OK, maybe LOVE is overstating it, I mean, I love eating food and if the training wheels were off and no consequences could be had I would almost certainly eat continuously for about 15 hours per day (subtract 8 hours for sleep and one hour for swinging some kettlebells) so I definitely love that more, but there’s nothing like a bit of clickbait in a blog title. It seems, however, that this is most people’s problem. They have no control, they eat more than they need and they get fat and sick as a result.
Intermittent fasting puts in place a set of rules which govern how much you can eat in a given period of time and, as a result, controls the number of calories you put into your body. This is why Intermittent Fasting (IF) is also known as Time-Restricted Eating (TRE).
Below this article I have listed the more meaningful studies I have read to help come to my conclusions and, believe me, I was looking for that magic bullet, so no bias here. What magic bullet? Well IF zealots (there are a LOT of zealots in the fitness industry) will have you believe that by not eating for extended periods of time you can turn your body into a fat burning machine, develop superhuman resilience against chronic illness and live forever.
That’s obviously not true. The evidence quite clearly shows like EVERY diet there is NO metabolic advantage to fasting over standard calorie restricted eating in terms of the amount of weight or fat lost.
Does it improve Autophagy and Apoptosis?
These are automated cell deaths, it happens naturally in everyone and in certain situations it is unregulated. A common argument in favour of TRE is that it increases or speeds this process up. The trouble with these claims are that they are based on studies done on very fat rats. No meaningful research has been conducted on humans and what research there is seems unconvincing at best. Autophagy will happen if you are in an energy deficit anyway.
Until there are large, long-term human trials done we cannot say that Autophagy or Apoptosis happen to any meaningful degree in any fasted period of less than 24-hours. Anton SD et al. observed that there is, what they referred to as, a flipping of the metabolic switch where ketone production is elevated, and levels of circulating glucose are reduced. This might be useful for very overweight people with metabolic syndrome. But, it’s not a cure for cancer.
Do you burn more fat?
Nope. You will only lose body fat if you are in an energy deficit for any length of time and the timing of your meals has no impact on this whatsoever. Fasting for extended periods of time does increase fat oxidation and ketone production but neither of these things appear to translate to improved fat loss.
TRE does seem to reduce appetite in some people which is an obvious advantage when trying to lose weight but, again, this isn’t magic, it’s just common sense. Besides, high protein diets do the same thing.
If you compared a 16:8 IF (or any other restricted timing protocol) diet versus a standard daily feeding protocol but matched both diets for both Calories and protein intake there would be zero difference in body composition. Well there might be one…
Does IF make it easier to build muscle?
Nope! Being in an energy deficit is catabolic, catabolism is where you metabolise muscle for energy. This means that your body will build less muscle in an energy deficit than if you are at energy maintenance or in a surplus.
Therefore, fasting won’t help you to build muscle. But, if you do resistance training you can still maintain lean mass while dieting down. Also, some evidence does point to improved sensitivity to muscle protein synthesis so that when you do eat, this mechanism is elevated, making it easier to maintain that lean mass despite the fast.
Fasted training is superior for fat loss
Again, not really. Once the metabolic switch has been flipped and ketone production increases you may feel more alert, so it might be that people who train in the fasted state feel more focused and believe that their training is more effective.
Anecdotally, I often train fasted and what I find is that low to moderate intensity exercise seems to help reduce appetite and allow me to fast for longer without even thinking about food. But, on the flip side, I find that higher intensity training sucks arse while fasted. The reason for this is simple. Being fasted means that you are energy depleted. You have less glycogen stored in your muscles and liver, you may well be producing more ketones, but ketones do fuck all for intense exercise performance. Rate of Perceived Exertion is also elevated, meaning that exercising while depleted feels harder so you may not even be training with as much intensity as you believe.
But, there are some benefits for endurance performance from fasted training and I explain all about that in this blog.
Is Fasting bad for women
This is a weird one, I’m not entirely sure where this comes from. I think it’s something that Martin Berkhan, the creator of the Leangains diet, said in one of his books and it’s just stuck. It’s probably anecdotal or observational at best. In other words it has been observed that some women don’t respond as well to IF as some men do. This makes sense as women are statistically more likely to develop disordered eating than men and many have enough stress in their lives as it is, what with having a menstrual cycle to deal with, bearing children and being married to men, so IF might just be a step too far.
