Man is an anatomically herbivorous
We most often label people as omnivores. This classification is based on observation, as people generally eat a wide range of plant and animal foods. However, observation is not the best technique for determining the most natural diet. A better and more objective technique is a look at human anatomy and physiology. Because mammals are anatomically and physiologically adapted to the food we eat, we can determine whether we are natural carnivores, omnivores, or herbivores based on these characteristics.
Comparison of carnivores and herbivores
Carnivores have a very large mouth opening compared to the size of the head. This gives them great advantages when it comes to grabbing, killing and dismembering prey. The facial muscles are less developed so that they do not interfere with a wide bite. In all mammalian carnivores, the jaw joint lies in the plane of the teeth and thus serves as a very stable junction (hinge) between the upper and lower jaw. The main muscle that serves carnivores to move their jaws is the well-developed shadow muscle. The mandibular angle is small in carnivores. The reason for this is that the muscles that attach in this area (chewing and pterygoid muscles) are of little importance to them. The lower jaw of carnivores does not move forward and has very limited movement in the left-right direction. The incisors are short and pointed, suitable for raking and cutting prey. The eyelids are greatly elongated and arched, with which the carnivore tears and kills its prey. The braces are sharp, serrated and spade-shaped and act as saw blades. Saliva does not contain digestive enzymes, as carnivores swallow pieces of meat whole and do not chew them.
The characteristics of herbivores suggest that these evolved later. Herbivores have well-developed facial muscles, fleshy lips, a relatively small mouth opening, and a thick, muscular tongue. The lips help push food into the mouth and participate in chewing food along with the facial muscles and tongue. The jaw joint moved above the plane of the teeth. Although this type of jaw joint is less stable than the hinge joint of carnivores, it is much more flexible and allows for the complex movement of the jaw required to chew plant food. The mandibular angle is widened, thus allowing a wide area to attach to well-developed masticatory and pterygoid muscles (the main muscles involved in chewing herbivores). The shadow muscle is small and does not matter much. Chewing gums and pterygoid muscles move the jaw left and right and allow lateral movement of the jaw, which is necessary for grinding food. Herbivorous incisors are broad, flat, and spatulate in shape. Eyelids may be small (horses), protruding (hippos, pigs, some primates) or absent. The molars are flattened at the top and can slide horizontally next to each other, crushing and grinding food. Herbivores chew food well, which enables the mechanical breaking down of plant cell walls and the release of their intracellular contents, as well as the proper mixing of chewed food with saliva. This is important because the saliva of herbivores contains enzymes for the metabolism of carbohydrates, which partially break down food molecules already in the mouth.
Stomach, small and large intestine
Striking differences between carnivores and herbivores can be seen in these organs. The stomach volume of carnivores represents 60-70% of the total volume of the digestive tract, which allows them to prey on average only once a week and then fill the stomach very much, and then digest the victim later. Because meat is easily digested, their small intestine (where food molecules are absorbed) is short – about 3 to 6 body lengths. The stomach of carnivores also has an exceptional ability to excrete hydrochloric acid, so they can maintain a very low gastric pH even in the presence of food in the stomach (1-2). Low gastric pH facilitates protein digestion and kills dangerous bacteria that are often present in decaying meat. The colon of carnivores is simple and very short, as its function is only the absorption of salt and water. Bacteria in the colon are involved in putrefaction.
Because plant foods are more difficult to digest due to their fiber content, herbivores have a much longer small intestine (10-12 body lengths), which allows enough time and space to absorb nutrients. Their stomach occupies a relatively small part of the total volume of the digestive tract, it can be simple or multi-part. Gastric juice has a much higher pH than carnivores in the presence of food (4–5). In herbivores, the large intestine is a highly specialized organ involved in the absorption of water and electrolytes, the synthesis and absorption of vitamins, and the fermentation of fiber. It is usually wider than the small intestine and relatively long.
Omnivores are actually carnivores with some digestive tract adaptations typical of herbivores. They still have certain physical characteristics of carnivores that allow them to prey effectively. A typical representative of omnivores (anatomically speaking) is the bear, whose diet consists of 70-80% plant foods (herbs, tubers, berries), the rest is meat. The omnivorous jaw joint lies in the plane of the teeth, the shadow muscle is massive, the mandibular angle is small. Their small intestine is short (less than 5 body lengths), the large intestine is simple, smooth and short. The most obvious adaptation to the plant diet of omnivores is the teeth – their braces are flat with notches on a complex surface, suitable for grinding and crushing. The nails of omnivores still have the characteristics of carnivores (sharp claws), while those of herbivores are flattened.
What about man?
The human digestive tract is characterized by anatomical features observed in herbivores. We humans have muscular lips and a small opening in the oral cavity. Many of the t.i. facial expressive muscles are actually the muscles we use when chewing. The muscular and well-moving tongue, which is primarily intended for eating, has adapted to speech and other functions. The jaw joint is cartilaginous and flattened and lies high above the plane of the teeth. The shadow muscle is small, the mandibular angle is dilated, the masticatory muscles and the pterygoid muscles are well developed. The human jaw can move back and forth and left and right, which is important when crushing and grinding food. The teeth of humans are similar to those of other herbivores. The incisors are wide, flat and spade-shaped, and can be used to bite relatively soft food. The eyelids are short and blunt, and the cheekbones are flat with knotted notches, suitable for crushing, grinding, and softening softer foods.
Human saliva contains enzymes for the metabolism of carbohydrates (amylase), which are responsible for the metabolism of starch. The esophagus is narrow and allows small amounts of well-chewed food to pass through. Swallowing quickly, swallowing large amounts of food or poorly chewed food (usually meat) often causes suffocation in humans. The human stomach is simple, gastric pH in the presence of food is high (4-5). The volume of the stomach in relation to the total volume of the digestive tract represents about 21-27%. The small intestine is long (10-11 body lengths). The large intestine is wrinkled and long, absorbing water and electrolytes, synthesizing and absorbing vitamins, and extensively fermenting plant fibers.
As we can see from the comparison with carnivores, omnivores and herbivores, man is a complete herbivore without any anatomical features of omnivores. Our digestive tract is perfectly adapted to plant foods.