Friday, February 13, 2015

Is Meat Unhealthy? Part VIII

Health can be defined as the absence of disease, and that is the lens through which we've been examining meat so far.  However, most of us have a broader view of health that also includes optimal growth and development, physical and mental performance, well-being, fertility, immunity, robustness, and resilience.  What role does meat play in this broader view of health?

Non-industrial cultures

One of the things I keep coming back to in this series is the strong natural affinity that our species has for meat.  Every culture that does not prohibit meat consumption for religious reasons (e.g., Indian Hindus) seeks and eats meat avidly.

A key fact that stands out from my recent conversations with anthropologists is that hunter-gatherers and subsistence agriculturalists place a high value on meat, even if they already have regular access to it.  Here's an excerpt from a paper by Kim Hill, Magdalena Hurtado, and colleagues (1):
Observations of the exchange rate between other foragers and their agricultural neighbors indicate that meat is worth much more than carbohydrate calories (e.g., Hart 1978; Peterson 1981). Hart, in his study of exchanges of meat and casava between Pygmy foragers and neighboring agriculturalists, found that approximately four and one half times as many calories of casava were exchanged for each calorie of meat given. In addition, it appears that almost everywhere in the world meat calories from domestic animals are probably expensive to produce relative to plant calories, and yet subsistence farmers continue to use at least some of their "cheap" plant calories to produce "expensive" animal calories (see Harris 1985 for discussion)
Why do humans around the globe value meat so much?  This strongly suggests that we've evolved an affinity for meat because eating it provides a reproductive advantage.  In other words, meat may increase our "Darwinian fitness".


Susceptibility to chronic disease plays a part in Darwinian fitness, but it's not the whole story.  The other factors I mentioned in the introduction, including optimal growth and development, physical and mental performance, well-being, fertility, robustness, and resilience, also play key roles.  Is there any evidence that meat provides an advantage in these other facets of Darwinian fitness?

Growth

Growth and development are processes that demand a lot of energy and nutrients.  If a diet provides insufficient energy or nutrients, it often results in stunted growth.  Do vegetarian and vegan diets support optimal growth?  Height is a simple, objective measure of growth that we can use to explore this question.

I think the macrobiotic diet is a good place to start, because in many ways it's a distillation of what many would consider to be the ultimate healthy diet.  It's a vegan diet that's based primarily on brown rice, with lots of vegetables, soy, and some fruit.  Macrobiotic children are often deficient in multiple important nutrients and they do not grow as tall as their omnivorous peers (2, 3, 4).  The following quote from a study on macrobiotic children is instructive:
This follow-up study revealed that children from families which, since the initial study, had increased the consumption of fatty fish, dairy products, or both, had grown in height more rapidly than the remaining children (P less than 0.05). Since no indications were found for the presence of adverse social circumstances, infectious diseases or other confounding factors, our data clearly demonstrate that linear growth retardation in children on macrobiotic diets is caused by nutritional deficiencies alone.
These people are not going to develop cardiovascular disease, obesity, or diabetes on the macrobiotic diet.  Yet they exhibit "growth retardation" that is readily corrected by meat and/or dairy.  Does this qualify as a healthy diet?

The macrobiotic diet is a more restrictive version of the vegan diet, and there are certainly more nutritious ways to be vegan.  There is some evidence that non-macrobiotic vegan children tend to be a bit shorter than their omnivorous peers, but the studies have not all been consistent (5, 6, 7).  Vegetarian children tend to be similar in stature to omnivorous children (8, 9, 10).

One of the most informative studies was conducted on schoolchildren in Kenya, in an area where the diet normally contains little animal food (11, 12).  Supplementing the diet with meat increased cognitive development, academic performance, muscularity, and high-intensity physical activity.  Milk supplementation had some of the same effects, and also increased height in younger and stunted children.  Feeding additional fat also improved development somewhat, but not to the same extent as meat, suggesting that meat was not acting exclusively via added calories.

Well-planned vegetarian and vegan diets seem to support linear growth relatively well.  However, vegan diets may slightly restrain linear growth, and more restrictive vegan diets such as the macrobiotic diet often lead to more serious stunting.  A diet that includes animal foods probably offers a child the best chance of achieving his or her maximum physical and cognitive potential.

