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Comment by wutbrodo | Hacker News Reader

From the beginning of the article...

> Although previous studies have found an increased risk of depression with higher consumption of added sugars, none examined the role of ‘reverse causation’. If people with anxiety and/or depression tended to consume more sugary foods and drinks, this could be the real reason why a link between sugar intake and poorer mental health is observed. Although the study looked for this link, it was not seen in the data: men and women with mental disorders were not more likely to consume more sugar. As a result, the evidence that mental health is adversely affected by a high sugar intake is strengthened.

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Mental disorders are also correlated with sleep problems; sleep-deprived brains often crave sugar. This might also be another avenue for causation.

> This might also be another avenue for causation.

If people with mental disorders were more sleep-deprived and then consumed more sugar, wouldn't that also show up in the data?

> Although the study looked for this link, it was not seen in the data: men and women with mental disorders were not more likely to consume more sugar.

A causal A > B > C link would look similar (data-wise) to a A > C link.

Not if A => B for only a small population of A. But in that case, you still might see a C => A link.

That really doesn't mean much.

Let group S be sugar eaters.

Let group A be all people w/o mental disorders.

Let group B be all people w/ mental disorders.

We have the main correlation between sugar and mental disorder:

p[A/S] <= p[B/S]

Using bayes rule:

p[A]p[S/A] <= p[B]p[S/B]

We also have "men and women with mental disorders were not more likely to consume more sugar":

p[S/A] >= p[S/B]

Comparing the inequalities gives us:

p[A] <= p[B]

So you're more likely to have a mental dissorder than not according to this study???

>p[A/S] <= p[B/S]

This doesn't follow. Just because mental disorders are correlated with sugar doesn't mean that most sugar eaters have mental disorders.

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