People have practiced fasting since the beginning of time — whether intentionally (often for religious purposes) or out of necessity. For our ancient hunter-gatherer ancestors, food wasn’t always readily available, and they may have gone several days in between each big meal. Turns out, there are benefits to this lifestyle.

Our bodies aren’t designed to be in a constant state of digestion. Nowadays, we tend to eat a lot — too much, in many cases. We’re also constantly snacking, eating late into the night, and eating things that are difficult for our bodies to digest and process. All of this puts additional strain on our digestive system.

Health benefits of fasting

When our bodies are constantly in digestive mode, they can’t enter into a state of repair and rejuvenation, which happens only after digestion is complete. Fasting allows our bodies to enter into repair mode, which can have numerous positive impacts on our health — including weight loss, reduced abdominal fat, lower blood pressure, improved blood glucose control, reduced inflammation, a stronger immune system, increased energy and mental clarity, and more.

Different types of fasting diets

Fasting is defined as abstaining from all or some kinds of food or drink. For health purposes, there are several different approaches you can take to fasting, including time-restricted fasting, intermittent fasting, or prolonged fasting.

Time-restricted fasting

With time-restricted fasting, eating is limited to a certain part of the day or a certain number of hours per day. This may mean skipping breakfast and not eating until lunch or dinner, or eating an early dinner and not eating again until breakfast. Or you could limit eating to a six-hour period, such as from 10:00 AM to 4:00 PM, in order to alleviate the constant strain on your digestive system.

Intermittent fasting or alternate-day fasting

Intermittent fasting is characterized by reducing calorie intake on certain days of the week. A popular form of intermittent fasting is the 5:2 diet, where you eat a normal diet for five days of the week, and limit your calorie intake on two non-consecutive days. The typical caloric intake on these days is 500 for women and 600 for men. This type of fasting has been shown to lead to meaningful weight loss as well as improvements in other metabolic markets, but the diet must be continued in order for results to last.

Short-term or prolonged fasting

With short-term and prolonged fasting, food intake is restricted for multiple consecutive days. Short-term fasting consists of less than three days, while prolonged fasting lasts for three or more days. According to Valter Longo, cell biologist and Director of the Longevity Institute at the University of Southern California’s School of Gerontology, prolonged fasting is the only method that stresses the body enough to stimulate a protectionist and rejuvenation mode. Prolonged fasting has been shown to extend longevity and healthspan — the period of our lives characterized by optimal health. It can also activate blood stem cells, triggering regeneration of the immune system, and help repair DNA damage, which can be caused by exposure to carcinogens.

As a result of his extensive research on aging, cancer, and cell biology, Dr. Longo developed a five-day fasting mimicking diet, which produces the same effects as prolonged fasting but allows for consumption of healthy, plant-based foods. The ProLon diet consists of 1,100 calories the first day and 750 calories for each of the next four days. The fasting mimicking diet can be used for five days once a month for people who need to lose a significant amount of weight or have other chronic health problems, or 3-4 times per year for healthy individuals who wish to reduce their risk of chronic illnesses associated with aging. Learn more about the ProLon fasting mimicking diet and find out if it’s right for you.

Fasting may not be appropriate for individuals with certain health conditions or taking certain medications. Talk to your doctor before beginning any type of fast or special diet.