Are humans meant to be omnivores?

Are humans meant to be omnivores?

Does the ideal human diet include animal products like meat, fish, cheese, eggs, and dairy products?

Or should the ideal diet be devoid of all animal products?a vegetarian diet?

Though the argument is distorted by modern food processing methods (e.g., factory farming, long-term administration of antibiotics), convenience foods, and pseudo-foods crafted by food manufacturers, there are, obviously, proponents of both extremes.

The Atkins’ diet, for instance, advocates unrestricted intake of animal products, regardless of production methods or curing (sausage and bacon). At the opposite extreme are diets like Ornish (Dr. Dean Ornish’s Program for Reversal of Heart Disease) and the experiences of Dr. Colin Campbell, articulated in his studies and book, The China Study, in which he lambasts animal products, including dairy, as triggers for cancer and heart disease.

So which end of the spectrum is correct? Or ideal?

For the sake of argument, let's put aside philosophical questions (like not wanting eat animal products because of aversion to killing any living being) or ethical concerns (inhumane treatment of farm animals, cruel slaughtering practices, etc.). Does the inclusion of animal products provide advantage? Disadvantage?

The traditional argument against animal products has been saturated fat. If we accept that we’ve demoted the saturated fat question to a place far down the list of importance (though this is yet another argument to discuss another time), several questions emerge:

• If humans were meant to be vegetarian, why do omega-3 fatty acids (mostly from wild game and fish) yield such substantial health benefits, including dramatic reduction in sudden death from heart disease?

• Why would vitamin K2 (from meats and milk, as well as fermented foods like natto and cheese), obtainable in only the tiniest amounts on a vegetarian diet, provide such significant benefits on bone and cardiovascular health?

• Why would vitamin B12 (from meats) be necessary to maintain a normal blood count, prevent anemia, keep homocysteine at bay, and lead to profound neurologic dysfunction when deficient?

Omega-3 fatty acids and vitamins K2 and B12 cannot be obtained in satisfactory quantities from a pure vegetarian diet. The consequences of deficiency are not measured in decades, but in a few years. The conclusion is unavoidable: Evolutionarily, humans are meant to consume at least some foods from animal sources.

That's not to say that we should gorge ourselves on animal products. Gout (excessive uric acid) and kidney stones are among the unhealthy consequences of excessive quantities of meats in our diets.

It pains me to say this, since I’ve always favored a vegetarian lifestyle, mostly because of philosophical concerns, as well as worries about the safety of our factory farm-raised livestock and rampant inhumane practices.

But, stepping back and objectively examining what nutritional approach appears to stack the odds in favor of optimal health, I believe that only one conclusion is possible: Humans are meant to be omnivorous, meant to consume some quantity of animal products in addition to vegetables, fruits, nuts, and other non-animal products.

The question is how much?

Comments (24) -

  • Francis

    9/28/2008 4:55:00 PM |

    From the title I thought the debate would have been omnivore vs carnivore instead of omnivore vs vegetarian. Any solid arguments against a carnivorous lifestyle?

  • GK

    9/28/2008 6:21:00 PM |

    Hm, fingering meat as a cause of gout again?  Peter's Hyperlipid blog had some fairly convincing arguments that fructose may be worse.  See and


  • Jeremy

    9/28/2008 9:09:00 PM |

    The comment about gout is not true. Loren Cordain, author of the Paleo Diet, has reviewed the literature on gout in his Paleo Diet Newsletter, Volume 2, Number 4.

    The back issues of the newsletter are products you must pay for, so I won't discuss the contents in extreme detail. But he argues the body adjusts uric acid execretion in response to purine intake. Meanwhile, he cites studies showing fructose and alcohol for increase uric acid levels in the body.

    He cites a study where a high-protein diet relieved gout in 7 out of 12 patients!


  • rabagley

    9/28/2008 10:24:00 PM |

    Personally, I find the analysis of the paleolithic diet to be most compelling.  In that analysis, we were almost entirely meat eaters, with the occasional smattering of vegetables, fruits, nuts, etc.

