About a decade ago I read an interview with an applied mathematician about how he applied his knowledge of math to practical applications. I don't recall if he was working for the NSF or the NIH at the time, but his work for the past few years had to do with this.

He said that of all the contributing factors to being overweight, the factor that was clearly the most significant by a margin was food production per capita. If you produce a lot more food, people will consume a lot more as well.

Putting down the fork may not be an effective solution, but the problem definitely is eating too much. Other factors like how our bodies absorb more from the same food than they did 40 years ago pale in comparison.