Intermittent Fasting & weight loss:
Intermittent fasting (IF) is also known as time restricted eating/feeding or intermittent energy/calorie restriction.
What is it?
Restricting your eating to a certain time frame.
For weight loss, this reduced window of eating should result in reduced calorie intake (and thus, a calorie deficit, causing weight loss).
There are 3 different types of intermittent fasting:
- Alternate day fasting (ADF): 24-hour fasting alternated with 24-hour feeding.
- Whole day fasting (WDF): 2 days within the week of fasting.
- Time-restricted feeding (TRF): Reduced feeding window daily.
Side note: “Fast” days may be “very low-calorie intake” (≤800kcals as defined by Harris et al 2018) opposed to no food intake.
TRF is the typical method of IF used by people. Typically fasting for 16-20 hours with a feeding window of 4-8 hours.
The reviews listed below as references compared IF to continuous energy restriction (CER), often referred to as “conventional dieting”.
Collectively there are 55 studies (as some are in two or all reviews), all concluded that the two (IF vs CER) diet types resulted in “equivalent outcomes”.
Does it work?
If it enables you to achieve, sustain & adhere to a calorie deficit then yes, it will work.
The same results can be achieved by simply controlling calorie intake, which can be facilitated by any dieting method reduced portion size, meal frequency, food choices, etc, etc.
What advantages has it over other methods of dieting in terms of weight loss?
None. No inherent benefits over any other method of dieting. It doesn’t cause greater weight loss or higher fat loss when you equate calories from a non-time restricted (CER) approach to weight loss.
Personally, it’s not for me on a continual basis. However, it doesn’t need to exist as a standalone method. People nowadays seem to think you must pick a side IF or CER.
Some days, if I have an event (socialising, dining out, etc…..writing this during lockdown those are distant memories) and I’d like some additional kcals for it, on that day I may skip “break-fast” (prolonged fast compared to typical day) and enjoy those kcals later at the event. There are many tactics/strategies you can use to navigate through life while being on track and this is just one tool. Therefore, it makes sense treat it as such, a tool, to allow for enhanced flexibility opposed to a structured rigidity.
- Seimon, R.V, Roekenes, J.A, Zibellini, J., Zhu, B., Gibson, A.A, Hills, A.P, Wood, R.E, King, N.A, Byrne, N.M, Sainsbury, A., (2015) Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials, Molecular and Cellular Endocrinology.
- Varady, K.A.. (2011). Intermittent versus daily calorie restriction: Which diet regimen is more effective for weight loss?. Obesity reviews : an official journal of the International Association for the Study of Obesity. 12.
- Harris, Leanne & Hamilton, Sharon & Azevedo, Liane & Olajide, Joan & De Brún, Caroline & Waller, Gillian & Whittaker, Vicki & Sharp, Tracey & Lean, Mike & Hankey, Catherine & Ells, Louisa. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis.