I don't think that is true, becoming fat is all about your mind and body. We don't become fat because we sleep late, if that was the case i think very many people would be fat including myself. I love to sleep late and that has never made me fat. I think it's all about what we consume and how we treat our bodies, do we treat it right, or do we ignore what goes on from the inside. I guess when we say what you think is what you become, the same saying with a little twist to it, like what you eat is what you become, can also work. When we eat junk food all the time we can expect to put on some weight, too much sugar and refined foods are also a culprit when it comes to weight gain. When we consume this foods and we do not do any exercises, that is a recipe for disaster. If you do not want to gain weight, eat the right foods, do exercises, cut down on sugar not completely because you need it for energy as well. That way fats in your body will be kept away.