This paper explores the diets of gorillas and uses it to recommend a diet for humans low in fat and high in dietary fiber. This is a common mistake. Dozens of vegetarian groups say that because the great apes are vegetarians (which they aren't...but animal food intake is fairly low) that humans are also naturally vegetarians. The most extreme groups say we should eat only fruit because, as primates, we thrive on sugar.
But read the paper carefully. The gorilla diet is very very high in fiber, but that fiber is getting converted into free fatty acids. This conversion is vital for gorillas, providing them with 57% of their calories. That leaves 15.8% of calories from carbohydrate, making the gorilla a defacto low carber! Humans claiming to emulate ape diets by eating lots of fruit aren't able to get the same nutrition. Fruits that are palatable to humans are much higher in sugar and lower in fiber than what the great apes eat. Furthermore, the human colon is tiny in comparison to great ape colons, so even if we did eat high-fiber fruit we wouldn't be able to process very much of it into free fatty acids.
Here is why a fruity "ape" diet is bird-brained:
- There is some fermentation of fiber into FFAs in humans, but much less since our colon is only 17% of gut volume. In apes it is typically around 50% of gut volume.
- Since apes are basically converting most of their food into FFAS, they are basically low-carbers. Humans gorging on melons are eating an amount of sugar that no ape in the history of the world has ever eaten.
- Humans are a fairly unusual species. Contrary to popular misconception, gorillas and chimps are our relatives, not our ancestors. Re the latest fossil evidence "indeed, the new evidence suggests that the study of chimpanzee anatomy and behavior—long used to infer the nature of the earliest human ancestors—is largely irrelevant to understanding our beginnings." It also means that comparing our digestive system to lions and cows is pretty pointless since we are a unique clade.
- Humans are the longest lived primates. A diet high in sugar cannot support this longevity. Without modern dental-care, humans eating high sugar diets would not live very long because they would lose all their teeth. Our "natural" diet would not be the one that makes our teeth fall out. Apes experience tooth decay in the wild, but it matters less since they don't live as long.
- Our brains require nutrients like iodine and DHA that simply can't be found on a diet of forest foods. Furthermore, our brains are big and hungry for calories. While modern fruit eaters can survive because of the wealth of sugar-rich fruit at the grocery store, there is no evidence that a homo sapien could survive by foraging for only wild fruit. In fact, there is strong evidence that homo sapiens could not survive in a forest environment at all without access to cultivated foods.