Fertility

Fertility is a good marker of a diet's overall calorie and nutrient adequacy.  This is particularly true of women, for whom reproduction is a costly endeavor.

Although the findings remain controversial, several observational studies have found a higher prevalence of menstrual problems among vegan and vegetarian women (13, 14, 15).  In some studies, the difference was quite large (e.g., 5% vs 20%).

A small randomized, controlled trial published in 1986 supports a link between meat and fertility (16).  Women were randomized to a vegetarian or an omnivorous diet for six weeks.  By the end of the study, seven of nine vegetarian women had ceased to ovulate, while only one of nine omnivorous women had done the same.

What about men?  A recent small study suggested that vegan and vegetarian men have lower sperm concentrations, and lower sperm motility than omnivorous men (17).  This study was performed on California Seventh-Day Adventists-- one of the super-healthy "Blue Zone" populations.  Does this mean they may be less healthy than we thought?  This finding still needs to go through peer review, be formally published in more detail, and be independently replicated.

The evidence suggests that vegan and vegetarian diets may impair fertility, making it easy to speculate why natural selection has produced a meat-loving species.

Immunity

I wasn't able to find much information on immune function of omnivores vs. vegetarians and vegans.  One study found that vegans have lower concentrations of certain circulating immune cells, but that their functional immune capacity is similar to omnivores (18).

In a follow-up to the study in Kenyan schoolchildren mentioned above, meat supplementation reduced the probability of falling ill from infectious disease (19).  However, calorie supplementation seemed to have a similar effect, so the benefit may not be attributable to meat per se.

Overall, I don't think this provides evidence that vegetarians or vegans have poorer immune function than omnivores.  I'm going to have to invoke the old truism that more research is required.

Athletic performance

Now we arrive at a topic that is much more thoroughly researched.  Most of the meat we eat is muscle tissue-- precisely the tissue that is most stressed during physical activity.  It stands to reason that eating muscle tissue might support the growth and maintenance of a person's own muscle tissue, and this seems to be the case.

A joint position statement titled "Nutrition and Athletic Performance" by the American Dietetic Association, the Dietitians of Canada, and the American College of Sports Medicine states that "well-planned vegetarian diets appear to effectively support parameters that influence athletic performance, although studies on this population are limited" (20).  They go on to point out a number of potential nutritional problems that face vegetarian and vegan athletes.  These include iron deficiency or insufficiency, inadequate intake of zinc, protein (particularly the amino acids lysine, threonine, tryptophan, and methionine), B12, riboflavin, vitamin D, calcium, and calories.  They note that these nutrients are "readily available from animal proteins".

I'll add that vegetarians and vegans have lower levels of muscle creatine, a non-essential nutrient that is supplied by meat and contributes to strength and power performance (21, 22, 23).  When vegetarians are supplemented with creatine during a strength training routine, their strength increases more than supplemented omnivores, suggesting that a vegetarian diet impairs strength potential.

Most studies, both observational and intervention, have not found any link between meat consumption and performance in endurance/cardiorespiratory activities, although there are a few isolated studies that found that omnivores or vegetarians perform better (24, 25, 26, 27, 28, 29, 30).

In contrast, most observational and intervention studies show that omnivores out-perform vegetarians in strength/power activities (31, 32, 33, 34).  One study also suggested that omnivores recover better than vegetarians (35).

Two studies are worth highlighting.

Campbell and colleagues assigned older men to omnivorous or lacto-ovo-vegetarian diets and observed each diet's impact on the response to 12 weeks of resistance training (36).  The omnivorous group experienced a significant increase in muscle mass and a decline in fat mass, while the vegetarian group experienced a decline in lean mass and an increase in fat mass.  Strength gains tended to be higher in the omnivorous group, but the differences were not statistically significant.

Neumann and colleagues supplemented the diets of Kenyan children with meat, and found that it increased their muscularity and tendency to engage in high-intensity physical activity, when compared to a fat supplement or no diet supplementation (37).

My impression is that vegetarianism is not a catastrophe for the casual athlete.  The differences in performance are modest, and may not be present at all for endurance activities.  However, meat does seem to increase muscularity and offer a performance advantage for activities that demand strength and power.  It may also be more important for high-level athletes who place major demands on their bodies.  Although we have very little data on vegans, I suspect these differences would be further exaggerated.

