Is That Can of Diet Soda Making You Fat?

• Soda cans are coated with polycarbonate, a hard plastic, which is with bisphenol A (BPA).
• BPA is linked to obesity and type 2 diabetes, among other disorders.
• Because BPA is so widely used, it is very difficult to determine whether soda cans might compound the adverse effects of exposure.

If you’re trying to lose weight and you’re thirsty, you might choose a diet drink like Diet Coke or Diet Pepsi. The diet drink has zero calories, so how would it cause you to gain weight? Maybe it’s not the liquid in the can but the can itself that’s the culprit.

The insides of many soft drink cans are coated with polycarbonate, a hard plastic. The polycarbonate is made with bisphenol A (BPA) which may be linked to obesity and type 2 diabetes, among other disorders. For example, in one suggestive but not conclusive study, 1,000 nurses provided urine samples for BPA testing. Ten years later the nurses with the highest levels of BPA weighed an average of five pounds more than nurses with lower BPA levels.

BPA and Obesity in Children

There’s more substantial evidence linking BPA to obesity in childhood. A recent meta-analysis investigated the relationship. The researchers combined the data from 13 epidemiological studies which included over 11,000 participants. They concluded that their findings “… suggested possible causality between BPA exposure and childhood obesity…” The researchers suggest that prolonged low-level exposure to BPA causes adipocyte metabolic dysfunction which increases the likelihood of obesity and related diseases like type 2 diabetes.

These studies are controversial. Coca-Cola acknowledges that BPA is used in the linings of their cans and bottle caps in order to protect the taste and guard against contamination of the beverage. They note that virtually all cans have BPA in their linings and BPA is widely used elsewhere including in medical devices.

Coca-Cola Responds

On their website, Coke states that “…there is no risk to the public from the minuscule amounts of BPA found in Coca-Cola or other beverage cans.” It cites reviews by the U.S. Food and Drug Administration as well as regulatory agencies in Australia, Japan, and the European Union which have determined that the trace amounts of BPA in can linings don’t present any health risks. Critics argue that governments rely on toxicology studies that just look for gross signs of illness. They contend that these studies could miss subtle changes that might contribute to chronic illnesses.

The Impossibility of Avoiding BPA

It’s almost impossible to avoid BPA. Aside from can linings and reusable bottles, BPA coats those shiny receipts from ATM machines and cash registers. Although there’s less evidence that exposure to BPA is harmful to adults, BPAs may be riskier for children. Fortunately, kids are not likely to use ATMs so they won’t have that exposure. But it wouldn’t hurt to minimize their consumption of canned drinks.