Speak to your doctor prior to gaining any weight.  It's important to get your doctor's perspective on how much weight-gain is appropriate for you.  In addition, they may be able to refer you to a registered dietitian for additional one-on-one counseling.  Talk to your doctor about why you want to gain weight, how much weight you want to gain, and how you think it will improve your health. Visit the EatRight website and click on the orange "Find an Expert" button on the top right to search for a dietitian in your area. Before starting a new diet to help you gain weight, find out how much weight you want or need to gain.  This information will help determine your eating pattern and give you a timeline to track your progress.  One way to determine how much weight you should gain is to calculate your BMI.  You can use a a formula like this one or use an online calculator.  If your BMI is less than 18, this signifies that you are underweight and may need to gain weight.  Then calculate how much you would need to weigh to have your BMI fall between 19-24.9 (healthy/normal range).  The difference between these two values can give you some insight into an appropriate amount of weight gain. You can also calculate your body fat percentage or have your doctor, dietitian, or even a trainer at your local gym calculate this for you.  For an average woman, body fat percentage should fall between 25%–31%.  For an average man, body fat percentage should fall between 18%–25%.  If you exercise regularly or you are an athlete, your body fat percentage might be lower. In general, women's body fat percentage should never fall below 14% and men's shouldn't fall below 6%.  If your body fat percentage is low (especially if you're not an athlete), this may also indicate the need for weight gain. Ask your doctor what is an appropriate weight range for your gender, age, and height. When aiming to gain weight, your focus should be gaining lean muscle mass and minimize gains in body fat.  Large increases in body fat is not recommended....

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Write a summary of the previous text in Vietnamese:
Trò chuyện với bác sĩ. Xác định bạn muốn tăng bao nhiêu cân. Tính toán lượng calo. Mua sổ nhật ký ghi chép quá trình ăn uống.