Both cursory and detailed studies into the human anatomy, indicate clearly that the human body has the greatest similarity with herbivores, and not with either omnivores or carnivores. The human body is optimized for eating mostly or exclusively plant based foods.
Ability to hunt
Anatomy of Carnivores: All carnivores have a body structure that is designed to help catch, overpower and tear apart prey. Carnivores have well developed claws, powerful jaws, sharp front teeth, reduced facial muscles to enable a wide mouth gap, a large mouth opening relative to the head size and swallow their food whole (as compared to chewing)
Anatomy of Humans / Herbivores: Humans are simply not designed to be able to catch or eat animals. We have no claws, out teeth would not render flesh, our mouths are not large enough to catch or wound an animal, nor do we have the speed and reflexes required to ambush and overpower an animal.
Instincts of Carnivores: Humans also seem to lack basic instincts which are natural for all carnivores. Carnivores hunt, attack and tear apart animals which are still alive. They get excited and will salivate at the sight and smell of blood and raw flesh.
Human instincts: Humans on the other hand, are instictively sickened by the sight and smell of blood and guts of a dead animal, which is why we pay butchers to do our killing. We eat our meat, cooked with all sorts of sauces and spices, to cover the taste of raw meat. However, we enjoy fruits and vegetables raw and fresh.
Ability to digest meat
Intestine Tracts: Meat decays quickly. This is the key reason behind the significantly shorter intestinal tracts of meat eaters (3 times their body length). The short funnel like intestine of meat eaters, ensures that meat is digested and excreted within a few hours. Similar to all herbivores, humans have a significantly longer (10-12 times their body length) and more convoluted intestine. This causes meat to stay in the intestines for much longer – between 24-36 hours. The putrification and rotting of meat which is not expelled from the body within a few hours, produces toxins and amines that accumulate in the liver, kidneys and large intestines. These toxins poison out bloodstream leading to diseases including diabetes, cancers and kidney diseases amongst others.
Salivary glands, saliva and molars: Humans (or herbivores) have flat molar teeth used for grinding, have well developed salivary glands and an alkaline saliva (with ptyalin enzyme) all of which are used to grind and pre-digest grains & fruits prior to swallowing. Meat eaters on the other hand, swallow their food whole, letting acids in the stomach digest the food. They have sharp molars, lesser developed salivary glands and a more acidic saliva.
Hydrochloric acids in stomachs: Carnivores require a high concentration of hydrochloric acids in their stomachs to help in the digestion of meat. Humans (or herbivores) have a significantly lower concentration of hydrochloric acids in their stomachs (almost 20x less than that of carnivores), which prevents the efficient digestion of meat in our stomachs.
Natural carnivores have an almost unlimited capacity to handle saturated fats and cholesterol without adverse health effects, as their digestive tracts are well equipped to digest raw meat. However, if half a pound of animal fat is added daily to a rabbit's diet, in just two months his blood vessels become caked with fat leading to the heart disease (due to an inability of a herbivores digestive system to digest the fats and expel toxins from the body).
Similarly, when people consume meat, the meat remains in their intestines for significantly longer (24-36 hours, as compared to a few hours for carnivores) due to the larger length and structure of the human intestine. We also do not have the required acidic levels in our saliva and stomachs, essential to break down and digest meat. This results in meat putrifying (meat typically putrefies within 4 hours of consumption) and rotting within our bodies, producing a range of toxins and amines that accumulate in our livers, kidneys and large intestines. These toxins poison our bloodstream, leading to a number of diseases including diabetes, cancers and kidney diseases. Human bodies are simply not designed for an efficient and harmless way to digest meat.