It's good to help out your partner with their health.
Jack's girlfriend has been feeling self conscious about her weight and tells him about her desire to change her diet.
Jack wants to react to his girlfriend's goal.
Jack encourages the pursuit of the goal and volunteers to change his diet as well.
Jack simply agrees with his girlfriend and wishes her luck.
His girlfriend thanks him for his support and is able to stick to the diet.
His girlfriend eventually loses the motivation to change her diet and reverts back to her old ways.