It's telling that nearly all elite athletes eat meat.  There are a few notable exceptions, however on the whole, vegetarian and particularly vegan diets are unpopular among elite athletes.  This is less true among endurance athletes, and more true among strength and power athletes.

From an evolutionary perspective, a stronger, more muscular person would be more capable of defending him/herself and seeking food, providing another possible reason why natural selection has produced a meat-loving species.

Possible mechanisms

I'm not going to go into great detail about what specific nutrients could be responsible for the differences I detailed above, because I don't think it's necessary.  I'm simply going to focus on one simple, key point: an omnivorous diet is the easiest way to supply all essential nutrients in optimal quantities.  The further one gets from an omnivorous diet, the more difficult it becomes to be optimally nourished.  The less well nourished a person becomes, the less well that person's body will perform.

There is an overwhelming amount of evidence demonstrating that vegetarian, and particularly vegan diets, are associated with a higher risk of specific nutrient deficiencies:
  • Vitamin B12 is only found in animal foods.  Vegans must supplement B12 to avoid the debilitating long-term consequences of B12 deficiency.  Vegetarians have a higher prevalence of B12 deficiency than omnivores, and vegans have a higher prevalence of B12 deficiency than vegetarians.  B12 deficiency is linked to poor cognitive development (38).
  • Macrobiotic vegan diets are associated with a long list of vitamin and mineral deficiencies, and this often manifests as a failure to thrive in infants and children.  
  • Zinc status is best in omnivores, intermediate in vegetarians, and worst in vegans (39).  
  • Iron deficiency is extremely common among vegetarians and vegans (40, 41, 42), even though iron intake appears adequate.  
It's no coincidence that meat is a rich source of the nutrients that vegetarians and vegans tend to be deficient in.  In many cases (e.g., zinc and iron), vegetarian and vegan diets appear nutritionally adequate on paper, but when blood or saliva is analyzed, vegetarians and vegans are often deficient.  This is because many of the minerals in certain plant foods are poorly absorbed (due to anti-nutrients such as phytic acid, and a lack of heme iron).  These differences in nutrient absorption aren't reflected on nutrition labels or typical online nutrition databases, which means that many conscientious, knowledgeable people think they're eating a nutritionally adequate diet when in fact they are not.

Another issue is calories and protein.  A typical diverse, omnivorous diet is richer in both calories and high-quality protein than a typical vegetarian or vegan diet.  That can be good or bad, depending on who you are.  However, when it comes to reproduction, (up to a point) calories and protein are important.  Body fat is the primary signal that tells the female body it's competent to reproduce, and vegetarians and vegans tend to be leaner than omnivores.  When body fat drops too low, leptin levels decline, and that tells the brain to shut down ovulation.  Of course, the flip side is that too many calories can lead to obesity, which can reduce fertility.

Synthesis and conclusion

Humans around the globe have a strong natural affinity for meat, and this suggests the possibility that meat plays an important role in our reproductive success or Darwinian fitness.  In fact, there is good evidence that meat does support aspects of physical function that would have been critical for survival and reproduction in an ancestral environment.

These things may not be as critical today, particularly in an era of B12 supplements, and many vegetarians and vegans successfully have children and perform at a high level in life.  However, an omnivorous diet does seem to offer the best shot at maximizing a person's physical and cognitive development, fertility, and physical performance throughout the life cycle.  For these reasons, I would argue that meat plays an important role in health.


12 comments:

Hafthor Bjornssen said...

Hi Stephan, :)

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.

It is interesting to note that Usain Bolt ate nothing but Chicken McNuggets during his record breaking performance in the 100 and 200 meter races. That was his go to food. LOL ! He swears by them.

I also know that Michael Jordan, before games, ate potatoes steak and eggs. He said it on camera and in an article somewhere. I wish i could still find the video. That was part of his pregame ritual, along with wearing his North Carolina University shorts during warm-ups. :)

These two athletically supreme humans are some of the best athletes human kind has known. I believe Jordan's vertical jump was 48 inches ! Plus that unmatched hang time. O.M.G. Athletically, I 'd put a YOUNG Michael against ANYBODY who ever played in the NBA.

