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Is Substance Unhealthy? Purpose Iii

When nosotros consider the wellness impacts of eating meat, cardiovascular illness is the foremost affair that comes to mind.  Popular diet advocates oft conduct maintain diametrically opposed views on the occupation of meat inward cardiovascular disease.  Even alongside researchers as well as populace wellness officials, opinions vary.  In this post, I'll do my best to variety through the literature as well as decide what the weight of the evidence suggests.

Ancel Keys as well as the Seven Countries Study

Ancel Keys was i of the foremost researchers to contribute substantially to the study of the link betwixt diet as well as cardiovascular disease.  Sadly, at that spot is a lot of low-quality information circulating close Ancel Keys as well as his inquiry (1).  The truth is that Keys was a pioneering researcher who conducted some of the most impressive nutritional scientific discipline of his time.  The military machine "K ration" was designed past times Keys, much of what nosotros know close the physiology of starvation comes from his detailed studies during World War II, as well as he was the master Mediterranean Diet researcher.  Science marches on, as well as non all discoveries are buttressed past times additional research, but Keys' move was alongside the best of his solar daytime as well as must endure taken seriously.

One of Keys' earliest contributions to the study of diet as well as cardiovascular illness appeared inward an obscure 1953 newspaper titled "Atherosclerosis: Influenza A virus subtype H5N1 Problem inward Newer Public Health" (2).  This newspaper is worth reading if y'all acquire a jeopardy (freely available online if y'all poke precisely about a bit).  He presents a issue of dissimilar arguments as well as supporting data, most of which are widely accepted today, but i graph inward particular has remained controversial.  This graph shows the association betwixt total fatty intake as well as pump illness mortality inward half-dozen countries.  Keys collected the information from publicly available databases on global wellness as well as diet:


The graph shows that at that spot was a real strong positive correlation betwixt total fatty intake as well as reported pump illness mortality alongside the half-dozen countries Keys selected for his analysis.  Critics Yerushalmy as well as Hilleboe after pointed out that information for 22 countries were available at the fourth dimension of Keys' analysis.  When all 22 countries were considered together, the human relationship betwixt total fatty intake as well as pump illness mortality weakened but remained statistically important (3).

These data, alongside others, stimulated Keys to blueprint the most ambitious diet-heart study ever conducted at the time: the Seven Countries Study.  This study investigated the link betwixt diet, lifestyle, cardiovascular risk factors, as well as illness risk alongside sixteen populations inward seven countries.

Keys' diet assessment methods were extremely rigorous.  To decide the nutrient as well as nutrient intake of each population, for i calendar week his squad invited selected families to laid duplicate meals: i for themselves, as well as i for the study.  The extra meals were thence weighed as well as chemically analyzed to decide their nutritional characteristics.  This method is far to a greater extent than rigorous that the questionnaires used inward most observational studies today.

However, the study blueprint suffered from a critical weakness: Keys' squad used information from 20-50 people to extrapolate the average dietary intake of the population equally a whole, as well as these average population information are what they used for their analyses.  In other words, rather than comparison the dietary intake as well as cardiovascular risk of individuals, the Seven Countries Study compared the dietary intake as well as cardiovascular risk of populations.  This is called an ecological study and it's considered to endure a weaker study blueprint than the numerous individual-level observational studies that followed it.

What did Keys' squad find?  Here are some of their primary findings:
  • Circulating cholesterol was strongly correlated with cardiovascular risk.
  • Dietary saturated fatty intake was strongly correlated with circulating cholesterol.
  • Dietary saturated fatty intake was strongly correlated with cardiovascular risk.
  • Animal foods were the primary source of dietary saturated fat.
  • Meat intake, except fish, was correlated with cardiovascular risk, although that was mostly explained past times its saturated fatty content.
The graph below is from a 1970 newspaper detailing the human relationship betwixt saturated fatty consumption as well as 5-year risk of pump assail mortality alongside most of the populations of the Seven Countries Study (4):



This is a real strong correlation showing that populations that eat to a greater extent than saturated fatty receive got to a greater extent than pump attacks, as well as it was confirmed inward a 25-year follow-up study of the same populations (5).

