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Comment by recallingmemory | Hacker News Reader

It doesn't look like meat consumption was mentioned anywhere.

Frequent consumption of red and processed meat is strongly linked to a higher risk of colorectal cancer, with studies showing a 30% to 40% increased risk for high consumption levels [1]. Processed meat, in particular, raises CRC risk by about 18% for every 50-gram daily portion [2].

Your ultra-endurance athletes might be convinced they need more protein in their diets and are most likely consuming large quantities of meat.

1: https://pmc.ncbi.nlm.nih.gov/articles/PMC10194058/

2: https://www.umassmed.edu/news/news-archives/2015/10/umms-col...

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Why would meat cause a decrease in incidence for older folks but a higher incidence for younger folks?

Additionally, the risks you quantify for general cancer incidence are at the bottom odds ratios listed at the end for early-onset. Speculating that ultra-endurance athletes eat tons of meat, without any evidence, seems quite misplaced.

2025 study on the diet quality of ultra-marathon runners: https://pmc.ncbi.nlm.nih.gov/articles/PMC11820624/

From the discussion section, "It is important to note that inadequate intake in the athletes of the present study may carry significant negative health implications. Insufficient consumption of fruits and wholegrains has been linked to the development of chronic diseases, including CVD, cancer, T2D, and hypertension. Additionally, high intake of sodium, saturated fat and discretionary food items are correlated with higher incidence of obesity, T2D, CVD, dementia, and cancer. Paradoxically, despite exceeding the WHO guidelines for physical activity by a substantial margin, these athletes are not meeting dietary recommendations essential for long-term health, highlighting the potential risks posed by these inadequacies."

Interestingly no mention of meat there.

Low fiber is quite interesting though, even if it alone doesn't quite explain the massive increase in risk that is observed, at least as I understand it. Correlation between low fiber and high meat consumption would be interesting to investigate as well.

Though ostensibly supportive of your claim, the first article says it best a few pages in (surprisingly honest):

"To date, there are no clearly established biological mechanisms that could explain the role of red and processed meat in the process of CRC carcinogenesis."

In other words, we see some small signal in epidemiological studies, and we want to speculate about mechanistic causes, even though this has been tried before to no success.

I would point to the conclusion of the study: "Red and processed meat consumption and its interaction with the gut microbiota are found to be major associated factors. The CRC-associated gut microbiota is made of pro-inflammatory or pro-carcinogenic bacteria and opportunistic pathogenic bacteria that enrich the tumor microenvironment by promoting disease progression."

I would also add that the World Health Organization after evaluating 800 studies classified processed meat as a Group 1 carcinogen back in 2015, indicating a strong causal link to colorectal cancer, placing it in the same risk category as tobacco. [1]

While I linked to a single study in my original comment, I believe the results are more than a small signal.. enough for the WHO to come out and say processed meat does in fact have a causal link to CRC.

1: https://nutritionsource.hsph.harvard.edu/2015/11/03/report-s...

I just hate associative claims that delicately prance around the word “causality”.

I’m sure that we could run a casual analysis on this, though my cursory search yielded nothing, probably because the claim that a certain level of red meat consumption causes certain cancers in humans is not really falsifiable (though we have a plausible biological mechanism to explain it).

I know some biostatisticians but only one or two would have the training to conduct such an analysis, and I wouldn’t trust a statistician in theoretical causality to handle it.

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