Your logic that fat comes from eating is, of course, correct. Now take it further. Why are obese people eating too much? We do not usually eat because our bodies need fuel. My gosh, most of us have enough stored fuel for months! Obese people are eating out of both habit and out of psycological reasons. Financial help in learning new habits from dieticians is necessary. More importantly for most of us is learning the underlying resons why we overeat and dealing with it. No diet pill will take the place of doing that work.
I'm tired of people who are thin telling obese people to just cut back on calories. They don't understand. But the worse are people who have lost 20 or so lbs. They usually don't have the psycological problems that cause them to overeat, but they think because they lost their tiny bit of weight they are experts and can speak for the rest of us.
I don't like to admit that I have a disease that needs treatment. It's similar to drug or alcohol addiction in that way. Sheer force of will will not cure this epidemic. Physician assisted treatment is needed to help an obese person get healthy.
Being thin is not all it's cut out to be.........trying to put on weight for some people is as difficult as losing weight is for some other people.