Monday, April 8, 2013

Does Red Meat Cause Inflammation? - Kresser

By on April 5, 2013  
So far in my series on red meat, I’ve discussed why red meat is good for you and why grass fed is a better choice than grain fed. We now know that red meat is a healthy choice, due to its high nutritive value and superior fatty acid profile among other reasons. In the comments on these posts, however, I’ve noticed a few readers have mentioned other components in red meat that are concerning, due to evidence for the potential for inflammation or carcinogenesis.

Yet is this evidence strong enough to advise a reduction in red meat, or is this yet another false alarm creating unnecessary fear of eating meat?
Red meat and inflammation: another myth bites the dust.
Two different controlled trials have measured inflammation markers in response to increased red meat intake, and both have found that red meat does not elevate these markers. The first study concludes that increasing red meat consumption by replacing carbohydrates in the diet of non-anemic individuals actually reduces markers of inflammation. (1) The other study showed that in anemic women, inflammation markers on a diet high in red meat were not significantly different from those on a diet high in oily fish. (2) This evidence suggests that red meat is not more inflammatory than other meats for most people, and is potentially less inflammatory than dietary carbohydrates.

However, I’d like to discuss a couple of other specific mechanisms that are often blamed for inflammation.


Despite the lack of controlled trials demonstrating that red meat is inflammatory, there has been recent concern over a compound in red meat called Neu5Gc. (3) Neu5Gc is a monosaccharide that acts as a type of signaling molecule in mammalian cells, and one of its functions is to help the immune system distinguish between ‘self’ cells and ‘foreign’ cells. (4) Humans lost the ability to produce Neu5Gc millions of years ago through a genetic mutation, although we still produce the closely related compound Neu5Ac. (5) Humans are unique in this respect, because most other mammals still produce Neu5Gc, which is why that compound is found in mammalian meat.

When humans consume red meat and milk products, we incorporate some of this compound into our own tissues, especially tissues that grow at a fast pace such as fetuses, epithelial and endothelial tissue, and tumors. (6) The concern is that most of us also have anti-Neu5Gc antibodies circulating in our blood, and some researchers have suggested that these antibodies react with the Neu5Gc in our tissues to create chronic inflammation, leading to chronic diseases such as cancer.

The problem is that researchers are nowhere near proving that hypothesis. Research is in the very earliest stages, and while some fascinating hypotheses involving this molecule are being generated, the studies needed to confirm or refute these hypotheses are nonexistent. Most of the studies done on the topic acknowledge that at this point, any role in chronic inflammation is speculative, but many who have cited their research neglect to acknowledge that limitation. Thus begins a new round of fear mongering at the expense of red meat.

In the absence of conclusive evidence one way or another, it can be helpful to remember that red meat has been part of the human diet for much of our history, and remains an important dietary element of many healthy cultures. For example, the traditional diet of the Masai was composed almost entirely of red meat, blood, and milk – all high in Neu5Gc – yet they were free from modern inflammatory diseases. (7) If Neu5Gc really caused significant inflammation, the Masai should’ve been the first to know, because they probably couldn’t have designed a diet higher in Neu5Gc if they tried.

Arachidonic Acid

Arachidonic acid (AA) is often cited as a source of inflammation, and because AA is found primarily in eggs and meat, this concern could contribute to the view that red meat is inflammatory. AA is an essential omega-6 fatty acid that is a vital component of cell membranes and plays an important role in the inflammatory response. (8) It’s especially necessary during periods of bodily growth or repair, and is thus a natural and important component of breast milk. (9) AA is sometimes portrayed as something to be avoided entirely simply because it is ‘inflammatory,’ but as usual, that view drastically oversimplifies what actually happens in the body.

It’s true that AA plays a role in inflammation, but that’s a good thing! It ensures that our body responds properly to a physical insult or pathogen, and it also helps ensure that the inflammatory response is turned off when it’s no longer needed. AA interacts with other omega-3 and omega-6 fatty acids in intricate and subtle ways, and an imbalance in any of those fats has undesirable effects. For example, low doses of EPA tend to increase tissue levels of AA, while high doses decrease levels of AA, which probably explains why the benefits of fish oil supplementation are lost at higher doses. (10) In epidemiological studies, higher plasma levels of both AA and the long-chain omega-3 PUFA were associated with the lowest levels of inflammatory markers. (11, 12) And clinical studies have found that adding up to 1,200 mg of AA per day—which is 12 times higher than the average intake of AA in the U.S.— to the diet has no discernible effect on the production of inflammatory cytokines. (13, 14) What’s more, our Paleolithic ancestors (who were largely free of chronic, inflammatory disease) consumed at least twice the amount of AA that the average American does today. (15)
Finally, it’s important to note that red meat actually has a lower concentration of AA than other meats because of its lower overall PUFA content. (16)(17) Additionally, red meat has been shown to increase tissue concentrations of both AA and the long chain omega-3s DHA and EPA, preserving the all-important balance of omega-3 and omega-6. (18)

Charred meat and cancer

The final concern I want to address involves compounds that are produced when meat is cooked, including advanced glycation end products (AGEs), heterocyclic amines (HAs), and polycyclic aromatic hydrocarbons (PAHs). Again, this applies to all meat, not just red meat, but it can still contribute to the perception that red meat is unhealthy.

HAs and PAHs have both been shown to cause cancer in animal models, and although these results can’t necessarily be extrapolated to humans, it’s probably wise to limit exposure to these two compounds. (19)(20) HAs and PAHs are formed when meat is cooked using high-heat or dry cooking methods such as frying, grilling, or smoking. But while cooked meat is the only significant source of HAs, PAHs are a ubiquitous environmental contaminant, and the bulk of dietary PAHs actually come from vegetables and grains. (21) In fact, levels of PAH in leafy vegetables are comparable to levels in smoked meat! However, the highest food levels of PAH are found in charred meats that have been cooked over an open flame.

AGEs are different from the other compounds in that they can be formed both endogenously and exogenously. (22) Like HAs and PAHs, AGEs are formed when foods – particularly meat – are cooked, although they are also naturally present even in uncooked meat. However, dietary AGEs do not tell the whole story, because they can also form through various metabolic pathways in the body.

One study showed that while omnivores generally have higher dietary intakes of AGEs than vegetarians, vegetarians actually end up with higher concentrations of AGEs in their plasma. (23) The authors hypothesized that their results were due to the increased fructose intake of vegetarians, although another plausible mechanism appears to be the inhibition of AGE formation by carnosine, an amino acid found in meat. (24)(25) Either way, I wouldn’t be terribly concerned about AGEs in meat, although I still recommend favoring lower-heat cooking methods to avoid HAs and PAHs.

If you do want to grill or fry your meats, you can significantly reduce the formation of all of these compounds by using an acidic marinade, which has the added bonus of tasting great! Marinating beef for one hour reduced AGE formation by over half, and marinades can cut HA formation in meat by up to 90%. (26)

Overall, there’s no good evidence that red meat is more inflammatory than other meats, and some evidence indicating that it’s less inflammatory. Just like any other food, it’s certainly possible for people to have individual intolerances to red meat that might induce inflammation, but there’s no reason for most people to restrict red meat on the basis of inflammation. Additionally, AGEs from meat are probably not a concern, and meat eaters might even be better off when it comes to plasma levels of AGEs. Any concerns about other compounds produced by cooking meat can be minimized simply by favoring wet or low-heat cooking methods, or using a marinade when high-heat methods are desired.

I hope I’ve addressed all the remaining health concerns with eating red meat, but I’d like to hear your thoughts in the comments below.
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