It can be easy to notice when you gain weight. Your body may look or feel different, or your clothes may not look the same as they used to. But when you decide to lose weight, what happens to it then?
You might have heard that the fat you lose can turn into muscle. It may seem like it turns invisible, only to reappear months later when you stop going to the gym. Neither is accurate. Diet and exercise can be challenging, but the way they burn fat is much simpler than you might think.
What Is Body Fat?
Body fat, known medically as adipose tissue, is a type of connective tissue that runs throughout your entire body, says Pamela Peeke, MD, MPH, assistant professor of medicine at the University of Maryland and author of The Hunger Fix.
“People vilify body fat, but it’s not your enemy,” she says. “You need it to live.”
Adipose tissue contains not only fat cells, but nerve cells and blood vessels. It stores energy to power your body and helps insulate you from heat and cold. It also releases hormones that control your metabolism, such as leptin, and hormones that affect your body’s ability to regulate insulin. “It’s a dynamic hormonal organ,” Peeke says.
When fat sits just under your skin, doctors call it subcutaneous fat. Another type, called visceral fat, sits deeper in your belly under the abdominal wall.
“Visceral fat is important because it cushions your organs, but you don’t want to have too much of it,” Peeke says. Why? It makes proteins called cytokines, which trigger inflammation and raise your risk of heart disease.
You need calories
Calories are units of heat energy you get from the food and drinks you consume. They act as fuel to give your body energy.
Everything your body does requires calories. It even burns calories when your heart beats and your lungs breathe.
How many calories should I eat a day?
You need a certain number of calories to support body functions and provide energy. How many you need depends on several things. These include:
- Age
- Sex
- Weight and height
- How active you are
Adult women generally need between 1,600 and 2,400 calories per day, and adult men between 2,000 and 3,000 calories. Taller, heavier, or more active people will be at the higher end of each range.
How do calories turn into fat?
When you consume more calories than your body burns, the excess calories (or energy) have to go somewhere. Your body converts these excess calories into body fat. It can either create new fat cells or make existing ones bigger.
Do fewer calories equal less fat?
It’s not necessarily that simple. It's true that how much you weigh is related to how many calories you take in, burn, and store. But your genes, your metabolism, and your environment all play a role.
How Is Fat Burned?
To lose weight and burn body fat, your body needs to use more energy. You can do this through diet and exercise.
Calories from food
Excess calories are stored as fat in your body. The first step toward burning fat is to take in an appropriate amount of calories.
You can cut calories in many ways. You might choose a low-fat or low-carb diet. You could follow a Mediterranean-style plan or eat only during certain hours. No matter what method you choose, the goal stays the same: Use more calories than you take in.
If you want a simple way to build a healthy meal, try filling half your plate with fruits and vegetables. Use one-quarter of the plate for whole grains (such as brown rice or quinoa) and the other quarter for healthy proteins like fish, poultry, or beans.
Exercise and calories
Along with keeping your caloric intake in check, you can increase the number of calories your body uses through exercise.
If you don’t increase your caloric intake at the same time, your body starts burning the stored energy in your fat.
Over time, this helps you lose body fat. Research shows that many people who are successful at losing weight and keeping it off get about an hour a day of moderate to vigorous movement, like brisk walking. Some people may need more, others less. If you mix in other types of exercise, like resistance training, you might see even more benefits.
Does tirzepatide burn fat?
Tirzepatide (Mounjaro) works indirectly to burn fat by reducing your appetite, Peeke says. It acts like two natural hormones, GIP and GLP-1, which help control blood sugar and curb hunger. Your intestines normally release these hormones after you eat.
"This enhances insulin secretion, which improves your blood sugar control, and also helps to reduce your appetite since it slows down the time it takes your stomach to empty," Peeke says.
Since you eat fewer calories, your body will burn its fat stores to give you the energy you need to get through your day.
Does semaglutide burn fat?
Like tirzepatide, semaglutide (Ozempic, Wegovy) works indirectly to burn fat. It's also a GLP-1. It helps you lose weight by taking in fewer calories, in much the same way as tirzepatide.
Some research suggests that tirzepatide may be slightly more effective than semaglutide in reducing body fat.
A recent study found that people on tirzepatide lost about 20% of their body weight after 18 months. People on semaglutide lost about 14%. "Some of that weight loss includes muscle, which your body needs to burn fat efficiently," Peeke says. No matter which medication you use, regular activity helps protect your muscle mass.
How Does Fat Leave the Body?
When you lose weight, fat goes through a series of metabolic processes.
