Yes, diets do help people lose weight. The problem with a diet is the fact that they require commitment, which is what most people lack in terms of weight loss. It's not something you can take on half-hearted. You must be committed. I used a low-calorie diet for two years and lost almost 80 pounds.
I think a good diet can help you lose weight. Many people do not understand which foods contain the most calories and which foods are better for you when losing weight, and a diet can give them that information. It also gives them a routine to follow, which some people find helpful.
I think overall diets along with proper exercise do help people lose substantial amounts of weight, when you are watching what you are putting into your body you can avoid loading yourself lots of fats that cause you to gain weight, I think that a diet is one of the key tools to use if you want to lose weight.
A diet can help one turn the tide on one's weight, but is not, in and of itself, capable of helping on permanently lose weight. Rather, if used in conjunction with better lifestyle and behavior, it can help one find an ideal weight that other factors must maintain. Simply dieting means the weight stays off until the diet ends.
Diets are not healthy and will not help people lose weight for the long run. Short term it might help them lose weight but they usually gain the weight back and then some if they go on a diet. People need to eat healthy and work out and then they will lose weight.