Saving leftovers can help with weight loss.
My grandmother was part of the group that survived the Great Depression. They thought that food wasted was a sin and encouraged us all to clean out plates. They encouraged us to eat every last bite on our plates. They even encouraged us to eat more by promising dessert. They did this because they grew up in a time in which food may or may not be available from time to time.
Today, we are in the time of plenty, and there is almost always food available, and it is near dirt cheap compared to the 1930s-50s. We engorged our stomachs and was the rest. We see more and more food waste because the food is readily available to us and is cheap enough not to save leftovers.
Instead of wasting and engorging yourself, I am going to recommend that you measure out a serving and eat just that. If you have extra left over, place each serving in a container and either refrigerate or freeze them for later. If you are eating out, divide the food and half and take home a doggy bag for later. If you avoid wasting, it will prevent guilt, and you have had a meal for later, so you will not have to cook. The goal here is not to overstuff yourself and feel sick and to prevent negative emotions such as guilt. You will be able to save a few extra bites of something delicious to save for another meal.
The bottom line: The change of saving leftovers may seem small, but it can make a big difference in your waistline. This change will be a good test for your willpower but is key when you are trying to eat reduced portions. Not only will you be eating fewer calories, but you will also have a meal for the next time you want to sit down and eat.