A super common "trick" that first time dieters, or people who are unfamiliar with nutrition tend to do is eat a lot of "diet food". The 100 calorie snack packs, fat free yogourt, tons if products marked "light". Some of those products are okay, some are terrible. The problem with simply trying to switch to diet food, is that it doesn't really involve changing how you feel about food and health, it's simply a crutch.
One of the biggest problems with diet food is that despite being sugar free, they actually precipitate our desire for more. Diet foods (like yogourt, granola bars, juices, soda) are full of artificial sweeteners, which actually make us crave sugar more. Artificial sweeteners simply fool our taste buds, not our brains into satisfying a sugar craving. When the body naturally has sugar, dopamine (the reward hormone) gets released from the pleasure centre in the brain. When people stick to diet foods, the body continues to build up a craving for sugars, which makes the craving more intense and makes people more likely to succumb to a larger craving. A happy medium is the have natural sugars (like fresh fruits) in moderation. Top plain yogourt with fresh fruit instead of opting for diet yogourt and you'll be better off!