Please if i take only 600calories of food a day would i slim down n how fast?

Fast: Fast yes, but that's a very low calorie count! that may be ok for someone 600 lb who has a lot of reserve calories. But that's too low for someone who weighs less than 200. Really it's the kind of calories that matter. Avoid foods that stimulate insulin. Insulin causes the body to make fat. Ironically, many "low-fat" foods actually make us fat by stimulating insulin. Google "glycemic index.