However, there is some compelling human evidence that Muslim women, during the month of Ramadan, experience no ill effects and, furthermore, female Muslim athletes have been shown to be able to both train and compete during this time and not die of male imposed female fragility (or whatever Berkhan was getting at). That said, you women should probably avoid fasting during menstruation unless they know their body REALLY well.
Why bother with Time Restricted Eating?
Here’s the pragmatic part. TRE or IF (whichever acronym you prefer) is shown to be both safe and effective and may have some additional (albeit minor) health benefits. If you find it fits your daily routine, is easy to understand and adhere to (adherence is the most important part of any diet) then there is no reason why you shouldn’t do it.
I use it, sometimes I do two 16-hour fasts per week, just to keep weekly energy balance in check. When I want to lean down a bit I go to 5 days per week, eating only between the hours of 12pm and 8pm. This is usually 3 meals spaced 3-4 hours apart. This way I don’t have to bother with counting Calories and I have the whole morning to get a shit tone of work done without even thinking about food. I can then afford a little more flexibility at the weekends because I have likely banked close to 3,000kcals over the week.
I personally prefer the 16:8 model but you can adopt any of the following if you choose.
- 5:2 = 5 days eating ad hoc and 2 days restricted dieting
- 16:8 = explained below
- 18:6 = basically the same as 16:8
- 20:4 = just a smaller feeding window
- Alternating fasting = this is where you fast for 24-hours every second day
Those are the main methods, feel free to try the one that appeals to you the most but don’t get drawn in to the marketing bullshit. IF/TRE is simply the application of Calorie controlled dieting.
Watch this video for the TM Fitness method of 16:8 time-restricted eating.
- Alirezaei M, Kemball CC, Flynn CT, Wood MR, Whitton JL, Kiosses WB. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010;6(6):702-710. doi:10.4161/auto.6.6.12376.
- Longo VD, Mattson MP. Fasting: Molecular Mechanisms and Clinical Applications. Cell metabolism. 2014;19(2):181-192. doi:10.1016/j.cmet.2013.12.008.
- Anton S, Leeuwenburgh C. Fasting or caloric restriction for Healthy Aging. Experimental gerontology. 2013;48(10):1003-1005. doi:10.1016/j.exger.2013.04.011.
- Gotthardt, J., Verpeut, J., Yeomans, B., Yang, J., Yasrebi, A., Roepke, T. and Bello, N. (2016). Intermittent Fasting Promotes Fat Loss With Lean Mass Retention, Increased Hypothalamic Norepinephrine Content, and Increased Neuropeptide Y Gene Expression in Diet-Induced Obese Male Mice. Endocrinology, 157(2), pp.679-691.
- Collier R. Intermittent fasting: the science of going without. CMAJ : Canadian Medical Association Journal. 2013;185(9):E363-E364. doi:10.1503/cmaj.109-4451.
- Wegman MP, Guo MH, Bennion DM, et al. Practicality of Intermittent Fasting in Humans and its Effect on Oxidative Stress and Genes Related to Aging and Metabolism. Rejuvenation Research. 2015;18(2):162-172. doi:10.1089/rej.2014.1624.
- Hayward S, Outlaw J, Urbina S, et al. Effects of intermittent fasting on markers of body composition and mood state. Journal of the International Society of Sports Nutrition. 2014;11(Suppl 1):P25. doi:10.1186/1550-2783-11-S1-P25.
- Memari A-H, Kordi R, Panahi N, Nikookar LR, Abdollahi M, Akbarnejad A. Effect of Ramadan Fasting on Body Composition and Physical Performance in Female Athletes. Asian Journal of Sports Medicine. 2011;2(3):161-166.
- Norouzy, A., Salehi, M., Philippou, E., Arabi, H., Shiva, F., Mehrnoosh, S., Mohajeri, S., Mohajeri, S., Motaghedi Larijani, A. and Nematy, M. (2013). Effect of fasting in Ramadan on body composition and nutritional intake: a prospective study. Journal of Human Nutrition and Dietetics, 26, pp.97-104.
- Moro T, Tinsley G, Bianco A, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine. 2016;14:290. doi:10.1186/s12967-016-1044-0.
- Templeman I, Thompson D, Gonzalez J, et al. Intermittent fasting, energy balance and associated health outcomes in adults: study protocol for a randomised controlled trial. Trials. 2018;19(1):86. Published 2018 Feb 2. doi:10.1186/s13063-018-2451-8
- Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2017;26(2):254-268.