How many times do you see people who have suffered being overwight go up and down in their weight during their lives? Switching from diet to diet and continually losing weight only to put it all back on with interest when they go off it? This is the problem with "going on a diet". Some people seem to see a diet as a way to eat for a specified period to lose weight then once they have lost the weight go back to their normal eating habits. Inevitably that will led to failure because those eating habits lead to them being overweight in the first place. Some people also seem to be seasonal yo-yo dieters whereby they let themselves gain pounds over winter and then when the warmer weather 
(and swimsuit season) aproaches they "go on a diet".
Not only is yo-yo dieting a sure way to stop you from ever reaching your dream of being slim and healthy for life it also plays havoc with your metabolism. The more times you lose weight and then put it back on again the harder it gets each time to lose it again.
In order to lose weight and keep it off you need to recognize what constitutes a healthy eating plan and stick with it. That's not to say once you have reached your goal weight you can't enjoy the occasional fast food meal, pizza or chocolate bar but you have to have it moderation. Indulging in these things more than every now and then will more than likely lead you back on the path to being overweight. A lot also depends on your age, metabolism and the amount of exercise you do. A younger person or a person who does more exercise daily will generally be able to "get away" with more treats here and there and still be able to keep their weight in check.