When your body breaks down fat for energy, it leaves behind two substances: water and carbon dioxide. They leave your body in one of three ways:
- You sweat water out through your skin.
- You pee water out through your kidneys.
- You breathe carbon dioxide out through your lungs.
While your body can get rid of fat, your fat cells are here to stay unless you have them liposuctioned out. When you lose body fat, those fat cells simply shrink.
“If you examine your fat cells in the lab, under a microscope, they look like beautiful round balloons,” Peeke says. When you lose weight, “they deflate, like when you untie a balloon and let all the air out."
How to Burn the Fat Easier
There's no effective way to speed up your metabolism to help you burn fat faster. Once you figure out about how many calories you need, you'll need to start making lifestyle changes if you want to to lose extra fat.
Here are some tips to help you get started:
Observe your habits
Monitor your current eating and exercise habits using a notebook or an app. This will make you more aware of the choices you're making and can help direct you toward change.
But don’t overdo it, and don't beat yourself up for an occasional indulgence.
“When you make food choices, ask yourself what are the high-ticket items that have the most sugar and fat in them,” Peeke says. “Those are the foods that should be avoided. You don’t have to weigh out a serving of cantaloupe and log that it has exactly 79 calories.”
In fact, if you get overzealous with calorie counting, it can trigger or lead to disordered eating patterns, Peeke says.
Find your favorite exercise
You don’t have to run a marathon to help your body burn excess fat. If you find an activity you enjoy, you're more likely to keep doing it. That might be:
- Swimming
- Dancing
- Recreational sports
- Physically interactive video games
- Playing with your children or pets
The CDC recommends that all adults aim for at least 150 minutes each week of moderate aerobic activity, like brisk walking, or 75 minutes of vigorous activity, like swimming laps. That's the equivalent of 30 minutes a day, five days a week.
You also need at least two days a week of muscle-strengthening activity like resistance training. "All of these activities are important not only because they burn fat, but also because they build muscle, which raises your metabolism," Peeke says. Muscle tissue burns slightly more calories than fat, even when you're at rest.
Peeke also recommends adding intervals — brief periods of faster or more intense movement — into your workout. If you normally walk, for example, follow a route with hills, or speed up your pace every few minutes. This type of exercise, known as interval training, has been shown to significantly increase fat loss, especially in women.
Sleep
When you're trying to lose fat, make sure you're getting enough sleep. One study found that people lost 55% less fat when they spent 5 1/2 hours a night sleeping than when they spent 8 1/2 hours in bed.
"If you don’t get enough sleep, your body produces more of the hormone ghrelin, which increases appetite, and less of the hormone leptin, which helps you feel full," Peeke says. As a result, you’ll be hungrier and eat more.
Eat mindfully
Take your time while eating, and pay attention to each bite you take. This can help you be more aware of how much you're eating and your body's fullness cues. Some research shows mindful eating may help with weight loss.
“A lot of times, we act like a vacuum and suck our meal down, rather than take the time to eat slowly and savor each bite,” Peeke says. One easy way to do this is simply to put your fork or spoon down for a few seconds after each mouthful.
Fat Burn Takeaways
How does fat leave the body? Once your body burns fat for energy, its waste materials leave through your pee, sweat, and breathing. The best way to burn fat is to consume fewer calories than you use. To lose fat, aim to both cut calories and increase your physical activity. Get enough sleep, and practice mindful eating to help you consume less. Certain medications like semaglutide and tirzepatide help control your appetite, so you take in fewer calories and burn fat.
Fat Burn FAQs
Do you pee out fat?
You don’t actually pee out fat, but your body does remove the byproducts of burned fat, mainly water and carbon dioxide. Once your body breaks down fat for energy, it gets rid of this waste through your breath, sweat, and urine. In this way, your kidneys help flush out part of the waste after fat loss.
What burns the most body fat?
To lose fat, you must take in fewer calories through food and drinks than your body burns. The more you move, the more fat you'll burn. Physical activity uses fat for energy and helps your body remove the waste that comes from breaking it down. The more intense the exercise, the more you burn. But it's best to choose an exercise you enjoy, since you'll be more likely to keep doing it
Do you sweat out fat?
You don’t sweat out fat itself. But when your body burns fat for energy, it produces waste, mainly water and carbon dioxide. Some of that water leaves your body through sweat, so sweating helps remove some of the byproducts of fat loss.
How long does it take for your body to start burning stored fat?
It typically takes about 30-60 minutes of exercise for your body to start burning stored fat. At first, your muscles use stored sugar (glycogen) for energy, but as you keep moving, your body shifts to mainly using fat as a fuel source.
