Soft drink consumption has increased dramatically in recent decades. The increase corresponds with the rise in obesity and diabetes in the United States. Some evidence suggests that sugar-sweetened beverages increase the risk of childhood obesity. No study has shown that these drinks increase the risk of diabetes, although this relationship is plausible not only because of the added sweeteners but also because the caramel coloring may increase insulin resistance. In this study of a cohort of young and middle-aged women, Schulze and colleagues sought to determine the impact of soft drinks on weight gain and diabetes risk.
The Nurses’ Health Study II followed a cohort of 116,671 female nurses 24 to 44 years of age when the study began by administering a questionnaire every two years. In the qualifying sample of 51,603 women, participants had completed a food frequency questionnaire that included questions on the number of nondiet and diet soft drinks, fruit drinks, and fruit juices they had consumed in the past year. Information on weight and exercise was obtained, allowing body mass index calculations and energy expenditure estimates. Finally, new diagnoses of diabetes were recorded.
The authors drew data from two time periods (1991 to 1995 and 1995 to 1999) calculating mean weight changes in participants who had reported a change in soft drink consumption during those periods. Soft drink intake within the first period was compared with intake in the second period to estimate the impact of dietary change on diabetes risk.
The health habits of women with lower soft drink consumption were healthier overall than the habits of those with higher soft drink consumption. Participants who increased their soda intake also increased their overall energy intake over the same period, with changes in the consumption of other foods accounting for only about one third of that caloric increase. The reverse pattern was true in women who decreased their soda intake. The group with consumption that increased from low to high had significantly greater weight gain and increase in body mass index than women with low intake or decreased intake. Similar weight increases were found in those with intakes of fruit punch and fruit juice. An increase in diet soft drink consumption was associated with lower weight gain compared with decreasing diet drink consumption.
Greater sugar-sweetened soft drink consumption was associated with an increasingly higher risk of acquiring diabetes, with a relative risk of 1.98 among those drinking daily soft drinks compared with those rarely drinking them. Adjustment for confounding factors, particularly body mass index and caloric intake, attenuated these results somewhat. Fruit drink and diet drink consumption increased diabetes risk, but fruit juice intake did not.
The authors speculate that the increased diabetes risk associated with sugar-sweetened drinks may be because people who drink sweetened liquids do not feel full. Therefore, the energy intake from these drinks does not prevent people from eating their usual amount of food. Short-term studies have shown that people gain weight if sodas are added to their regular diets. Given the findings of this study, it appears that drinking soft drinks is associated with increased energy intake overall, suggesting that the sodas may actually make people hungrier. The fact that fruit juices did not increase diabetes risk may be due to the lower glycemic index of these drinks as well as to the presence of nutrients.
editor’s note: According to the surveys taken from 1977 to 1998, soft drink portion size increased during this period by 49 kcal.1,2 The National Health and Nutrition Examination Surveys suggest that the rate of increase in body weight is only about 0.1448 kg per year, which calculates to an excess of 3 kcal daily. From these data, it is easy to see how sugar-sweetened drinks, which do not seem to provoke the same satiety response as other foods, could partly account for the obesity epidemic in children and adults.—c.w.