Brief note: the definitions of IF and CR vary widely. For the sake of simplicity, in this article, if IF results in weight loss, then it’s also CR. CR, by definition, results in weight loss and typically includes ~3 meals a day. Neither diet specifies macros. Weight loss is a confounder to keep in mind.
For example, in this 3 month-long study, 30% CR was compared to an increased unsaturated fatty acid group and a control group (Witte et al., 2009). CR group lost weight whereas the other two groups actually gained weight (unintended). In this study, 30% CR resulted in an apparently pretty impressive improvement in memory:
HOWEVER: The actual dietary changes in each group were… interesting (see Table S1) — the control group ended up doing dietarily almost exactly what the CR group did… so why didn’t their memory score improve? Why didn’t they lose weight? I don’t know, but something seems fishy.
CR garners zero points for this.
Next on the docket is a systematic review (Benau et al., 2014), which concluded: “The combined results are equivocal: several studies report no observable differences as a result of fasting and others show specific deficits on tasks designed to test psychomotor speed, executive function, and mental rotation.” That was based on 10 studies. Given the nature of human biology, “no effects of IF” would not have been unexpected. Kinda surprised at all of those negatives.
The ice age fairy tales go something like this: no food for a day or two improves your cognitive capacity, makes you sharper so you can get your next meal (be it via hunting, gathering, or whatever).
I’m not anti-IF; in fact, I think everyone in weight maintenance should be able to go through the night without the need to wake-up to eat. I’m just commenting on the available studies by people who aren’t selling books on the topic.
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