What happens to your body when you do intermittent fasting?

Intermittent fasting is the trendiest weight loss trick around at the moment, but its roots are centuries old. Humans have always fasted, either by necessity or, in modern times, for religious reasons — or even to prepare for surgery. 

In its simplest terms, intermittent fasting requires the restriction of your calorific intake for certain periods, often for 16 to 18 hours daily (or overnight), or even for a couple of days at a time. The rest of the time, you eat normally. As endocrinologist Ahmet Ergin, MD, told Share Care, its effectiveness is primarily based on how our bodies absorb food. 

How does intermittent fasting work?

When we eat, we absorb energy from the glucose in food. Insulin, a hormone produced by the pancreas, helps to deliver this glucose to the body's cells, where it's either used for energy or stored for later. "When you do not ingest carbohydrates or any sort of energy, your body immediately reduces insulin production," explains Dr. Ergin. If insulin levels drop far enough, your body will begin to use stored glucose for energy instead. Once those stores are gone, your body will feast on fat, causing weight loss.

The most common types of intermittent fasting include time-restricted fasting, which entails fasting for 12 to 16 hours daily (usually while asleep) and then eating only during a specific, short block of time. Another method is the super-popular 5:2 diet, which involves eating normally for five days per week and then restricting your intake to 500 to 600 calories on the other two. 

Is intermittent fasting effective for weight loss?

It's worth noting, however, that intermittent fasting usually only leads to minimal weight loss and, as with all diets, once you stop doing it the weight will most likely return. According to a 2018 study, participants lost on average just 0.38 of their body weight over a period of 24 weeks.   

Recently, however, there have been suggestions that intermittent fasting could have other health benefits, too. Dr. Ergin claims you could see "significant improvements" in cholesterol, triglycerides, blood pressure, and inflammation levels. It's important to note, though, that there are also certain risks associated with this type of fasting to consider.

What are the risks associated with intermittent fasting?

A variety of healthcare experts spoke to Men's Health at length that much more research still needs to be done on the subject. They also warned that those susceptible to eating disorders or who suffer from diabetes should steer clear of intermittent fasting, and pregnant or nursing mothers should also avoid trying it out. 

Be warned that side effects of intermittent fasting include (but are not limited to) hunger, irritability, tiredness, and dehydration. You should also watch your alcohol intake, and keep track of whether you're feeling dizzy or lightheaded. 

If you're considering trying intermittent fasting, as with anything else, always discuss it with your doctor first.