What happens to your body when you quit eating fast food?

1) Calories

One of the most noticeable impacts that quitting fast food can have on your body is a reduction in weight. Fast foods are typically high in calories, with portion sizes that are too large to maintain a healthy diet. By reducing your fast food intake and replacing fast food with healthier meals from home, you decrease your total calorie intake, helping create the calorie deficit needed for your body to lose weight. Pair removing fast food from your diet with exercise to see even better results.

2) Saturated fat

Many fast foods contain high levels of saturated fat, especially hamburgers and foods that are breaded and fried in oils containing saturated fat. Foods high in saturated fat typically increase your consumption of bad LDL cholesterol. As LDL cholesterol levels get too high in your bloodstream, the excess cholesterol can calcify, or harden, into cholesterol plaque. Plaque restricts and clog the flow of blood through your blood vessels. As your blood vessels become more clogged, your blood pressure increases, along with your risks for developing heart diseases.

3) Salt

Cutting back on your fast food can significantly decrease your overall sodium or salt intake. Most restaurants overuse salt, which can quickly increase your daily consumption above the American Heart Association's recommended limit of less than 1,500 mg per day. When you consume too much salt, you increase the salt content of your blood. Salt attracts water, which can increase your blood volume. The higher your blood volume goes, the higher your blood pressure becomes. High blood pressure over time damages your cardiovascular system, putting you at a higher risk of heart disease. Lowering your sodium intake by cutting out fast food can help reduce these risks.

References: http://www.livestrong.com/article/513055-what-happens-to-your-body-when-you-quit-eating-fast-food/
http://www.nbcnews.com/id/20825325/ns/health-diet_and_nutrition/t/any-other-name-its-still-supersize/
http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/PreventionTreatmentofHighBloodPressure/Shaking-the-Salt-Habit_UCM_303241_Article.jsp