Eating fast food regularly increases the odds of becoming obese and/or a type 2 diabetic. That’s the conclusion of the CARDIA study (Coronary Artery Risk Development in Young Adults), which followed 3,031 young adults for 15 years. This study, funded by private and federal grants, had a nearly equal number of black and white participants, who were 18 to 30 years old at the start. This is the first large-scale, long-term study to investigate the link between fast-food consumption and changes in body weight and insulin resistance (The Lancet, 1/1/05).
The study participants live in Birmingham, Chicago, Minneapolis, and Oakland. They filled out extensive questionnaires about such topics as physical activity, time spent in leisure, and hours per week watching TV. Their fast-food habits were elicited with this question: “How often do you eat breakfast, lunch, or dinner at places such as McDonald’s, Burger King, Wendy’s, Arby’s, Pizza Hut, or Kentucky Fried Chicken?” Over the 15 years, six complete physical examinations were given that included insulin and glucose measurements.
The CARDIA study found strong associations between frequent consumption of fast food and increased weight and insulin resistance in young adults. Those who ate the most fast-food meals showed a higher weight gain at 15 years (about ten pounds) of follow-up than those who ate infrequently at fast-food restaurants. The CARDIA researchers determined this finding to be independent of other potentially important lifestyle factors, such as physical inactivity and TV viewing.
As for the insulin resistance and increase in the risk of diabetes, the CARDIA researchers suggest an explanation: “Certain fast foods contain large amounts of partially hydrogenated oils, and this class of fatty acids can cause insulin resistance and increase the risk of type 2 diabetes.” They also suggest that there might be some merit to the prevailing, though controversial, diet theory that holds so-called high-glycemic foods responsible for the increase in type 2 diabetes (which, in turn, increases the risk of heart attack). Foods with the highest glycemic index are highly refined starchy foods with added sugar that cause a rapid rise in blood sugar after a meal.