Intermittent fasting: how it’s done, benefits and risks

Intermittent fasting involves alternating periods of fasting with periods of eating.

Although lately it is considered a diet, specialists discard this categorization and prefer to speak of a caloric restriction nutritional model. The objective of this practice is to obtain different health benefits, but how effective and safe is it? Here we will review its main features.

The effects of intermittent fasting, a practice that consists of cyclically alternating periods of eating and fasting, have been studied for years.

The available evidence indicates that this nutritional model could work as a preventive and therapeutic approach against different diseases and conditions. Among its main benefits we find:

  • Help control weight, preventing overweight or obesity.
  • Promote neuronal plasticity (the brain’s ability to recover and restructure itself).
  • Promote appetite control.
  • Improve glucose use and insulin sensitivity.
  • Prevent the development of cancer cells.
  • Reduce indicators of inflammation.
  • Reduce cholesterol and triglyceride levels in the blood.
  • Delay aging, both physical and mental, and reduce mortality.

There are clinical trials that have proven that intermittent fasting can help you lose weight when practiced:

  • Eating for 8-hour periods and fasting for the remaining 16 hours.
  • Eating healthily for five days a week, and restricting caloric intake on the remaining two (non-consecutive) days.

Weight loss is due to the fact that, fasting, the glucose stored in the liver (about 700 calories) is slowly consumed, which takes between 10 and 12 hours to be used.

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When you eat three or four times a day, you can’t use that “deposit”.

  • Possible health benefits of intermittent fasting

Much of the evidence on the benefits of intermittent fasting comes from animal studies.

An example of this is the work published in the magazine Cell Researchwhich found potential in intermittent fasting to increase metabolism and fat burning.

Over 16 weeks, the authors compared the diet of two groups of mice: one group ate normally for two days and then went an entire day without food, while the other group ate the same amount of calories, albeit uniformly, over three days.

After the evaluation period, they found that the fasted mice tended to have lower body weight, along with less white fat and more brown fat. The latter is used for energy and body heat.

Intermittent fasting was also associated with greater stability of glucose and insulin levels.

Other research published in Cell reportsshowed that intermittent fasting could help reprogram many cellular responses, favoring the health and general function of the body, while preventing diseases linked to aging.

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However, the mechanisms behind this, as well as other benefits associated with intermittent fasting, are still not fully understood.

Types of intermittent fasting

There are different intermittent fasts, depending on the feeding cycle that is carried out:


It consists of consuming 500 calories for two days a week, while the other five days you eat a healthy and normal diet.

To more easily specify fasting models, experts advise incorporating fiber and protein, to extend the periods of satiety between meals.

Remember: fasting days should never be consecutive.

Alternate fast day

Every two days fasting is done, consuming only 500 calories or the equivalent of 25% of the normal intake (there are even cases in which zero calories are chosen). On non-fasting days the diet should be healthy and normal.

Restrict food for time

This form of fasting, also known as 16/8, involves fasting for 16 hours of the day, then eating for the remaining eight hours.

Since the sleep period lasts about eight hours, it is easier to comply with this method and it has become very popular. It is advised not to skip breakfast when you wake up.

One day fast

It consists of stopping eating for 24 hours and is practiced between one and two times a week. To specify this nutritional model, fasting is usually started after breakfast, until breakfast the next day, or from lunch to lunch.

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Certain side effects linked to this practice have been reported, including headaches, body aches, fatigue, hunger, irritability, and low energy.

Risks of intermittent fasting

Intermittent fasting is a widespread practice in the world, but health professionals explain that many people may not tolerate or sustain it, exacerbating problematic relationships with food.

Although it appears to work for weight loss, its other benefits are still under discussion. In addition, those who fast intermittently may experience greater sensitivity to temperatures, poor work, physical and mental performance, irritability, general aches and fatigue.

Intermittent fasting is not recommended for pregnant women, children, and people at risk of chronic diseases.

To remind:

Until there is meaningful scientific evidence from human trials, people interested in using herbal therapies and supplements should be very careful.

Do not abandon or modify your medications or treatments, but first talk to your doctor about the potential effects of alternative or complementary therapies.

Remember, the medicinal properties of herbs and supplements can also interact with prescription drugs, other herbs and supplements, and even alter your diet.

Sources consulted: Academy of Nutrition and Dietetics, Natural Medicines Comprehensive Database, US National Library of Medicine, Mayo Clinic, National Institute of Complementary and Alternative Medicine.

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