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Comment by brigadier132 | Hacker News Reader

Those studies that link red meat to cancer are all epidemiological and causal relationships can't be drawn from them. For example, one possible confounder could be that population of people that eat red meat also eat higher amounts of fast food or they might have higher bmi than those that don't.

Also, always note how the studies never say "red meat causes cancer", they say "red meat is linked to cancer". Linked being the key word.

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> Those studies that link red meat to cancer are all epidemiological and causal relationships can't be drawn from them.

There is an extensive body of studies that show a direct link between amines produced from exposing meat to high temperature in animals. You can disagree on the dosage used in the studies but I wouldn't ignore them completely. Here are a few:

Sugimura T, Wakabayashi K, Nakagama H, Nagao M. Heterocyclic amines: Mutagens/carcinogens produced during cooking of meat and fish. Cancer Science 2004; 95(4):290–299.

Ito N, Hasegawa R, Sano M, et al. A new colon and mammary carcinogen in cooked food, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Carcinogenesis 1991; 12(8):1503–1506.

Kato T, Ohgaki H, Hasegawa H, et al. Carcinogenicity in rats of a mutagenic compound, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline. Carcinogenesis 1988; 9(1):71–73.

Kato T, Migita H, Ohgaki H, et al. Induction of tumors in the Zymbal gland, oral cavity, colon, skin and mammary gland of F344 rats by a mutagenic compound, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline. Carcinogenesis 1989; 10(3):601–603.

Ohgaki H, Kusama K, Matsukura N, et al. Carcinogenicity in mice of a mutagenic compound, 2-amino-3-methylimidazo[4,5-f]quinoline, from broiled sardine, cooked beef and beef extract. Carcinogenesis 1984; 5(7):921–924.

Ohgaki H, Hasegawa H, Suenaga M, et al. Induction of hepatocellular carcinoma and highly metastatic squamous cell carcinomas in the forestomach of mice by feeding 2-amino-3,4-dimethylimidazo[4,5-f]quinoline. Carcinogenesis 1986; 7(11):1889–1893.

Shirai T, Sano M, Tamano S, et al. The prostate: A target for carcinogenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) derived from cooked foods. Cancer Research 1997; 57(2):195–198.

Don't those studies accout for such types of influence?

They try isolate confounders using statistical methods but these are not intervention studies and they rely on self reported data. There are obvious limitations with such approaches. You could imagine that people who are careful enough with their diet to completely avoid red meat also probably do physical activity of some sort. How many people that avoid red meat in their diet also eat at mcdonalds?

They aren't locking people up in a resort and strictly monitoring and controlling what they ingest.

Would you also bite that bullet with regard to the association between cigarettes and lung cancer? We don’t have RCTs.

How do we know that it’s not just the fact that people who smoke also don’t exercise? Well, it’s simple: we trivially adjust for exercise. Just like we have prospective cohort research on unprocessed vs processed red meat: we can design studies that measure it.

(This is aimed at your sibling comment) If you’re saying there’s a confounder we don’t know about in play: then what is it and what evidence would you bring to the table to justify its inclusion in our inference model? Note: that evidence would have to be at least as good as the evidence you’re rejecting for not having that magical secret confounder.

That said, even before getting to cancer outcomes, I would replace red meat with another protein source just to avoid saturated fat. And if I was only moved by cancer outcomes and refused to change my high red meat diet, I would ensure I'm eating lots of veg/fruit to insulate myself against the risks which is what you see in the Tomorrow Alberta Project prospective cohort analysis among the highest red meat eaters who also ate the most fruit/veg.

They try to. Unfortunately you can’t account for all of them, because we don’t know all of them.

Once it’s published that X is healthy or Y is unhealthy then people change their lifestyle in accordance. You can’t tell if some other thing that people do because they heard it is healthy is the real cause.

They try, but not successfully. It is called the healthy user effect. If something is already considered unhealthy by conventional wisdom then people trying to be healthy dont do that thing. And it's extremely difficult to account for because the differences between those people and everyone else are very large and difficult to lock down, since they will tend to do lots and lots of things that you are supposed to do for good health, but most people dont.

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