Hi LVerenn,
It is fine to take a fiber supplement with alli.
People fear getting the treatment effects from alli and are surprised if they develop constipation. Any time you change your diet there are changes in your bowel movements also. The addition of a multivitamin which contains iron and calcium does have a tendency to be binding especially the initial few days. Keeping yourself hydrated and eating plenty of fiber does help alleviate this.
Are you also eating close to the fat gram target? Your body does need minimal fat to function efficiently. The bowels need fat to lubricate the stool so that is passes through smoothly. It is all a matter of balance.
One 60mg alli dose will block about 25% of the fat that has been consumed, the excess fat will be eliminated.
Hope this helps.
Sophia De Monte RPh