Comparative ultra-processed reports

Q: Did you see  Every bite of ultraprocessed food will increase your chance of an early death.

A: How could they possibly have shown this?

Q: New study says

A: But think about it. How do they measure people’s consumption of ultraprocessed food down to the single bite level? How do they find a comparison group with just one bite less consumption? What does it even mean?

Q: Don’t I get to ask those questions?

A: <sigh>

Q: Where is the new research? And how many people or mice did they study?

A: It’s in the American Journal of Preventive Medicine, and it doesn’t involve any new data collection.  It’s a combination of a bunch of existing studies that looked at correlations between diet and health

Q: Does the claim about “every bite” appear in the journal paper?

A: No.

Q: Where does it come from?

A: As text, I’m not sure.  As an idea I think it comes from a claim in the paper for a “linear dose-response relationship”, ie, that risk goes up in a straight line with consumption of ultra-processed foods

Q: Does it?

A: That’s the model they assumed. They don’t really seem to have assessed the evidence for non-linearity in the paper, and they certainly can’t say anything meaningful about the “single bite” dose. The combined estimate is that groups of people whose consumption of these foods was higher by about 10% of their diet had a risk of premature death that was about 3% higher.

Q: But what would the risk from “one bite” be?

A:  You mean if the relationship was exactly linear extrapolated way down to that level and perfectly causal?

Q: Yes, just for fun

A: One bite of what? Different bites have different calorie levels

Q: Just work with me here. Make something up, ok?

A: Ok. So if one bite was 2% of one day’s energy intake it would be  0.0055% of one year’s energy intake, or 0.00055% of ten years’. At a increase of 3% per 10 percentage points, that’s an increased risk of premature death by a factor of 1.000016.  Which would be quite hard to detect.

Q: We were promised comparisons

A: Ah, yes. The BBC also wrote about this study, with the perfectly reasonable headline Ultra-processed foods may be linked to early death

Q: “May be“?

A: As one expert they quoted said “It’s still far from clear whether consumption of just any UPF at all is bad for health, or what aspect of UPFs might be involved. This all means that it’s impossible for any one study to be sure whether differences in mortality between people who consume different UPF amounts are actually caused by differences in their UPF consumption. You still can’t be sure from any study of this kind exactly what’s causing what.”

Q: He’s not saying ultra-processed food is good, though?

A: No, I think the most negative opinion you’ll see is just that it’s not necessarily a helpful way to categorise food