What are the benefits and risks associated with fasting? Fasting over the past few years has become pretty mainstream with various iterations featured in books that grace the shelves of high street shops. Popular versions include 16/8 where you don’t eat for 16 hours and limit your intake to an 8 hour window, 18/6 same but longer restriction period, 5/2 this is 5 days of normal eating and 2 days of 5 to 800 calories. The eat fast eat methods all come under the umbrella of intermittent fasting. Then there are the longer or prolonged fasts and fasting mimicking plans such as Prolon which is a scientifically designed very low calorie plan.
Claims made by proponents of fasting include:-
Improved fat burning
Improved weight loss
Reduced risk of cancer
Optimized hormone levels
Improved cholesterol levels
Improved body composition
Better blood sugar regulation
Reduced risk of heart diseases
Increased activation of stem cells[1]
All sounds pretty amazing doesn’t it? Especially if it’s just a case of skipping breakfast! Except the science is not yet behind the idea of intermittent fasting, in fact a year long study disputes the majority of the claimed metabolic benefits[2][3]
That is not to say there are no benefits and that if you personally find it helps with weight loss, calorie maintenance or feel it suits your lifestyle that you should give it up. The science is also not entirely conclusively against intermittent fasting, for example a study of breast cancer survivors found that those who had more than 13 hours between the last time they ate in the evening and the first time they ate in the morning was associated with a 36% reduction in the recurrence of breast cancer.[4] It would seem that our bodies being constantly bathed in calories is not long term good for us. It needs periods of rest and recovery.
However, it looks unlikely that some of the really interesting aspects such as autophagy take place over such short periods of restriction. Autophagy translates as self eating, in this process when the body is not taking in enough calories in particular it seems proteins it will scavenge it’s own system in order to find the necessary proteins. In particular damaged cellular matter is broken down first, this makes sense, if we face financial hardship we will mend or repurpose damaged items while leaving new perfect goods alone.
It is the process of autophagy where the real magic of fasting lies, through this process we can reduce inflammation, reduce our risk of tumors, delay the aging process and increase the production of tumor killing cells.[5]
When fasting is combined with chemotherapy it seems according to some studies reduce the risk of side effects by sending the healthy cells into a protective state while leaving the fast growing mutation cells open to attack.[6]
It’s all pretty exciting stuff really and a great deal of research is currently going on looking at various medical applications of both fasting and fasting mimicking diet. The fasting mimicking diet is the brain child of Professor Valter Longo and allows for a small almost protein free intake of calories over the fasting period.[7]
The caveat in all this is that it takes at least 2 to 4 days for this to take place and not the few hours of restriction we were all hoping for.[8] The ideal period of fasting is around 5 days.
It should be noted that autophagy can also be triggered by long periods of calorie restriction which may be a more suitable path for many, in order to trigger autophagy a restriction of 40% of normal intake is necessary, so for example if your intake is 2000 a day reducing it to 1600 for a few weeks will result in a degree of autophagy[9]. I will likely write a separate post on this another day.
Such longer term periods appeal to me less purely because at the moment training is very important to me which means I eat at or slightly above maintenance calories which supports my energy and post training recovery. Fast and hard is my preferred method (pun intended) to this and many aspects of life.
I have used Longo’s fasting mimicking plan a few times now, 4 maybe 5 times I can’t quite remember. The last time was nearly 9 months ago! I had planned on before Christmas but family responsibilities, social engagements etc meant I kept having to bump it forward. I set a specific date for Feb, which is next week, put it in the calendar and turned everything that tried to crop up down other than a couple of non-negotiable appointments for my daughter!
I prefer during fasting weeks to turn life down, I did during my first one attempt to train and live as normal and by day 4 I felt awful. I mean really really awful. After that experience the next attempts were undertaken a little more sensibly. I take the week off work and focus on nurturing myself and allowing for rest while I push my cells into a repair cycle. I think it’s reasonable to allow myself time to do this and as it’s 2 to 3 weeks in a year maximum stepping back a little is no bad thing. It’s also one of the many benefits of being self employed! Plus if it gives me chance of
Of course it is necessary to mention that fasting and fasting mimicking plans are not without risk, during the 5 days it is possible to experience fatigue, dizziness, feeling cold and of course hunger. As I mentioned earlier when I pushed too hard I did feel genuinely dreadful and learned my lesson. The biggest risk however is something called re-feeding syndrome which can be deadly
“Refeeding syndrome can be defined as the potentially fatal shifts in fluids and electrolytes that may occur in malnourished patients receiving artificial refeeding (whether enterally or parenterally). These shifts result from hormonal and metabolic changes and may cause serious clinical complications.”[10] It is rare but necessitates that the two days after fasting involve a gentle re-introduction of food rather than rushing to McDonalds for a big mac. It is less likely with the fasting mimicking plan due to the very small caloric intake keeping the digestive mechanisms running. However they still recommend a slow return to nutrition.
There are a number of scientists working in the realm of aging and longevity all with different ideas and methods, however one area in which they all seem to agree is that short periods of fasting (5 days for full benefits) are one of the most reliable methods of reducing disease risk and promoting a longer healthy life. Nothing in life is guaranteed, but if a short period of discomfort can shift the odds in my favour I’m all for it! See you on the other side!
[1] https://www.doctorkiltz.com/16-8-intermittent-fasting/
[2] https://www.nytimes.com/2022/04/20/health/time-restricted-diets.html
[3] https://www.nature.com/articles/s41574-022-00638-x
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4982776/
[5] https://www.cell.com/cell-metabolism/fulltext/S1550-4131(15)00224-7
[6] https://www.cell.com/cancer-cell/fulltext/S1535-6108(16)30265-3
[7] https://www.valterlongo.com/fasting-mimicking-program-and-longevity/
[8] https://www.medicinenet.com/how_long_do_you_need_to_fast_for_autophagy/article.htm
[9]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6950580/#:~:text=Calorie%20restriction%20(CR)%20and%20CR,initiation%20of%20the%20autophagy%20process.
[10]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440847/#:~:text=Refeeding%20syndrome%20can%20be%20defined,may%20cause%20serious%20clinical%20complications.
Sam Kelly Fitness 