Have you ever wondered whether us humans were meant to eat meat? What about animal products in general?

I don’t want to convert you or convince you and I certainly don’t want to delve into ethics or the environment. All I want is to present a case for our biological preference for animal-foods, without all the politics.

In a roundabout way, Nutrition is really the science of what our bodies can’t make themselves. After all, if humans could photosynthesize like plants, human nutrition would be a whole lot simpler. When you’re gardening, you don’t have to worry about how much vitamin D is in the soil, or if the plants are eating before bed-time. With animals it’s not so easy. Since we’re not born with a user manual we have to look at what happens when we don’t get a nutrient to figure out that we need it.

In cats for instance, pet food companies tried to cut costs by taking out certain ingredients. What they discovered was that cats aren’t able to synthesize the amino acid Taurine from Cysteine (like us humans do). The result, sadly, was a slow degeneration of the cats retinas, sort of like a feline macular degeneration. At least now we know, and Taurine is an essential additive to cat food.

So how does this apply to human nutrition and animal products?

By looking at what our bodies can and can’t make, as well as what our bodies absorb easiest, we get a glimpse of what we adapted to eat.

Let’s take a look at one you’ll all recognize, Vitamin D.

Sunshine vitamin, liquid sun, call it what you will but what you might not know is that there’s more than one Vitamin D. They do have unique chemical names, but let’s call them what you would buy them as, Vitamin D2 and Vitamin D3. Vitamin D2 is often what is used for food fortification, like milk and cheese, and it comes as a powder. Vitamin D3 almost always comes in liquid form, whether in yogurt or supplements. So how do these differ? Vitamin D2 is found in mushrooms, plants, and lichen (vegetable sources basically), while D3 is sourced from animal fats, aka from grease. That might not sound appetizing but you probably already know that your body is able to make its own Vitamin D with the help of sunlight.

Want to take a guess at which one your body is making? If you guessed D3 you’re right on the money.

Now the official statement by the FDA is that the two both qualify as Vitamin D, but what does the research say? For one, studies looking at the beneficial effects of Vitamin D found that the reduction in mortality associated with supplementation was present with D3 but was not found with D2 (source). Interestingly, another study found that the negative symptoms associated with excessive supplementation were seen with a much lower dose of D2 than D3, suggesting the body is better able to handle higher amounts of D3 in the diet. What we’re seeing is that despite the two sharing similarities, the body prefers D3, the kind found in eggs, and the kind it naturally makes.

What about minerals? Are there differences between plant and animal sources?

Iron is the oxygen-loving friend of our blood cells and without it we would have a terrible time trying to breathe. The quicker you lose blood cells, let’s say routinely once a month, the more important it is to make sure you’re getting enough iron in your diet. So is all Iron created equal? If you’re reading this far you should already have a guess to that. When iron comes from plant sources, the structure looks kind of like a lollipop, and we call this kind non-heme iron. If you took a grinder to a piece of iron bar and ate it for breakfast this is the iron you’d be eating. Iron from animal sources is quite different, it looks like a 4 leaf clover, and is called heme-iron. The ‘heme’ in both of these is short of Hemoglobin, the little protein found  in the blood cells of animals.

So does the body treat them differently? You bet it does.

The National Institute for Health states that diets containing significant quantities of meat and seafood show iron absorption rates of 14-18%, whereas vegetarian diets show rates of 5 – 12%. If the goal is to have more nutrients with fewer calories, animal sources are going to be key.

So we’ve covered instances of Vitamins and Minerals, should we try a macronutrient? What about protein?

There’s a range of methods used to figure out how ‘efficient’ a protein source is. In other words, how easy the protein you eat is absorbed and used in your own body. The prevailing method nowadays is what is known as the Protein Digestibility Corrected Amino Acid Score. A dry name if you ask me so let’s just call it PDCAAS from now on. You can find a basic list of each protein and its score on Wikipedia but what I want to point out is that of the top 4 with a perfect efficiency score, 3 of those are animal based; Whey, Egg Protein, and Casein. Soy protein is almost an anomaly in terms of plant proteins, but if you take Soy out of the mix the next highest plant protein comes from yellow peas with an 18% drop in efficiency.

But let’s finish this up with one more example.  I wanted to cover Vitamin B12 but I felt that it’s well known that vegans and vegetarians should supplement B12 in their diet.

I mentioned before that we can often tell what the body needs based on what it can’t make itself, so let’s look at how the body handles Essential Fatty Acids.

If you didn’t guess from the name, these fats are necessary in the diet because our bodies aren’t able to make them. Both EFAs, alpha-linolenic acid (ALA) and linoleic acid (LA), are primarily found in plants, so it’s clear we can’t have a meat only diet. That’s not what I’m getting at though, the real key is that alpha-linolenic acid has a problem. See the body needs other fats, like EPA and DHA, that it should be able to make from ALA. Somewhere along the course of human history though our bodies lost this ability. Ok, we didn’t lose it completely, but the system is so inefficient that only a few percent of the ALA we eat can become EPA and DHA, much lower than shown to be necessary.

So where do we get more? Fish and algea mostly.

Now I’m not sure about you, but I’ve never seen a culture who relied heavily on algea for food, leaving a biological preference for fish. Will you die without fish or fish-oil in your diet? No, at least not right away. The benefits of EPA and DHA come more from their anti-inflammatory effects on cardiovascular health, so it’s a long-term need, but one that can’t be ignored.

I could go on with Vitamin K1 vs K2, or Vitamin B12, but what I want to stress is that whether strict vegetarian or vegan diets are feasible with modern chemistry, the fact that our bodies show a clear preference for animal products is undeniable.

In other words, if you want to make an omelette, you gotta break a few eggs.

Be Good To Each Other.

– Joshua Iufer, RD