The lowest cardiovascular risk occurred on the rural Greek isle of Crete, as well as a rural Japanese farming community at Tanushimaru.  At the offset of the study, both cultures ate starchy omnivorous diets relatively depression inward brute foods as well as high inward grains as well as potatoes (6).  The diet at Tanushimaru was real depression inward fat, whereas the Cretan diet was moderate inward fat, mostly from extra-virgin olive crude but also from dairy.  The diet of Crete was depression inward meat as well as fish but averaged close i loving cup of milk per solar daytime as well as three medium eggs per week.  The diet at Tanushimaru averaged 1/5 lb of fish per solar daytime as well as 2-3 medium eggs per week.  Both cultures consumed polyphenol-rich flora foods such equally extra-virgin olive crude as well as light-green tea, as well as exhibited the diverse lifestyle factors typical of non-industrial cultures (e.g., regular physical activity, Sun exposure, absence of processed foods, slower footstep of life).

Blue Zones

The diets of Crete as well as Tanushimaru are consistent with the diets of populations that alive inward so-called "Blue Zones"-- areas of notably depression cardiovascular illness risk as well as long natural lifespan (7).  Blue Zone populations typically eat meat, as well as oft dairy as well as eggs, inward little to moderate quantities (significantly less meat than is typical of affluent Western cultures).  There is i Blue Zone inward Loma Linda, California, that contains a high proportion of vegetarians, but the other populations all eat meat.  None of the Blue Zones are vegan.  The diets inward these areas are centered precisely about carbohydrate, as well as to a greater extent than oft than not, grains as well as legumes of some sort.  This doesn't seek out that their nutrient choices are optimal, but it does seek out that such diets are, at a minimum, compatible with wellness as well as long life inward the context of a to a greater extent than traditional lifestyle.

Non-industrialized Agriculturalists as well as Hunter-gatherers

The populations with the lowest documented cardiovascular risk are agricultural (and horticultural) cultures living a traditional lifestyle that resembles how our ancestors powerfulness receive got lived 5,000 years ago.  In an impressive pump autopsy study on thousands of subjects, Lee as well as colleagues determined that rural West Africans (Nigerians as well as Ugandans) inward the 1940s, 50s, as well as 60s were essentially immune to pump attacks, fifty-fifty inward quondam historic stream (8).  Their coronary arteries also exhibited less atherosclerosis than Americans, including African-Americans.  In the same study, urban Asians living inward Nippon as well as Korea had a lower charge per unit of measurement of pump attacks than Americans, but higher than Africans.  A issue of other studies receive got reported similar findings inward diverse traditionally-living agricultural/horticultural societies (91011, Trowell as well as Burkitt. Western Diseases. 1981).

These cultures tend to eat a starch-based omnivorous diet depression inward brute foods.  It's possible that the Nigerian as well as Ugandan samples may receive got included some pastoralists with a high intake of brute foods, but the vast bulk of people would receive got followed a starchy low-animal-food diet.  The dietary pattern inward these agricultural/horticultural cultures may non endure the only factor inward their resistance to pump attacks, but their diets are at to the lowest degree compatible with particular cardiovascular health.

We receive got much less information close traditional cultures that eat diets higher inward meat, for example, most hunter-gatherers.  The only autopsy studies nosotros receive got of hunter-gatherers were performed inward a few Inuit (Eskimo) individuals, as well as they suggest that these individuals tended to endure from advanced atherosclerosis but that no signs of pump assail are introduce (1213).  Atherosclerosis did non appear to interpret into a high pump assail risk inward semi-traditional Inuit populations that receive got been studied, suggesting that they may receive got somehow been protected from the consequences of their vascular illness (14).  In whatsoever case, the Inuit are belike non representative of hunter-gatherers inward full general because they ate extreme diets, lived inward an extreme environment, as well as inhaled a lot of indoor smoke.

