Let’s just state the obvious first: whatever their nutritional value or health status, diet sodas are delicious. Sweet but not syrupy, with a slightly bitter aftertaste, we love everything from the shiny silver cans, the delightful Sofia Vergara Diet Pepsi ad or the cheeky-sweet "sexy gardener" Diet Coke ad. We consume plenty of diet soda ourselves, so we’d love to be able to report that diet sodas are 100 percent perfectly, unequivocally, ok for you.
Sadly, the answer to the question "Are Diet Coke and Diet Pepsi bad for you?" is a little more complex than we’d like for it to be. There have been a huge variety of serious concerns raised about the health implications of aspartame, the popular sugar substitute used as the primary sweetener found in both of these sodas. Potential issues raised for both drinks include everything from brain tumors to cancers.
The good news first: many of these concerns are unfounded. In fact, as of right now, the official stance on aspartame, according to both the European Food Safety Authority and the U.S . Food and Drug Administration is that aspartame has been studied at length and is safe for human consumption.
However, for anyone suffering from the genetic disorder phenylketonuria (frequently shortened to PKU), a component of aspartame called phenylalanine can cause really serious conditions such as brain damage, seizures, and mental retardation. Phenylalanine doesn’t just occur in diet drinks, though. It’s a natural part of many foods, including eggs, milk, and meat.
Aspartame is also considered unsafe for people who are taking certain medications, such as levodopa, neuroleptics, or monoamine oxidase inhibitors. If you’re taking a medication that you think may be contraindicated with aspartame, you should check with your doctor.
On the other hand, since they are sugar-free, Diet Coke and Diet Pepsi are options that are currently considered safe for people who have diabetes.
Some have claimed that aspartame-laden drinks actually make people gain more weight. There has been some conflicting evidence on this, but it seems that diet drinks may not have the weight-loss effects that regular drinkers may have desired. It appears that in one study, rats gained the same amount of weight whether they were ingesting saccharin, aspartame, or sucrose (sugar-water).
Other studies have shown that weight-gain was promoted by the use of aspartame or saccharin as compared with sucrose, although it was suspected that this might have to do with less energy being expended and that the diet drinks may have encouraged fluid retention.
Other concerns have been raised about the general health effects of aspartame. Dr. Morando Soffritti, Director of the Ramazzini Institute in Bologna, Italy, has suggested that the initial 1970s studies on aspartame showing that it was safe were deeply problematic. Since then, he claims, people have done better studies testing the long term potential of aspartame to cause cancer — and those studies suggest that there is genuine cause for concern. Soffritti has been doing active research on aspartame for some time. In 2006, he published a large-scale study on the long-term effects of aspartame based on his own research, and he has since urged reform for the way we evaluate aspartame's risks.
So there’s no short answer to the question "Are Diet Coke and Diet Pepsi Bad for You?" We can assert that these drinks probably won’t help you lose weight as much as we'd all like to think, and that if you suffer from PKU, you should avoid diet sodas. In terms of cancer, the scientific community seems to still be out on this one: there is plenty of contradictory evidence both ways. We're going to have to wait and see. And if you're like us risk-taking optimists, you might just do some of that waiting and seeing with a Diet Coke in hand.