All programs – whether a big commercial program like Weight Watchers, Jenny Craig or a physician or hospital-based weight loss program – can be deducted, providing your doctor has confirmed that your current weight is a threat to your health, and has therefore ordered you to enroll in a program to treat a specific disease, whether obesity (a designated disease as of 2002), hypertension, heart disease, or high cholesterol, for example. You must have this in writing.
You cannot deduct the cost of diet foods as diet foods are considered a personal expense.