While there are undoubtedly many factors behind the increasing obesity epidemic in the U.S. (think super-sized fast food portions and decreased physical activity, to name a couple ~ energy in doesn’t equal energy out, etc.), a new scientific review suggests that sugar-sweetened beverages, particularly carbonated soft drinks, are a key contributor. In a report published Tuesday in The American Journal of Clinical Nutrition, Dr. Frank Hu and others at the Harvard School of Public Health reviewed 30 studies (15 cross-sectional, 10 prospective, and five experimental) on the relation between sugar-sweetened beverages and weight gain published over the past 40 years. Although not all studies conclude that beverages are at fault, the researchers found “an overwhelmingly strong case... for a causal relationship” between beverage trends and obesity, which “clearly justifies public health efforts to limit sugar-sweetened beverages.”
Soft drink consumption has increased dramatically over the past four decades, in parallel with the increase in obesity. According to this report, an extra can of soda a day can lead to 15 additional pounds in a single year. Scary. Experimental studies suggest that the mechanism by which sugar-sweetened beverages may lead to weight gain involves high-fructose corn syrup (HFCS), the main sweetener in these beverages. HFCS makes beverages less satisfying than other carbohydrate sources because it fails to stimulate insulin, which processes calories, and leptin, which helps regulate appetite.
Not surprisingly, the beverage industry is quick to point out that there is more than one factor contributing to the obesity epidemic. While this is almost certainly true, that does not mean that we should ignore it. As Dr. David Ludwig, director of the obesity program at Children’s Hospital in Boston put it, “Could you imagine someone saying we should ignore the contribution of hypertension to heart attack because there are many causes? It’s ludicrous.”
In addition to weight gain, sugar-sweetened beverages provide little nutritional benefit and may increase the risk of diabetes, fractures, and dental carriers. In one study, intake of soft drinks was significantly associated with an increased risk of diabetes, even after adjustment for BMI. The authors postulate that this association is probably due to the high amount of rapidly absorbable carbohydrates such as HFCS in soda, which contribute to a high glycemic load. Several studies have also suggested that rapidly digested and absorbed carbohydrates may exacerbate the proinflammatory process underlying diabetes, such as C-reactive protein and haptoglobin. Furthermore, consumption of sugar-sweetened beverages displaces milk and other more nutritious beverages from the diet. Reduction in consumption of milk, which contains high amounts of calcium, combined with the high phosphate content of cola, may also contribute to an increase risk of fractures. Low calcium intake during the adolescent years is particularly hazardous because it jeopardizes the accrual of peak bone mass.
The authors therefore conclude that “it is imperative that current public health strategies include education about beverage intake. Consumption of sugar-sweetened beverages such as soda and fruit drinks should be discouraged, and efforts to promote the consumption of other beverages such as water, low-fat milk, and small quantities of fruit juice should be made a priority.” Recent restrictions on the sale of sugar-sweetened drinks in schools are certainly a step in the right direction! (Go California, and thank you Dr. Kaufman!) However, far far more needs to be done and lots of politics stand in the way - we hope to see things change on this front as the dangers of the public health epidemic (diabetes and obesity) emerge.