Maria Kirkeland lost 159 pounds in two years.Maria KirkelandSmall, sustainable dietary changes can lead to substantial weight loss over time.Five people who lose weight shared how their diets changed before and after.Most focused on portion control, calorie counting, and incorporating whole foods.It's rare to lose fat without changing your eating habits — after all, a calorie deficit (consuming less energy than you burn) is the only way to lose weight.However, you don't need punishing diets or to cut out all your favorite foods.For many people, small tweaks like focusing on protein and eating smaller portions make big differences.Five people — each of whom lost between 50 and 200 pounds — told Business Insider how their diets changed.Less fast foodClark Valery before and after his weight loss of 140 pounds.Courtesy of Clark Valery.Clark Valery, an assistant manager at a pharmacy chain in New York, lost 140 pounds by cutting down on fast food and cutting portion sizes.Before he lost weight, a typical meal could be two Big Macs, 20 chicken nuggets, two large fries, and a soda from McDonald's, or eight tacos from a Mexican restaurant.