    There have been several indigenous cultures, both modern (Masai) and in recent history (Inuit) that lived long and healthy lives almost entirely free of diseases like diabetes or heart disease while eating almost 100% animal products.  I refer to the Inuit as "recent history" because their modern diet only rarely resembles their historical (and much healthier) diet of seal and whale fat and meat.

    After reading "Good Calories, Bad Calories", I'm convinced of the merits of the position that humans are non-obligate carnivores.  We can fall back to non-animal foods if absolutely necessary, but it's a bigger compromise to our health the farther you go.

    I do agree that the biggest problem with being a modern-day carnivore is the inhumane treatment of meat animals by agribusiness.  I spend quite a bit of money on meat that I trust has come from humanely treated animals.  I know the names and faces of the people who raised those cows, chickens, pigs and lambs.  This is a luxury.  Most people don't have the food budget that I do.

  • JD

    9/29/2008 1:13:00 AM |

    I think a better question is what diet was mankind's genetics formed from over 2 million years. Agriculture is only 10,000 years old. If you read Good Calories Bad Calories by Gary Taubes, there were cultures such as the Inuit and the Masai who basically only ate meat and did not suffer from the diseases of civilization including heart disease, cancer, etc.

  • Stephan

    9/29/2008 3:26:00 AM |

    Hi Dr. Davis,

    I agree there are many animal nutrients that seem important to human health: you mentioned long-chain n-3s, vitamin K2 MK-4, and vitamin B12; I'd also add preformed vitamin A and heme iron to the list.

    I read a paper a while back in the AJCN that analyzed the diet composition of 229 historical hunter-gatherer groups (Loren Cordain's group).  The average percentage of calories from animal foods was about 70%.  Many groups were completely or almost completely carnivorous, while none ate less than about 15% of calories from animal foods.  

    That being said, the diets varied widely, from complete carnivory to plant-rich omnivory.  By all accounts, none of them suffered from the modern diseases of civilization such as cardiovascular disease.  I posted on this study a while back:

  • Peter

    9/29/2008 12:23:00 PM |

    Hi Dr Davis,

    Great post. I have to agree with your concerns about modern meat production techniques and animal welfare as serious issues which need addressing, but we humans have always been pretty awful to our prey. Just thinking of traditional "harvesting" of marine mammals in the Faroes and subsistence whaling techniques here. No excuse for any of us to feel comfortable with these practices or to support factory farming, but humans are humans and we are top level predators after all. Lions are not exactly kind to their prey either.

    To be driven to omnivory acceptance by logic and evidence, against ones basic inclination, shows a great respect for facts and evidence that is seriously thin on the ground in both conventional and more alternative cardiological circles.

    What else can anyone say? Great post.


  • Jeanne Shepard

    9/29/2008 3:00:00 PM |

    Vegans say that if the walls of slaughter houses were glass that noone would eat meat. I'm inclined to think that instead, there would be demands for humane animal handling.
    Agriculture kills many small mammals and ground nesting birds, with heavy farm machinery and fertilizers/pesticides. If you want to eat, there is no free lunch, in terms of animals losing their lives.
    As someone who is humane but feels that being a carnivore is essential to my health, I buy locally grass fed beef that is is humanely slaughtered.

  • Anonymous

    9/29/2008 3:32:00 PM |

    I wonder how it would be possible to gather 2000 to 2500 calories' worth of wild plant foods every day to survive.  It would amount to something like a bushel-basket full of stems and leaves and fruits -- every single day, for every member of the group. Maybe 20 pounds a week per person.  The only way around this is to include relatively large amounts of high-fat nuts, or high-starch tubers, or high-starch grass seeds, such as wheat.  And to have to do that ALL YEAR LONG.  Nuts and seeds aren't always available year round.

    Leaf-eating vegetarians, such as the gorilla, have HUGE guts amounting to some 70% of their body volume to process the vast amounts of leaf matter needed to survive.  And they eat pretty much constantly.

    That isn't us.


  • Anonymous

    9/29/2008 5:03:00 PM |

    Man evolved eating lots of animal products, with some vegetation thrown in seasonally for hundreds of thousands of years. Then about 10,000 years ago we began introducing agricultural products into our diet. So rationally, we have evolved to process animal products much better than vegetation.

