Friday, February 27, 2015

Is Meat Unhealthy? Part IX

Welcome to the last post in the series.  Time to summarize and wrap it up!


I respect each person's right to choose the diet they prefer.  This includes vegetarians and vegans, particularly because most of them make daily sacrifices to try to make the world a better place for all of us.  I'm an omnivore, but I sympathize with some of the philosophy and I often eat beans or lentils instead of meat*.

Our history with meat

Our ancestors have probably been eating some form of meat continuously for at least two hundred million years.  However, the quantity has waxed and waned.  The first mammals were probably largely carnivorous (insectivores).  Yet our primate ancestors went through a 60-million-year arboreal phase, during which we probably ate fruit, leaves, seeds, insects, and perhaps a little bit of vertebrate meat.  We only outgrew this phase in the last few million years, when we developed the tools and the brains to pursue prey more effectively.

During our 2.6 million-year stint as hominin hunter-gatherers, we ate an omnivorous diet, although we really have very little idea how much meat it contained (it probably varied by time and place).  Historical and contemporary hunter-gatherer cultures are all omnivorous, and typically eat significant to substantial quantities of meat, suggesting that our ancestors may have done the same.  Non-industrial agricultural populations eat as much meat as they can get, although they usually can't get as much as hunter-gatherers.

If there is such thing as a natural human diet, it is clearly omnivorous.

Meat, obesity, and chronic disease

Vegetarians and vegans do tend to be leaner and have a lower risk of some chronic diseases than omnivores, although it's difficult to separate meat avoidance from the other trappings of the vegetarian and vegan diet and lifestyle.

Regularly replacing meat with plant protein such as beans may reduce cardiovascular risk, and for people at very high cardiovascular risk, a very-low-fat, high-unrefined-carbohydrate vegan (or near-vegan) diet may be something to consider.

Most of the chronic disease risk associated with meat consumption comes along with red and processed meats-- particularly the latter.  There are good reasons to believe that processed meat increases the risk of digestive cancer, obesity, diabetes, and perhaps cardiovascular disease.  As much as I dislike this conclusion, unprocessed red meat probably does increase the risk of digestive cancer, and possibly also diabetes in people with elevated iron stores.  There are hints that it might also contribute to cardiovascular disease, although the overall evidence is not very strong in my opinion.  That doesn't mean we need to completely eliminate these meats from our diets to be healthy, but moderation is probably in order.

Seafood is one category of meat that tends to be associated with positive health outcomes.  Again, it's difficult to completely disentangle seafood eating from socioeconomic factors, but the evidence overall does suggest a protective effect.  Poultry tends to be neutral.

Meat and mortality

Vegetarians, vegans, and omnivores all have a similar total mortality risk.  Overall, there is little association between total meat consumption and mortality in the general population.  The only type of meat that is consistently associated with higher mortality is processed meat.  This suggests that avoiding meat, even red meat, probably isn't an effective way to live a longer life (even if it does impact the risk of specific diseases).

Meat, development, and physical function

If we take a broader view of health that includes more than just disease resistance, meat seems to play a positive role.  Meat supplies nutrients that are complementary to those contained in plant foods. This is expected, since our nutritional requirements have presumably been shaped by hundreds of millions of years of omnivory.

A whole food-based omnivorous diet is the easiest and most effective way to meet the nutritional needs of the human body, and the further a person departs from this pattern, the harder she has to work to be well nourished.  For example, vegan diets require a lot more thought and planning than omnivorous diets to meet nutritional needs, and because of this, vitamin and mineral deficiencies are more common among vegans.

As one would expect, these nutritional limitations sometimes restrain the body from achieving its full potential.  When we look at the most physiologically demanding scenarios, such as reproduction, growth/development, and athletic performance, omnivores tend to have an advantage.

This may explain why many people don't feel well on vegan diets, and often develop strong cravings for meat over time**.  Those who stick with the diet for many years are those who are able to tolerate it the best and have the most resolve.

