What is intermittent fasting?
Intermittent fasting is a dietary practice that involves alternating between periods of fasting, with no food intake or reduced food intake, and periods of normal eating without restriction. During fasting periods, the consumption of non-caloric beverages, such as water, coffee, tea, or broths, is generally allowed. Regarding the duration and frequency of fasting periods, they can vary depending on the methods. The most common methods include alternate-day fasting, modified fasting, and time-restricted feeding.
Alternate-day fasting
Alternate-day fasting is a type of fasting that involves alternating between days without dietary restrictions and fasting days, where food intake provides up to 25% of daily energy needs.
Modified fasting
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 a week and fasting the other two days.
Time-restricted feeding
Time-restricted feeding is a type of fasting that involves limiting the daily period during which food intake can occur. Generally, this period ranges between 4 and 8 hours. For example, the 16:8 diet, a type of time-restricted feeding, involves fasting for 16 hours and eating during an 8-hour window 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 various risk factors. The eleven included trials lasted from 8 to 24 weeks. All intermittent diets provided up to 25% of daily energy needs on fasting days but varied in diet type (5:2 diet versus other diets) and/or food intake on other days (ad libitum versus balanced). Both intermittent and continuous approaches resulted in similar weight loss. 5:2-type intermittent diets led to a slight decrease in fasting insulin concentrations, but it was not clinically relevant, as 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 for short-term weight loss and metabolic factors in overweight or obese adults. More long-term studies are needed to confirm these observations.
Contraindications
As with many diets, there are also contraindications to practicing intermittent fasting. According to The Nutrition Source, a nutrition reference based at the Department of Nutrition of the T. H. Chan School of Public Health at Harvard University, intermittent fasting is not recommended for people with diabetes, those with eating disorders involving restriction (e.g., anorexia, bulimia), those taking medications requiring food intake, growing individuals (e.g., adolescents), as well as pregnant or breastfeeding women.
Furthermore, The Nutrition Source reminds that many questions remain unanswered regarding intermittent fasting. To date, the optimal fasting period and frequency have not been determined, and long-term effects remain unknown. It is also unclear whether it is safe and beneficial for all individuals (e.g., elderly people) and whether it may negatively affect the eating behavior of children whose parents follow this type of diet.
Finally, it is recommended to consult a qualified healthcare professional before starting any diet.
References
- https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/
- https://observatoireprevention.org/2020/09/15/lalimentation-limitee-dans-le-temps-un-outil-pour-perdre-du-poids-et-ameliorer-la-sante-cardiometabolique/
- Cioffi, I., Evangelista, A., Ponzo, V., Ciccone, G., Soldati, L., Santarpia, L., Contaldo, F., Pasanisi, F., Ghigo, E., & Bo, S. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. Journal of translational medicine, 16(1), 371. https://doi.org/10.1186/s12967-018-1748-4