Intermittent fasting: What is it and how does it work?

By now, you've probably heard of intermittent fasting from fitness influencers and fanatics, all preaching about its weight-loss magic... But what exactly is it? And how does it work?

What is it?

Many diets focus entirely on what to eat, but intermittent fasting (IF) is all about how to eat. IF simply describes an eating pattern that cycles between fasting and eating periods, there are no specific foods you cannot or must eat.

Intermittent Fasting Methods

Popular methods for intermittent fasting include:

• The 16/8 method: Otherwise known as the 'Leangains protocol'. This method involved skipping the breakfast period and restricting your eating period to 8 hours - meaning you'll fast for 16 hours between.

• Eat-Stop-Eat: This method involves a 24 hour fast, once or twice a week, ie: you could fast between dinner on Monday day to dinner on Tuesday, but eat normally the rest of the week.

• The 5:2 diet: This method requires a weekly cycle of eating normally for 5 days and consuming only 500–600 calories for two days of the week, so long as they are not consecutive.

Reducing your calories in this way should lead to weight loss, so long as you aren't compensating by overeating in the eating windows of the cycle. The most popular is perhaps the 16/8 method due to its simplicity, lack of 24-hour fasts which can be quite difficult and the results that it provides.

How does fasting affect your cells and hormones?

Fasting has several effects on our bodies on a cellular level, some of which promote losing weight.

Here are some changes that occur in your body when you fast:

• Human Growth Hormone (HGH): HGH levels can increase drastically with fasting, which can contribute to fat loss and muscle gain. (1)

• Insulin: As insulin levels drop in our bodies, while insulin sensitivity increases, stored fat in our body becomes more accessible and therefore tends to burn more under fasting. (2)

• Cellular repair: Research shows that while fasting, cells initiate a cellular repair process. This includes autophagy - a process where cells digest old proteins that build up inside cells. (3)

• Gene expression: Research also suggests that changes to our gene functions occur when we fast. As a result, it is believed that it can help protect against disease. (4)

Potential health benefits

Countless studies have been carried out, researching the effects of intermittent fasting on our health - many of which point to weight loss as the clearest and most consistent. But there are many more:

• Weight loss: As stated above, intermittent fasting can help you lose weight - namely lower your body fat percentage. (5)

• Insulin resistance: Intermittent fasting can lower insulin resistance which in turn can lower blood sugar by 3–6%, which could protect against type 2 diabetes. (6)

• Inflammation: Some studies show that intermittent fasting can reduce inflammation, which is a known catalyst for many diseases. (7) (8)

• Heart health: Along with inflammation and insulin resistance reduction, intermittent fasting may also reduce cholesterol levels and blood triglycerides - all factors that affect heart disease. (9)

• Cancer: Some animal studies suggest that intermittent fasting could help prevent cancers. (10) (11) (12)

• Brain health: Intermittent fasting has been shown to increase the brain hormone known as BDNF, which may aid the growth of new nerve cells and protect against the development of Alzheimer's. (13) (14) (15)

Weight loss

As the most popular reason for many turning to intermittent fasting, it's certainly worth covering in more depth.

The simple explanation for why this occurs when we fast is that we put our bodies in a calorie deficit, meaning you consume less calories that your body needs. Doing this on a regular basis will encourage your body to find other sources of energy, namely the stored fat on your body.

This also occurs as a result of hormone changes such as lowering insulin and increasing growth hormone levels. It also increases the release of norepinephrine (noradrenaline) - a fat burning hormone. As a result, your metabolic rate could increase by just 3.6% all the way up to 14%. (16) (17)

A 2014 review study showed that intermittent fasting can lead to a 3-8% total weight loss over 3-24 weeks - a significant amount compared to most other weight loss techniques. The same study found that people also lost 4–7% of their waist circumference, which tends to be the main aim for those looking to lose weight, as belly fat loss reduces harmful fat that builds up around our organs. (18)

Safety and side effects

The main side effect of intermittent fasting is the feeling of hunger as your body adjusts to a new eating structure. This should only be temporary and will likely fade as you become more comfortable with the different meal schedule.

Close and careful monitoring of your eating structure is particularly important if you:

• Have diabetes.

• Have problems with blood sugar regulation.

• Have low blood pressure.

• Take medications.

• Are underweight.

• Have a history of eating disorders.

• Are a woman who is trying to conceive.

• Are a woman with a history of amenorrhea.

• Are pregnant or breastfeeding.