Do I still need to eat healthy and exercise when I'm on a weight loss medication?

Written by Dr. Meera Shah, M.B., Ch.B., a Mayo Clinic endocrinologist. 

Why do I need to still follow a diet and exercise program when I am on a weight loss medication?

That is a great question and is one that is often asked by patients interested in a weight loss medication.

The current FDA-approved weight loss medicines are almost all appetite suppressants.  These medicines help to control appetite, change food choices and reduce portion sizes.  The net result is a decrease in caloric intake and therefore weight loss.  What these medicines do not do however is to change the capacity of the body to burn calories, i.e. metabolism.

Before receiving FDA-approval, all weight loss medications were tested in rigorous clinical studies involving large numbers of participants taking either the medication or a placebo pill.  Both groups were provided with a lifestyle intervention prescription, typically consisting of a calorie-reduced diet as well as an activity plan.  The difference in observed weight loss between the groups was then compared.  On average, these weight loss medications produce 5 to 10% additional weight loss when compared to placebo. To therefore achieve the same degree of weight loss as was seen in the studies, there also needs to be attention paid to food intake as well as activity.

This becomes even more important when we think about what naturally happens to body composition over time as a result of weight loss.  When a person loses weight, loss of fat mass (good) is accompanied by loss of muscle mass (not so good) and the latter contributes to the body being less able to burn calories at rest.  Having an exercise program after losing weight helps to maintain muscle mass and preserves the body's ability to burn calories.  Typically, the larger the weight loss, the greater the need for exercise to maintain that weight loss.

Finally, even though these prescription weight loss medications are approved for long-term use, many patients are interested in weaning off after a period of time.  Although we do not know how to predict who will do well off the medication, it is clear that when there is already a good program in place for activity, and sustainable changes have been made to dietary habits, the effort tends to be more successful.  In other words, having a diet and exercise program not only helps patients get the most out of an appetite suppressant, it also makes it more likely for them to come off the medication successfully in the future.

These FDA approved weight loss medications can be costly and are associated with drug interactions and side effects.  Therefore, before these medications are prescribed, we do try and ensure that lifestyle changes have been optimized so that the patient experiences maximal benefits while on (and potentially off) the medicine.

Related links:

Weight Loss Medication 101
Is Phentermine a good option for weight loss?
Is a weight loss medication right for you?
Medications Overview