Diet-related treatment effects
You’re in control
what are diet-related treatment effects?
alli contains orlistat which works in a unique way by preventing some of your body’s enzymes from digesting about a quarter of the fat you eat. As undigested fat can’t be absorbed, it passes naturally out of the body in your stools. Each alli capsule works on one meal at a time.
As a result of this mode of action, you may notice changes to your bowel movements. If you stick to your fat targets (follow the alli programme’s healthy, reduced calorie, lower-fat diet) these should be manageable. However, if you eat too much fat, you increase your chances of diet-related treatment effects, including fatty or oily stools, loose, soft stools, sudden bowel motions and wind (flatulence) with or without oily spotting.
Diet-related treatment effects
Most users only have one episode of diet-related treatment effects. Also, it’s important to remember that these diet-related treatment effects are largely due to what you eat. If you stick to the recommended fat levels per meal, you’re less likely to have any problems.
For example, it you eat a chicken breast containing 15g of fat and then take alli, about a quarter of the fat (4g) is undigested and passes out of your body (less chance of diet-related treatment effects).
On the other hand, if you take alli with a fatty meal, such as a burger and chips containing 80g of fat, about 20g of fat passes out of your body (and you are more likely to experience diet-related treatment effects).


The surplus fat that passes naturally out of your body is simply undigested fat resulting from how alli works. If you get a diet-related treatment effect, see it as a signal that you’ve eaten a meal or snack that may have contained more than your recommended fat target.
Tips to avoid diet-related treatment effects
- Find out more about how much fat a portion of your favourite foods typically contain (check the labels). By getting used to the recommended portions, you’ll be less likely to accidentally go over your fat target.
- Distribute your fat allowance evenly across your meals for the day. Don’t "save" fat grams from lunch and "spend" them at dinner - each meal and snack must be within your fat target – check your fat and calorie targets for more details.
- Be patient. It may take a little time to familiarise yourself with your targets. Most users who experience diet-related treatment effects at the start, learn how to reduce them.
- Make the most of the alli weight loss programme – take the tour
- use the tools, keep a food diary. It’s an invaluable tool to help you recognise which foods can lead to diet-related treatment effects or any foods that might contain hidden calories or fat
- use the alli recipe finder, the meals are quick and easy to prepare and clearly state the fat and calorie content
- visit the alli discussion forum to learn from other alli users - swap tips, recipes and other advice
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