Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis


(Deb) #1

https://www.thelancet.com/article/S2468-2667(18)30135-X/fulltext


(Todd Allen) #2

My take on the study, it is a meta-analysis (a subjective interpretation) of observational studies (a subjective selection) based on dodgy methods such as food frequency questionnaires. At best it provides a hypothesis but it tells us nothing.


(Jack Bennett) #3

How good is an estimate of actual foods eaten based on a dietary questionnaire at enrollment?

This suffers from the fundamental FFQ problems - people don’t remember, and people lie (not even maliciously, they just guess wildly and make stuff up).

How can we make valid inferences from self-reported recall data gathered at very long intervals?


(Bacon by any other name would taste just as great.) #4

I remember one study that came out last year, in which the food frequency questionnaire had been administered once during the study, and that was something like 25 years before the results were tabulated. :man_facepalming:

I hope the studies in this metanalysis were better-conducted than that one.


(Michael - When reality fails to meet expectations, the problem is not reality.) #5

This tells you all you need to know that this is worthless:

Procedures

Participants completed an interview that included a 66-item semi-quantitative food frequency questionnaire (FFQ), modified from a 61-item FFQ designed and validated by Willett and colleagues16, at Visit 1 (1987–89) and Visit 3 (1993–95). Participants reported the frequency with which they consumed particular foods and beverages in nine standard frequency categories (extending from never or less than one time per month, to six or more times per day). Standard portion sizes were provided as a reference for intake estimation, and pictures and food models were shown to the participants by the interviewer at each examination. We used the Harvard Nutrient Database to derive nutrient intakes from the FFQ responses.16


(Jack Bennett) #6

I guess two FFQs in 4-8 years is better than two in 25 years? But “better” is relative. It’s better to get stabbed than stabbed, shot, and thrown off a building - but that doesn’t mean that it’s good.

I find it amazing that “scientists” feel like they can learn anything from this. My academic background is in the physical sciences, where you measure things, change just one input, and measure things again. And even then it’s very hard to discern cause and effect.

I’m amazed that there’s any signal in all the noise from this recalled, self-reported data. (And maybe there isn’t…)


(Bacon by any other name would taste just as great.) #7

Nutritional science is very hard to do, as Gary Taubes points out. Some of the difficulties are insuperable. But that doesn’t excuse the reliance on very high p-values and the “conclusions” drawn from very small observed effects. And even when the results are statistically significant, it doesn’t guarantee that they’ll be clinically useful. A little more humility on the part of the researchers and less willingness on the part of journalists to overhype results would go a long way.

As for food-frequency questionnaires, they are a joke, but no one has been able to come up with anything better.


(Michael - When reality fails to meet expectations, the problem is not reality.) #8

Food log. But since it’s a lot more work no one does it unless it’s in a controlled clinic. Even then, it’s a matter of days to weeks, not years. Relevant example: how many folks on this forum actually log their food intake daily? I doubt very many.

PS: When I say ‘log’ I mean weigh and measure. Everything.


(Jack Bennett) #9

Good point … and people here are probably much more diet, health, and nutrition-aware than the average. It’s been made easier with apps like MyFitnessPal and so forth, but not necessarily more accurate. (“Was that steak 6oz or 8oz?”, etc)


(Joey) #10

Scatology?


(Bacon by any other name would taste just as great.) #11

So you’re saying it will all come out in the end? :rofl:


(Joey) #12

Precisely. Regularity rules.

That’s why people can more accurately complete a PFQ than a FFQ.


(Bacon by any other name would taste just as great.) #13

And we are all familiar with the adage, carbage in, garbage out! :grin: