[kingkongrevenge]

The walkability and culture things are pretty critical, but my armchair opinion is that the biggest factor is fat consumption. Americans eat something like 20% as much fat as they did in the 40s, and the drop off since the early 80s has been fairly sharp. People are eating much less fat and much more starch, with all the insulin and fat storage implications that brings.

Across time and between nations now the role of fat is pretty clear. More fat, thinner people. The recent studies that have put people on high fat, low carb diets are unmatched. People lose the weight and keep it off when you tell them to cut the potatoes and eat butter instead.

[xiaoma]

I disagree. On average, the Japanese get over 80% of their calories from carbohydrates, and over half from rice alone. They're also the thinnest of all economically developed people in the world, and have the greatest longevity.

Furthermore, in the 1970's the Japanese diet was even more dominated by carbohydrates and people the populace was even thinner. At that time, 75%　of calories were supplied by rice, and close to 90% by carbohydrates in general.

The phenomena isn't restricted to Japan either China is also seeing increasing obesity, heart disease and diabetes as its people living in top-tier and second tier cities adopt diets higher in fat and higher in protein.

The current American diet is actually unusually high in protein and fat by historical (i.e. pre-WWII) standards.

[kingkongrevenge]

Japanese lifespan and health have improved as fat consumption has risen almost geometrically. The healthiest Japanese are the Okinawans, with the highest fat consumption.

I can't comment on why Japanese have relatively low rates of obesity for the industrialized world with a starchy diet. But the pattern does generally hold true.

> The current American diet is actually unusually high in protein and fat by historical (i.e. pre-WWII) standards.

This is simply wrong with regard to fat. I don't know about the exact change in protein intake, but people eat much less fat and oil now than historically. You can't even get things like beef kidney, suet, or lard anymore at American grocery stores.

[menloparkbum]

People also consume many more calories in places where they didn't in the past. For instance, a soy latte from Starbucks has 210 calories. If you don't change anything in your diet or exercise habits and drink one of these every work day, you'll gain 15 pounds in a year.

[kingkongrevenge]

I don't know this for sure, but if I recall correctly people eat fewer calories now than they did in the 70s. I know it's not a dramatically different number either way. It's the composition of the calorie that has changed. I'm firmly convinced of the fat vs starch theory. People eat much less fat and oils now and eat more starch.

[chandler]

I doubt I'd recommend replacing fat with carbohydrates, but you're correct in that sugars (starches/carbohydrates break down into...) cause the body to store fat (more specifically, the elevated insulin levels that accompany this).

Regarding weight loss: I work & exercise with a variety of body types (these body types have people names too!), and, within this small sample, I've found that the dominating factor in overall weight is diet, not exercise.

Essentially, exercise controls muscle tone and how "tight" the skin is, while diet seems to control the overall body shape.

[xiaoma]

Total fat intake and calories have both increased steadily since at least 1849. Starches have jumped up as well starting in the 1970s.

http://www.chiroweb.com/mpacms/dc/article.php?id=38225