The basic formula to lose weight is simple: move more, eat less & keep your metabolism up while doing it. How we go about accomplishing these things gets a little more complicated, but in all cases, that’s how it works. Move more to burn calories & strengthen the body, eat less and eat cleaner foods that the body can USE efficiently, and keep your metabolism up by eating enough to keep your body going strong.
Millions of people lose weight each day and can give you every detail about how they did it. But very few would be able to answer the question “where did the weight go?”
So… where does fat go when we burn it off?
Well, it doesn’t really ‘go’ anywhere - rather it gets used. And to understand how that happens, I’ll explain a wee bit more about calories & fat.
CALORIES & FAT CELLS
A calorie is a unit of energy: you can think of it as gasoline. The calories we eat are either used (through movement or various body functions) or stored as fat (our body’s primary source of energy). They fat is stored in our fat cells: it’s like our body’s pantry.
The number of fat cells we have doesn’t change: they simply get bigger (when they’re storing) or smaller (when the body is pulling energy from them). They develop in childhood, and as we get older they steady off (about 8% die each year & get replaced). Someone who has more fat cells than average, but each is small, can be a relatively thin person. Someone with fewer fat cells, but each is large, can be overweight.
Someone who has a high number of fat cells will find it easier to gain weight & harder to lose weight (NOT impossible, but slightly harder). Overweight children develop a higher number of fat cells, and enter adulthood with more fat cells to work with. While they can still reduce the size of these cells, they have more of them to begin with, putting them at a slight (very slight) disadvantage. It’s more difficult to lose weight and easier to gain it when you have more fat cells to start with.
When we have more calories than our bodies need they get stored in our fat cells, making them bigger. This is a calorie surplus - leading to fat (or weight) gain. When we’re demanding more energy from our body than we have, it takes it from our fat cells, thus making them smaller. This is a calorie deficit - leading to fat (or weight) loss.
This is why myths about spot reduction are false: the rate at which your body removes energy from your fat cells is exactly the same, for every single cell. They get bigger and smaller at the same rate everywhere on the body. Women have deep ends and shallow ends when it comes to fat: we lose fat quicker in the shallow ends and slower in the deep ends. The fat is “emptied” at the same rate everywhere, but there’s simply more fat cells in the deep ends: it takes longer to see progress than in the shallow bits. These areas are different on every woman: ankles, butt, thighs, bellies, arms, boobies etc.
Ultimately, the fat we feel, see (and don’t see) is the result of how big or small our fat cells are.
WHERE DOES FAT GO?
It doesn’t disappear - it changes form (think water & steam).
Once the body has used up carb reserves (glycogen), it starts using fat for energy, a process called ketosis. When the body needs energy, it releases hormones. Those hormones signal your fat cells to release the fat into the bloodstream: the fat cells break it up and kick it out at the level being demanded. After it’s been broken down, it enters the bloodstream, which then takes it where it needs to go. The liver grabs glycerol from the bloodstream fat & breaks it down further, and some of the fatty acids go to your muscles so they can use it for energy.
Once they reach their destinations, the glycerol & fatty acids are broken down again: during this process they produce heat, water, carbon dioxide and adenosine triphosphate (ATP). The ATP keeps some potential energy for use later like a back up system or storage. The rest leaves our bodies through natural methods: the water exits as pee and sweat, and we breath out the carbon dioxide. At that point, it’s not fat anymore really - it’s been broken down chemically. It’s been used for energy, chemically altered and exits through natural substances that always leave the body. And whatever’s left of it takes up MUCH less space.
When we use fat for energy, it leaves our fat cells - making them smaller than when we started. The fat then gets ‘used’ up like gas in a tank: it gets broken down & breathed/peed out for the most part. That’s how fat is lost. The cycle repeats constantly, with surpluses of energy making your fat cells bigger and deficits leaving them smaller.
When our metabolism is low (we’re not eating enough) our bodies stop sending out the hormone to use fat for energy: it needs fat for survival and will protect its stash. Instead, it will signal your fat cells to collect and store fat, while using proteins from your muscles for energy. This is why people stop or have trouble losing fat when they’re over-restrcting their calories: also known as starvation mode.