What Is Intermittent Fasting and How Does It Work?

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 starts important cellular repair processes.

Here are some of the changes that may happen in your body as a result of intermittent fasting:

• Insulin level: Your blood level of insulin drops significantly, which promotes fat burning.
• Human growth hormone (HGH) level: Your blood level of HGH may increase dramatically. Higher levels of this hormone promote fat burning and muscle gain and have numerous other benefits.
• Cellular repair: Your body starts important cellular repair processes such as removing waste material from cells.
• Gene expression: Beneficial changes occur in several genes and molecules related to longevity and protection against disease.

Many of the benefits of intermittent fasting are related to these changes in hormones, cellular function, and gene expression.

SUMMARY

When you fast, your insulin level drops and your HGH level increases. Your cells also start important cell repair processes and change which genes they express.

Many people try intermittent fasting in an effort to lose weight.

Generally, 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 promote weight loss. Lower insulin levels, higher HGH levels, and increased levels of norepinephrine all increase the breakdown of body fat and make it easier for your body to use fat for energy.

For this reason, short-term fasting actually improves your metabolism, helping you burn even more calories.

In a 2022 study involving 131 people with obesity, researchers found that those who participated in 12 weeks of intermittent fasting lost an average of 9% of their body weight — more than those who engaged in other weight loss methods.

But this study focused on the 5:2 intermittent fasting plan, which means the participants ate normally for 5 days and restricted their calories for 2 days each week.

The authors of a 2020 review of 27 studies noted that participants doing intermittent fasting lost 0.8–13% of their baseline body weight.

In a 2020 trial, researchers focused on people who followed the 16:8 method, which involves fasting for 16 hours per day and eating within an 8-hour window.

The people who fasted didn’t lose significantly more weight than those who ate three meals per day. But after testing a subset of the participants in person, the researchers found that those who fasted had lost a significant amount of lean mass, including lean muscle.

More studies are needed to investigate the effect of fasting on muscle loss. But, all things considered, intermittent fasting has the potential to be an incredibly powerful weight loss tool.

SUMMARY

Intermittent fasting helps you eat fewer calories while slightly boosting your metabolism. It’s a very effective tool for losing weight and visceral fat.

Intermittent fasting has been shown to have major benefits for insulin resistance and to lead to an impressive reduction in blood sugar levels.

Anything that reduces insulin resistance should help lower your blood sugar levels and protect against type 2 diabetes.

In a 2022 review of 10 studies on intermittent fasting, the authors concluded that fasting blood sugar was reduced by an average of 0.15 millimoles per liter.

A 2018 study in mice with diabetes also showed that intermittent fasting improved survival rates and protected against diabetic retinopathy, a diabetes complication that can lead to blindness.

These results suggest that intermittent fasting may be highly protective for people who are at risk of developing type 2 diabetes.

However, there may be some differences between the effects in men and women. One 2015 study, as reported in a 2017 meta-analysis, showed that blood sugar regulation in women actually worsened after a 3-week intermittent fasting protocol, whereas men experienced an improvement in blood sugar regulation.

SUMMARY

Intermittent fasting can reduce insulin resistance and lower blood sugar levels, at least in men.

Oxidative stress is one factor that can contribute to aging and many chronic diseases.

It involves unstable molecules called free radicals, which react with other important molecules, such as protein and DNA, and damage them.

According to a 2018 review, intermittent fasting may enhance your body’s resistance to oxidative stress.

Additionally, a 2019 study suggests that intermittent fasting can help fight inflammation, another key driver of many common diseases.

SUMMARY

Studies suggest that intermittent fasting can reduce oxidative damage and inflammation in your body, leading to benefits related to aging and the development of numerous diseases.

Heart disease is currently the world’s top cause of death.

Various health markers, known as risk factors, are associated with either an increased or decreased risk of heart disease.

Intermittent fasting has been shown to improve several risk factors for heart disease, including:

• blood sugar levels
• blood pressure
• blood triglycerides
• total and LDL (bad) cholesterol
• inflammatory markers

SUMMARY

Research shows that intermittent fasting can improve many risk factors for heart disease, including blood pressure, cholesterol levels, triglyceride levels, and inflammatory markers.

When you fast, the cells in your body start a cellular waste removal process called autophagy.

