by Monica Reinagel, M.S., L.D./N.
People often ask my opinion about diet sodas. Many see them as a harmless substitute for sugar-sweetened beverages. Others are deeply distrustful of the artificial sweeteners they contain—and there are plenty of scary rumors circulating on the internet to bolster these suspicions. Although I’ve discussed the pros and cons of sugar substitutes in the past, there’s some new research to update you on—in particular, regarding aspartame, which is marketed under the brand names Equal and Nutrasweet and is the sweetener most commonly used in diet sodas.
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Does Diet Soda Make You Gain Weight?
The research on artificial sweeteners and how they affect things like appetite, metabolism, and body weight continues to be all over the map—contradictory and inconclusive.
There is little doubt that diet soda drinkers are more likely to be overweight—but, as I never tire of repeating, correlation is not causation. It’s very likely that they are drinking diet soda because they are overweight and not the other way around. Even so, it doesn’t seem to be helping. The more diet soda you drink, the more likely you are to gain weight.
Do Artificial Sweeteners Trigger Fat Storage?
Does the sensation of sweetness somehow trick your body into storing more fat?
It’s clear that artificial sweeteners don’t elevate your blood sugar, but there are still lingering doubts about whether the sensation of sweetness might somehow trick the body into storing more fat. Just last month, for example, a study found that mice who were fed aspartame gained more weight than mice who were fed sugar water—despite the fact that both groups ate the same amount of calories. But the bigger news is a recent study on humans, regarding diet soda and cancer risk.
Do Artificial Sweeteners Cause Cancer?
Until recently, there hasn’t been any solid evidence to support a link between artificial sweeteners and cancer in humans. But researchers recently published findings from a study that tracked a very large group of people for over two decades. They found that men who drink more than one diet soda a day have an increased risk of blood-borne cancers like non-Hodgkin lymphoma and leukemia—although no association was found in women. Curiously, the link between diet soda and cancer was strongest in men who drank the fewest alcoholic beverages.
In the body, aspartame is broken down into methanol, which is then converted to formaldehyde in the liver before being eliminated. Formaldehyde is a known carcinogen. Now here’s where it gets interesting: The enzymatic pathway involved in metabolizing methanol is the same as the one used to break down ethanol, or alcohol. This pathway is also more active in men than women, which is why women become intoxicated more quickly than men—their bodies aren’t as efficient in clearing alcohol from their bloodstream.
The researchers theorize that the higher activity of this enzymatic pathway in men means that they are exposed to more formaldehyde when they consume aspartame. But if they also consume alcohol, some of that enzymatic activity might be diverted to metabolizing the alcohol, reducing the conversion of methanol to formaldehyde.
Now this is still a long way from definitive proof. Men who drank non-diet soda had an even greater increase in these cancers, so there are legitimate questions about whether the association between aspartame and cancer is real or perhaps just a statistical anomaly. But if I were a tee-totaling guy with a serious diet soda habit, this finding would definitely get my attention. I certainly don’t recommend increasing your alcohol intake in order to reduce your risk! You could seek out some of the newer diet sodas sweetened with stevia instead of aspartame. But I think it might be even smarter to ditch the soda altogether.
My Advice: Limit the Sweet Stuff (All of It)
Obviously, sugar-free beverages avoid the problems associated with added sugars. But that doesn’t mean they belong in the all-you-can-eat category. With so many unanswered questions about artificial sweeteners—and the fact that they don’t contribute anything positive to your diet—my advice is to use them (if you must) in limited amounts. In other words, sweet stuff shouldn’t take up more than a small proportion of your diet—no matter how it is sweetened.
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