In the world of nutrition, there’s no debate as fiery and fierce as the one between meat eaters and vegetarians. In this Spotlight feature, we ask whether or not humans were designed to be vegetarian.

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Fight, fight, fight!

Some people choose a plant-based diet for health reasons, while others do so with more ethical concerns in mind. On the other side of the dinner plate, some meat lovers put little thought into whether they should or shouldn’t eat meat, while others will defend their right to chow down on animal muscles until the end of time.

Passions can run surprisingly high when it comes to dietary decisions. Food is a matter of survival, and deep down in our primate brain, we still feel that we need to defend our food sources.

Today, we are not concerned with the ethics of the meat industry; it’s not that they aren’t important, but that we are more focused in the biology involved. Similarly, we tend not to dabble in the debate surrounding the environmental impact of meat rearing; we will leave that for others to chew over.

This article will be served in two courses. First, we ask whether or not humans are “designed” to eat meat — did we evolve to consume it? Then, we will ask which option is best for our health.

This is the first question to answer, and, anatomically, it seems to be a simple one. We don’t look like carnivores; our teeth are no good for ripping flesh, and our guts are too long. Are we herbivores, then? No; our guts aren’t long enough, and our teeth don’t quite fit the bill.

We are, it seems, omnivores; our bodies can handle both meat and plant matter pretty well. It’s not quite that simple, though. Just looking at an animal’s teeth and gut is no surefire way to distinguish its diet. The panda — with killer canines and a bamboo diet — is an excellent example.

That being said, it is true that most creatures have a gut suited to the diet that they consume. Lions, for instance, have huge, smooth-walled stomachs for holding hunks of animal. Many herbivores, meanwhile, have massive, plant-destroying factories in their abdomens, where bacteria smash apart the tough constituents of plant matter.

We humans like to think of ourselves as special, and, in many ways, you could argue that we are. But when it comes to our internal tubing, we are monumentally average.

Rather boringly, the human gut is very similar to that of our closest relatives: monkeys and apes. It follows that, if we are looking to work in harmony with our guts’ design, our diet should be at least similar to our cousins’.

When we examine the diet of virtually all monkeys and apes, it’s nuts, fruits, leaves, insects, and the occasional snack of flesh. You may have seen rather shocking footage of adult chimpanzees killing and eating baby ones, but that’s a relative rarity compared with the quantities of non-meat products consumed.

From these observations, we can perhaps conclude that evolutionarily speaking, we shouldn’t necessarily be vegetarian and evolved to eat only the occasional tidbit of animal matter.

Eating meat, according to some evolutionary scientists, gave early humans a vital head start. Meat is packed with energy and protein that may have helped us to develop and nurture the over-sized bundle of cabling between our ears.

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Can human evolution help to settle the debate?

The expensive tissue hypothesis states that to have a larger brain, we need to save metabolic energy elsewhere. To do this, our guts were shortened.

But this brought another issue: having a shorter gut meant that our diet had to be of a higher quality to provide enough nutrients. Enter the animal-based diet. It is worth noting that this theory is not roundly supported.

Some researchers believe that hunting prey contributed to our bipedal stance, and that planning and conducting a hunt could have assisted the development of language, communication, and complex societies.

But, just because something has been done for eons, it doesn’t mean that we necessarily need to continue down the same path.

Modern life is different; the options that lie on the dinner table are much more varied. Our forebears did not have access to tofu, for instance, and a human living in colder climes would struggle to find cashew nuts on her daily forage.

Evolution is endless, adaptation ongoing. Animals don’t continue to drink milk after weaning. If they tried it, it would make them sick. The enzyme that mammals need to break down lactose in milk — lactase — is not produced into adulthood. But now, entire populations of humans produce lactase long after they have stopped drinking their mother’s milk (known as lactase persistence).

At some point, a group of humans began making this change, and, because it gave them access to more calories and other nutritional goodies, they survived in favor of those who couldn’t stomach cow (or goat) juice. We have adapted to make use of an energy-rich source of protein, vitamins, and minerals. So, is it natural to drink milk? If not, does that mean that we shouldn’t drink it?

Our bodies are layered with a range of evolutionary changes: from a shift to meat millions of years ago, to microbiome shifts when we started eating wheat, barley, and other crops. We are a now mishmash of compensations and add-ons that have helped us to survive over the years.

If we say that we want to eat as our ancestors did, do we mean Homo erectus, Neanderthals (who may well have eaten more plants than is often imagined), Australopithecus (who walked the earth around 4 million years ago), the earliest primates (around 50–55 million years ago), or something in-between?

If the preceding ramblings mean anything, it is that we should only eat meat if it benefits us now. The important question is how it impacts our bodies today.

Whether eating meat is natural or not doesn’t make a lot of difference. Nobody realistically thinks that we should meticulously go back to what our earliest ancestors ate simply because it was a long time ago.

From a medical point of view, we should only eat meat if it is healthful to do so. Over recent years, there has been a growing mountain of evidence in support of the health benefits of a vegetarian diet and the health risks of pounding too many burgers into our bodies.

A large-scale meta-analysis carried out in 2016 reported “a significant protective effect of a vegetarian diet versus the incidence and/or mortality from ischemic heart disease (25 percent) and incidence from total cancer (8 percent). Vegan diet conferred a significant reduced risk (15 percent) of incidence from total cancer.”

Vegetarian diets are also tied to a lower risk of metabolic syndrome, diabetes, cancer (again), and lower blood pressure, and they may fend off childhood obesity. On this matter, at least, the jury is well and truly in.

Meat is rich in protein and vitmain B-12 and is also a good source of iron, so it’s easy to see how incorporating meat into their diet might have helped our ancestors to survive.

Today, however, protein is much easier to come by — in nuts and beans, for example. Vitamin B-12 can be found adequately in cheese, eggs, milk, and artificially fortified products, and iron can be picked up from legumes, grains, nuts, and a range of vegetables.

With this in mind, rather than asking, “Should we eat meat?” we should probably be asking, “Is there a safe level of meat?” and, “Which types are worst?” In short, we can split meat into four types: white, red, processed, and fish.

Fish and white meat are roundly considered fairly healthful — as long as you aren’t deep frying them or wrapping them in bacon. For red meat and processed meats, though, it’s the reverse.

Red and processed meats are associated with colon cancer and heart disease. The majority of studies conclude that eating more of this meat is a bad idea. But how much is too much, and what levels are safe, are harder to quantify.

Dr. William Kormos, editor in chief of Harvard Men’s Health Watch, writes, “As for how much meat consumption is ‘safe,’ many studies show a small rise in the risk of disease at levels of 50–100 grams (1.8–3.5 ounces) of red meat consumed daily.”

Processed meats (salted, smoked, or cured) are also associated with a higher risk. In contrast, there does not appear to be a measurable risk from eating red meat once or twice a week.”

Dr. William Kormos

So, should we be vegetarians? Well, when the burger hits the fan and the kebab lady sings, there will still be no clear answer. Humans have eaten meat for a really long time, but a diet with minimal meat is much more healthful. And today, we don’t need meat nutritionally. I can’t make your choice for you though — sorry.