People who eat a lot of meat are at risk for gout—one of the most painful conditions known to medical science. Gout results when crystals of a uric acid salt build up in the joints. These crystals can also build up in the urinary system, producing kidney stones—another of the most painful conditions known to medical science. A recent theory suggests that our high risk for gout is a side effect of an adaptation that enabled human beings, gorillas, and the other great apes to survive a shortage of sodium.
Although eating meat and seafood causes gout in people, it doesn’t cause gout in a natural carnivore like a cat. That’s because cats, like most mammals, produce an enzyme called uricase, which breaks uric acid down into something that dissolves easily in water and passes right out through the kidneys. Human beings and the great apes are practically the only mammals that can’t make uricase. This fact suggests that people, like gorillas, should probably be eating a highly plant-based diet.
In the wild, apes are free from gout because their plant-based diet is low in purines, which the body converts to uric acid. Fruit and vegetables are also mildly alkalinizing, and the mild metabolic alkalosis enables the blood to keep more uric acid dissolved. So the great apes can live gout-free even though they can’t make uricase. Similarly, human beings can avoid gout simply by eating a plant-based diet with a heavy emphasis on fruit and vegetables.
It’s surprising that human beings and the great apes can’t make uricase. We’re practically the only mammals that don’t. The gene for uricase has survived almost unchanged through hundreds of millions of years of evolution. That’s generally a sign that the gene does something important. Yet the lack of uricase might actually be an advantage for wild apes. The extra uric acid in their blood might enable them to survive on a diet that would otherwise be dangerously low in sodium.
As we’ve seen, gorillas eat a very low-sodium diet. Meat-eaters don’t run a risk of sodium deficiency, because meat and other animal-based foods are high in sodium.