Many well-studied traditional cultures have demonstrated that an omnivorous dietary pattern including modest quantities of meat, dairy, and eggs, and also including plant protein such as beans, can support excellent health and longevity over multiple generations.  We have limited evidence that the same can be true of a vegetarian diet containing dairy and eggs, however we do not have such evidence for a vegan diet containing no animal foods.  While I have no problem with adults eating a vegan diet in general, I remain uncomfortable with vegan pregnancy and feeding children a vegan diet.  Adults can choose but children can't.

The bottom line

The overall evidence leads me to believe that meat is a valuable part of the diet, but we don't necessarily need to eat much of it to reap the lion's share of the benefits.  From a chronic disease perspective, it probably is preferable to focus meat intake primarily on seafood and poultry, and limit processed meat.

* I don't think I would ever become completely vegetarian or vegan again, even if I was convinced meat is unhealthy.  The all-or-nothing phase of my life is over, and I have little desire to completely eliminate anything from my diet.  I occasionally eat unhealthy foods such as pizza, ice cream, and potato chips-- and I don't feel guilty about it.  I keep 90+ percent of my diet in the healthy range and don't worry too much about the rest.

**Although personally, I felt fine during my six months of eating vegan.  I missed eating meat, but I don't recall my desire for it intensifying over time.


Teech said...

Great articles Stephen,

I've been following your blog for about 4 years now and I agree with many of your positions on health and nutrition.

I know vegans often mention that deficiencies can be avoided through supplementation. But is there any weight to the idea that animals tend to have more complex biological compounds as opposed to plants. Could there be things other than b12 that we can only get from animals?
Also, after a little research, I found that the most water intensive crops are chocolate (no!) and almonds. Its seems like we would have to give up more than meat to be sustainable.


Gretchen said...

"I have little desire to completely eliminate anything from my diet."

You're more of an omnivore than I am. I have great desire to eliminate lutefish and Cheese Whiz from my diet.

Ash Simmonds said...

We may come at things from divergent paths of the spectrum, but we're all fallible to criticism levelled via the tu quoque logical fallacy (thanks Amber!) - basically like you and your readers I eat what I feel is an optimum diet as much as I can - but still occasionally do pizza or chips or cake or ice cream or even AGE-inducing sugar-marinated ribs or whatever, for the same reason a dog licks its balls.

I think the overall TL;DR of this series is: you should eat meat; you can eat plants.

David L said...

Salmon, and other similar fatty fish, have a much lower protein to fat ratio. Since your evidence tends to support high protein/low fat, doesn't it make such kinds of fish less desirable for weight loss?

J said...

Thank you for this erudite summary. I sit reluctantly with the conclusions as I would prefer to eliminate all meat and animal products.
Personally I can attest to the nutritional deficiency of even a well supplemented whole foods vegan diet.
I stringently stand against processed and refined foods; these are health compromising, an unecessary attachment and dont belong in my vision of health.
I am learning slowly to disengage from the idea of treats and rewards and indulgences such as those.
We are all free to choose - the great gift; and curse - of our times.

Carl M. said...

Regarding red meat: a significant fraction of red meat consumption is in the form of ground beef. Should this be considered processed? While there are no added nitrates, the grinding process mixes the heme iron with the fat which may cause some bad chemical reactions.

I suspect the far more important factor with red meat is the myth that searing seals in the juices. Steak houses advertise how hot their broilers are. Steaks are often cooked outdoors over flames. Many people heat up cast iron frying pans in order to char the outside of the meat. Fast food restaurants char the beef to the point where I question how much useful protein is left in the patties.

Anonymous said...

Thank you so much for all your work and what you put on your blog. And the summary is invaluable.

Unknown said...

I wouldn't think simply altering the physical state of beef makes it processed. Don't we readily "process" our meats by cutting it, chewing it, digesting it? Now if it were chemically changed with things such as smoke then processed is a yes. Ground meat is, in my opinion, purely for convenience.

pawpaw said...

