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Comment by krasney | Hacker News Reader

The most recent critiques I've seen for intermittent fasting have to do with how it may not preserve lean body mass unless you are extremely conscientious about getting enough protein (and probably resistance training). That is, if you don't get enough protein during your feeding windows, you'll lose lean body mass along with fat mass, which harms body composition. I'd expect to see the TRE arm losing more lean body mass.

Table 2 seems to show this effect. The TRE arm lost more lean body mass and fat mass, although without a difference in visceral fat. If compliance is the issue, I'd be curious to understand what regime can help TRE participants comply with a minimum protein threshold in their diet to minimize the risk of lean body mass loss.

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Different intermittent fasting regimens result in different results re: losing lean muscle. The longer intermittent fasting cycles seem to show no significant loss of lean muscle. (i'm way too lazy to go find the studies to back this up claim, but they're out there somewhere)

An old fashioned way of fasting preserves muscle mass way better due to hormonal response. It only kicks in after 30-40 hours of fasting. I don’t think that a lot if people practice 3-4 of fasting when doing IF.

Longer periods of fasting reduce testosterone, which probably negates whatever GH benefit it provides: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9182756/

And why would your body go out of its way to preserve metabolically more expensive tissue during longer periods of deprivation?

Any kind of caloric restriction lowers it temporarily. There is some evidence that testosterone levels can be even higher after the fasting https://josepheverettwil.substack.com/p/how-fasting-changes-...

> The longer intermittent fasting cycles seem to show no significant loss of lean muscle. (i'm way too lazy to go find the studies to back this up claim, but they're out there somewhere)

Absolutely wrong: https://news.ycombinator.com/item?id=38194372

"Absolute" means "unquestionable, fundamental, ultimate, no exception", etc. You've linked to a single study which did not test all forms of IF. You can't say you know something absolutely if you haven't even tested for it.

Specifically, there are much longer periods of fasting which may have a different impact on the result which are not tested for here. There is a claim about alternate-day fasting which is actually not supported in the linked study.

In addition, the longer alternate-day fasting practices may include ad libitum which may have a detrimental effect. Lack of adequate protein is presumed by many to be linked to loss of lean muscle, and the quality and form of feeding during feeding windows would therefore be of high importance, but doesn't seem to be accounted for in these studies.

To be fair, any substantial calorie restriction TRE or not means you will lose some muscle/lean mass. I’m not sure table 2 shows evidence that TRE is more detrimental to lean mass than CR given that the TRE group had fewer calories on average than the CR group.

It’s possible to minimize the loss by consuming large amounts of protein, but some amount of it will be converted to glucose unfortunately. The difference is very drastic, you can preserve a lot of muscle mass by doing proper diet vs IF. It all adds up when you so it for 6 months.

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