Studies on intermittent fasting

Intermittent fasting (IF) is currently one of the most popular health and fitness trends worldwide.

Last update: 28th May 2020

How IF affects cells and hormones

Here are some of the changes that occur in the body during fasting:

  • Muscle building, fat loss, growth hormone (GH): The GH level rises and can increases 5 fold. This is advantageous for fat reduction and muscle building. (Trusted Sources: 1, 2, 3, 4).
  • Blood sugar levels & diabetes: Insulin sensitivity improves and the insulin level decrease. Lower insulin levels make stored body fat more accessible (Trusted Source: 1).​
  • Cellular repair: During fasting, our cells initiate cellular repair processes. These include autophagy, during which cells digest and remove old and dysfunctional proteins that accumulate inside the cells (Trusted Sources: 1, 2).​
  • Gene expression: There are changes in the function of genes that are related to longevity and protection against disease (Trusted Sources: 1, 2,).

These changes in hormone levels, cell function and gene expression are responsible for the health benefits of IF.

 

A very powerful tool for weight loss.

Weight loss is the most common reason for people to try IF (Trusted Source: 1).

IF lowers insulin level and increases growth hormone levels. Due to these hormonal changes, fasting can increase the metabolic rate by 3.6-14% (Trusted Sources: 1, 2).

A study reviewed in 2014 showed that IF can assist weight loss of 3-8% over a period of 3-24 weeks, which is a significant result compared to other weight loss studies (1).

According to the same study, people also lost 4-7% of their waist circumference, indicating a significant loss of harmful abdominal fat that accumulates around organs and causes illnesses (1).

Another study showed that IF causes less muscle loss than the more common method of continuous calorie restriction (Trusted Sources: 1).

 

Health benefits of Intermittent Fasting

Studies have shown that it can have significant benefits for weight control and health of body and brain. It can even help to live longer.

Here are the main health benefits of IF:

  • Weight Loss: As mentioned above, IF can help to lose weight and abdominal fat without explicitly limiting calories (1, 2).

  • Insulin resistance: IF can reduce insulin resistance by lowering blood sugar by 3-6% and insulin levels by 20-31%, which should protect against type 2 diabetes (1).

  • Inflammation: Some studies show a reduction in markers of inflammation, a major cause of many chronic diseases (Trusted Sources: 1, 2, 3).

  • Heart health: Fasting can reduce bad LDL cholesterol, blood triglycerides, inflammation markers, blood sugar and insulin resistance – all risk factors for heart disease (123).

  • Cancer: Animal studies suggest that IF can prevent cancer (Trusted Sources: 1234).​

  • Health of the brain: IF increases the brain hormone BDNF and can promote the growth of new nerve cells. It can also protect against Alzheimer’s disease (Trusted Sources: 1234).

  • Anti-Aging: IF can extend the lifespan of rats. Studies have shown that rats who fasted lived 36-83% longer (12).

It is important to bear in mind that research is still at an early stage. Many of the studies were small or short-term. Many questions still need to be answered in higher quality human studies (Trusted Source: 1).

 

Who should be careful or avoid it?

You should only start intermittent fasting when you are healthy, do not have a health problem and are not pregnant.

You should consult a doctor before starting IF, if you:

  • Have diabetes.
  • Have problems with blood sugar regulation.
  • Have low blood pressure.
  • Are taking medication.
  • Are underweight.
  • Have a history of eating disorders.
  • Are a woman trying to get pregnant.
  • Are a woman with a history of amenorrhea.
  • Are pregnant or breastfeeding.

Apart from that, IF has an excellent safety profile. It is not dangerous not to eat for a while if you are generally healthy and well nourished.


Further links to studies and press releases:

National Institute on Aging – Research on intermittent fasting show health benefits

The New York Times – Benefits of intermittent fasting

Harvard Health Publishing: Surprising update on intermittent fasting

National Library of Medicine: Intermittent fasting versus daily caloric restriction for weight loss