 In the U.S., we tend to get less than 20 grams of fiber a day, only about half the minimum recommended intake. But in populations where many of our deadliest diseases are practically unknown, rural China, rural Africa, they're eating huge amounts of whole plant foods, up to 100 grams of fiber a day or more, which is what it's estimated our paleolithic ancestors were getting, based on dietary analyses of modern-day primitive hunter-gatherer tribes, and by analyzing coprolites, human-fossilized feces. In other words, paleo-poop, these most intimate of ancient human artifacts were often ignored or discarded during many previous archaeological excavations, but careful study of materials painstakingly recovered from human paleo-feces says a lot about what ancient human dietary practices were like, given their incredibly high content of fiber. Undigested plant remains, strongly suggesting that for over 99% of our existence as a distinct species, our gastrointestinal tract has been exposed to the selective pressures exerted by a fiber-filled diet of whole plant foods. So for millions of years before the first stone tools and evidence of butchering our ancestors were eating plants. But what kind of plants? One way you can tell if animals are natural folivores or frugivores, meaning leaf-eaters or fruit-eaters, is to map the area of absorptive mucocin, our gut, versus their functional body size. Folivores are those meant to eat mostly foliage leaves. While frugivores are better designed to eat fruit, the phonivores eat the fauna, another name for carnivore. If you chart animals out this way, they fall along distinct lines. So where do humans land? Here's our functional body size, and here's our absorptive area. So while eating our greens is important, it appears the natural dietary status of the human species is primarily that of a fruit-eater. Why does it matter how much fiber we used to eat? Well, one theory for the rising levels of obesity in Western populations is that the body's mechanisms for controlling appetite evolve to match how many plants we used to eat. Our ancestors ate so many plant foods, we were getting like 100 grams of fiber a day. So for millions of years, food equaled fiber. So no surprise, one of the physiological mechanisms our body evolved to suppress our appetite involved this fiber. For example, fiber is metabolized by our gut flora into short chain fatty acids which bind to and activate receptors on the surfaces of our cells that alter our metabolism. For example, activating receptors on fat cells to increase the expression of the weight-reducing hormone leptin. Other hormones are affected as well. Since until recently, food meant fiber. An increase in food intake meant an increase in fiber intake, which made our gut bacteria so happy that it made lots of short chain fatty acids. Activating the cell surface receptors, releasing a bunch of hormones that make us lose our appetite and down-regulate hunkers. So we eat less, but if we eat less, there's less fiber in our gut, so less of these hormones are released, which boosts our appetite. We get hungry and we want to eat. But what if food doesn't equal fiber like on the standard American diet? Then we keep just getting those signals to eat, eat, eat. We're always hungry. If we haven't eaten our 100 grams of fiber for the day, our body may be like, what are we starving here? Discovering this mechanism makes the food and pharmaceutical industries very excited. They figure they can now come up with the new drugs in the fight against the current obesity onslaught, or we could just eat as nature intended.