Comment by rsync | Hacker News Reader

Comment by rsync | Hacker News Reader

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The most important - and as yet, unanswered - question I have about fasting is: are the benefits (if they exist) the result of absolute fasting or is relative fasting just as effective ?

If I require an extra 600 calories per day due to exercise, but I "fast" by cutting caloric intake by 15%, do I receive a comparable benefit to someone who does not exercise but also cuts their caloric intake by 15% ?

All evidence seems to point to exercise regimens as providing quite pronounced longevity benefits - equal to or greater than what we expect from fasting. But this is counterintuitive since exercise - and the calories it requires - represent an absolute increase in total metabolism.

So if we each fast our way down to the same trim and lean low calorie existence, but you are consuming 2000 of your previous 2500 calories and I am consuming 2400 out of my previous 3000 calories (assuming we are the same size, weight, etc.) who gets more longevity benefits ?

Valter Longo's research is essentially aiming to answer some of these questions. He was looking for the 80/20 point at which reduction in calories produces much the same outcome as fasting. His current position is expressed by the fasting mimicking diet; you might go read the papers in which he outlines trial results and the data that forms the basis for the diet.

From a gene expression in mice point of view, none of it is exactly the same. Different but overlapping patterns of change for calorie restriction, isocaloric intermittent fasting, intermittent fasting with calorie restriction, methionine or other protein restriction, etc, etc. All different.

Also, all the data on exercise shows it does little to life span in comparison to calorie restriction, while both are vaguely comparable when considering healthspan. There are plenty of papers on this topic to read. Again, completely different set of changes and benefits.

Not answering your question directly, but I don't think you can compare calorie restriction with fasting in that way. Over time, reducing calories by 15% just causes your body to lower its metabolic rate accordingly (see Biggest Loser contestants), while fasting turns off the digestive system completely, allowing the body to focus on other tasks. That's when you get benefits like persistent low insulin levels, autophagy, etc.

In other words, if you have 1000 calories to eat over two days, you're better off fasting entirely one day and eating the 1000 calories in one meal the second day rather than many small snacks over the two day period.

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