Did you know that it takes approximately 20 minutes for your body to produce hormones to tell your brain that you are getting full? When you start eating, right away you taste and feel the food and are satisfied, but then it has to get into your stomach, release glucose, insulin goes up, and all the other satiety hormones have to get back to your brain to let you know you are full.
Eating slow is a habit that can change your portion sizes without you even measuring or trying. It's true that it may not exactly 20 minutes, but wolfing down your lunch or dinner in 5 minutes is probably not allowing enough time to actually be in tune with true satiety from your meal.
When you sit down to eat your meal, make a conscious effort to eat slow and eat until you are 80% full. In Okinawa this is said like a prayer before every meal. “Hara hachi bu.” Okinawa is also one of the countries listed as a Blue Zone; a country where an extraordinary number of people live to be 100!
We often eat and continue eating because of external cues. We are going out with friends, we are relaxing at night, we are at a celebration with family, that pasta is just so damn delicious, we really want to clean our plate, or not waste any food. Mindful eating, eating slow, and trying to eat only until you are 80% full can change your body, and relationship to food in very important ways. This is true even if you don't change what you eat. I'm not saying eat whatever want but I am saying that this habit is one of the most important ones if you want to stay healthy and at a healthy weight.