For optimal results with alli, you should be eating well balanced meals where 30% of the calories come from fat (this ranges from 12-20 grams of fat per meal, with most people having a target of 15 grams). One 60mg dose of alli will block about 25% of the fat that has been consumed, blocked fat equals blocked calories.
You should not be eating more calories than you have been in the past or if it makes you feel uncomfortable. The key is balance and moderation as your body needs all nutrients to function well, this includes fat. A balanced ratio is 30% fat, 30% protein and 40% carbohydrate.
There are calorie charts available to you. Snacks should be low or non-fat, such as fruits. When you are eating well balanced meals you will not be feeling as hungry between meals.
Hope this helps.
Sophia De Monte RPh