Vegetarian and Vegan Diets, Part 1: Why They Aren’t Healthy
Ever since the publication of my first book, The Paleo Diet, I have been asked time and again if there is a vegetarian version of The Paleo Diet®. There is a simple answer, a true Paleo Diet is not vegetarian.
Vegetarian diets are a bit of a moving target because they come in at least three major versions:
- The most well-known vegetarian, those who do not eat meat, poultry, or fish.
- Less restrictive are lacto/ovo vegetarians who limit their animal food choices to dairy products and/or eggs.
- The most restrictive type of vegetarian, also known as vegans, who eat plant foods exclusively.
A 2008 article published by Vegetarian Times magazine revealed that 3.2% of U.S. adults or 7.3 million people follow a vegetarian-based diet, and nearly 1 million Americans are vegan.  The study also showed that over half (53%) of current vegetarians indicated that they ate a plant-based diet to improve overall health.
Motivations for Being a Vegetarian
- Animal welfare cited by 54%.
- Environmental concerns named by 47%.
- Natural approaches to wellness mentioned by 39%.
- Food safety issues brought up by 31%.
- Weight loss and weight maintenance issues were cited by 25% of the respondents. 
First, let me say I respect everyone’s choice to eat whatever diet they like and those foods that they feel are best suited for themselves and their families. I also respect people’s decisions to abstain from eating meat for religious, moral, and ethical reasons. Nevertheless, as a scientist, I hope that we all try to make dietary decisions based not just on philosophical reasons, but also on foods that are good for our bodies and long-term health.
Accordingly, I simply can’t lend my support to any version of vegetarian diets that people may adopt with the idea that these diets improve health.
Without supplementation, vegetarian diets simply don’t work. They invariably cause nutrient deficiencies that adversely affect our health and well-being. Let’s dive into the science of why this is.
Humans Evolved Preferring Meat
Vegetarianism has deep historical roots dating back to at least 500 BC with such ancient Greeks as Pythagoras, Porphyry, and Plutarch. However, this manner of eating has only been with us for the mere blink of an eye on an evolutionary timescale. [106, 115, 134] In our comprehensive analysis of 229 hunter-gatherer diets, my research group found no evidence that any foragers were vegetarians.  In fact, whenever and wherever animal foods were available they were always preferred over plant foods.  The chart below from my study shows the overwhelming preference for animal foods in all 229 hunter-gatherer societies that we studied. Notice that not a single foraging society fell into the (0 – 5%) animal subsistence category.
Most (73%) of the 229 hunter-gatherers consumed 46% or more of their daily energy as animal food.  The compelling reason for their preference for animal foods over plant foods was because hunter-gatherers got more bang (food calories) for the buck (their energy expended to obtain the food), as verified by the optimal foraging theory.
There is no credible fossil, archeological, anthropological or biochemical evidence to show that any hunter-gatherers or pre-agricultural humans ever consumed all plant-based diets.
Human preference and appetite for meat, marrow, and animal food has an incredibly long history in our ancestral line. [18, 33] Fossils of butchered animals with stone tool-cut marks on their bones were discovered in Africa dating back 2.5 million years.  These definitive “smoking guns” in the archaeological record leave little doubt that all human species ate animal foods from the very get-go of our existence.
Scientists are also able to determine the relative percentage of plant and animal food in extinct human (hominid) species by analyzing element isotopes within their fossilized bones. [10, 104, 105] Every single hominid skeleton examined since the emergence of our own genus (Homo) 2.5 million years ago shows an isotopic signature characteristic of meat-based diets. [10, 83, 104, 105, 124]
Further, if we compare our biochemical and anatomical machinery to cats, who are absolute or “obligate” carnivores, we both share evolutionary enzyme pathways characteristic of processing a large amount of meat. 
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Loren Cordain, Ph.D.
As a professor at Colorado State University, Dr. Loren Cordain developed The Paleo Diet® through decades of research and collaboration with fellow scientists around the world.More About The Author