    Speaking for myself, gout runs in the family (among other things). Eating high animal products/low vegetation, relieves all my pains (gout and arthritic) and solves dozens of my other health complaints. And my bloodwork is the envy of people 1/2 my age.

    My only concern is how the animals are treated and raised. I only buy organic free-range eggs and try to buy organic meats and wild fish.

  • Anonymous

    9/29/2008 5:57:00 PM |

    I think we don't lose the abilities formed as evolving.  We evolved to eat nuts and bugs, then fish, then plants and finally meat. We're a true omnivore with the ability to choose.  I choose not to eat meat because I'm a veterinarian with 25 years experience dealing with unwholesome meatpacking industry.

  • stephen_b

    9/29/2008 7:38:00 PM |

    In my opinion any conversation about vegetarian vs. omnivore diets or low-carb vs. low fat diets need to take into account how the food is prepared. Any diet with high advanced glycation endproduct (AGE) content will be unhealthy.


  • Jeff Consiglio

    9/29/2008 9:11:00 PM |

    Holy synchronicity Batman! This is the exact question I've been mulling over for a long time and have just recently resolved the issue in my own mind, to my satisfaction. Having done and advocated low carb diets for a long time, I no longer do.

    There are numerous traditional cultures that live on a high carbohydrate intake - WITHOUT obesity, diabetes etc. So that inarguable fact always bothered me, when it came to trying to justify extreme low carb.

    For instance, here's a link to a Men's Health article on a tribe in Mexico that thrives on about an 80% carbohydrate diet.

    Also, I believe the science is pointing more and more toward fructose being the primary "bad carb" as opposed to starches which are chains of glucose. It is the fructose half of sucrose causing the problems, rather than the glucose.

    Not that eating pure glucose is a good idea. Nor starches that convert too rapidly into glucose.

    But I can tell you from my personal experience that as someone who once was sure that I was "carb intolerant" I now thrive on a high carb diet of WHOLE FOODS.
    I eat legumes, sprouted grain bread, slow cooked rolled oats etc. And yes I eat lean, and minimally processed meats as well.

    And my grocery bill is MUCH cheaper than it was when my wife and I were both living the low carb lifestyle. By the way, I used to suffer from reactive hypoglycemia, yet I thrive on plenty of UNREFINED carbs now.

    Here's a link to an amazing interview with a Dr. Lustig who discusses how fructose causes de-novo lipogensis, insulin resistance and high uric acid levels. he also discusses the Atkins diet and why Asians are able to thrive in spite of high intake of white rice. Ties in very nicely with this topic.

    And here's just one more link that I think ties all this together. it's an seminar by Micheal Pollan who wrote  "In Defense of Food."

    Having read literally thousands of books and scientific papers on the topic of nutrition, I feel Micheal's is the all time best. It exposes the fallacy of nutritional reductionism - what he calls "nutritionism - the idea that we should study individual macro or micro nutrients, rather than looking at overall eating patterns. He makes a brilliant case for the notion that to discover the "secret" to what constitutes the ideal human diet we need look no further than what traditional healthy cultures eat. Traditional, healthy cultures have all kinds of varying macro-nutrient ratios. But they all eat REAL FOOD.

    And I now believe that explains why totally "opposite" diets like Atkins and vegetarian can both work. Because they are both based on real food!

    Sure, some folks don't do well on high carb intake. Some don't seem to tolerate a lot meat very well. But I do not believe most people need to go to extremes in regards to high/low carb. Forget about macronutrient ratios and just eat real food and avoid sugar and refined carbs.

    And probably take a vitamin D3 supplement since most of us do not get enough sunshine to make it on our own these days.

    Sorry to make this so long, but I just had to get this off my chest.

    Keep up the good work. I enjoy your blog very much.

