How Does Fat Leave the Body When You Lose Weight?

Key takeaways:

• When you burn fat, it’s expelled from your body through a combination of breathing, sweating, and urinating.
• Although sweating is a mechanism of losing body fat, sweating alone primarily results in losing water weight.
• Different individuals are more prone to hold fat in different areas of their bodies, and the areas from which you lose fat first mainly depend on your genetic makeup.
• You can potentially build muscle while burning body fat, especially as a fitness beginner, by transforming energy from fat reserves into the energy required to build new muscle.

One of the most frequently asked questions about weight loss is where does fat go when you lose weight. This guide answers this and other common weight loss questions. As always, if you have any specific questions about your own weight loss journey, please speak to a licensed Canadian healthcare practitioner. 

Body fat basics

Although we typically want to lose body fat as quickly as possible, it’s important to remember that fat serves an essential, life-sustaining purpose: providing energy.

Instead of thinking of body fat as purely undesirable, think of it as an energy storage reserve. When the body undergoes stress and needs additional energy, it will sometimes access these fat reserves to meet its needs. 

For example, imagine you suddenly found yourself stranded in the wilderness struggling to find food. In this scenario, you would want to have some fat on your body to provide energy.

If you had very little body fat to burn as energy, your body would generally start to use less optimal energy sources — like muscle — to produce energy.

How does fat leave the body?

We talk about “burning” fat. But when we lose weight, where does fat actually go?

When the body uses fat for energy, it produces two primary byproducts: carbon dioxide and water. When you exhale, sweat, and urinate, these byproducts are expelled from the body. Surprisingly, you exhale the majority of lost body fat through your lungs in the form of carbon dioxide.

In this way, your body literally breathes away fat. And through hard breathing and sweating, you’re literally getting rid of body fat in the form of its metabolic byproducts, too.

What happens to body fat when you diet and/or exercise?

Diet and exercise can both contribute to fat loss, but their mechanisms of action are slightly different. 

When you exercise, you burn calories for energy.

Depending on the amount of exercise you get, your body may use more calories than you consume through your diet. When this happens, your body uses those same fat stores to compensate. As a result, you lose body fat and reduce your weight.

Which part of the body loses fat first?

Where you store body fat — and where you lose body fat first — depends largely on your genetic makeup.

Different people will store fat in different areas of their bodies. Some people carry more weight in their hips and thighs, while others tend to store fat in their midsection.

A tendency to store more fat in a particular area is no guarantee that you’ll start losing fat from that spot first. 

Research indicates that fat storage patterns also change with age. As we age, fat storage tends to move from the arms, legs, and face to the midsection. This also results in more visceral fat — fat stored around the organs.

Can you spot-reduce fat?

Spot reduction is the idea that you can lose weight in a specific area of your body by focusing on exercises that target that area. For example, you might try to do extra core exercises, hoping it will help you eliminate body fat around the abdomen.

Unfortunately, there has been no conclusive evidence that spot reduction works. In fact, studies show the opposite is true. In general, although some individuals may lose fat in a given area at a higher rate than others, the human body generally gets rid of body fat from the entire body at a relatively equal rate.

However, it’s worth noting that exercising a particular part of your body is a good way to build muscle in that area, which might reduce the unwanted appearance of fat. For example, if you tend to store fat in your upper arms, building muscle in your biceps and triceps may reduce the appearance of the fat in that area being “saggy.”

Do you lose weight when you sweat?

You do lose weight while you sweat. It’s one of the body’s natural mechanisms for removing water (and fat is converted to water and carbon dioxide).

It’s important to note that simply sweating without exercise — for example, if you’re sitting in a sauna or lounging by the pool on a hot day — will cause you to lose water weight rather than fat. In other words, you’ll just be dehydrating yourself.

Professional fighters often intentionally take advantage of this phenomenon by dehydrating themselves before a big fight to “make weight” for their particular weight class. While dehydrated, they weigh less. However, they don’t actually lose any muscle or fat. They’ve simply lost water weight, which can quickly be regained after they’re weighed by the fight officials.

Final thoughts

Fat leaves your body through sweat, urine, and breath when you lose weight. How the body processes fat is complex and unique to an individual which makes everyone's weight loss journey unique.  

If you’re looking for support with your weight management and want advice on how to get started, talk to one of Felix’s healthcare practitioners today.