It just ain't so. Although some people may be congenitally susceptible to putting on weight, they are not helpless against this predisposition. People who are naturally shy can overcome that tendency, and people who tend to gain weight can curtail their eating. Even if your body tends to convert calories into fat, it cannot do that unless those calories are consumed. People with weight-gaining tendencies can also counter this predisposition by burning calories through physical labor or exercise. As one ages, metabolism slows down. If you're eating as much at 40 as you did at 20, and haven't increased your exercise, you're going to gain lots of weight.
Among the hazards of unemployment, I was told recently, was weight gain. Jobless people tend to ease their frustrations and depression by snacking a lot. After a year of joblessness, I have had the opposite experience. I've actually lost about 10 pounds while unemployed — and not because I've quit eating.
What I have done is reduce consumption of prepared foods. When we both worked, my wife and I tended to eat instant meals more often — microwave dinners, fast food, hot dogs, etc. Since I have the time to cook, we've prepared more meals from scratch (or nearly scratch), and we've eaten healthier. We've also paid attention to portion size. I've also exercised more, by doing yard work, walking the dog and actually going to the gym (gym membership is one luxury I did not give up as we reduced our living expenses). As a result, I'm leaner and healthier and feel better (in part because job stress is gone).
Controlling weight is not easy. Fad diets won't do it. Intermittent starvation won't do it. A commitment to eat healthily, exercise regularly and avoid snacking as part of an overall lifestyle change will prevent the common pound or two or four a year weight gain over 30 years that most people experience as they age.
My challenge, when I get a job, will be to maintain my eating habits while working in sufficient exercise in a desk-job environment. It's not easy, but it's not impossible.