Most of the calories we consume can be attributed to one of the catagories in the set of Protein, Fat, and Carbohydrate. Protein is everyone's friend. It provides all those nice amino acids which your body uses to build more you. Eat your proteins and enjoy clear skin, strong muscles, and shiny hair. Hooray. Fat gets a bad rap. Fat is a great way to store energy, high fat foods can be excellent sources of oil soluable vitamins like A, E, and D, and high fat foods can help promote high-density cholesterol. While not every high fat food is good for you, there are many healthful foods which are very high in fat and can be included in a heathy diet.
This brings me to the last catagory: Carbohydrates. The set of compunds which are called "Carbohydrates" includes what are known as trisaccharides. Trisaccharides include cellulose and starch. These compunds provide energy to those animals capable of digesting them. Since humans and other monkeys can't digest cellulose, it really only acts as a transport agent by helping the body to push food from one end of the digestive tract to the other. There are lots of good foods which are high in both cellulose and starch and since the body does need a very small amount of them, they are a necessary evil.
This brings me to the unneccessary evils: mono and di-saccharides: glucose, fructose, galactose, sucrose, maltose, and lactose... These are the enemy. Your body doesn't really need you to consume them directly but for some reason people not only want to suck down all the high sugar foods that they can, they fill their kids up with it. It's not good for you and it never was. Moreover making heathful choices is made difficult by modern marketing: sugar is everywhere. You have to stay VERY vigilent in order to avoid it.
This Thanksgiving, do your body a favor. Enjoy all the turkey, ham, or tofu that you want, have a second helping of mashed potatoes, rice, or stuffing if you like, and say no to any dish described as a "pie", "cake", "cobbler", or "crisp". Your body will thank you.