a) Why do you expect a rational person would necessarily avoid the environmental problems that cause overweight and obesity? Especially given that scientists are very unclear amongst themselves as to what causes obesity and weight gain? Even if you adhere to the notion that weight gain and loss is simply a matter of calorie consumption and willpower, why would you assume a rational person has more willpower?

b) Why do you expect that a rational person would necessarily value the optimum amount of exercise (presumably optimal for health) over everything else they might have done with their time this week? And again given that scientists have even less certainty about the optimum amount or type of exercise, than they do about the optimum amount of food we should eat.

c) Why do you assume that a rational person is financially able to save for retirement? There are many people on this planet who live on less than a dollar a day. Does being born poor imply a lack of rationality?

d) Why do you assume a rational person does not waste time on occasion?

Rationality is not a superpower. It does not magically produce health, wealth, or productivity. It may assist in the achievement of those and other goals, but it is neither necessary nor sufficient.