Discussion of everything related to the Theory of Evolution.
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I was thinking about these two harvard studies.
http://news.harvard.edu/gazette/story/2 ... -diabetes/
http://news.harvard.edu/gazette/story/2 ... red-flags/
Our oldest ancestors would not have eaten cured or processed red meat. Those are the two kinds of red meat linked with diabetes and heart disease. However, all red meat is linked with cancer. This means our ancestors may have been eating the same kind of red meat that causes us to die of cancer. However, we didn't have to worry about cancer until we started living into old age.
However, cancer is caused by a build-up of mutations as one ages. So, even if the red meat wasn't harmful to our ancestors through cancer, it might have caused them to give birth to more mutated children. Indeed, mutations in offspring tend to increase with the age of the parents. Since we are sexual, not asexual, a trait that caused more frequent mutations in the offspring definitely wouldn't have been favored. However, our ancestors probably gave birth to offspring earlier in their lives.
What do you think?
Unless I am mistaken, the higher rate of mutations in older parents is not linked to eating red meat. What comes to the increased cancer risk red meat, as far as I know, affects the gut epithelium and mostly increases the cancer rate in the lower digestive tract. However, mutations happening in the gut do not get passed on to the children, since only mutations in the germ line cells do so (which increase when people age, like any mutations).
The increased cancer rates caused by red meat seem to be linked to the lack of fibre in that kind of diet, which in turn slows down the passage of food in the gut and thus the gut is exposed to some possibly toxic or carcinogenic byproducts of digestion. It could be so that increasing fibre in one's diet negates this phenomenon by making the gut contents pass faster in one's bowels. This is also supported by the finding that high-fibre diet seems to lower the prevalence of colorectal cancer. Diabetes and cardiovascular issues are another story, mostly linked to metabolic problems and obesity, and according to the current knowledge do not increase mutation rates in the children (by the same principles as with cancer).
In any case, like you said, the average lifespan of our ancestors was typically so short that the issue of increased cancer, diabetes or heart disease risk caused by red meat in the diet was likely to be not a problem for adults. And I would speculate that it was not a problem for the offspring either - to the contrary: high-energy, high-protein fat and meat from animals was probably a welcome addition to the neolithic diet, making mothers (and babies alike) more healthy and strong.
You are right that they probably didn't have to worry about heart disease or diabetes either. However, I would suspect that heart disease and diabetes have been problems for much longer than cancer.
Indeed, we haven't been farming animals for milk for very long, but we already see genetic differences in places where milk was a necessity. In those people, the enzyme lactase is present beyond childhood.
Wait wait wait wait wait wait wait wait...
Red meat has a higher correlation with cancer than fish or poultry. Neither of those contain fiber either. You could argue that red meat is more filling, so a person eating red meat is less likely to eat any fiber afterward. However, I don't think red meat is any more filling than poultry. Furthermore, white meat (poultry) is associated with a lower cancer risk.
http://www.sciencedaily.com/releases/20 ... 161109.htm
Sorry, I wasn't being too clear. The lack of fibre is not the only "harmful" trait of red meat. But it is a factor that, if eliminated, also negates many of the harmful effects of red meat. Not all, though, but enough for most people if it is consumed in moderation. Red meat contains several substances that can indeed be harmful in higher concentrations that is not present in poultry or fish. Some studies indicate that heme iron, for example, could be one of these (even though iron is essential for humans, high intake of heme iron from diet for prolonged periods can be harmful).
Also, any diet that lacks fibre is linked to increased risk of colorectal cancer. Red meat is just a factor that further increases it. As far as I know, the exact reasons for this are not completely known and the role of fibre in the diet is perhaps only one among many factors that contribute to the overall outcome. In that article you linked they also mention carcinogenic agents caused by the cooking and saturated fast, and I they sound like plausible explanations as well. But also their effect could be lessened by higher fibre content, because the exposure time to these compounds could become shorter.
In other words, the so-called paleo diet for example, is thought to be good for humans because (among other things), it contains lots of fibre and red meat only in moderation.
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