What is intermittent fasting?
Intermittent fasting is a dietary practice that alternates between periods of fasting, without or with reduced food intake, and periods of normal, unrestricted eating. During periods of fasting, the consumption of non-calorie drinks, 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 alternative fasting, modified fasting, and time-limited eating fasting.
Alternative fasting is a type of fasting that involves alternating days without food restriction and days of fasting, where food provides up to 25% of the daily energy requirement.
The modified fast
Modified fasting is a type of fasting that is best known for 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-limited food
Fasting with a time-limited diet is a type of fasting which consists in limiting the daily period when 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-limited 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 assessed the effectiveness of intermittent energy restriction versus continuous energy restriction on weight loss and various risk factors. The eleven included trials lasted 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 vs. other diets) and / or food intake on other days (ad libitum vs. balanced ). The intermittent approach and the continuous approach resulted in similar weight loss. Intermittent type 5: 2 diets resulted in a slight decrease in fasting insulin concentrations, but this 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 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 Nutrition Department at the TH Chan School of Public Health at Harvard University, intermittent fasting is not recommended for people with diabetes, suffering from eating disorders involving restriction. (eg: anorexia, bulimia), taking drugs requiring food intake, growing (eg: 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 has not been determined and the long-term effects remain unknown. It is also not known 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 follow this type of diet.
Finally, it is recommended to consult a qualified healthcare professional before starting any diet.
- 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