacterial cell, needs a source of energy to do its processes to fight entropy and to do the other things it does.
Energy is measured in calories as already covered earlier in this series.
What is metabolism?
You already know that energy can neither be created nor be destroyed. It can only be converted from one form to another.
When an ancient hunter gatherer threw a spear at a wild animal, he was converting energy from his body into kinetic energy into the spear.
The energy expenditure (or calorie burn or work) done by your body is exactly equal to the kinetic energy you put in the spear. (Somewhat oversimplified here as we ignore things like muscular efficiency, heat generation, friction with air, etc.)
All the cells in the world (from your body down to each individual bacteria) are converting energy from one form to another. Like a muscle cell will turn chemical energy into kinetic energy and heat by contracting.
Basically when you say “metabolism”, it refers to all the work done by your cells. Or the combined energy expenditure of all the cells in your body. Because work done and energy expenditure are the same thing by definition.
Metabolism is not a mystical or hazy concept as many people think. It is a concrete and measurable thing that exactly equals your energy expenditure (measured in calories, or joules, or any other unit).
Your life is your metabolism. The day your metabolism hits 0 kcal is the day you’re dead.
Components of your metabolism/energy expenditure
Your metabolism or total daily energy expenditure (TDEE) can broadly be divided into a few main parts:
1) Basal Metabolic Rate (BMR) [Also called Resting Energy Expenditure (REE)]
This is the amount of calories you burn just to stay alive at rest. This is the energy you would burn if you had no movement at all (say you were lying awake at complete rest).
It is by far the largest part of your energy expenditure simply because all the cells in your body continuously burn energy just to stay alive.
The ion pumps in your cells are actively maintaining the right osmotic pressure, the brain is using energy, the heart is pumping, you are breathing, the liver and kidneys and all your organs are functioning, damaged cells are being repaired or replaced, etc.
BMR largely correlates with the lean mass in your body as adipose tissue (your fat stores) barely need any calories to stay alive. A kilo of fat burns about 4 calories a day.
For comparison, your heart burns about 450, your brain about 250, your liver around 200, and your muscle about 13 calories (all per kg per day).
Overall, your brain and your liver are your costliest organs, and holding more fat adds the least to your BMR.
Then there is your immune system doing its thing of keeping you safe from invading organisms. People who live in unsanitary environments have higher BMR because their immune systems are so active (to the point that it stunts their growth because the immune system is pulling in so many calories).
2) Non-Exercise Activity Thermogenesis (NEAT)
All non-structured movement and posture: standing, fidgeting, pacing, chores, walking to the store, carrying the baby, yard work, stair-taking, job movement, etc.
This varies hugely from person to person. Some people have very high NEAT while others have very little.
The NEAT difference between someone who sits on a chair all day and someone with an active job can be over a 1000 calories a day.
3) Thermic Effect of Food (TEF)
This is the amount of energy needed to digest the food you eat.
Protein is the costliest to digest. About 20-30% of the calories in protein get used up just in the process of digesting it.
Carbs cost about 5-10%, and fats about 0-3%. Alcohol about 10-15%.
In general, a higher protein diet means a higher TEF.
Ultra-processed foods tend to have lower TEFs than equivalent whole/minimally processed foods. This is because they contain more “pre-digested” like being composed of fine particles, contain emulsified fats, gelatinized starches, less protein and fiber, etc.
4) Exercise Activity Thermogenesis (EAT)
This is all the structured exercise you do like going to the gym, doing cardio, playing sports, etc.
How much you burn depends on the type of exercise you do and for how long. Overall the effect of exercise on TDEE is not as high as people think because of adaptive effects and the concept of constrained energy expenditure.
I should point out that the reason we exercise is not to burn calories but to retain youthfulness for as long as possible. I don’t want you to think that exercise is not important because it doesn’t burn much net calories (in fact it actually makes it more important – I will discuss it when I talk about constrained energy expenditure later in this series).
5) Adaptive effects
This is something I will do an entire post about later in the series. The short version is that the human body is not like a simple machine where running it harder means you burn more energy.
It is a product of millions of years of evolution in an environment where energy was hard to acquire.
Your body tries very hard to match your expenditure to your energy intake. When you exercise a lot, it makes you hungrier (so you eat more), it reduces NEAT (less fidgeting, alertness, walking, etc.), reduces immune system activity, reduces reproduction (this is why you lose interest in sex during deep cuts), etc.
Over long periods of low energy intake, the body makes bigger adaptations like reducing your thyroid hormone production (which in effect tells every cell in your body to do its processes slowly and thus conserve energy).
Fast and Slow Metabolism
As you can see above, your BMR is the largest source of your metabolism/energy expenditure.
There are online calculators that estimate BMR using different equations (Mifflin-St Jeor, Cunningham, etc.). Are they right?
The answer is that they cannot be on the mark because there is a lot of individual genetic variation in BMR.
Two people with the same fat free mass (or lean body mass) can burn very different amounts of energy to stay alive.
Put in simpler terms, some people’s cells just seem to burn more energy than average. While others burn less than average.
Your BMR can differ from what the calculator says by 5-15% (hundreds of calories a day).
There are various hormonal and genetic reasons for this like your thyroid hormone levels, thyroid hormone sensitivity, your mitochondrial proton leak rates, ion pumping rates, cell protein turnover rate and autophagy rate, futile substrate cycles, core temperature set point, etc. – all of which are well beyond the scope of this series.
Some people have a fast metabolism and some have a slow metabolism. It is a fact and not made up nonsense.
This is why you cannot blindly use a number a calculator gave you as your true TDEE. Use my simple method to calculate your maintenance calories and you’ll have a much better idea of your metabolism.
Now that you understand what metabolism is, you will actually be able to understand the next few pieces in this series that will talk about the aspects of your metabolism (energy production in the body, constrained energy expenditure, metabolic damage, etc.).
– Harsh Strongman
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