Meat did not hurt these guys, and athletically speaking, there is nobody in the entire Blogoshpere who could match Jordan or Bolt head to head athletically- even the gurus with the aesthetically pleasing physiques etc. The above world-class athletes were all about performance. Looks were secondary. The fruitarians , vegans etc. should take note.

Meat was a big part of both of their diets, but to be fair, so were carbs. This is especially true in Jordan's case, as he mentioned he ate pancakes true and cereal for breakfast sometimes before practices and working out.

Take care,
Razz

pawpaw said...

As a beef producer, venison and pork eater, this series is welcome news. There are customers at our market who refuse to eat red meat. In your literature search, did you find any hints of differences between types of meat?

Tam said...

I've enjoyed this series quite a bit.

I've been trying to follow a pescetarian diet for a few months now, for ethical reasons, and although I haven't found it difficult, it does have some unintended side effects.

I eat much less fish than I used to eat meat, which is fine, but for me a bad effect of not eating (most) meat is that the food I make at home is no longer palatable enough for me to be willing to eat it.

For example, I often make some pasta for the week (something like whole wheat macaroni, sauce from a jar, plus beans or clams, served with some parmesan cheese), but putting beans or clams in my pasta means it's not very good. Pasta without any added protein doesn't seem like a complete meal. When I used to put ground turkey in it, it was delicious and I was motivated to cook it and then eat it over the course of the week.

That's just one example.

In theory I should eat less palatable food anyway, but in reality, I live in a hyperpalatable food paradise and if my food at home isn't good enough I can easily get fried rice or pizza or a filet o' fish at McDonald's instead. And I know vegetarian food can be just as delicious as food with meat, but making it that way requires more effort than I'm willing to put into cooking (which I don't enjoy at all). So I've been eating out a lot more, which definitely negates any health benefits of removing meat from the diet (if there were any).

Based on my observations and common sense, I think eating food made at home (even with some convenience items like soups, pasta sauce from a jar, canned vegetables, and so on) vs. eating out is a huge factor in the health of the diet. At home we don't usually put a whole stick of butter into a sauce, or inject meats with flavorants, or have food scientists optimize the palatability of our diet, and we usually do think to include some kind of vegetable. Still, most people aren't willing to eat a totally bland diet, and many people don't have the time and/or energy to cook good-tasting vegetarian food. So I wonder if the inclusion of meat can improve the diet in that way - by making it really simple to make foods that are moderately palatable. Something like baked chicken, rice, and a vegetable is really delicious and easy. I don't know.

I've also been low-grade sick for weeks now (cold, sinus infections, ear infection, etc.) after going years hardly ever being sick. It's probably not related to the change in diet, but I'm not sure.

Sunny said...

Stephan I appreciate this thoughtful and considered analysis.

I 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!

For me, the mists are clearing: much as I would aspire to a 100% plant based diet, for spiritual/intellectual reasons and have been frightened by the research conclusions of the plant based community; much of our dabbling is very recent relative to our evolutionary biological history.

Small/moderate amounts of high quality animal foods would appear to be a judicious addition to diet.

Now, if you could clear up the confusion around dairy, that would be superb.

Its voguish among some raw vegans/natural hygienists as well as the paleo/primal contingent to include raw dairy for the fat soluble vits - those which are certainly unavailable in plant foods.

Thank you for sharing and illuminating the conversation.

Chuck Steak said...

I think fertility is above all linked to adequate glucose intake. There are plenty of men and women on Atkins/low carb or Paleo who are neither deficient in calories nor protein but experience loss of libido, erectile dysfunction and disrupted/halted menstruation.

@Hafthor: don't look at Usain Bolt or Michael Jordan, they are genetic freaks like Wolverine and Cyclops. They are naturally born elite athletes, and their bodies can handle much more junk that us mortals. Also, that chicken nugget thing was probably a cheat day, or a pre-competition calorie blowout, not his actual daily diet. Bolt actually eats a lot of carbs, fried plantains for breakfast and rice and Jamaican yellow yams throughout the day. Yohan Blake, another up and coming Jamaican sprinter, eats 16 ripe bananas a day. Yes, 16.

glib said...

We eat meat because our guts have gone from 30 meters long, when we were chimps, to 7.5 meters now. We can not ferment our food as we used to, and in the process we lost our endogenous source of B12 and K2. Meat is from some other fermentation vat (some other animal), plus it has the advantages Stephan lists: available iron, zinc concentration in ruminants, collagen and fat. If you want more B12 (and probably more K2) with less meat, eat rabbit or other coprophagous animal (such as fly larvae).

