Odds are, you are among the two-thirds of the adult population in the U.S. who is overweight or obese, and you’re concerned about what this means for your health. Even if you’re at a healthy weight now, you’re probably working hard to stay there so you can minimize the chances that you will develop things like heart disease, Type 2 diabetes or high blood pressure.
New York City has considered legislation banning the sale of sugary beverages larger than 16 ounces. Forcing people to recognize that a 64 ounce bucket of soda is more than a single serving is a sensible approach, and these kinds of restrictions may help stem the tide of obesity, diabetes and heart disease.
But, these restrictions are too narrowly focused – they address only beverages sweetened with sugar. So-called diet sodas are exempted because people have been led to believe that artificially sweetened products are healthy, won’t cause the same problems as regular sodas and may, in fact, help them lose weight or prevent weight gain. Unfortunately, data to support these claims is weak.
Although it seems like common sense that sodas without calories would be healthier than regular sodas, common sense is not always right.
In reality, a growing body of research shows that people who drink diet sodas are more likely to develop heart disease, diabetes, high blood pressure and stroke compared to those who don’t. And the increases in the prevalence of these health complications are actually very similar for regular soda and diet soda.
Telling people it’s OK to consume 64 ounces of the diet option is not going to fix the problem.
For the past 20 years, I have studied food intake behaviors and health, and over the last dozen years I have focused specifically on how drinking sweetened beverages influences intake, weight management and basic physiology.
This work has led me to the conclusion that soft drinks represent an ongoing and escalating threat to public health, and recommending diet options is not going to solve the problem.
The possibility that diet sodas contribute to negative health outcomes has typically been dismissed, especially by those who benefit from sales of these items. Like the tobacco industry before it, the food industry refuses to accept the idea that its products contribute to public health issues such as Type 2 diabetes and heart disease. Instead, diet sodas are extolled as healthy options and continue to be sold in places like school vending machines.
A typical industry response to studies demonstrating that diet soda drinkers have worse health outcomes is to argue that the people who choose to consume diet sodas are those already struggling with weight and other health issues. That’s not always true; even people with healthy weights are more likely to develop problems such as diabetes and heart disease if they drink diet sodas.
These studies are also dismissed because, according to critics, there is no plausible explanation for how drinking diet sodas could lead to weight gain, diabetes or heart disease. But there are several explanations, and they are supported by scientific evidence.
For example, we know that food intake is influenced by what people think they are eating, and adding a healthy food to a meal can lead people to underestimate how much of the less healthy food they are eating. So, adding a diet soda to a cheeseburger and fries could lead to overeating because of such cognitive distortions.
But, distorted thinking isn’t the only explanation for how diet sodas cause problems. A hallmark of good science is the use of diverse approaches to a problem, and when these approaches converge on similar outcomes, we can be more confident that we’re onto something. Using approaches that exclude a cognitive component, for example by testing animals such as rats, science has indicated that diet sodas can contribute to weight gain and changes in biology by interfering with learning. In a nutshell, our experience usually tells us that sweet tastes are followed by sugar and calories. Our bodies learn to produce physiological changes to prepare for those calories to arrive. Those changes not only help us regulate how much we eat, but they also help us control our blood sugar. Once we start using artificial sweeteners, we disrupt this learning because sweet taste is no longer reliably followed by sugar or calories. What that means is that for someone who has been drinking diet soda, the taste of something sweet might or might not deliver calories. As a result, the body doesn’t know how to prepare when it gets a sweet taste. So when real sugar does show up, physiological changes are smaller and slower than they should be, leading to excess food intake and higher spikes in blood sugar. We know this happens in rats, and now there’s evidence that it happens in the brains of people who drink diet sodas.
The public should think of soft drinks as candy in a can. Responsible public policy must always balance risks and benefits, and it’s clear that the minimal benefits of cheap and easy access to sodas are outweighed by the health risks they pose. All of this leads me to conclude this problem won’t be solved unless consumers make smarter choices and restrictions placed on soft drinks sales are expanded to cover artificially sweetened beverages, too.