# How metabolism works

Many claims and premises by self-professed health experts are contradictory or false:

- They're trying to [sell a product](marketing.md), so they'll usually include the truth while [omitting key details](people-lying.md) that may make that product unnecessary.
- For that reason, there's a *lot* of [misinformation](stories-storytellers.md).

## 1. Saliva, stomach acid, and bile digest food

Saliva starts breaking down food.

Stomach acid and microbes in the stomach dissect the food into usable nutritional components.

Bile and microbes in the intestines break down anything that passed through the stomach.

The large intestine and colon take water out of the remaining waste before it's expelled.

## 2. The components that were food go where the body needs it

Carbohydrates become energy:

- Carbs are converted into glucose, then the body's cells use insulin to process it.
- The body digests simple carbs (sugars) first, but dietary fiber (often from fruits and vegetables) slows down the metabolism of simple sugars.
- Complex carbohydrates (starches) such as grains digest more slowly because they're a chain of simple carbs.
- The digestible parts of fiber and complex carbs are a steady feed, so the body can easily produce enough insulin without creating a "sugar crash".
- The indigestible parts of fiber often go right through the body, often scraping (and therefore "cleaning") the sides of the intestines along the way.

Proteins are building blocks for most of the body.

Fats serve a wide variety of purposes including storing energy, insulating the body from harm, and helping synthesize/transfer protein.

Salts are used to power muscles.

Vitamins and minerals have a vast variety of small, specific uses.

## 3. The body converts extra components for another purpose or throws them out

Extra glucose is stored as glycogen in the muscles and liver until needed, converted into fat, or discarded in urine.

Extra proteins and fats are turned into energy to fuel the body.

Our body fat is either white or brown:

- White fat is what we tend to think of, and is a blubbery consistency.
- Brown fat is denser and generally less risky to have, helps insulate us better, and tends to come from exposure to freezing weather.

Surplus salts and some vitamins are discarded (water-soluble).

Some extra vitamins are stored in body fat (fat-soluble).

Any food still in the stomach when someone [goes to sleep](sleep.md) *will* get stored.

## 4. Anytime the body needs, it pulls from storage

First, the body pulls from whatever's in the stomach.

Then, it'll draw from a quick-access calorie storage reserve.

Following that, it'll get rid of extra tissue it doesn't need (e.g., unused muscle).

Finally, it'll use stored body fat.

After over a day, the body will move into "starvation mode", where metabolism decreases.