It all depends their fitness level, the frequency of their training schedule and what are their goals (loose or gain weight, training for an event, the type of the event-100 meters dash vs. Ironman, etc.). Also, they should take in consideration any medical issues they might have and consult with a physician and a dietitian or nutritionist before they start any diet program.
I should have been a bit more specific. That’s what I get for having posted this when my mind was done before my body realized it. This is for a 22 year old woman, current weight 68.18KG with an RMR of approximately 1741. Her goal is to reduce her weight by approximately 20 pounds and maintain a steady weight loss of approximately 2#/week. She is concerned about negative net calories and I have attempted to reassure her that consuming a minimum caloric intake of 1200 for a woman of her size, age, height, and PAL she should see those results without any ill effects. Do you concur?
Yes, there are formulas to use and calculate the caloric intake, the RMR and all of those calculations that are needed. But, without knowing your client, her health history, her daily activities, diet, and BF% I can’t suggest anything that might be useful to you. When it comes to dieting I refer my clients to a dietitian.
A dietitian or a nutritionist would be more appropriate to help you with this question.