Intermittent Fasting: is it all that?

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?

This is one of the biggest claim. 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 and, so far, research hasn't shown normal Calorie restriction to be be any less effective compared with fasting. This means that if you eat fewer Calories than you burn, which is a catabolic event, cells shrink, including fat cells. But there's no evidence that skipping breakfast makes you immune to cancer, as some of the more implausible claims suggest.

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 there may some benefits to cardiovascular health when coupled with resistance training according to Moro T, et al. But that might be as much to do with the daily energy deficit as is it is the extended fast, it’s not a cure for cancer, and these results are often seen with normal Calorie controlled diets too. Basically, if you are very overweight, eating less and losing at least 10% of your body mass almost always results in significant improvements in health markers.


Obesity (Silver Spring). 2018 Feb; 26(2): 254–268.

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. If you don't eat early in the day fat oxidation is elevated and when you eat fat oxidation is suppressed, but over a 24-hour period it all balances itself out, so there's no advantage one way or the other.

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, but if appetite control is something you struggle with this might be something that works well for you. But, eating higher amounts of protein and high fibre foods also increase satiety, so maybe you just need to sort out the nutritional density of your meals and stop scoffing scones.

But this doesn't mean that you won't lose fat on a well controlled IF/TRE diet. It's just one way to manage the Calories in part of CiCo. Usually, when you buy a diet book that advocates IF it also encourages you to start exercising. Now you have not only reducing the Calories in part, but you're also increasing the Calories out part too. Eat less and move more, lose weight. It ain't a new concept.

According to the Canadian Medical Association 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?

Advocates of IF often cite it's [potential to increase muscle mass. Is that a thing? Hard nope! Being in an energy deficit is catabolic, catabolism is where you metabolise muscle protein for energy. This means that your body will build less muscle, or even LOSE muscle in an energy deficit rather than if you are at energy maintenance or in a surplus, both of which are anti-catabolic conditions.

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.

The ISSN did show that combining time restricted eating with resistance training resulted in a reduction in fat mass but, again, those are the adaptations you would expect when you combine a daily energy deficit with a strength training program and not uniquely because of the fasting protocol. 

Fasted training is superior for fat loss

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 just stuck. It’s probably anecdotal or observational at best. In other words it may have 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 you know your body REALLY well. If I may sum this section up with an anecdote of my own: I have known and worked with women of all walks of life and with varying levels of health or fitness and have never known any female who has adopted a fasting protocol to experience any ill-effects. If anything, they seem to adapt to it better than many men, and it has been noted that women have a slightly more efficient fat metabolism than men, so maybe that's it? Either way, like with anything just listen to your own body and if something feels wrong, change the approach.

Why bother with TRE/IF?

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. Unless you have a high training volume and are trying to build muscle.

I use it it myself and personally prefer something close to the 16:8 model. The main reason is that I just got into the habit of skipping breakfast, which makes me more productive in the mornings, 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. 

Make sure that your first meal is planned ahead of time and that is a nutrient dense meal, with a base of lean protein and plants. If your taste preferences tend towards a low carb approach you can do that, otherwise make sure you have some wholegrains or root veg with that meal too. During the fasting period consume unsweetened beverages like plain water, black coffee/tea, etc. Basically, you're trying to avoid Calories. That said, I'll often have a little snack before a training session, as I prefer to train early and then I'll break the fast afterwards, but you do you. 

Like I said, this is ONE way to control Calories in and is a great time saver. But it does take some planning and doesn't suit everyone, so if you don't fancy it don't do it. Do something else, that fits in with your lifestyle and dietary needs.

And ignore anyone who tries telling you that there is anything more to this than simply restricting Calories, they're probably trying to sell you something.

To learn more about personal nutrition and to become your own nutrition coach sign up for my online program THE NUTRITION SOLUTION.

And don't forget to support my work on Patreon.

Coach Troy


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  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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
  12. 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.



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