Diet Soda, Sugar Substitutes, and Brain Trickery

Lindsey asks: "Are diet drinks really all that bad for you? I've heard stuff about the 'sugar' in them being addicting."

Great question! The arguments about this have been all over the place over the past 20 years, ever since sugar substitutes really began taking off, so this is a hefty topic. The most common charges against diet soda (or other beverages sweetened with sugar substitutes) are:

• Diet soda can cause an increased risk of type II diabetes, metabolic syndrome (high blood pressure, abdominal obesity, and other health issues), heart attack, and stroke.

• Diet soda contains aspartame and other artificial sweeteners which cause: cancer, headaches, depression, nausea, mood swings, kidney problems, liver problems, respiratory problems, skin irritation, gastrointestinal distress... and pretty much anything else you can think of.

• The sweeteners in diet soda are more addicting than normal sugar, and actually cause people to gain weight rather than lose weight.

Some of these claims are (partly) true, others false, some misleading, and most simply unknown. Here's what I found after researching each claim individually.


Claim #1: Diet soda can cause an increased risk of type II diabetes, metabolic syndrome, heart attack, and stroke.

First off, diet soda has never been found to cause any of these conditions. Correlations have been found, but as we know, that doesn't necessarily imply causation.

That said, a study published by the American Diabetes Association in 2009 showed that daily consumers of diet soda had a 67% increased incidence of type II diabetes compared to non-consumers. Although the study focused on diet beverages, it also accounted for consumers of sugar-containing beverages, but did not find the same correlation in those consumers.

That same study also looked at metabolic syndrome; here the researchers found the daily consumers of diet soda had a 36% increased incidence of metabolic syndrome compared to the other groups, but after adjusting the data for other factors, the correlation turned out to be statistically insignificant. On the flip side, a later study led by the University of North Carolina at Chapel Hill showed that consumers of the typical "Western" diet (fast food, lots of carbs, fat, salt, and sugar), in addition to diet beverages, were at a much higher risk for metabolic syndrome than their healthy-eating, non-diet-soda-consuming counterparts. So what do the conflicting conclusions mean? Probably not very much for diet soda. Both studies strongly suggest that overall diet--not a single type of beverage--is what truly impacts one's risk for metabolic syndrome.

So what about heart attack and stroke? A study published in the Journal of General Internal Medicine in 2012 found increased incidence of heart attack and stroke in daily consumers of diet soda (compared to those who drank none). No increased risk was found for consumers of regular soft drinks or those who drank diet beverages less than daily. However, researchers noted that drinkers of diet soda tended to be heavier, suggesting that those who consume diet soda are trying to lose weight--rather than diet soda causing them to be overweight and thus increasing their risks of heart attack and stroke. More studies are needed, but once again, overall diet is the main factor here.


Claim #2: Diet soda contains aspartame and other artificial sweeteners which cause [insert health problem here]

This claim is much more difficult to support or refute because the data is almost eerily lacking or insufficient. I could write a whole separate post about the controversy surrounding artificial sweeteners, but for the purposes of this one, I'll just mention a few general concerns about aspartame, the most commonly used sweetener in diet beverages. (This information comes from an article at MedicineNet, which gives a great, balanced overview of aspartame and other sweeteners while providing an accurate list of sources.)

A survey of  166 studies regarding human safety and aspartame revealed some unsettling information: 100% of the research conducted or funded by Nutrasweet industry (prime producer of aspartame) confirmed the product's safety... while 92% of the independently funded studies reported various health problems associated with it. One study conducted on 40 patients with depression was actually cut short because of how severe the reactions were in the first 13 patients tested. Another study reported that migraine sufferers experienced increased frequency and intensity of their headaches due to aspartame. Other suggested symptoms of the sweetener include nausea, abdominal pain, diarrhea, fatigue, and seizures. Cancer, of course, has been the most common concern, but although many more studies are still needed, the information currently available more strongly supports that aspartame consumption does not contribute to cancer.

While food safety organizations around the world stand by aspartame as a safe product, once again, more studies are needed.


Claim #3: The sweeteners in diet soda are more addicting than normal sugar, and actually cause people to gain weight rather than lose weight.

Vaguely implied by many studies and specifically explored in this 2008 study is the idea that diet soda is more "addicting" than regular soda because our brains aren't as satisfied with artificial sweeteners as with regular sugar. Functional MRI (fMRI) brain scans showed that while both artificially sweetened and sugar-containing beverages lit up the brain's reward system, the normal sugar did so more completely. This may be one reason why some diet soda drinkers don't lose weight--even if their tastebuds can't tell the difference in sweetness, their brains can, thus making them crave more sweet foods or beverages and consume more calories. (Of course, there's the other suggestion that some diet soda drinkers may just be making poorer dietary choices in general because they think diet beverages will help negate some of those choices.)



So to answer your question...

Your choice of beverage is obviously a personal decision, but hopefully it can be an informed one, too. Before researching this I was wary about aspartame because of the general concerns I had heard over the years. I also don't like the taste, and since I rarely drink soda, I've mostly just avoided the diet versions all together. But until more data is available on potential health risks, the old standby in nutrition advice is probably best: "Enjoy in moderation!"




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Frank, Guido K W, Tyson A Oberndorfer, Alan N Simmons, Martin P Paulus, Julie L Fudge, Tony T Yang, and Walter H Kaye. "Sucrose activates human taste pathways differently from artificial sweetener." NeuroImage 39.4 (2008): 1559-1569. ScienceDirect.com. Web. 3 July 2012.

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Nettleton, Jennifer A, Pamela L Lutsey, Youfa Wang, João A Lima, Erin D Michos, and David R Jacobs. "Diet Soda Intake and Risk of Incident Metabolic Syndrome and Type 2 Diabetes in the Multi-Ethnic Study of Atherosclerosis (MESA)." Diabetes Care 32.4 (2009): 688-694. Diabetes Care. Web. 3 July 2012.