March 14, 2016

Where does the fat go when you lose weight?

The vast majority of doctors, dietitians and personal trainers believe that during physical exercise fat is converted to energy or heat (hence the term ‘burn’) and that the metabolites of fat are excreted in the faeces or converted to muscles.


According to a new study by two Australian scientists, Professor Andrew Brown and a researcher Ruben Meerman, it is a widespread misconception. So, where does the fat go when you lose weight? We actually breathe the fat out in the form of carbon dioxide.

Excess dietary carbohydrates and protein are converted to a type of fat called triglyceride. When people attempt to lose weight, they are attempting to metabolize these triglycerides while keeping their fat-free mass intact, explain the authors.

Triglycerides are comprised of three types of atom: carbon, hydrogen and oxygen. Triglyceride molecules can be broken down only by unlocking these atoms, through a process known as oxidation.


The researchers found out that when somebody loses 10 kg of fat, 8.4 kg is converted and excreted as carbon dioxide (CO2) via the lungs, and 1.6 kg becomes water (H20)  which may be excreted in the urine, faeces, sweat, tears, or other bodily fluids.


So, don’t start breathing faster to lose weight. You’ll only hyperventilate, the study authors say. Although the findings my change how weight loss is understood, the strategy for losing weight should remain the same:  ‘Eat less, move more.’

The amount of carbon that is lost can be increased with exercise. By substituting 1 hour of rest for 1 hour of moderate exercise such as jogging, the metabolic rate is increased sevenfold, removing an additional 40g of carbon from the body, increasing the daily total by around 20% to 240g.

However, this can easily be offset with unhealthy eating. A single 100g muffin, for example, provides around 20% of an average person’s total daily energy requirement. “Physical activity as a weight loss strategy is, therefore, easily foiled by relatively small quantities of excess food,” write the authors.

You can also stimulate your weight loss by taking good quality dietary supplements.


Source:BMJ 2014;349:g7257