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What You Should Know About Intermittent Fasting

Updated: Nov 29, 2021

In Canada, in 2018, 63.1% of adults were classified as either overweight or obese, putting themselves at increased risk to their health. Obesity is associated with several chronic diseases such as type 2 diabetes, cardiovascular disease, high blood pressure and certain types of cancer (2). Many try to lose weight in multiple ways, such as with intermittent fasting. This article discusses what intermittent fasting is and the possible side effects.

What is intermittent fasting?

As the name suggests, this way of eating is usually to eat within a narrow window of time each day and fast the rest of the time. Then, it restricts when you eat, how much you eat, and sometimes both. Of course, by restricting the hours you eat, fewer calories are consumed and you can lose weight. Usually, calories are not counted and there are no restrictions on food choice.


- Classic method (variable fasting time): Popular: 8/16 (16 hour fast, approximately 8 hour meal period);

- Fasting of 1 day or more (0 to <500 kcal per day).

Possible positive effects

  • Weight loss via energy restriction (not more than other calorie restricted diets) (3);

  • For some people, it may be beneficial not to eat until about 3 hours before sleep to decrease the risk of gastric reflux (fasting about 11 hours).

Possible negative side effects

  • Undernutrition and malnutrition: People who adopt intermittent fasting do not necessarily eat well. (note: we can lose weight by eating only cake and that does not mean that our weight loss is done in a healthy way);

  • Depending on the length of the fast: increased headache, drowsiness, bad mood and constipation (5);

  • Increased risk of eating disorders;

  • Unbalance in the level of certain electrolytes (potassium and sodium) for those taking medication for the heart or blood pressure;

  • Possible decrease in certain sports performances;

  • Deprivation of small pleasures in life (meals with family and friends);

  • Effect of the last meal: gorging on food since fasting time arrives;

  • Diabetes: increased risk of suffering from hypoglycaemia (medication to be adjusted).


The best way to eat is the one that we can keep for life, that satisfies us mentally and physically. Intermittent fasting is not recommended and it is no better than other diets for weight loss. However, it may be beneficial for those who are in good general health, want to lose weight, and find it easier to fast for a while than another calorie-restricted diet. If a person wants to go on intermittent fasting, it is important to do so following Health Canada's guidelines for meeting our nutrient needs, that is, following the Health Canada healthy plate.


Karine Drouin Dt.P., Nutr.



  1. Image retrouvée le 12 octobre 2021 en ligne au

  2. Statistiques Canada. (Juin 2019). Embonpoint et obésité chez les adultes, 2018. Retrouvé le 12 octobre 2021 en ligne au

  3. Patterson RE et coll. Intermittent fasting and human metabolic health. J Acad Nutr Diet 2015;115(8):1203-1212.

  4. Harvard Health Publishing. (Décembre 2020). 4 intermittent fasting side effects to watch out for. Retrouvé le 13 octobre 2021 en ligne au

  5. Harvard Health Publishing. (Avril 2020). Is intermittent fasting safe for older adults? Retrouvé le 1er octobre 2021 en ligne au

  6. Image retrouvée le 18 octobre 2021 en ligne au

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