Intermittent fasting has gained significant attention in recent years for its potential health benefits, including weight loss, improved metabolic health, and even longevity. As more and more people try it out as a possible means to improve their overall health and well-being, it’s important to take a deeper look into the science behind this way of eating.

Exploring the existing evidence behind the purported benefits of intermittent fasting can provide valuable insights into how it affects our bodies and whether it lives up to the hype.

How Is Intermittent Fasting Different From Fasting?

Intermittent fasting and fasting are two different approaches to the timing of meals and calorie intake. Traditional fasting is refraining from consuming calories—whether from food or drink—for an extended period.

There are myriad ways to fast, from drinking only water to a more modified approach that includes some calories from drinking bone broth or fresh-pressed juices. The duration of the fasting period also varies and may last up to 28 days or more.

Intermittent fasting is an eating pattern that involves cycling between periods of eating and fasting. Intermittent fasting does not dictate what you eat but rather when you eat. It is a shorter period of fasting and involves adding blocks of time-restricted eating to your daily schedule.

While there is no standard set delineation, the most extended duration of intermittent fasting before it is considered general fasting is commonly agreed upon as 48 hours.

Types of Intermittent Fasting

Here are several of the most popular approaches to intermittent fasting:

16:8 Method

The most common approach to intermittent fasting, the 16:8 method, involves fasting for 16 hours and eating all meals within an eight-hour window each day.

Eat-Stop-Eat

This method consists of fasting for 24 hours once or twice a week.

5:2 Intermittent Fasting

This approach involves following a regular diet five days a week and significantly reducing caloric intake on the other two days.

Alternate-Day Fasting

This method includes alternating between days of regular eating and fasting.

One-Meal-a-Day (OMAD)

With this method, you fast for 20 hours daily and eat one large meal, typically at night.

The Benefits of Intermittent Fasting–What We Know

While an evolving area of research, evidence supports several health benefits of incorporating intermittent fasting into your regime.

Weight Loss

Many people seek out intermittent fasting as a means to reduce body fat. Mrinal Pandit, a registered dietitian, clinical nutritionist, and certified nutritional counselor, told The Epoch Times in an email, “Intermittent fasting can aid in weight loss by reducing calorie intake and enhancing hormone function to facilitate weight loss.”

Research supports that intermittent fasting may lead to increased metabolic rate, allowing the body to burn more calories, even at rest. There is also evidence that it can lead to a decrease in insulin levels, which allows the body to burn stored fat.

However, some research suggests that intermittent fasting produces no additional benefit to weight loss other than simple overall continuous caloric restriction. Yet the authors of an article published in the BMJ Open Sport & Exercise Medicine in 2022 noted that intermittent fasting may be responsible for weight loss and a reduction in waist circumference that is independent of just calorie restriction.

More research is needed to uncover the exact mechanism, but weight loss is often seen in people who adopt an intermittent fasting approach to eating.

While intermittent fasting is a means of weight loss, it’s worth noting that in 2023, a review published in Nutrition Reviews highlighted that it takes between five and 20 days of prolonged fasting to see a weight loss of 2 percent to 10 percent of a person’s total body weight. Given the extended period of fasting time needed to see significant weight loss results, intermittent bouts of fasting may not be the best method if a reduction in body weight is the primary goal.

Metabolic Health

Metabolic health is how well the body breaks down the food you eat and converts it into energy. It refers to markers including optimal body mass index, cholesterol, blood pressure, and blood sugar levels. Metabolic dysfunction, or poor metabolic health, is a contributor to many chronic illnesses and a cause of diabetes, heart disease, and stroke.

A study published in 2022 in the BMJ Open Sports & Exercise Medicine saw overall improvements in metabolic health because of intermittent fasting.

“Fasting can improve various metabolic markers of health, including improved insulin sensitivity and reductions in blood sugar levels,“ Pandit said. ”These benefits are typically observed with fasting windows ranging from 14 to 16 hours daily.”

Autophagy

Autophagy is a process in the body that involves the destruction of cells. It allows the body to rid itself of damaged cells and regenerate new ones. It’s like a self-cleaning oven within cells that helps to maintain their function.

Autophagy has been linked to various health benefits, including the potential to protect against certain diseases and promoting longevity.

Decreased autophagy is linked to various health issues and conditions. Research suggests that a reduction in autophagy may contribute to neurodegenerative diseases, cancer, and metabolic disorders. Additionally, impaired autophagy may lead to accelerated aging and a decline in cellular health.

