Facts on Fasting

This post is part of the series weight

Other posts in this series:

  1. Let’s talk about the value of ideal weight
  2. Let’s talk about weight- why are we so fat?
  3. Diets do not work

Somewhere along the line, we got the message that three meals a day plus snacks is the healthiest. That if we let ourselves get hungry we risk binging to catch up on – and then overshoot – our daily calorie requirements. We know that breakfast is the most important meal of the day and we must not skip it under any circumstance. The idea behind breakfast is that we are hypoglycemic in the mornings, so need breakfast to get our metabolisms going.

It seems that we have to once again change how we think about food. Current evidence supports the benefits of fasting

Fastings seems to have several benefits. If we let ourselves get hungry, we start the physiological process of ketosis. Ketosis is when fat starts getting burnt for energy, but this can only happen when the body’s glycogen stores are depleted. With five meals a day, we never deplete our glycogen stores (unless we vigorously exercise).

This process of ketosis is good for the brain. It decreases inflammation and oxidative stress, big problems in degenerative diseases like Alzheimers, Parkinsons and stroke. Neurotrophic factors (growth factors) increase, which means more cells and synapses, which means better learning and memory. Mitochondria in the neurons increase, which means more energy.

Metabolically it is also good for us. There seems to be a decreased incidence of cancer and longer life expectancy when fasting regimes are followed.

I am not saying that you must send your kids to school without breakfast. Children are so active and have such high metabolisms, that they need their calories. Fasting is not recommended for them, running around all the time is. When we get older, our calorie requirements change.

Interestingly, fasting seems no better for weight loss than calorie restriction diets. It should be better. If you follow intermittent fasting every alternate day (less than 500 calories on fasting days), the amount of food needed to feel full should be less.

One of my patients described how she would fast one day, then “eat whatever she liked” the next day. She said that she felt so deprived on fast days that she would binge on sweets and carbs on eat days. I often see this starve/ binge cycle in eating disorders. Eating healthily on feed days is very important. If you binge on sweets, you are going to get hypoglycemic (which is horrible) when fasting, instead of hungry (which is normal.)

Fasting has been around for a very long time. Religions have long claimed its benefits for spiritual growth. Feasting for Christmas and fasting for Lent is a sensible way to reign in excesses. Famous, clever people like Plato and Pythagoras, have extolled its physical and mental benefits. From an evolutionary perspective, it makes sense. When you get hungry, your brain and body must get sharper to source food.

Dr Mark Mattson, from John Hopkins University, has done a lot of research on the benefits of fasting and he follows the day on/ day off pattern of eating. The 5:2 diet (eat 5 days, fast 2) is a firm Hollywood favourite.

Gaining popularity is daily abstinence of 12-16 hours. Dr Panda, a researcher at the prestigious Salk Institute, explains that humans have all kinds of rhythms: biological clocks which work all the time. Like we have sleep/ wake rhythms, we have eating/ fasting rhythms. If we eat for about 8 hours a day, our bodies seem to be in a good cycle of degeneration and regeneration. (Both regeneration and degeneration are equally important in healthy organisms.) If we eat for 16 hours a day, there is not enough time for optimum repair. It seems as if when we eat might be as important as what we eat.

To fast every second day seems very rigorous and not much fun. If we eat like Buddist monks or Facebook executive Dan Zigmond, between the hours of 9-5, it seems as if we can still glean most of the benefits of fasting. We just have to be careful not to nibble in front of the TV for those long hungry evenings!



  1. I have been fasting for 18 hours a day and only eating two meals a day over a period of 6 hours, not a crumb after that. I didn’t plan it that way but what with my shifted body clock and late working hours it has. My weight has been a stable 60kg for about 16 years whereas before that my maximum was in the 90kg range and I resorted to ephedrine derivatives to suppress my appetite but I’m pretty sure they not good for one’s mental health. I haven’t looked into it much but I would bet that they can precipitate paranoia and psychosis.

    About the mediterranean diet, I can say something because I did ancient Greek at varsity and we learned a bit about their culture and geography. The classical period of Greek history spans most of the 5th and 4th centuries BC. It was a time of prosperity, high culture and relative peace. The steep hills and mountains of the region made keeping cattle almost imposible. More agile and sure footed animals such as goats could mostly take care of themselves. Besides their meat occasionally, they could be relied on for milk with which to make cheese. The hilly slopes were excellent for growing olives and grapes and other crops that like good drainage and these were incorporated into the diet.

    Of Course no Greek city state was far from the coast and therefore seafood formed a part of almost every meal, in some way. Even though the state became immensely wealth towards the end of the classical period, the average citizen could not afford to eat three times a day. Supper was therefore the main and only meal of the day. Something else the ancient Greeks introduced was the gymnasium where citizens went to workout daily. Woman and slaves were unfortunately not counted as citizens and so were barred from the gymnasium and the Olympics.

  2. Idyllic with respect to diet, high art, poetry, drama, philosophy, mathematics and the like but generally as seedy and disgusting as any old world classical culture. There were regular outbreaks of disease, infanticide was a method of birth control. There were petty feuds with neighboring states; pedophilia was tolerated and encouraged by some in the gymnasia and the attitude towards woman can be summed up by the word they used for cowardly – i.e. “womanly”.

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