Could you please define "processed meat"?

We raise and butcher a hog each year, making ham and bacon, but without nitrite. Also deer jerky, deer confit.
And from our grass-finished beeves, we make corned-beef. Etc, etc.

Which meat-preserving processes, additives, or end products are to be avoided? There's only so much freezer space!

Swede said...

"The all-or-nothing phase of my life is over, and I have little desire to completely eliminate anything from my diet."

I second that. We can be healthy and enjoy life. It's inevitable when you have social contact - eat their food or be "that guy." I'm sure most readers here at some time have been him/her?

Reijo said...

Thanks for this series. This might be the first time a researcher/expert with inclination to paleo diet scrutinizes scientific literature on red meat without letting preconceived ideas of the community to color the conclusions too much.

The questions still remains; what is the optimal dose of red meat (per week). IMO, world cancer research fund and AICR have got it right for long, less than 500 grams/ 18 oz per week. Seafood, dairy and poultry seem healhier but it's even more difficult to define how much we should/could eat them.

Jenny said...

I wonder whether some of the negative effects attributed to processed "meat" are actually caused by the inorganic phosphates added to these foods as emulsifiers and preservatives.

I was shocked when I started researching the subject to learn that there is a strong link between high intake of these inorganic phosphates and heart disease. Apparently they help promote calcification in the arteries. There is also a very well documented link between over-consumption of inorganic phosphates and kidney disease, again due to increased calcification.

Processed meats are full of these phosphates, as are a shocking number of other foods, including many beloved by people on low carb diets, like cream and cheese. Coconut milk, almond milk and other "health food" products also contain these added inorganic phosphates. Spend any time in a health food store and you will be shocked at how much of them you are consuming when you eat a supposedly healthy diet.

There is no requirement that labels disclose how much phosphate is added to processed food so it is hard to calculate our intake. But estimates are that most people are eating 2 to 3 times as much as appears to be safe.

I assume the reason there is very little research on this is that the cost to the food industry of correcting this problem would be high and there is no company that would be enriched by funding the research that would further illuminate it.

I sure wish someone would, though. It's yet another completely unnecessary factor that is harming our health.

David L said...

I tend to agree with Carl M. Humans have been eating red meat for a long time and ought to have adapted to it just as some have adapted to the presence of milk in their diet. And this meat was all initially done at high heat, as they had no access to pots and pans for most of the time that they were consuming meat.

Since hamburger is such a high proportion of meat that we consume, I would agree that perhaps the processing of the meat and the cooking using high heat/high fat methods might be the reason that we see the observed correlations between red meat and observed life spans.

Unknown said...

Very good article. I follow a balanced diet myself with decent amounts of produce to balance it out. Many meat bashers out there, but it is exaggerated.

Think it is important to define and understand one's motivation in selecting diet: as most would aspire to optimum health in accordance with the factors you elaborate today. AND, to remain disease free. AND to live long!
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Stephan Guyenet said...

Hi Steve,

You asked "Could there be things other than b12 that we can only get from animals?" Yes, I think so. Some people aren't good at making vitamin A from plant-based carotenes, and they may require fully formed vitamin A from animals. Many people also require long-chain polyunsaturated fats from animal sources, because plants only supply short-chain PUFA and people vary in their ability to synthesize long-chain from short-chain. Vitamin K2 may also be a relevant animal-derived nutrient. Then there are a number of non-essential compounds that may support health/performance, such as creatine and carnitine.

Hi David,

Eating some fatty fish is probably good for you due to the high level of n3 fat. If you ate large amounts of very fatty fish it could possibly increase weight, but most people don't eat it in that kind of quantity.

Hi Karl, David, and pawpaw,

Please refer to part VI for my definition of processed meat.

