Although it is bad to do how much weight will someone lose in one week by only eating dinner?

Unfortunately, you will probably GAIN weight on that plan. The body is constantly adapting to current conditions. If your body senses that no food is available (since you haven't eaten all day) anything that you eat at dinner will be turned to fat for storage. It's the body's way of preparing you for what it perceives as a shortage of available food. Instead, try eating constantly but cautiously. Carry snacks of fruits and veggies that you can munch on when you get a minute. Make sure you get protein, since you don't want to loose muscle mass. After all, it's the muscles that burn the calories so if you go on some kind of starvation diet you will loose muscle mass and not be able to loose fat. It's almost a certainty that if you eat one meal a day, you will gain weight, but in the process you will also loose muscle. That's the opposite direction that you want to go. Eat healthy, exercise and you will loose weight. You will lose more weight by eating breakfast, and 2 very small meals for lunch and dinner than if you skip everything except dinner, plus you will boost brain power. For breakfast, choose things like sausage, bacon, eggs, a glass of milk and other things that a farmer would eat (call it the farmers diet if you want). If you will notice, farmers live longer than city people, they seem to look/feel better and are stronger. There is no way to tell you how much you will lose from eating only dinner because each body is different and responds differently to diets. I will say there is no substitute for healthy eating and exercise. The old rule "burn more calories than you consume" is true and will always be true. All of the fad diets and diet pills only take off weight temporarily, but do nothing long term and certianly don't help your long term health.