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, the 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 fasting, modified fasting, and time-restricted feeding.
Alternate fasting
Alternate fasting is a type of fasting that involves alternating between days without dietary restrictions and fasting days, where food provides up to 25% of daily energy needs.
The modified fast
Modified fasting is a type of fasting whose most well-known approach is the 5:2 diet. This diet involves eating normally, without restriction, five days a week and fasting on the other two days.
Time-restricted eating fasting
Time-restricted eating is a type of fasting that involves limiting the daily window during which food intake can occur throughout the day. Generally, this window ranges between 4 and 8 hours. For example, the 16:8 diet, a type of time-restricted eating, involves fasting for a 16-hour period 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 the type of diet (5:2 diet versus other diets) and/or food intake on other days (ad libitum versus balanced). Both the intermittent and continuous approaches resulted in similar weight loss. The 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 several 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 suffering from eating disorders involving restriction (e.g., anorexia, bulimia), those taking medications that require food intake, growing individuals (e.g., teenagers), as well as pregnant or breastfeeding women.
Furthermore, The Nutrition Source reminds us that many questions remain unanswered regarding intermittent fasting. To date, the optimal fasting period and frequency have not been determined, and the long-term effects are still unknown. It is also unclear whether it is safe and beneficial for all individuals (e.g., elderly people) and whether it can have a harmful effect on 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/time-restricted-eating-a-tool-to-lose-weight-and-improve-cardiometabolic-health/
- 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