Is a term that covers a family of diets consisting of alternating periods of fasting and periods of normal feeding. These diets can reduce weight and fat. Intermittent fasting can be a viable strategy to reduce caloric intake, weight, body fat and improve insulin sensitivity.
Intermittent fasting alternates between fasting and normal feeding periods. The duration of the fasting phases can be adjusted.
Intermittent fasting patterns can be grouped into three categories:
- Complete fasting or water fasting, where only water or non-caloric drinks such as tea or coffee are consumed on fasting days. Alternate day fasting is a form of complete fasting that alternates a day of normal nutrition for a day of fasting.
- The duration of fasting can be variable, from 12h to 48h Intermittent energy restriction, such as alternate day modified fasting or 5:2 diet, which allows food on “modified fasting” days but with a much lower caloric intake on fasting days in the order of 20% of normal days, or approximately up to 600 calories.
- These variants are supposed to have less impact on mood and facilitate tolerance compared to complete fasting Time-restricted feeding allows power to be supplied during a restricted time window each day10.
- A common form is to fast for 16 hours each day and eat only the remaining 8 hours11, and there are variants with 12 hours of fasting and 12 hours of feeding or 23 hours of fasting and 1 hour of feeding.
For example: skip breakfast and start eating at noon if your last meal the day before is at 8 p.m. is a 16-hour fasting cycle.
For foods that can be consumed during fasting periods, recommendations vary, with some recommending only water, others allowing tea or coffee (without sugar or milk) or “0 calorie” drinks with sweetener. Fasting can increase the risk of dehydration
Intermittent fasting has a different duration (up to 48 hours) than periodic fasting (2 days or more)
Studies have been conducted on this subject since 1943.
Fasting is on the rise. It is attributed benefits on the line and probably on cardiovascular risk. But it is not always easy to stop eating for several days by drinking clear broths. Nor to follow a low-calorie diet: the impression of depriving oneself, cravings, not to mention social constraints. To combine the benefits of fasting with the absence of deprivation and coercion, many choose to follow an intermittent fast.
What is intermittent fasting?
Intermittent fasting consists of alternating periods when we eat with periods when we do not eat (but continue to drink), on a regular basis.
We naturally fast 6 to 10 am every night. A longer fast can be practiced in different ways: eat 25% less (in terms of calories) every other day, skip a meal every day, fast 24 hours at least once a week (from 2pm to 2pm or 7pm to 7pm the next day), or eat 5 days full and then for two days eat only 25% of the usual calories.
What does the research say?
Most people who fast intermittently do so to lose weight. There are many studies on the slimming effects of intermittent fasting.
Here is what recent studies show:
- According to a 2016 study, limiting food intake to a period of 8 hours per day or less (which is equivalent to fasting for 16 hours) both reduces and improves your risk of cardiovascular disease and diabetes (1). This is true whether the weight is normal or too high. In another recent study, American researchers compared the effects of intermittent fasting and those of a low-calorie diet in obese people (2). Their conclusion: “Intermittent fasting is an effective slimming method, and perhaps superior to the low-calorie diet because it is easier to follow, causes more fat loss and better preserves muscles”.
- Taken together, studies indicate that intermittent fasting can reduce body fat and waist circumference in a few weeks. Researchers believe that intermittent fasting can help you lose weight, either by reducing energy consumption because there are fewer opportunities to eat, lowering insulin (a hormone that promotes fat storage), or restoring a circadian rhythm that supports weight loss.
- Intermittent fasting also reduces insulin and insulin resistance and blood sugar. However, studies have sometimes reported a deterioration in blood glucose levels and glucose tolerance depending on the type of intermittent fasting (e.g. every other day). Intermittent fasting is accompanied by positive changes in genes associated with longevity and immunity, decreased oxidative stress and inflammation.
How to set up an intermittent fast in adults
- First, you must check with your doctor to make sure there are no contraindications. If your blood sugar is a little high, or clearly high, it should be monitored: it is likely to drop, but for some people, blood sugar levels may deteriorate.
- In his book Le Fasting, JB Rives recounts that he chose, on the basis of published scientific data, to fast for 16 hours. He therefore advises to set up an intermittent fast between 8pm and 12pm the following day at least. But everyone can find the 16-hour period that suits them best. Fasting for 16 hours a day is not very restrictive, and is compatible with a social life.
- Physical exercise can be combined with a 16-hour fast. It is recommended for general health, but not essential for losing weight. Intermittent fasting is usually accompanied by an increase in hormones that promote fat mobilization, such as growth hormone (in response to lower blood sugar levels). It is also usually accompanied by an increase in basal metabolic rate (calories burned at rest).
Choose the method that suits you best
- Fasting every other day: do not eat anything (and drink only unsweetened, unsweetened water or drinks) for 24 hours and then eat normally for the next 24 hours.
- Diet 5: 2: we fast two days a week.
- Fasting: fast 16h/day every day.
- Partial fasting: alternate a day when only 25% of the usual caloric intake is consumed with a normal feeding day.