According to a new study published in the British Medical Journal, lots of people believe that fat gets "burned" off by being converted into heat and energy. And others believe that it gets turned into muscle.
These are commonly held incorrect beliefs. In fact, many doctors and dieticians and personal trainers believe them.
But they're wrong! So where does fat actually go when you lose weight?
The researchers found that when you lose weight, you actually BREATHE out 84% of that fat and the other 16% of fat escapes your body in the form of water (in your sweat, pee, breath and so on).
The study's researchers figured this out by tracing every atom's pathway out of the body. And here's what they found: If you lose 10 kg of fat (about 22 pounds), 8.4 kg will be in the form of carbon dioxide, and 1.6 kg will be in the form of water (about 18.5 pounds and 3.5 pounds respectively).
When we talk about weight loss and fat burning we are talking about a specific type of fat — one that accumulates when we eat excess carbs and protein that our bodies don't need to use at the moment. These excess macronutrients get converted into things called triglycerides, which are then stored in adipocytes (fat cells) in your body. If you are trying to lose weight, you are attempting to metabolize (use, burn, convert) those triglycerides. Essentially, they need to go through a process of chemical reactions in order to change into something else that is no longer fat. That is how fat loss works.
Here's the key finding: Once those triglycerides do go through the chemical reactions... they leave the body in the form of carbon dioxide and water. Mostly carbon dioxide, and mostly through your breath. You are breathing out your fat!
The researchers note, however, that if your goal is to lose weight, simply breathing more or working out more isn't necessarily going to help you achieve that. You also will need to eat less, so your total carbon intake is less than your output. As they write in their study: "Physical activity as a weight loss strategy is, therefore, easily foiled by relatively small quantities of excess food."