I'd refine it as 'If feasible, try fixing your diet before going for pills'. The body is adapted to function within a healthy nutritional range. If your diet falls outside that range, it's expected that your body won't function properly. If problems persist despite a good diet, then pills become a more reasonable option.
Based on what? You seem to be assuming that the only way to be deficient in something is to have a junk diet. It is quite easy to be deficient in just one nutrient.
I'd refine it as 'If feasible, try fixing your diet before going for pills'. The body is adapted to function within a healthy nutritional range. If your diet falls outside that range, it's expected that your body won't function properly. If problems persist despite a good diet, then pills become a more reasonable option.
Because it's unlikely that a specific deficiency is your only single problem.
Based on what? You seem to be assuming that the only way to be deficient in something is to have a junk diet. It is quite easy to be deficient in just one nutrient.