Hi 93182,
For optimal results with alli, you must follow a reduced calorie, well balanced diet where 30% of the calories come from fat (healthy fat as in fish, nuts, extra virgin olive oil), this roughly comes to 15 grams of fat per meal. If your diet is too low in fat you will not be inhibiting enough calories to see desired results.
Treatment effects occur when you are eating more fat recommended. Excess fat will be eliminated, the more in the gut the greater the urgency. Most people do not experience treatment effects while on alli.
BMI charts are established guidelines but not perfect. Other parameters include your waist size and muscle mass (muscle weighs more than fat).
Calories are calories. When we take in more than we burn they will be stored in the body as fat. It does not make a difference if we are eating healthy calories or not it is the quantity. A diet high in fruit and vegetables is great, but you do need fat for efficient body functions as well as lean sources of protein and other carbohydrates (whole grains).
Going over the literature in the starter pack and here on the site will provide you with more information
Hope this helps.
Sophia De Monte RPh