Research published in the journal Autophagy showed that intermittent fasting activates and upregulates autophagy in many of the body’s organs. According to Pandit, “Fasting periods of at least 16–18 hours can initiate autophagy, with the process becoming more pronounced as the fasting window extends.”

Human Growth Hormone

The human growth hormone (HGH) has a myriad of responsibilities in our growth and development in adolescence, but it begins to decrease around middle age. HGH maintains our tissues and organs throughout the body and is believed to play a role in our immune system function, aging process, and mental health and well-being.

Such benefits are seen in periods of forgoing food that are more extended.

“A fasting window of about 16 to 24 hours is often associated with a noticeable increase in HGH ... production,” Pandit said.

Levels of the hormone significantly increase after 24 hours of intermittent fasting, and research published in the Journal of Clinical Endocrinology & Metabolism found that after 48 hours of intermittent fasting, the amount of HGH present is five times that seen at the 24-hour mark.

Additionally, there is research tying spikes in insulin levels with an interference in HGH communication in the body. Because intermittent fasting involves refraining from eating—and insulin is released upon food intake—blood levels will be lower throughout the majority of the day. Thus, there may be less interference.

Oxidative Stress

Oxidative stress occurs when the body’s free radical and antioxidant levels are imbalanced. This imbalance can lead to cellular and tissue damage, inflammation, and cellular aging. Chronic oxidative stress is a driver of many chronic diseases.

“Fasting for 16 to 24 hours can activate pathways that enhance cellular resistance to stress,” Pandit said.

A study published in 2019 in the Federation of American Societies for Experimental Biology suggests that “prolonged nighttime fasting, without altering daily caloric or dietary intake, may improve antioxidant capacity,” thus aiding with any imbalance with free radicals. The study also concluded that intermittent fasting “significantly reduced markers of inflammation while supporting antioxidant function” when combined with physical activity.

A study published in the International Journal of Exercise Science in 2020 found that intermittent fasting also reduced oxidative stress in the heart and brain. However, some research indicates that the oxidative stress benefit may be because of weight loss. Whatever the mechanism, intermittent fasting ultimately mitigates oxidative stress and enhances health.

Cognitive Function

Intermittent fasting is associated with cognitive benefits such as improved brain function and a potentially reduced risk of neurodegenerative diseases. A three-year study published in Nutrients in 2020 found that such benefits are beneficial, particularly as we age.

A systematic review published in 2021, also in Nutrients, highlighted the benefits of intermittent fasting on mental health, especially stress, anxiety, and depression. Further, according to the findings of a 2020 randomized controlled trial published in Nutrients, it may have the ability to improve memory function as well.

There is also research suggesting that intermittent fasting may increase the generation of brain-derived neurotrophic factor (BDNF), which is strongly linked to improved cognitive function. Low levels of BDNF are linked to diseases such as Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and Huntington’s disease.

“These cognitive benefits are observed typically with longer fasting periods, usually 18—24 hours, which stimulate protective processes in the brain,” Pandit said. However, more research is needed to fully understand the cognitive effects of the practice in their entirety.

Cardiometabolic Health

A review published in the Annual Review of Nutrition in 2021 suggests that, in particular, alternate-day fasting, the 5:2 diet, and time-restricted eating may lower blood pressure. The review determined that these specific types of intermittent fasting could benefit cardiometabolic health by decreasing insulin resistance and oxidative stress.

“[The improvements] have been associated with fasting periods of 16–24 hours. These benefits arise from hormonal adjustments and improved metabolic responses,” Pandit said.

Conversely, research released by the American Heart Association in March suggested that 16:8 intermittent fasting increases the risk of death from cardiovascular disease. However, it’s important to note there are limitations to the study, including self-reported data from only two days per week.

Gut Health

A study published in the American Journal of Clinical Nutrition in 2021 found that, after fasting for 16 hours per day for the entirety of the month of Ramadan, participants had higher levels of beneficial bacteria in the gut. Once the fasting period ended at the end of the month, the levels returned to baseline.

A study published in the British Journal of Nutrition in 2020 found a similar increase, as well as an enhanced diversity in the gut microbiome of participants who fasted for 16 hours a day for 25 days.

“In regard to gut health, shorter fasting times of 12–16h [hours] might be beneficial for the gastrointestinal tract and could improve gut barrier function and the composition of gut microbiota when compared to non-fasting state,” Pandit said.