Yes, it's important to follow the alli recommendations for best results. The alli diet is designed around 30% total daily calories from fat, 20% protein and 50% carbohydrate; it's a healthy diet and similar to the diet of the Ameican Heart Association. It's also designed to provide a wide variety of foods that are satisfying so people don't feel deprived and wind up bingeing.
As you lose weight your calories will be lowered -- but NEVER below 1,200 calories. Starting too low doesn't leave much room to go from there. Not eating enough fat makes taking the capsules pointless if there's little or nothing for them to block. The Personal Calculator is generally very accurate because it's based on all the information an individual provides.
You might also take a look at the top two posts about why calories and fat are so important -- it's great information.
I hope this helps.
Pat Baird, MA, RD, registered dietitian