Bob has a negative attitude toward healthy eating. bob’s doctor describes research showing that healthy eating can him live longer. bob does not pay attention to what he is saying, but is impressed by his doctor’s confidence and intelligence, so he changes his attitude toward healthy eating. bob has changed his attitude based on the route to persuasion.

Peripheral.

Explanation:

The individual should focus on eating habit to attain a healthy life style. The junk and oily food is not good for health and can cause the condition like obesity, hyper tension and even heart attack.

Bob's impressed by his doctor and changed his attitude by the peripheral persuasion. The peripheral route of persuasion occurs when the individual listens the listener and get agreed by his conversation and follow him by getting impressed by the listener.

Thus, the answer is peripheral.