Although nosotros don't receive got autopsy studies inward to a greater extent than typical hunter-gatherer cultures, nosotros do receive got some information close their cardiovascular health.  Hunter-gatherers invariably exhibit evidence of practiced cardiovascular health, including depression torso fatness, depression cholesterol, depression blood pressure level that doesn't ascension with age, as well as high physical fitness (15, Trowell as well as Burkitt. Western Diseases. 1981).  It would endure hard to imagine a high cardiovascular risk inward these populations that rely heavily on meat (16), but in i trial to a greater extent than nosotros receive got piddling straight evidence of this.

The Communist People's Republic of China Study

The Communist People's Republic of China Study was a massive ecological study relating diet as well as lifestyle to chronic illness risk inward China.  It has been invoked past times researcher as well as vegan diet advocate Colin Campbell to back upwards the thought that brute foods promote cardiovascular illness as well as cancer, fifty-fifty inward the little quantities that were typical of the regions studied.  After having reviewed the study data, the publications based on it, as well as the diverse commentaries on it, it appears relatively clear that the Communist People's Republic of China Study does non back upwards the determination that meat consumption is associated with cardiovascular illness or cancer risk (1718192021).  Everyone seems to concur on that, except Campbell as well as for sure other vegan diet advocates.  I won't hash out the Communist People's Republic of China Study further.

Modern Observational Studies

What do modern observational studies receive got to say close the human relationship betwixt meat intake as well as cardiovascular risk?  Overall, they pigment a substantially dissimilar pic than the Seven Countries Study.  Here is a summary of the weight of the evidence, equally I sympathise it:
  • Total meat, saturated fat, as well as dietary cholesterol intake typically exhibit piddling or no human relationship with circulating cholesterol, over 2-3 crease differences inward intake (22232425262728).  It remains unclear whether this reflects a lack of a long-term causal relationship, or limitations of the study methods.
  • Total saturated fatty intake is non associated with cardiovascular risk (29).
  • Intake of eggs as well as dairy (whether full-fat or reduced-fat) are non associated with cardiovascular risk (3031).
  • Intake of seafood is typically associated with reduced cardiovascular risk (32).
  • Intake of poultry is associated with neutral or reduced cardiovascular risk (33).
  • Intake of fresh blood-red meat is inconsistently associated with higher cardiovascular risk (3435), although meta-analyses suggest the effect size is small.
  • Intake of processed meat (e.g., hot dogs, bacon, salami) is typically associated with higher cardiovascular risk (36).
Because these findings are observational as well as most rely on relatively inaccurate nutrient questionnaire data, nosotros receive got to choose them with a grain of salt.  However, my agreement is that most epidemiologists would weight them to a greater extent than heavily than the Seven Countries Study, at to the lowest degree when it comes to deciding what nosotros should eat equally individuals.  If y'all are an epidemiologist as well as y'all disagree with that statement, delight portion your thoughts inward the comments.

The Harvard Healthy Eating Pyramid is based primarily on a synthesis of this observational evidence (37).  It recommends eating fish, poultry, eggs, as well as 1-2 servings per solar daytime of dairy, but advises limiting blood-red meat, processed meat, as well as butter.  Whole grains, flora oils, as well as vegetables/fruits cast the base of operations of the pyramid, as well as nuts, seeds, beans as well as tofu are recommended, especially equally an option to blood-red meat.  It's notable that the Healthy Eating Pyramid includes meat equally a staple food.

Do Vegetarians as well as Vegans Have Fewer Heart Attacks than Omnivores?

Overall, yes.  Although non all studies receive got supported this conclusion, the weight of the evidence suggests that vegetarians as well as vegans receive got a lower pump assail risk than omnivores (38).  Risk alongside lacto-ovo vegetarians, vegans, as well as seafood eaters appears similar all the same (39).  If nosotros assume for a minute that these associations reverberate crusade as well as effect, at that spot appears to endure piddling to gain from completely avoiding brute foods or fifty-fifty avoiding all types of meat.

