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What is Intermittent Fasting?

Intermittent fasting is a dietary practice that consists of alternating between periods of fasting, with no food intake or with reduced food intake, and periods of normal eating, without restriction. During periods of fasting, the consumption of non-caloric beverages, such as water,coffee, tea or broths, is generally permitted. Regarding the duration and frequency of fasting periods, they may vary depending on the method. The most common methods include alternate fasting, modified fasting, and time-restricted fasting.

Alternative fasting

Alternate fasting is a type of fasting that involves alternating between days without food restriction and fasting days, where food provides up to 25% of daily energy needs.

The Modified Fast

Modified fasting is a type of fasting whose best-known approach is the 5:2 diet. This diet consists of eating normally, without restriction, five days of the week and fasting the other two days.

Fasting with time-restricted eating

Time-restricted fasting is a type of fasting that consists of daily limiting the period in which food intake can take place during a day. In general, this period varies between 4 and 8 hours. For example, the 16:8 diet, a type of time-restricted eating fast, involves fasting for 16 hours and eating for 8 hours every day.

Intermittent fasting and weight loss

In 2018, a systematic review with meta-analysis evaluated the effectiveness of intermittent energy restriction compared to continuous energy restriction on weight loss and different risk factors. The eleven included trials had a duration of 8 to 24 weeks. All intermittent diets provided up to 25% of daily energy requirements on fasting days, but varied in diet type (5:2 diet versus other diets) and/or food intake on other days (all-you-can-eat versus balanced). ). The intermittent approach and the continuous approach resulted in similar weight loss. Intermittent 5:2 diets caused a small decrease in fasting insulin concentrations, but this was not clinically relevant because all participants were overweight or obese and likely insulin resistant. In conclusion, the study suggests that intermittent energy restriction is as effective as continuous energy restriction on weight loss and short-term metabolic factors in overweight or obese adults. More long-term studies are needed to confirm these observations.


As with many diets, there are also contraindications to the practice of intermittent fasting. According to The Nutrition Source, a nutrition reference based in the Department of Nutrition at Harvard University's T. H. Chan School of Public Health, intermittent fasting is not recommended for people with diabetes, eating disorders involving restriction (e.g. anorexia, bulimia), taking medications requiring food intake, growth (e.g. adolescents) as well as pregnant or breastfeeding women.

In addition, The Nutrition Source reminds that many questions remain unanswered regarding intermittent fasting. To date, the optimal period and frequency of fasting have not been determined and the long-term effects remain unknown. It is also unknown whether it is safe and beneficial for all individuals (eg, the elderly) and whether it may have an adverse effect on the eating behavior of children whose parents observe this type of diet.

Finally, it is recommended to consult a qualified health professional before embarking on any diet.


Article written by:

Marie-Noël Marsan, Nutritionist

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