Not true. There aren't enough fasting days, and even on those days, people can gain weight, since by eating one big meal, and more carbs (less protein), they can actually change their metabolisms. AND a lot of the food people can afford is poisoned garbage that wrecks the metabolism, creates insulin resistance, etc. (particularly the high fructose syrups).
I just came sick the past week, could not eat for almost 3 days, i dropped almost 15 lbs and I'm not a big person and I was resting in the house trying to get better. Can you imagine if I got out everyday and kept my normal routine or did a 5 day fast?
Fasting is a miracle gift from God, it can even heal disease, I hear it can cure cancer, anything is possible, but brings clarity of the mind, strenghtens the spirit and brings the body into submission. Fasting is for us, not for God and our culuture rejects it, that's why every third person you see should be on the other end of a whale watch.
We could cure the obesity " epidemic" , and a lot of other things if we merely cut our meals down to two a day and fasted one day a week, for at least 3 months for starters.