When you restrict calories you are hungry. Eventually you give up and fail. It's not about willpower, it's about eating fewer carbs, not spiking insulin, not getting hungry, and being ablet to eat a sustainable diet. The calories in-calories out model is being challenged by the carb-insulin model and having tried both types of diets (USDA grains, veg, fruit, low fat vs. keto) there is no comparison. USDA diabetic "heart healthy" diet doesn't work, except in the very short term. Keto works, and many studies support this: people lose more weight on keto and stick with it.