Subjects in a large 20-year study of lifestyle factors and weight change gained an average of 20 pounds in 20 years. Less exercise led to weight gain, but the kinds of foods people ate had a larger effect than changes in physical activity. Increased consumption of French fries alone led to an average weight gain of 3.4 pounds every 4 years. Greater intake of fruits, vegetables, whole grains, yogurt, and nuts resulted in weight loss or no gain. The results of this study show how small changes in eating, exercise, and other habits can result in large changes in body weight over the years. The study design was a:.
a. prospective cohort study.
b. randomized, controlled trial.
c. retrospective cohort study.
d. case-control study.