prolly. mostly psychology (people eat what you put in front them....)

I doubt that it's a big factor in American obesity. But the existence of racial differences in ability to metabolize different kinds of food is not a new idea. For starters you have the well-known difference in ability to digest whole (cow) milk, but as I recall it has also been shown that Native Americans do not digest wheat as well as Europeans, who in turn do not digest corn [maize] as well as the Native Americans. I would also expect Asians to have an advantage in digesting rice, but as far as I know no such thing has been demonstrated.

I think Americans' high consumption of refined sugars has more to do with the obesity epidemic than anything other factor. Sugar is bad stuff -- practically a poison, in my opinion. It has a lot of calories with almost no nutritional value, screws with your blood sugar and emotions, is addictive, etc. Sugar has only been widely available for the past few hundred years -- it's not really a natural part of our diet.

If anyone reading this has a weight problem try not eating any refined sugars for at least six months (you have to read labels -- sugar or "high fructose corn syrup" is in a LOT of processed foods including many that you wouldn't expect) and see if that helps. I lost 30 pounds just from eliminating sugar from my diet. That was almost a year ago and I've kept it off.

Being able to eat anything you want whenever you want has the most to do with it. I often find myself eating out of boredom. Places where meals are scheduled and ritualized tend to have less random snacking, I think.

Jacqueline,
Did you give up refined sugar as part of one of the low-carb diets, or for other reasons. Personally I stay away from sugar, for weight reasons, but the best part of not consuming sugar is not having to fight to taste your food after you take a gulp of overly-sugared Soda-Pop.

P.S. Try giving up bleached flour also, it is not historically a part of our diet and has far more digestible carbohydrates and less fiber.

I don't think sugar is poison. I can eat all the sugar I want and don't gain weight or get sick. That doesn't make either one of us less human, it's just a reminder that we have to be careful before we define "optimum diet" and "average human". What we were "designed" to eat may not be what keeps us alive very long. Back in those long tribal years when we were evolving,"optimun" was what kept us healthy to about 25 ro 30- reproduction was the key. We certainly didn't develop diets to optimize our health at 90.
We eat very differently than we used to because we can get the good stuff now. Now instead of grueling hunts and fighting for a hunk of fat, we go get a burger. Fat tastes good because it was tough to come by. Foraging for fruits is replaced by Slushies and candy bars. We used to get tons of potassium from vegetables, so our bodies crank it out efficiently; we used to have trouble finding NaCl (we only need 50milligrams a day for our nerves etc.)so we developed a taste for it- now we pound down 7-9 *grams* of the stuff and eat less veggies/fruits- and NaCl actually promotes potassium excretion.
Mammals can live on a wide variety of stuff- some eat only leaves, polar bears can almost live on fat alone. And we can adjust well. Which is why a vegetarian can survive pretty well, as did my old college roomate who stayed alive for 18 months apparently on mac&cheese, Labbatts and Sun chips.
My opinion is we need to not eat anything excessivley- and EXERCISE. (We also never sat around on a couch for hours, we were built to move.) Any serious nutritional jouranl/article/diet will contain that word- *exercise* at "medium" intensity an ~hour a day. It benfits the heart, the bones, our weight, even our brains.

Some links-

http://www.who.int/en/

http://www.beyondveg.com/nicholson-w/hb/hb-interview1a.shtml

http://www.lib.berkeley.edu/PUBL/nutrition.html