Many Seventh-Day Adventists avoid eating meat for religious reasons, although they typically eat eggs as well as dairy.  There's a large population of SDAs inward California that researchers receive got studied extensively.  These studies demonstrate that SDAs receive got a substantially lower pump assail risk than the full general population, as well as SDAs that are vegetarian receive got a lower risk than SDAs inward the same community that eat meat (40).  Vegetarian SDAs are also noted for their longevity.

Studies of vegetarians as well as vegans aren't piece of cake to interpret, however.  Vegetarians as well as vegans differ from the full general population inward many ways likewise meat avoidance, as well as this is especially truthful of SDAs.  These populations tend to endure to a greater extent than health-conscious as well as receive got overall healthier lifestyle behaviors.  Can nosotros decide how much of their cardiovascular payoff is due to meat avoidance, as well as how much is due to factors unrelated to meat?

The Health Food Shoppers Study attempted to tease this out.  This Great Britain study recruited vegetarians as well as omnivores from wellness nutrient stores as well as vegetarian societies as well as magazines-- ensuring that both groups were composed of health-conscious people.  After 17 years of follow-up, the results showed no statistically important divergence inward total mortality, pump attacks, or stroke betwixt vegetarians as well as non-vegetarians, although at that spot was a tendency toward lower pump assail risk for vegetarians (41).  

Overall, the evidence suggests that factors other than meat avoidance concern human relationship for at to the lowest degree some of the cardiovascular do goodness associated with vegetarian as well as vegan diets.  However, at that spot may soundless endure some cardiovascular do goodness from avoiding meat, as well as this would endure consistent with the LDL-lowering effect of meat avoidance (discussed below).  The observational evidence does non appear to back upwards the thought that avoiding seafood, dairy, or eggs reduces cardiovascular risk.

Vegan Diet Interventions for Cardiovascular Disease

Dean Ornish, Caldwell Esselstyn, John McDougall, as well as others receive got used vegan or near-vegan diets equally portion of a diet, lifestyle, and/or drug strategy to cut back cardiovascular illness risk inward high-risk patients.  Some of them receive got published studies (424344).  These studies vary inward quality, but overall they do suggest that these diet/lifestyle/drug strategies may indeed endure effective for reducing cardiovascular risk inward high-risk patients (typically, people who receive got had a pump assail or receive got been diagnosed with severe cardiovascular disease).  They are belike to a greater extent than effective than conventional medical therapy.

However, it's hard to know what seem of the intervention is responsible for the cardiovascular benefits.  Ornish's intervention, for example, involves a comprehensive diet overhaul including reducing fatty intake, avoiding processed food, focusing on minimally refined foods, as well as increasing vegetable intake.  The intervention also includes smoking cessation, regular exercise, as well as stress reduction.  Esselstyn's intervention is non quite vegan but it excludes nearly all dietary fatty as well as includes lipid-lowering statins for patients who aren't able to consider stringent blood lipid goals through diet alone.

What occupation does meat avoidance play inward these results?  Are patients benefiting from reducing their intake of processed as well as high-heat cooked meat?  Are patients benefiting from reducing their intake of blood-red meat?  Are patients benefiting from reducing their intake of all types of meat?  There are a lot of remaining questions here, as well as these studies are non able to respond them.

It is plausible that brute nutrient avoidance could play some occupation inward the therapeutic effect of these diet as well as lifestyle strategies, but the studies don't allow us to come upwards to that conclusion.  There are too many confounding factors.  It would endure informative to study the effectiveness of these interventions with or without added meat.

Animal Studies as well as Possible Mechanisms

Beginning with the pioneering studies of Nikolay Anichkov inward the early on 1900s, researchers receive got long known that high levels of dietary cholesterol tin forcefulness out chop-chop promote cardiovascular illness inward for sure animals.  Dietary cholesterol inward the human diet comes solely from brute foods, with egg yolks existence the most concentrated source, thence dietary cholesterol is an obvious suspect inward the possible link betwixt brute foods as well as cardiovascular disease.

