Marcus wants to get extremely lean and 'shredded' like the fitness influencers he sees on social media. He is on a highly restrictive low-calorie diet. Every time he diets, he ends up regaining all the weight. He finds himself constantly daydreaming about forbidden foods and browsing food-delivery apps. Yesterday, after accidentally eating a single slice of garlic bread at a family dinner, he felt he had completely ruined his diet. He then went on to eat a large tub of ice cream and a whole family-sized chocolate bar.

Using your knowledge of psychological explanations of eating behaviour, explain why Marcus's dieting attempt is likely to fail.