--I've never been a fan of eating just once or twice a day, though I understand why some people have done that; I think what those people are ultimately looking to do is restrict calories, as there is some preliminary evidence, mostly from rodent studies, that dropping the number of calories that one eats each day by about a quarter to a third might result in longer life. (The mechanisms of this are still open to interpretation.)

Now, given the huge OVERAGE of calories many people in the West consume each day, and the lack of physical activity engaged in, cutting back on calories is likely not a bad idea. Most sedentary people of moderate size can get by quite well on 1500-1800 calories each day. A little less than that promotes weight loss, a little more, weight gain. There are individual differences, of course--my wife, who runs 60-70 miles each week (ultramarathoners are crazy), needs more, though her metabolism has now become so efficient it's really hard for her to lose weight. Metabolisms do adjust to long-term condition changes, so I imagine people who do caloric-restriction diets will make the reduced calories "go farther" in time.

I still think, though, that our bodies tend to do better in "grazing" mode. Beyond the caloric content, eating a bit at frequent intervals helps to keep our blood sugar and energy levels more stable. And though humans certainly evolved in environments in which there were long stretches of hunger punctuated by rapid ingestion of calories when a hunt was successful, far more frequently the day-to-day foraging resulted in an "eat a bit at a time, several times a day" scenario. (Our closest relatives, the great apes, still show this pattern, though they occasionally "feast" as well.)

There are individual differences in TYPE of food that works best for people. Not everyone can digest dairy products past childhood, for example--that ability seems to have been conveyed to certain groups of humans fairly recently, as a result of benevolent mutation that is thought to have started in Northern Europe. And some people seem to work better on a diet higher in animal protein that others. But I don't know too many who work better on large amounts of simple carbohydrates. Sure, eating sugar is VERY rewarding; our brains have that pleasure pathway well mapped out, and our bodies know how to very quickly store those kinds of calories for the future, but that was an evolutionary mechanism to get us to stock up for presumed times of famine. It was never designed to be experienced continuously, which is what the easy availability of sugary drinks and processed foods now allows.