I think they key question is "overweight" compared to what? Yes, far less than 98% of people are overweight compared to a baseline created by doctors that was essentially biased by the existing distribution of weights in western society. But 100% of Americans are overweight compared to how much they would weigh if the Earth's mass was reduced by 50%.

Yeah, it's much closer to 65%. And it's been constantly ticking upwards for years. Haha, uh oh.

e: overweight Americans are about 32.5% of the population. Obese is another 36.5%.