  • Stephanie

    10/1/2008 12:31:00 AM |

    Just to concur with your findings, at a recent 'food aid' symposium at Columbia University, sponsored by Doctors Without Borders, and a WHO conference in Geneva, it was concluded that animal proteins must be included in international food aid in order to save the millions of children who die each year of malnutrition. The standard emergency food distributions of grain-based flours (corn-soya blend) are not working. The milk powder seems to be the essential ingredient that prevents both wasting and stunting in children under 5.

  • Anonymous

    10/1/2008 6:33:00 PM |

    As a vegetarian this sort of thing interests me. I used to think it necessary to supplement with lots of nutrients (such as omega-3 fats) and be careful in order to be healthy. However I'm lately beginning to wonder if a plant-based diet is actually the key to health.

    According to several studies such as the China study, cultures who eat a plant-based diet very low in fat and animal products (even if not expressly vegan very close to it)  tend to be protected from "diseases of civilization" such as obesity, diabetes, and heart disease.  Certain doctors who've researched this like Dr. Ornish have used this type of diet to reverse heart disease. This idea certainly has been attacked, but I'm sure it hasn't been actually refuted.

    If this is true maybe nutrients like K2 and fish oil become less important, (assuming you're getting the required amount of essential fatty acids and other nutrients). Afterall, if you don't have atherosclerosis to begin with you don't need large amounts of special nutrients such as vitamin k2 that fight against it. Still, I guess vitamin B12 is an issue.

  • Anonymous

    10/2/2008 2:43:00 AM |

    I think it's very telling about who stands to profit if Americans embrace a vegetarian or vegan diet.  Soy, rapeseed, and cereal grains are all much easier to make high profits from than factory farmed chickens, cows, and pigs, not to mention properly, humanely raised animals.  I've noticed the push to dissuade Americans from beef, and cattle are some of the hardest animals to fit into a factory farm model, because the calves must live on grass in a field for a while - they can't be jammed up eating grain the whole time.

  • donny

    10/2/2008 1:28:00 PM |

    They did a study in rats where they either fed the rats a certain amount of vitamin k alone, or a certain amount along with Nadh, and then measured gamma-carboxylation of certain proteins. Increased levels of Nadh increased the levels of gamma-carboxylation just as if more vitamin k had been administered.
    Exercise, alcohol, and niacin all increase levels of Nadh. It's possible that something about our modern lifestyles is exaggerating our need for vitamin k2.
    The same goes for b12. Other vitamins like folic acid, b6, etc., either help in the b12 cycle, keeping it in the system, or spare it like b6 which cycles homocysteine into cysteine instead of back into methionine. People with low thyroid who receive replacement therapy have their homocysteine levels go down as well as their triglycerides, almost as if a b vitamin deficiency had been corrected.

    Dean Ornish shows increased bloodflow on his diet, but what is that diet's effect on calcium scores? Just eating a cup of sugar should increase blood flow, in the short term; vasodilation is an acute action of insulin.

  • rabagley

    10/2/2008 4:38:00 PM |

    First, the China Study authors didn't read the China Study data, or they would have noticed that the Chinese only eat about 12g/day of soy (almost entirely of one fermented form or another).  It is far from a dominant staple.  They also might have noticed that only those extremely close to starvation ate a nearly vegan diet.  Anyone who could afford to eat meat, ate meat.

    Second, Ornish is the master of selectively paying attention to study data.  Any study which can be spun to support his goals is blown all out of proportion to its actual significance.  Those studies that directly contradict his goals?  No mention...

    Personally, I know three people who've tried Ornish.  They were incredibly hungry all the time and gained all of the weight back within six months.  Their blood sugars and cholesterol numbers were even worse afterwards than before.  I and one other friend tried paleo (carnivory) instead.  Now one year into our meat-centered diet, we're both stable with moderate BMI's (me 22, him 23), normal hunger, few or no cravings, my blood sugar is way down, HDL is up, triglycerides are down...

    Ornish is a vegetarian activist claiming to be an authority on diet.  Too bad his diets are counter-productive for real people in the real world.

  • ganeshan

    10/3/2008 8:23:00 PM |

    not exactly ,humans can be carnivores too but they must go through the exact working so as to avoid any disease.being an omnivores will make us much safer.

    Sreevysh Corp

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