These artery-clogging high-cholesterol experimental diets by as well as large crusade massive 3-10-fold increases inward circulating cholesterol inward brute models, which is hard to compare to the human situation.  Humans only consider little increases inward circulating cholesterol when nosotros eat dietary cholesterol, as well as the increment typically occurs inward both "bad" LDL as well as "good" HDL* (45).  Most humans seem to endure able to conduct maintain normal amounts of dietary cholesterol efficiently, which substantially weakens the likelihood of a meaningful link betwixt dietary cholesterol as well as cardiovascular disease.  However, inward a minority of people, dietary cholesterol has a larger effect on circulating cholesterol, as well as could play a larger occupation inward cardiovascular risk.

Saturated fatty is some other possible link betwixt brute nutrient consumption as well as cardiovascular risk.  In typical Western diets, most saturated fatty comes from brute foods.  Saturated fatty feeding tin forcefulness out exacerbate the comport upon of high-cholesterol diets on circulating cholesterol as well as cardiovascular impairment inward brute models, at to the lowest degree when compared with polyunsaturated fatty (the latter of which has a cholesterol-lowering effect).  However, when animals are non overfed cholesterol, saturated fatty feeding per se doesn't enhance circulating cholesterol when compared with monounsaturated fatty (as inward olive oil), thence I'm non for sure to what extent saturated fatty itself is responsible (4647).

In humans, many trials receive got shown that short-term saturated fatty feeding increases circulating cholesterol.  This increment occurs inward both the LDL as well as the HDL fraction, although the increment inward LDL is oft somewhat greater than the increment inward HDL (48).  However, the fact that observational studies typically honor piddling or no correlation betwixt habitual long-term saturated fatty intake as well as circulating cholesterol (or cardiovascular risk) makes me wonder how durable these effects are (49).  Longer-term randomized controlled trials also oft exhibit piddling or no comport upon of 2-3-fold differences inward saturated fatty intake on circulating cholesterol, equally long equally other relevant dietary components including linoleic acid (n6 PUFA) as well as fiber are kept relatively constant (50).  Research is ongoing, but I'm non currently convinced that this machinery plays a major occupation inward cardiovascular disease.

High levels of brute poly peptide (from meat or dairy) tin forcefulness out increment LDL cholesterol as well as aggravate cardiovascular illness inward for sure brute models, patch flora poly peptide is oft protective (51).  This appears to endure due to the amino acid composition of brute vs. flora poly peptide (lysine-to-arginine ratio), as well as the phytochemicals as well as fiber associated with flora protein.  Certain flora proteins, such equally soy, also tend to lower LDL cholesterol inward humans, especially when they supercede brute poly peptide (5253).  This belike goes a long means toward explaining the LDL-lowering effect of vegetarian as well as especially vegan diets, as well as it is consistent with a protective cardiovascular effect.

Another potential machinery for harmful effects of meat is the compounds that are produced during high-heat cooking.  Some of these may endure carcinogenic as well as contribute to cardiovascular illness (54).  We powerfulness endure improve off focusing on low-heat-cooked meat rather than grilled, browned, roasted, or fried meats-- but this also applies to flora foods.

Red meat is real high inward iron, which some researchers receive got proposed could compromise cardiovascular health.  Free (unbound) atomic issue 26 is especially practiced at catalyzing powerful complimentary radical reactions that impairment surrounding molecules.  While atomic issue 26 is an essential nutrient as well as high-iron foods tin forcefulness out endure especially beneficial for pre-menopausal women, many men as well as post-menopausal women may acquire too much dietary iron.  Personally I retrieve excess dietary atomic issue 26 is belike detrimental to overall health, but the evidence is non currently real convincing that torso atomic issue 26 condition plays a major occupation inward cardiovascular wellness inward particular (5556).  The instance isn't unopen yet.

