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Fasting and Ketogenic Diets

Fasting and Ketogenic Diets

Fasting and keto fit together like the proverbial hand in a glove. Each complements the other and heightens the benefits of either. Both interventions on their own have their benefits, but doing them simultaneously magnifies the effects of the pair.

What Constitutes A Fast?

This is another of those ‘how long is a piece of string’ type questions. I have heard some people claiming that they are fasting because they finish eating at 8 pm and don’t have breakfast until 8 am the next morning. This seems to me to be pushing the definition of fasting a little too far.

Most of the benefits of fasting don’t really kick in until at least 12 hours of non-eating have elapsed. You would want at least a few hours in that state to achieve any significant gains from fasting whatsoever. My own preference is for the 16:8 pattern, i.e. 16 hours of fasting and an 8-hour window during which I allow myself to eat most days.

The most common benefits that most people currently aiming for with these time-restricted windows are autophagy and weight loss. Autophagy simply means ‘self eating’ and refers to a process whereby cellular debris is recycled to form new organelles (structures within the cell) or even create new cells altogether.

With longer fasting periods, up to a week or even ten days, come other benefits. Longer fasts are also much, much more difficult to perform, of course. For ketopensioners such as myself, the dangers of sarcopenia (muscle wasting) are perhaps greater than the potential gains offered by such longer terms fasts.

the fast 800 bookfasting and keto 800 Michael moseley

10 Benefits of Fasting

The benefits of fasting are innumerable, so for now I will just give those that are the most generally applicable:

  1. Weight loss – this is kinda obvious. If you don’t eat it is very difficult not to lose weight. Joking aside though, it is a very effective strategy. Before converting to a ketogenic diet, I did actually manage to lose 17 kilos (37 1/2 lbs) using variations of intermittent fasting.
  2. Autophagy – a major health benefit of fasting. In 2016 Yoshinori Ohsumi, a Japanese scientist, won a Nobel Prize for his groundbreaking work in this area. Basically, autophagy is a cellular system that the body utilises to clean up cells. It can only do this when its resources are not occupied with processing food, hence the effectiveness of fasting in triggering it.
  3. Increased Insulin Sensitivity – Many studies seem to indicate that fasting increases insulin sensitivity, a vital defence against metabolic disease and type 2 diabetes.
  4. Protection Against Heart Disease – having had a heart attack in my fifties, this area is of particular interest to me. Fasting seems to help protect the heart in several ways, such as lowering the amount of the dense LDL’s (the bad sort of cholesterol) in the bloodstream, helping the body metabolize sugar, and simply the weight loss that often accompanies following this discipline.
  5. Protection Against Cancer – again, this occurs on several levels. Fasting tends to lower insulin resistance and inflammation, both problematic in cancer. Fasting is also believed to be useful as an adjunct to chemotherapy, making the treatment more effective. A recent area of research has been based on the idea that being in ketosis effectively starves cancer cells of glucose they need to grow.
  6. Protection Against Alzheimer’s – I wrote a piece on this myself in 2020. Suffice it to say that there is considerable evidence both that a ketogenic diet and fasting can give a measure of protection from the ravages of this terrible disease.
  7. Cognitive Benefits – again, this is an area covered in one of my own recent pieces, at least as an adjunct to Keto. Basically, the brain seems to run particularly well on ketones. Fasting and keto are pretty efficient ways to force the body to produce this brain-friendly fuel.
  8. Longevity – Calorific Restriction (CR) has long been shown to improve longevity in all manner of creatures from nematode worms to dogs. To have this effect, it needs to be a long term strategy, and not just the odd fast here and there.
  9. Lowers Blood Pressure – fasting may well help to reduce blood pressure, perhaps because of the weight loss or maybe due to increased insulin sensitivity.
  10. Combats Inflammation – this is one of the main reasons I use this intervention on a regular basis. The anti-inflammatory effects have been shown on numerous occasions, although there is still some debate as to how this effect is achieved. Currently, fasting’s effect on the action on monocytes ( highly inflammatory immune cells) is thought to be the most significant factor, but the work is ongoing.
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These are just a few of the more generally accepted benefits. I could list many more. Suffice it to say that the benefits far outweigh the costs.

essential fasting bookessential fasting and keto

Combining Fasting and Keto

Fasting and Keto fit together like copy and paste, like coffee and cream, like fish and chips. One tends to exaggerate the effects of the other. The aim of the Keto diet is to reduce carbohydrate intake into the body and thereby promote the production of ketones. It’s very clear that carbohydrates cannot be reduced below zero, which is exactly the level of carb intake when fasting.

Historically, the Ketogenic diet was developed in the early part of the 20th century specifically as a medical intervention in the treatment of epilepsy. It had been noted that epileptic symptoms tended to be much reduced when patients fasted. Obviously, though, patients could not fast forever. Therefore researchers tried to develop a diet that would have a similar effect. It was found that the key was the elimination of carbohydrates from the diet. This diet is still used in the treatment of epilepsy to this day.

Personally, I have followed several intermittent fasting regimes in the last few years. Since adopting Keto last year, however, I have focused mainly on 16:8. In practice, it often morphs into 18:6 or even 20:4, although I have never gone all the way to the fabled OMAD (One Meal A Day). One’s personal situation affects which version of intermittent fasting one should adopt. What helps an overweight 30-year-old female may be less applicable to a 65-year-old male with diabetes.

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intermittent fasting bookintermittent fasting and keto

A Warning for the Mature

On that note, I would like to add a small warning for the more mature followers of a Keto diet or intermittent fasting. One of the big dangers of fasting, and one I feel is not mentioned enough, is the muscle wastage that can come with it. If done too regularly, or for too long, the negative effects can be quite dramatic.

As we advance in years, we need to be aware of the need to look after our bodies from the point of view of its musculature. For good health later in life, it is vital that we maintain our muscle health and tone. The dangers of Sarcopenia need to be taken very, very seriously as we age.

Therefore, be aware of the dangers of overdoing fasting. Whilst it is fine to follow a 16:8 style of fasting, or even include the occasional 24 or 36 hours fast, I would recommend avoiding longer fasts for those of us a little longer in the tooth. The recovery of the losses involved simply takes too long to be worth the effort at this stage of life.


As stated above, fasting and Keto are almost perfect bedfellows, a marriage made in heaven. Apart from being aware of the dangers of overdoing it, particularly for those of more advanced years, there are few downsides. If you are young and in relatively good health, then even fasting for several days will likely be beneficial and will certainly put you firmly into ketosis. The gentler forms such as 5:2 (five days a week of eating normally, two of fasting) are fine for most folks. Perhaps the simplest of all, and one I feel I can safely recommend to more or less everyone though, is 16:8.

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Given the long list of benefits, and the very few downsides beyond those mentioned above, what is there to lose, beyond unneeded cellular debris and a little weight?


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