Mexican nutrition program causing weight gain - oh, the irony

In Mexico, a country-wide initiative called Oportunidades encourages healthy habits in citizens and has been heralded as a model for the rest of the world. Under it, impoverished families were given cash rewards for attending medical check-ups and nutritional counseling -- the aim being, of course, to help the country slim down and get healthy. But recent reports are showing that this is not happening. In fact, it's quite the opposite -- residents are gaining weight.

What gives? It's not clear, but one hypothesis is that the cash rewards given to citizens weren't used to buy fresh fruits and veggies like they were intended. If that's the case, what's the solution? Providing vouchers that are only good for healthy fare? Would the promise of free fruits and veg be enough to entice low-income families to visit health professionals? What do you think?