A few days ago Jim Babcock stated

I care about nutrition because I believe it has a very large, very underappreciated impact on individual productivity. Low quality diets make people tired and depressed, so they don't get anything done.

There's obviously a sense in which that is trivially true. If you start consuming no more than zero calories per day, you will get very tired, maybe depressed as well, and you will eventually not be able to get anything done. And getting adequate iodine and other nutrients is very important for children to properly develop their cognition. But Jim Babcock is probably making a stronger claim. I think what he is claiming is something like "going from the 10th percentile in diet quality among Americans to the 90th percentile would have very large, very underappreciated impact on an adult's individual productivity (taking into account that diet quality is almost certainly at least partially dependent on individual factors)." 

I'd like to know what evidence we have for that claim. The strongest piece of evidence I can find is Rae et al., 2003, which showed that creatine supplementation increased the average IQ of their sample of vegetarians by 12 points, but that hasn't been replicated[1], and it seems extremely hard to substantially improve the cognition of adults. And, when it comes to depression, people have been trying really hard to show that omega-3 supplementation has substantial effects on it, but it's dubious that it does. L-methylfolate is a nutrient that is apparently effective enough that someone convinced the FDA to approve it to treat depression (as an add-on to treatment to another antidepressant), but only in quantities that far exceed those that anyone gets from their diet. 

So I have a fairly low credence that his claim (as I formulated it) is true. But I was wondering if there were any major pieces of evidence I have completely missed.

Update from the future (1/16/2023): iron deficiencies are really bad, worse than I thought when I wrote this.

[1] Apparently some rationalists planned to try to replicate this, but there seemingly hasn't been an update to that in three years.

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I'm the PI (supervisor) on the replication of the creatine trial. We have finished the trial but not the data entry+analysis. Extremely tentatively, it looks like the effect replicates but with much smaller effect size. If this result remains after data entry+analysis are complete, then I'd say this is a positive update for cognitive benefits of creatine --- given that the prior for this to work was pretty low (publication bias, and so on), I'd say that one trial with a large effect size and one with a small effect size is more convincing than just one with a large effect size.

But really, the result might still change in the process of us double-checking things. It's just my best guess right now. The preprint will hopefully appear in the course of the year.

This doesn't seem to be published yet (or I can't find it), but any updates on publication dates or your independent impression?

Thank you a lot! I’m looking forward to the preprint. If you don’t mind me asking, was your sample fully vegetarian?

We had two groups, one vegetarian/vegan, and one omnivore.

That quote suffers from the problem of so much punditry. It gets your attention, then leaves all the hard work of specifying a problem and gathering and evaluating evidence up to you.

creatine supplementation increased the average IQ of their sample of vegetarians by 12 points

Creatine didn't improve my iq, but it did improve my scores on a digit memory test and more importantly, my mental stamina. I took it for a year, decided it wasn't doing anything and quit. After about a week, I noticed that I was feeling tired after six or seven hours of programming instead of the eight or nine I had been doing. After taking creatine again my energy returned.

Anecdotal blah blah, but maybe you should try it? It doesn't cost that much for a month's supply, and you can find simple recall tests online and do one measurement before and one after.

I’m looking for answers less like “this thing made me feel better/worse” and more like “these RCTs with a reasonable methodology showed on average a long-term X-point IQ increase/Y-point HAM-D reduction in the intervention groups, and these analogous animal studies found a similar effect,” in which X and Y are numbers generally agreed to be “very large” in each context.

This also seems to be the kind of question that variance component analyses would help elucidate.

I do take a creatine supplement, despite expecting it to not to help cognition/mood/productivity that much.

Those studies could not falsify the thesis of Jim Babcock's given that he doesn't assume that the same nutritional intervention has the same effect on different people.
4Natália Coelho Mendonça2y
Those studies could elucidate evidence in favor of his thesis, though, which is why I’m looking for them.

Are you a vegetarian?

No, but I don't eat very much meat.

It occurs to me glycemic load may be a factor. This is only a small study but it suggests an effect of high glycemic load (eg from poor diets) on depression and maybe fatigue. Also that these are worse for obese people, and poor diet causes obesity.

Also "sugar rush" is a thing I've seen in children. I didn't used to think it was true, but having seen the same child over and over, and sometimes there is a sugar bomb in her evening and those evenings are weird for hours after in predictable ways, on a predictable timecourse... Its an N=1 study that I've seen replicate quite a few times, if that makes sense.

Also, if you want to try to model the next layer down, there's a whole universe of mechanisms aiming to keep fuel available in the blood at a steady level, with a liver full of glycogen ready to be r... (read more)

This is pretty interesting, I’ll take a look into it. Thank you.

I remember then Chris Pasek talking about how in his productivity tracking where we tracked it on an hourly basis nutrition had the highest effect.

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I don't believe nutritional RCTs are going to give a resolution of evidence necessary to support or refute.

If you start consuming no more than zero calories per day, you will get very tired, maybe depressed as well, and you will eventually not be able to get anything done.

While it's true that eventually you won't be able to get anything done, there's actually a phase of fasting when you have an energy rebound due to no energy being spent for digestion. Anecdotally it usually happens between day 3 and day 10 of fasting.