1977ub said...

Hi Stephen, was this meant to be ironic? Or is there sourcing? Thank you.

"These people are not going to develop cardiovascular disease, obesity, or diabetes on the macrobiotic diet."

Stephan Guyenet said...

Hi Sunny,

Thanks. I agree with your conclusions. Maybe I'll tackle dairy someday, who knows. Pedro Bastos has looked into milk quite deeply, mostly its potential downsides. This series has been a bear so my next few posts will be more self-indulgent: tinkering/DIY, gardening.

Hi 1977ub,

Not ironic at all. People on macrobiotic diets have body weights and lipid profiles consistent with low CVD, obesity, and diabetes risk. If you look at the (limited) data from very-low-fat high-starch vegan diet interventions cited in previous posts, you see reduced cardiovascular events, reduced body weight, and improved glycemic control.

I'd have to see some pretty strong evidence to convince me that the macrobiotic diet promotes CVD, obesity, or diabetes.

glib said...

These generic meat studies are nearly unusable. They should be sliced and diced as follows

- optimal diets for young and old (more methionine, more glycine)

- CAFO meat versus pastured/homegrown

- lean cuts vs fatty/gelatinous cuts and offal (includes bone broth)

- cured vs fresh

I can even agree that a diet consisting of cured meats, and lean CAFO meats (excess methionine, low fat) is sub-optimal. But what of a pastured, high-fat, high-gelatin, high-offal, 200 grams or less per day, diet? The top two Blue Zone tribes say it is very healthy indeed. And at the macro level, we only need gelatin and fat from meat.

Will Hui said...

Hi Stephan,

When you wrote, "In many cases (e.g., zinc and iron), vegetarian and vegan diets appear nutritionally adequate on paper, but when blood or saliva is analyzed, vegetarians and vegans are often deficient," did you have any particular research papers in mind? Or is this just a casual observation based on the stories of ex-vegetarians/ex-vegans?

I ask because I have often wondered the same thing, but I don't know of any actual research that corroborates this one way or the other. I recall reading somewhere that average nutrient bioavailability across food sources is supposed to be factored in to the RDAs.

mactheweb said...

Stephen, I've read your meat articles several times and appreciate your thoughtful analysis of meat eating. As one who was an avid rock climber and mountaineer, I have always been interested in getting stronger. I thought that I ate well and consumed a lot of meat.

Now, in my 60s and facing blocked arteries, I've followed a whole food plant based diet and have seen dramatic lowering of blood pressure and all my cholesterol levels. Inflammation from arthritis has dropped to a level that I no longer use NSAIDS and have canceled a knee replacement. (pounding down mountains with a heavy pack takes a toll) I tried Paleo but saw no relief from the inflammation, though it did help my cholesterol levels, albiet not as much as a whole food plant based diet. I emphasize the whole food part as well as eating a wide range of veggies.

I wonder if the quest for larger and stronger muscles leads us to eating something that will come back to haunt us in the long term. I also wonder what your opinions on this subject will be in 30 years.

I also wonder if there have been any controlled studies comparing whole food plant based diets with Paleo diets that contain a large portion of vegetables. I understand that my personal experience is idiosyncratic.

Stephan Guyenet said...

Hi mactheweb,

Thanks for sharing your experience. It sounds like you've found a way of eating that works well for you.

It's possible that there are tradeoffs between what maximizes vigor in youth and what maximizes long-term health and survival. There are rodent studies suggesting that high-protein diets create such a tradeoff. Low-protein, high-carb diets cause mice to be smaller, less fertile and less athletic, but they live longer and healthier. Whether this would apply to the complex world of humans remains an open question. The problem is that it's impractical to conduct controlled studies that last decades. All the long-term evidence we have is observational, which has such serious pitfalls that it has to be viewed skeptically.

One of the complexities to consider is that high-protein diets can help people maintain a healthy weight, which has an important impact on long-term health. Protein is one of the most effective tools in the fat loss toolbox.

Regarding RCTs that compare a whole food plant-based diet vs. Paleo, none have been conducted yet. All of the studies looking at these two diets have been too short to assess long-term impacts.