Sialic acids are unique sugars that are used equally edifice blocks for for sure classes of molecules inward the body.  Over the course of didactics of evolution, humans receive got lost the powerfulness to hit a particular sialic acid called Neu5gc.  However, nosotros absorb it from brute foods, especially blood-red meat, as well as it is incorporated into our (glyco)proteins as well as other molecules.  The human torso recognizes it equally unusual as well as produces antibodies against it.  Some researchers receive got proposed that the immune reaction that the torso mounts toward Neu5gc from meat causes inflammation as well as contributes to illness risk (57).  Although the newspaper introducing this machinery made a large splash when it was foremost published, to my noesis the finding hasn't been followed upwards sufficiently to brand a compelling instance that Neu5gc genuinely contributes to human disease.  Perhaps futurity inquiry volition clarify that.

There are many scary-sounding mechanisms past times which meat intake could potentially contribute to disease.  However, I'd similar to quest out that y'all tin forcefulness out honor something incorrect with whatsoever nutrient if y'all hold back hard enough.  Melissa McEwen illustrated this good inward her satire slice "Just Kale Me".  Mechanisms are relevant, but they only serve to explicate or bolster demonstrated effects.  For example, if poultry consumption doesn't genuinely increment cardiovascular risk, there's no quest earthworks precisely about for mechanisms.  When they receive got been identified, mechanisms tin forcefulness out increment our confidence inward an empirically demonstrated effect on health.

Synthesis as well as Conclusion

There is a lot of evidence nosotros tin forcefulness out choose to comport on this question, as well as non all of it is consistent.  This inconsistency is why nosotros consider dissimilar groups interpreting the inquiry inward contrary ways.

Here is my best endeavour to synthesize the overall evidence, equally I consider it.  Vegetarian as well as vegan diets belike do cut back cardiovascular illness risk, consistent with the LDL-lowering effect of replacing meat with flora protein.  However, the risk reduction afforded past times avoiding meat per se appears modest (as opposed to living the whole lifestyle of a vegetarian or vegan), as well as nosotros receive got no examples of salubrious vegan cultures.  There is piddling evidence that poultry or seafood promote cardiovascular disease, as well as some evidence suggesting that seafood is genuinely protective.  Although the evidence on blood-red meat isn't real consistent, as well as nosotros postulate to a greater extent than as well as improve research, it's belike prudent to continue intake modest for now.  It's belike a practiced thought to bound processed meat intake equally good (attn LCers as well as Paleos: bacon).

For people at high cardiovascular risk, it may endure useful to supercede some brute poly peptide with flora poly peptide such equally beans as well as nuts, as well as focus meat intake on seafood as well as poultry.  Randomized controlled trials such equally the Oslo Diet-Heart study receive got supported the powerfulness of similar dietary patterns to cut back cardiovascular risk (58).

The ideal strategy would also contain other factors that are relevant to cardiovascular risk, such equally controlling torso fatness, eating potassium- as well as polyphenol-rich fruit as well as vegetables, focusing on unrefined food, exercising regularly, avoiding prolonged sitting, managing stress, avoiding cigarette smoking, as well as working with a doc to monitor as well as maybe command blood pressure level as well as lipids.

So, does eating meat increment cardiovascular risk?  Yes!  And no!

In the side past times side post, we'll examine the comport upon of meat consumption on obesity risk.


* Nuance: nosotros know that people with high HDL cholesterol receive got fewer pump attacks, but nosotros soundless don't know whether a diet-induced increment inward HDL cholesterol is genuinely protective.  Recent drug trials receive got shown that using drugs to but pack to a greater extent than cholesterol into HDL particles does non cut back cardiovascular risk inward humans, as well as it may fifty-fifty increment risk.  This demonstrates that the protective portion of the HDL particle is non e'er associated with its cholesterol content.  We soundless receive got a lot to larn close why high HDL cholesterol is associated with cardiovascular protection inward humans, as well as what diet/lifestyle factors influence its protective actions.
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