Written by Kris Gunnars, BSc — Medically reviewed by Katherine Marengo LDN, R.D., Nutrition — Updated on May 13, 2021
Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting.
There are many different types of intermittent fasting, such as the 16/8 and 5:2 methods.
Numerous studies show that it can have powerful benefits for your body and brain.
Here are 10 evidence-based health benefits of intermittent fasting.
1. Changes the function of hormones, cells, and genes
When you don’t eat for a while, several things happen in your body.
For example, your body changes hormone levels to make stored body fat more accessible and initiates important cellular repair processes.
Here are some of the changes that occur in your body during fasting:
- Insulin levels. Blood levels of insulin drop significantly, which facilitates fat burning (1).
- Human growth hormone (HGH) levels. The blood levels of human growth hormone (HGH) may increase dramatically. Higher levels of this hormone facilitate fat burning and muscle gain, and have numerous other benefits (2, 3, 4, 5).
- Cellular repair. The body induces important cellular repair processes, such as removing waste material from cells (6).
- Gene expression. There are beneficial changes in several genes and molecules related to longevity and protection against disease (7).
Many of the benefits of intermittent fasting are related to these changes in hormones, the function of cells, and gene expression.
2. Can help you lose weight and visceral fat
Many of those who try intermittent fasting are doing it to lose weight (8).
Generally speaking, intermittent fasting will make you eat fewer meals.
Unless you compensate by eating much more during the other meals, you’ll end up taking in fewer calories.
Additionally, intermittent fasting enhances hormone function to facilitate weight loss.
Lower insulin levels, higher HGH levels, and increased amounts of norepinephrine (noradrenaline) all increase the breakdown of body fat and facilitate its use for energy.
For this reason, short-term fasting actually increases your metabolic rate, helping you burn even more calories (7, 9).
In other words, intermittent fasting works on both sides of the calorie equation. It boosts your metabolic rate (increases calories out) and reduces the amount of food you eat (reduces calories in).
According to a 2014 review of the scientific literature, intermittent fasting can cause weight loss of 3–8% over 3–24 weeks. This is a huge amount (10).
The study participants also lost 4–7% of their waist circumference over 6–24 weeks, which indicates that they lost lots of visceral fat. Visceral fat is the harmful fat in the abdominal cavity that causes disease (10).
One 2011 review also showed that intermittent fasting caused less muscle loss than continuous calorie restriction (11).
However, a 2020 randomized trial looked at people who followed the 16/8 method. In this diet, you fast for 16 hours a day and have an 8-hour window to eat.
The people who fasted didn’t lose significantly more weight than the people who ate three meals a day. After testing a subset of the participants in person, the researchers also found that the people who fasted lost a significant amount of lean mass. This included lean muscle (12).
More studies are needed on the effect of fasting on muscle loss. All things considered, intermittent fasting has the potential to be an incredibly powerful weight loss tool.
3. Can reduce insulin resistance, lowering your risk for type 2 diabetes
Type 2 diabetes has become a very common diagnosis in recent decades.
Its main feature is high blood sugar levels in the context of insulin resistance.
Anything that reduces insulin resistance should help lower blood sugar levels and protect against type 2 diabetes.
Interestingly, intermittent fasting has been shown to have major benefits for insulin resistance and to lead to an impressive reduction in blood sugar levels (10).
In human studies on intermittent fasting, fasting blood sugar has been reduced by 3–6% over the course of 8–12 weeks in people with prediabetes. Fasting insulin has been reduced by 20–31% (10).
One study in mice with diabetes also showed that intermittent fasting improved survival rates and protected against diabetic retinopathy. Diabetic retinopathy is a complication that can lead to blindness (13).
What this implies is that intermittent fasting may be highly protective for people who are at risk for developing type 2 diabetes.
However, there may be some differences between the sexes. One 2005 study in women showed that blood sugar management actually worsened after a 22-day long intermittent fasting protocol (14).