Mindfulness allows you to tune in to the signals your body sends out. By mindfully paying attention to these signals of when you are hungry and when you are satiated, you can naturally decrease the amount that you eat without feeling deprived.
Most people eat for many different reasons. Hunger is only one of them. Many people eat when they are bored, when they want to take a break from what they are doing, when they see other people eating, when they smell something good, or when the clock tells them it is meal time.
By being mindful of why you are eating, you can begin to align yourself with the wisdom of your body, which knows how much energy you need to take in via food.
Try this next time you want to eat. Take several mindful breaths and then tune into your body. Ask yourself why you want food in the present moment. Let yourself "hear" the answer.
If you really are hungry, then enjoy your food. Don't gulp it down. Eat it mindfully, savoring the colors, flavors, and textures. But if something other than hunger is motivating your desire to eat, then consider whether there is something besides food that can fulfill your present need.
For example, if you have been sitting at your desk working for a while and now you need a break, try fulfilling that need for a break directly instead of reaching for a snack. Get up and walk around for a few minutes, or stretch, or have a glass of water, coffee, or tea.
Many people have well-established habits of eating to meet their non-hunger needs. It can take some time to retrain yourself, but be patient because the rewards that come with eating in harmony with your body's true needs are amazing.