Eating is about two things:
This guide provides simple models for optimizing the first point, the rest is up to you! Don’t chose a «diet». Understand the rules and eat things you enjoy.
Your body is a complex machine, and like any machine, it needs energy to work. To measure this energy, we use the unit of calories (cal) or rather kilo calories (kcal), often shortened back to «Cal» (because no one wants to say «kilo calories» all the time).
Your body needs an amount of calories each day to perform some functions, like breathing, pumping blood... This is the resting energy, or, what you would need were you to stay in bed all day doing nothing.
To that, you need to add the energy you need to move around, think, exercise, etc. This is the active energy.
Sum those two up and you get your daily energy requirement.
This energy depends on your weight, height, age, activity, body fat...
daily requirements = resting energy + active energy
The calculator below can help you estimate your daily energy requirements:
Inside the things you eat and drink are many important elements called nutrients. A nutrient is something your body uses to do stuff.
There are two families of nutrients: macronutrients and micronutrients.
Macronutrients (proteins, lipids, glucides) are where you body draws its energy, and they each perform their own functions.
Micronutrients are numerous and need to be within some amount in your system for normal function. Lacking a micronutient can lead to a deficiency, which can lead to a disease.
Your energy comes from macros:
Let’s take an example of a big mac.
Total: 590Cal
Now, compare this to your daily energy requirements. Your body needs less than big macs per day (and nothing else) for the energy it needs.
But, what happens if I eat more calories then my body consumes? Well, these calories have go to go somewhere. Your body comes from thousands of years of evolution, and during those years there were no fast foods at hand and we did not know when the next meal would be. So, it made sense to store it for later use. That’s why you get fat.
Some share of your energy surplus (the difference between what you eat and what you consume) will be stored as fat. That depends again on the macro nutrients. Carbs will be converted at 75% (these are ballpark figures), proteins less, fat virtually 100%. That’s why people say fat makes you fat. If it happens to be in the surplus, 100% of the energy it provides will be stored.
If you eat your 3 big macs and reach your daily energy requirements, that should certainly suffice, right? Well, we both know that’s not true. Your body is sensitive to the volume of food you eat. 3 big macs is a small-ish volume, at most that of a meal. Maybe you won’t be hungry for the next few hours, but you will be hungry in a few hours and have no calories yet to spare.
This is why volume is critical to what you eat. If you eat 1kg of food of low energy density, you will be satisfied and for a lower calorie total.
The body needs energy, macronutrients, and micronutrients
Energy is measured in Cal, indicated on packaging
The energy I eat minus the energy I burn is the energy balance
If the balance is negative (deficit) I lose weight, if it’s positive, I put on weight
Macronutrients have to be provided in the right quantities
Micronutrients come from a varied alimentation
1kg of fat stores about 8000 Cal and has the size of ~1 grapefruit. 1kg of muscle stores about 600 Cal and has the size of ~1 orange.
Let’s say you stopped eating for 3 days, at 2000 Cal per day, you will not even burn through 1kg of body fat. The difference in weight will mostly come from your empty bowels. Food can stay for 3 days in your body travelling through your bowels.
Proteins comes mainly from meat.
One kg of beef roughly has 200g of proteins. One kg of chicken roughly has 200g of proteins.
As a comparison, one kg of chickpeas has 90g of proteins. You will need at least twice the mass of chickpeas for the same mass of chicken to get the same protein intake. Also, these proteins will be harder for your body to use, so you will need more for the same results.