Like, does it magically disappear into the air? Is there a super complicated mechanism that happens in your body that you don’t know about? This really isn’t something they cover in high school—or, at least, not in mine.
Turns out, fat can leave your body in a few different ways—and they’re all pretty fascinating. (More on those in a sec, but at least one is sci-fi level cool.)
Of course, there’s a right way to go about fat loss and a wrong way to approach this. Trying to lose too much weight too quickly can set you back and even put your health at risk, making it important to get this right from the start. While you’ve likely heard about some fat loss don’ts before, it never hurts to reiterate them.
So, how does fat leave the body and what can you do to speed up the process if that’s your goal? Obesity medicine specialists break it all down.
Meet the experts: Christoph Buettner, MD, PhD, is chief of the division of endocrinology at Rutgers Robert Wood Johnson Medical School. Colleen Tewksbury, PhD, MPH, RD, is a registered dietitian and adjunct associate professor at Penn Medicine. Fatima Cody Stanford, MD, MPH, MPA, is an instructor of medicine and pediatrics at Harvard Medical School and an obesity medicine physician at Massachusetts General Hospital. Mir Ali, MD, is a bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California.
What is body fat?
Body fat, or adipose tissue, is an important form of energy storage in your body. In fact, body fat functions as an endocrine system, secreting certain growth factors and molecules in your body, research in Frontiers in Cardiovascular Medicine shows. In other words, fat plays a role in hormone regulation, too—it doesn't just hang around, doing nothing.
There are different types of body fat, but they can be categorized into visceral or subcutaneous fat:
Visceral fat is fat stored within the abdominal cavity, surrounding the liver, pancreas, and intestines, says Christoph Buettner, MD, PhD, chief of the division of endocrinology at Rutgers Robert Wood Johnson Medical School. “It is also known as intra-abdominal or organ fat and can pose health risks when there is too much of it as it is associated with various metabolic and cardiovascular problems.”
Subcutaneous fat is the layer of fat tissue just below your skin, says Colleen Tewksbury, PhD, a registered dietitian and adjunct associate professor at Penn Medicine.
How does fat leave the body?
There are actually a few different ways that fat can leave your body. The main ways are through your sweat, pee, and even the air, says Fatima Cody Stanford, MD, MPH, MPA, an instructor of medicine and pediatrics at Harvard Medical School and an obesity medicine physician at Massachusetts General Hospital. Fat gets converted into water in the body and then it's expelled through these different ways.
“As water, it is expelled via your skin during perspiration and your kidneys during urination,” Dr. Stanford says. “As carbon dioxide, it is exhaled through your lungs.” Yep, you can actually breathe out fat. (Keep in mind, though, that sweating alone isn't going to make you burn fat—you have to do the work through diet and exercise to convert fat into water first.)
“Fat loss is the same whether you lose it through exercise or diet,” says Mir Ali, MD, a bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California. But following a healthy eating plan is more likely to help you lose weight (if that's your goal) than exercise, he says.
How To Monitor Fat Loss
Stepping on a standard scale used to be the main way people tracked fat loss, but that’s imperfect given that factors like how much food and water you have in your stomach at any given time, as well as muscle you’ve gained, can interfere with this reading, Dr. Ali says.
“A more accessible and potentially more helpful measure for people over time would be waist circumference,” Tewksbury says.
There are also body impedance (BIA) scales, which estimate your body fat percentage, Dr. Stanford says. While they usually provide more of an estimate vs. hard and fast results, they can be helpful in tracking progress over time.
You can also try a mix of both to get a sense of your progress, Dr. Ali adds.
Fat Loss Dos And Don’ts
Fat loss can be tricky, but there are some steps doctors recommend you focus on over others. While Dr. Stanford says the right fat loss moves are “highly individualized,” she suggests starting with these:
Eat a high-quality diet of lean protein, whole grains, vegetables, and fruits.
Do the CDC-recommended 150 minutes a week of cardiovascular exercise.
Incorporate at least two days of strength training into your workout routine.
But Tewksbury also suggests speaking with a healthcare professional for guidance. “Self-directed weight loss can be risky for both physical and mental health,” she says. “Discuss with your physician or a registered dietitian what approach may be best for you.”
As for what to avoid, Dr. Stanford warns against taking steps that are too drastic. “Significant caloric deficit or restriction is often harmful and can lead to fat loss initially, but it can also lead to muscle loss, nutrient deficits, and weight regain,” she says.
Dr. Ali says it’s also important to not write off what you’re eating if you’re exercising. “Some people are under the impression that, when they exercise, they don’t have to be as concerned about their diet, but both are important,” he says.
Frequently Asked Questions About Body Fat
Keep these in mind as you go on your weight loss journey.
What weight loss questions do doctors get the most?
“The most common thing I hear patients ask is, ‘I’m eating very little but I’m not losing weight—why?’” Dr. Ali says. “It’s often because they’re eating the wrong things. It’s not so much the amount you’re eating, but what you’re eating.”
How can you lose fat on certain areas of your body?
Unfortunately, you can’t pick and choose where you lose fat on your body. “The body deposits fat where it wants to,” Dr. Ali says. “A lot depends on genetics.”
Which is more important for fat loss: diet or exercise?
Experts say a mix of both is ideal for your health. “Combination is always most important, but it is important to sustain these practices over the long term,” Dr. Stanford says. Tewksbury agrees: “Studies have shown a combination is the most effective, followed by food intake, then exercise,” she says.
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