Fasting consists in depriving oneself of food, even of drink, for a more or less long period. With intermittent fasting, also known as intermittent fasting, you alternate periods of fasting with others where you eat normally.

Intermittent fasting: an accessible way to approach fasting
Whether practiced for religious or therapeutic purposes, fasting attracts many followers. However, some novices, tempted by this experience in order to improve their health, may fear that they will not be able to endure too long food deprivations.

Intermittent fasting, whose rules appear more flexible than in the case of strict fasting, has advantages for them. The principle of intermittent fasting consists of alternating:

• periods when you eat as usual: it is not necessary to count the calories provided by your meals
• periods of caloric restriction or no food at all, for a duration of at least 14 hours

The health benefits of intermittent fasting
Any caloric restriction leads to ketosis: from fats, the body produces ketones which will serve as fuel for the cells, instead of glucose. Thus, the ketogenic diet, chosen by some to lose weight or for its health benefits, aims to mimic the effects of fasting.

In 2017, two researchers from the University of California conducted a literature review on the benefits of intermittent fasting. To do this, they compiled the results of intervention and observation studies concerning fasts carried out in a religious context (Ramadan in particular), as well as epidemiological studies.

The majority of clinical trials observed significant weight loss associated with intermittent fasting.

The authors identified mechanisms explaining the benefits of this type of fasting:

• an influence on the biological cycle: the time of food intake – for example rather in the evening or rather in the morning – would play a role in the health of the individual
• a positive effect of fasting on the intestinal microbiota
• caloric restriction: intermittent fasting is generally accompanied by a reduction in caloric intake

Intermittent fasting reduces cardiovascular risk
Intermittent fasting also has benefits for cardiovascular health, as researchers showed in 2019 in a summary on this subject. They found that intermittent fasting reduces several risk factors:

• the body primarily uses fats and ketones as fuel, which induces a positive effect on the lipid parameters of the individual, with less triglycerides and cholesterol
• intermittent fasting limits the development of atherosclerotic plaques by reducing inflammation
• it prevents high blood pressure
• it promotes insulin sensitivity and improves glucose metabolism

These positive effects on cardiovascular and metabolic health may be linked to weight loss.

Contraindications to intermittent fasting
Generally, intermittent fasting is not dangerous, neither for physical health nor for mental health. However, there are some contraindications.

Intermittent fasting is not recommended:

• in the event of eating disorders such as anorexia (for which one seeks precisely to increase caloric intake)
• if the body mass index (BMI) is less than 18.5 (which indicates a state of thinness)
• in pregnant women or breastfeeding their babies (for whom nutrient intake is of paramount importance)

Moreover, if the caloric restriction is particularly important, it can lead to hormonal dysregulation. These disturbances may manifest themselves in the form of menstrual cycle disorders in women, while a drop in testosterone levels will be observed in men.

Knowing this, it is possible to imagine different methods to adapt the practice of intermittent fasting to the lifestyle and expectations of each.

Forms of Intermittent Fasting

Intermittent fasting 16/8
The 16/8 fast consists of reducing the period during which the individual eats during a day: the fasting phase lasts 16 hours (including the night), and normal eating takes place on a 8 hour window. For this, it is generally sufficient in practice to skip a meal, either breakfast or dinner:

• you can have dinner around 8 p.m., skip breakfast the next day and then have lunch at 12 p.m.
• for those who find it difficult to do without a breakfast, you can eat between 8 a.m. and 4 p.m. and skip dinner

This method of fasting is also similar to the practice of Ramadan, during which people of the Muslim faith abstain from food from sunrise to sunset. Dr. Jason Fung, co-author of The Complete Guide to Fasting, recommends in part of the practice of intermittent fasting to eat normally after dark and abstain from it before sunrise.

The benefits of 16/8 fasting on weight
According to a study of more than 50,000 people, those who eat only one or two meals a day have an overall lower BMI than those who eat three meals a day. When overnight fasting lasts longer, BMI is lower.

In addition, this study shows that those who eat breakfast have a lower BMI than those who skip it. Indeed, the researchers found that taking a snack late in the evening (between 10 p.m. and 11 p.m.) limits the oxidation of lipids, which is not favorable to the destocking of fat. In order to optimize weight loss, it is therefore preferable to eliminate dinner rather than breakfast.

16/8 Intermittent Fasting Improves Blood Sugar Control
Fasting 16/8 could be interesting to better control your blood sugar. A study published in 2019 tested this type of fasting, but with an even shorter daily eating window (6 hours instead of 8 hours), in 11 overweight people.

During a four-day period, the volunteers could eat between 8 a.m. and 2 p.m. during the day, which represented 18 hours of fasting. Over a control period, serving as a comparison, they ate between 8 a.m. and 8 p.m., which reduced the duration of the fast to 12 hours. The experimental phase and the control phase were separated by three to five weeks.

Compared to the control period, fasting resulted in a reduction in blood sugar. Also, before morning breakfast, there were more ketone bodies (ketones) in people who had done the 18-hour fast.

In another study on obese people who practiced this same type of fasting, weight loss was observed, as well as a decrease in insulin resistance and oxidative stress.

The bikids of intermittent fasting for cardiovascular health
A small US study from 2018 followed 23 obese people who practiced 16/8 intermittent fasting for 12 weeks: participants could eat between 10 a.m. and 6 p.m. and drank only water the rest of the day. They were compared to a control group of 23 people.

Compared to the control group, people who followed intermittent fasting lost weight (about 2.6%) and reduced their energy intake (341 calories per day on average). There was also a decrease in systolic blood pressure (-7 mm Hg), compared to the control group.

Participants adhered to the eating window approximately six days per week. Before starting the fast, they ate on average for 11 hours a day, which means the eating window was reduced by 3 hours.

The Importance of Food Choices During Intermittent Fasting
For the 16/8 fast to be effective, you obviously must not eat anything during the eating window! For example, a Mediterranean-type diet, rich in plants and olive oil, can be recommended for its cardiovascular benefits.

In addition, studies suggest that a 16/8 fast in which the evening meal is large has a negative impact on cardio-metabolic parameters. Compared to three meals providing the same amounts of calories, eating a meal in the evening over a four-hour period increases systolic blood pressure, hunger and fasting glucose levels in the morning.