What we need are cell-sized devices dispersed from desolvable pills to replace surgeries like liposuction or gastric bypasses.
These surgeries are terrible and don't really solve the problem. These cell-sized machines, "liposites", could follow the blood-flow to enter one's adipose tissue and cut off the supply of lipids to unneccessary fat cells. Millions of these liposites would make it vertually impossible for one to become obese, even if 99% of his/her brain's neurons become chemically dependant on donuts from stretching a stomach out with danishes on a daily basis.
Self-replicating bio-nano-tech-robots, a cure for the common cancer, alzheimer's, and obesity.
In a century, these things will have reached such stupendous levels of efficiency that they could possibly, and radically, replace all human cells. That our bodies will be like technology, immortal, repairable, customizable, and ever-improving.