Diet Cola and Weight Gain in Humans A study found that American senior citizens who report drinking diet soda regularly experience a greater increase in weight and waist circumference than those who do not drink diet soda regularly.

(a) From these results, can we conclude that drinking diet soda causes weight gain? Explain why or why not.

(b) Consider the results of this study on senior citizens, and the randomized experiment on rats introduced in Exercise 1.60, which showed a similar association. Discuss what these two studies together might imply about the likelihood that diet cola causes weight gain in humans.

Data From Exercise 1.60:
A study fed one group of rats a diet that included yogurt sweetened with sugar, and another group of rats a diet that included yogurt sweetened with a zero calorie artificial sweetener commonly found in diet cola. The rats that were fed a zero-calorie sweetener gained more weight and more body fat compared to the rats that were fed sugar. After the study was published, many news articles discussed the implication that people who drink diet soda gain more weight.