Hi pawpaw,

Let me get a bit more specific for your question. I sympathize with your situation and I think it's cool that you do all that. I would say that nitrite is a concern in processed meat, high heat cooking (e.g. dogs on the grill), and the high calorie density of fatty processed meats if body weight is a concern.

Hi Reijo,

Thanks. I'm not comfortable putting a specific figure on red meat consumption. The only dose-response data I'm aware of are observational (if you know of interesting dose-response RCTs please cite). Unless we think the relationship between red meat intake and health risk is non-linear (i.e., goes away below some intake threshold), then the recommended amount would depend on a person's risk tolerance.

There is too much uncertainty there for me to put a number on it right now, but I understand that health organizations have to pick a number so that there is something actionable. Their numbers don't seem unreasonable to me, but I bet if you looked closely at the evidence basis for that specific figure, it would be pretty weak.

Hi Jenny,

Thanks. I don't know much about that, but it seems like another potential reason to select the least processed food you can get.

glib said...

"The questions still remains; what is the optimal dose of red meat (per week)."

In my personal experience, it is of the order 5-6 ounces a day (less in summer), but it needs to be whole animal. Part of it is bone broth, animal skin, liver once a week (I do have problems with vit. A), and good amounts of coprophagous animals (rabbit), and some fatty fish. In practice I supplement with some grass fed gelatin and lots of lard (I made it from our pig last Fall).

tomR said...

Notice that in the history there was a confrontation between a fully agricultural population with "Starch solution" type economy; with mixed economy population - "the Corded Ware populations from Zerniki Gorne and Zlota (c. 4160-3900 BP) represent mixed, agricultural-breeding-pastoral economies supplemented with hunting and gathering."

The mixed economy culture won. Both health-wise, as well as militarily.

"Health status was examined through skeletal stress indicators, cribra orbitalia, enamel hypoplasia and Harris lines. The analysis of enamel hypoplasia showed the effect of different adaptive strategies on buffering adverse nutritional factors and diseases. The prevalence and severity of the condition proved significantly higher in the Lengyel sample than in the Corded Ware population (64.7% vs. 43.5%, respectively). "

As for the military otucome it looks like the agriculturalists were fully replaced, leaving no descendants.

Notice that in the article above the author uses word "invaders" for the Battle Axe mixed-economy people, and "locals" for the farmers but if you compare them to the original hunter-gatherer inhabitants of the territory they are reasonably closely related (while farmers are more from the South). It may be that they have just returned home...

Michael Cohn said...

Many thanks for this series, Stephan! Would you consider setting up a tag or a directory post for it? I keep wanting to point others to these posts, and it would be nice to have one link for all of them. Or is there already a tagging system that I'm missing?

Jenny said...

The most dangerous elements in processed meat are the inorganic phosphates. I began researching them originally because I knew they were very dangerous to people with kidney disease and that the amount or even presence of of phosphate does not need to be disclosed on labels.

But after some digging I found good quality research showing that inorganic phosphate intake correlates closely with heart disease as it appears to promote calcification. I also found evidence that people are taking in 2 to 3 times the safe level of phosphates eating processed foods.

Vegans and vegetarians are not spared this, as careful reading of labels finds these additives in many foods sold to them. Whole Foods is full of organic products where inorganic phosphates are added as an emulsifier.

Start reading labels looking for these additives and you will be surprised at how many places they turn up. And at how impossible it is to know what your daily total intake of them is.

karl said...

There is a huge difference between the mass produced meat in a grocery store and the meat that we ate before farming. For one, the increased content of PUFAs in the food chain has changed the meat. (PUFAs are selected for frost resistance - we now eat 5x more PUFA today than in 1960 - the positive health effects assumed fro PUFAs may be due to changes that negatively effect long term health. PUFAs are now suspected of messing with the insulin system - public policy was to support agriculture - not the public's health).

Vinayak said...

Can someone please tell me the exact definition of processed meat? I know hot dogs and pepperoni pizza contain processed meat. But how about KFC? Isn't that just chicken, fried?