Many promote intermittent fasting (IF) as a magic bullet to weight/fat loss; that you can eat as much as you like in the feeding window and still drop weight/fat. Others tout it as having superior weight/fat loss benefits to other diets - even when calories are matched. But does it? IF isn’t all that new – it’s been around for a lot longer than most people realise – which, thankfully, means it has a lot of research performed on it. We delve into what science has to say and how IF can be used to help you lose weight.
What is Intermittent Fasting?
IF is also known as time-restricted eating/feeding or intermittent energy/calorie restriction. Essentially, it just means you restrict your eating at times by fasting. IF is generally used by people to assist with weight/fat loss.
How it Works
For weight/fat loss, this reduced eating window should result in reduced calorie intake and thus a calorie deficit. If it does, it’s an effective means of losing weight/fat.
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.
Note: A fasting day does not necessarily mean no food at all – it may be just be very low-calorie intake (≤800kcals)(1).
TRF is the typical method of IF used by people. Typically, this involves fasting for 16-20 hours with a feeding window of 4-8 hours (e.g., fasting from 8 PM to 12 PM the next day).
Is it Better Than Easting Normally?
There have been a total of 55 studies completed comparing IF to continuous energy restriction (i.e., eating meals as normal throughout the day) for weight loss. The result? ALL of those studies determined IF had equivalent outcomes to continuous energy restriction (2,3). Yep, there was no greater benefit to just consuming the same number of calories in a regular dietary fashion.
Intermittent fasting does not promote greater weight loss than a regular calorie-controlled diet.
A Tool That May Help Some
While it’s not magic, if it helps you to achieve, sustain & adhere to a calorie deficit then it will work and could be a great tool for you to help control your calorie intake. However, if you find restricting your eating time to cause you to get extremely hungry, make poor food decisions, obsess over food, and/or negatively impact your mood, energy and training performance, then it may not be ideal for you and the same results can be achieved by simply controlling calorie intake while eating over a greater window, which can be facilitated by any dieting method reduced portion size, meal frequency, food choices, etc, etc.
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, as if it’s religion! Some days, if I have an event where I’m socialising, dining out, etc., (all a distant memory during lockdown at the moment!) and I’d like some additional calories for it, then on that day I may push back my first meal and enjoy those calories later at the event. At the end of the day, weight/fat loss is determined by a negative energy balance; you can use many tactics/strategies to navigate through life while being on track and this is just one tool. Therefore, it makes sense to treat it as such - a tool to use when needed - to allow for enhanced flexibility as opposed to structured rigidity.
- Harris L, Hamilton S, Azevedo LB, Olajide J, De Brún C, Waller G, Whittaker V, Sharp T, Lean M, Hankey C, Ells L. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database System Rev Implement Rep. 2018 Feb;16(2):507-547. doi: 10.11124/JBISRIR-2016-003248. PMID: 29419624.
- Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA, Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418 Pt 2:153-72. doi: 10.1016/j.mce.2015.09.014. Epub 2015 Sep 16. PMID: 26384657.
- Varady KA. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obes Rev. 2011 Jul;12(7):e593-601. doi: 10.1111/j.1467-789X.2011.00873.x. Epub 2011 Mar 17. PMID: 21410865.