In this process, the cells break down and metabolize broken and dysfunctional proteins that build up inside them over time.

Increased autophagy may provide protection against several diseases, including cancer and neurodegenerative diseases such as Alzheimer’s disease.

SUMMARY

Fasting triggers a metabolic pathway called autophagy, which removes waste material from cells.

Cancer involves uncontrolled growth of cells.

Fasting has been shown to have several beneficial effects on metabolism that may lead to reduced risk of cancer.

Promising evidence from animal studies suggests that intermittent fasting or diets that mimic fasting may help prevent cancer.

However, research in humans has had inconsistent findings, and more research is needed to help health experts understand how intermittent fasting might affect cancer risk.

There’s also some evidence that fasting may reduce the side effects of chemotherapy in some cases.

SUMMARY

Intermittent fasting has been shown to help prevent cancer in animal studies and some human studies. Research in humans also suggests that intermittent fasting can help reduce side effects of chemotherapy.

What’s good for your body is often good for your brain as well.

Intermittent fasting improves various metabolic features known to be important for brain health.

Intermittent fasting can help reduce:

• oxidative stress
• inflammation
• blood sugar levels
• insulin resistance

Animal research has shown that intermittent fasting may increase the growth of new nerve cells, which could have benefits for brain function.

Fasting also increases levels of a brain hormone called brain-derived neurotrophic factor (BDNF). A BDNF deficiency may be involved in depression and other brain conditions.

Additionally, research suggests that intermittent fasting may help protect against brain damage due to stroke.

SUMMARY

Intermittent fasting may have important benefits for brain health, including increasing growth of new neurons and protecting your brain from damage.

Alzheimer’s disease is the world’s most common neurodegenerative disease.

There’s currently no cure for Alzheimer’s, so preventing it from developing in the first place is critical.

The authors of a 2023 review concluded that intermittent fasting may help delay the onset of Alzheimer’s or reduce its severity.

Animal studies also suggest that fasting may protect against other neurodegenerative diseases, including Parkinson’s disease and Huntington’s disease.

However, more research in humans is needed.

SUMMARY

Studies in animals suggest that intermittent fasting may help protect against neurodegenerative diseases such as Alzheimer’s disease.

One of the most exciting applications of intermittent fasting may be its potential to extend life span.

Research in rodents has shown that intermittent fasting extends life span in a similar way to continuous calorie restriction.

In a 2017 study, mice that fasted every other day had about a 13% increase in life span.

Daily fasting has also been shown to improve the overall health of male mice. In a 2019 study, it helped delay the onset of conditions such as fatty liver disease and hepatocellular carcinoma, both of which are common in aging mice.

Additionally, intermittent fasting has been found to increase the life span of fruit flies.

While researchers have not yet determined that fasting has the same effect in humans, intermittent fasting has become very popular in anti-aging circles.

Given the known benefits for metabolism and all sorts of health markers, it makes sense that intermittent fasting could help you live a longer and healthier life.

SUMMARY

Intermittent fasting may help you live longer, according to studies in animals.

Why is 16 hours the magic number for fasting?

Fasting for 16 hours a day can be an effective way to lose weight. That said, according to a 2022 review, alternating your fasting days might actually be more effective than the 5:2 diet or time-restricted eating such as the 16:8 diet.

What are the benefits of 16:8 intermittent fasting?

Fasting for 16 hours and eating for 8 hours every day may help you lose weight, lower your blood sugar, and have other positive effects on your body that may be associated with a longer life span. However, more research is needed to find out whether this is the case.

What happens if I do intermittent fasting every day?

Generally, following an intermittent fasting diet, every day may have a positive impact on your overall health and your weight. But you might experience some negative side effects such as lethargy, headaches, and constipation. You also need to be careful not to overeat during the eating window.

Intermittent fasting is a very popular weight loss method, but its benefits extend beyond that. It may help you live a longer and all-around healthier life, according to studies involving animals and humans.

There are many ways to practice intermittent fasting. Some methods involve fasting during certain hours each day. Other methods require fasting on only some days of the week. Approaches — and results — vary.

If you’re interested in starting intermittent fasting, consider speaking with a doctor or a registered dietitian. They can help you decide whether it’s safe for you. Be sure to discuss any medications you’re taking, as some could cause negative side effects if you fast.

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