I see a lot of people, mostly young people, on edtwt who don’t understand how calories work and sometimes end up making unhealthier choices than they would otherwise.

Here’s a thread explaining the basics of fat loss and CICO.

Let’s start at the beginning: the fundamental laws of the universe. Energy can neither be created nor can it ever be destroyed. There is a finite amount of energy in the universe and it will never change in amount, only in form. This is known as the Law of Conservation of Energy.

To use energy, something must have energy. To have energy, something must be given energy by something else that already has energy. For example, a ball cannot start rolling on its own; it must be pushed (given energy). Once that energy is used up, it cannot continue to roll.

We can discuss the amount of energy in or used by something by talking about its “energy budget.”

When we’re talking about the energy budget of living things, such as humans, we use units called kilocalories (often shortened to calorie or kcal).

Remember: calories are units of energy. Therefore, all things related to calories are subject to the laws of energy, such as energy conservation.

For something to be considered living, it must use, consume, and store energy.

We use energy, or burn calories, when we walk, run, think, and do everything else we do. We consume energy, or intake calories, when we eat other organic (living) things such as plants and animals.

We store energy in the cells of our bodies, namely fat cells. This means that to get rid of fat, we must use the energy contained in our fat cells.

Everything living has calories because everything living has energy by definition. An apple has calories because the apple tree consumed energy from the sun and used that energy to build the cells to store energy in the apple.

Inorganic (nonliving) things such as salt, baking soda, or water do not have calories because they do not use, consume, or store energy.

We all know that exercise uses, or burns, calories.

However, we also use energy for basic life-sustaining functions such as breathing, circulating blood, process information (ie sights and sounds), producing & repairing cells, and keeping a stable body temperature.

The number of calories we use to stay alive is called our basal metabolic rate (BMR) and accounts for 60-75% of our caloric expenditure.

You can calculate an estimate of your BMR using this link.

https://www.calculator.net/bmr-calculator.html

This is the number of calories you would burn if you were bedbound, not thinking, not fidgeting, not chewing food or digesting, not blinking, etc all day long.

The average BMR for a woman is 1400, and the average BMR for a man is 1800.

Doing anything more than just being alive burns extra calories. The number of calories you burn doing things plus your BMR is called your total daily energy expenditure (TDEE).

The calculator linked above gives an estimate depending on your average activity level as well.

Since energy can’t come from nowhere, your body must get these calories from either consumed calories (food) or from stored calories (fat).

If you are alive, you are either burning food calories or fat calories, period.

You cannot be alive and burn no calories.

You cannot expend more energy than the calories you consume plus the calories your body breaks down from fat.

You cannot beak down more calories from fat than you burn in excess of your intake.

Let’s use X to represent your TDEE.

If you eat exactly X calories, you will maintain the exact amount of fat on your body.

If you eat more than X calories, your body will store this excess as additional fat; 3500 excess calories is equal to one pound of fat.

If you eat less than X calories, your body will use as much as your fat as it needs to make up the difference.

Pretty simple, right? This is called CICO — calories in, calories out. There is no other way to gain or lose fat. Otherwise, you would be breaking the laws of physics.

“But I ate less than my TDEE and didn’t lose weight!”

Weight ≠ fat. There are many tissues and materials in our bodies.

Maybe your body is storing water due to dehydration or cellular repair. Maybe you need to poo. Or maybe you miscalculated either your intake or output.

“What about starvation mode/metabolic damage?”

This is hugely overblown. When you’re starving (eating < BMR) your BMR will decrease because your body will slow non-essential tasks like keeping you warm or keeping your hair healthy, which is only a few calories difference.

This is known as adaptive thermogenesis. Your starved BMR will still stay within a hundred calories or so of your regular BMR.

“Starvation mode” cannot make you magically gain fat out of nowhere. Remember the Law of Conservation of Energy? Fat must be put there by excess intake.

However, eating less than your BMR can cause a psychological/hormonal phenomenon known as extreme hunger. This is typically what causes people with restrictive EDs to binge.

Your body wants to stay alive more than your mind wants to be skinny, so...

... effective restriction means appeasing your body in an intelligent way. This is why you see so many people praising high restriction.

“What about plateaus?”

As you lose weight, your TDEE decreases. It takes less energy for your body to pump blood through your body if your body is smaller. It takes fewer calories to lift your legs to walk if your legs weigh less.

If you’re eating close to your TDEE and hit a plateau, it’s likely because your TDEE changed.

If you’re not eating at your new TDEE and still experiencing a plateau, you’re storing water or need to poo.

“I’m eating < my TDEE and haven’t lost weight!”

Seeing fat loss reflected on a scale takes time. People may talk about losing a pound overnight, but that’s rarely how it really works. The time will pass and your weight will drop. Try not to let this make you do anything extreme.

I want to reiterate that effective restriction is about caring for your body’s needs in an intelligent, biologically-conscious way.

It’s not about getting your intake as low as possible.

Low restriction doesn’t make you skinny, it makes you sick. And binge. And bald. And dead.

That’s all for Professor Sarah’s biology lecture of the day!

If you have any questions about this topic, feel free to reply to this thread or DM me if you’re shy. I want you all to understand biology in order to stay as healthy as possible under the circumstances.