What is alli and what it is used for:nalli is clinically proven to help you lose more weight than dieting alone. The capsules work only in your digestive system to stop about a quarter of the fat in your meals from being absorbed. This fat passes out of your body and may cause changes to your bowel movements. Eat lower-fat meals to help manage these effects.nalli can make your hard work, work even harder, alli is designed to be used in conjunction with a support programme meaning that for every 2lb you work hard to lose by adding alli this can help you lose an extra 1lb more effectively, rewarding your efforts by boosting your weight loss.nalli is used for weight loss in adults aged 18 and over who are overweight and have a body mass index (BMI) of 28 or above. Body mass index (BMI) is a way to find out if you have a healthy weight, or are overweight, for your height. The Body mass index chart will help you find out whether you are overweight and whether alli is right for you.