What really happens to your body during intermittent fasting

What really happens to your body during intermittent fasting

The concept of intermittent fasting is something that has been around for a long time, but people rarely know what it is exactly, or why it’s effective. In a nutshell, intermittent fasting is a broad term for a variety of different weight loss approaches that all involve restricting your daily calorie intake to a relatively narrow window of time each day. While it may sound like a fad, it’s in fact highly effective and an ideal strategy for people wanting to achieve gradual weight loss.

The most popular method of intermittent fasting is the 16:8 method, which involves adopting an 8-hour eating window (e.g. 10am-6pm) and fasting for the remaining 16 hours of the day. People usually achieve this by simply extending the length of their normal overnight fast (time spent sleeping and not eating) and delaying their breakfasts.

But there are also other approaches to intermittent fasting, such as the 5:2 Diet, which involves eating normally for 5 days of the week while restricting calories to 500-600 on two days of the week, or the Eat-Stop-Eat method which involves doing a 24-hour fast once a week (for example fasting from dinner on Tuesday, to dinner on Wednesday).

Despite many of us being familiar with intermittent fasting, most people are in the dark about what happens to the body when they do it.

Weight loss

Of course, weight loss is the most common reason that people try out intermittent fasting. From a biological perspective, it works like this: during fasting, your body switches from burning glucose (carbohydrates) as its primary fuel source to burning fat for energy instead.

Most experts agree that the shift in metabolism usually occurs when the body has been fasting between 10 to 16 hours, hence the popularity of 16:8 fasting method. Interestingly, the body doesn’t begin to break down proteins for fuel until around the third day of fasting, which means that you can lose weight while still maintaining muscle mass.

Intermittent fasting also drives weight loss by lowering insulin levels. Insulin is a hormone that allows cells to absorb glucose, and a person’s insulin levels drop when a person is not consuming food. During fasting, decreasing insulin levels cause the cells to release their glucose stores as energy and repeating this process regularly can lead to weight loss.

Lastly, the time-frame restrictions can lead to reduced snacking and the consumption of fewer calories overall, which can also contribute to weight loss.

Improves brain health

When your body uses fat stores for energy, it releases chemicals called ketones into the bloodstream. In addition to playing a role in the weight loss cycle, ketones also trigger the release of a molecule called BDNF, which helps build and strengthen neural connections in areas of the brain responsible for learning and memory. A study of older adults found that a boost in ketones improved memory and the growth of new nerve cells in the brain in just six weeks.

Other studies have found that that brain’s reaction to intermittent fasting is the same reaction it has to regular exercise – both of which have the net effect of improving brain health: improved long-term memory, increased levels of focus, and even better mental health.

Combining intermittent fasting with low carbohydrate intake is another way to super-charge your ketone production.

Lowers your chance of long-term disease

A 16-week clinical study by the CSIRO found intermittent fasting led to improvements in cholesterol levels, blood pressure, heart rate and triglycerides (triglycerides are a type of fat present in the blood that has links to heart disease). These are all factors that lead to improved heart health, and a lower chance of cardiovascular disease.

A separate study by Translational Research found that because intermittent fasting successfully lowers blood glucose and insulin levels, it has proven be both a preventative measure, and an effective treatment for type-2 diabetes. This is because when you fast, your insulin levels drop, while your levels of human growth hormone and norepinephrine rise – which speeds up your metabolism, helps your body lose weight, and breaks down sugar in the body more effectively.

Enhances sleep quality

Intermittent fasting in many ways helps the body stay well aligned for sleep. This is because the timing of meals can affect our 24-hour circadian rhythm, which significantly influences our quality of sleep.

Eating heavily near bed time is proven to worsen sleep quality, making sleep more restless and less refreshing. But when you are fasting, your digestive system quiets down and your body goes into energy saving mode earlier in the night. This makes for a stronger, more synchronized body clock, and means you’ll have easier time falling asleep, staying asleep and waking feeling refreshed and energized.

The best thing about intermittent fasting is that it provides a wide range of positive health benefits without requiring a massive lifestyle change – it’s super convenient. In saying this, it’s still important to provide your body with all of the essential nutrients and vitamins it needs to function at its best.

Kate Save is the CEO and co-founder of Be Fit Food. She is also an accredited practising dietitian, diabetes educator and exercise physiologist.