I assume that you mean fat, not weight.
Let's call it what it is. Everything weighs something.
Extra fat is not itself unhealthy except for the strain that extra weight causes on your joints.
Extra fat is a visible sign of severe illness. It's from consuming too much fructose via sugar, HFCS, honey, nectar, juice,molasses,maple syrup and white flour products (most breads, crackers and pastas).
Skinny people who eat sugar, etc. are just as unhealthy, their signs usually being acne, IBS and/or eating disorders.
Too much fructose causes liver dysfunction that prevents the hormone leptin from stopping hunger, so you overeat every day, all day.
"Fat Chance" by Dr. Robert Lustig M.D.