The risks and benefits of sugar substitutes have been argued and studied since their invention. For those of us not old enough to remember, saccharin was invented in 1879 and used as a food sweetener for decades before it was banned in 1912. It was allowed back into the market during World War I, where it has stayed. The next big contender didn’t show up on the market until 1951. 
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Cyclamate was an accidental discovery made famous by one brilliant marketing move—the pink Sweet ’N Low package, which was an eye-catching alternative among the white sugar packets. During the same decade the first major diet soda, Diet Rite, was introduced and then the Coca Cola company followed up with Tab in 1963.
In 1970, the FDA banned cyclamate after studies showed it caused cancer in rats. Saccharin was placed on “hold” from 1977 to 1991 so that it could be studied. By the time the FDA declared saccharin wasn’t a carcinogen, the market had already found aspartame (Nutrasweet). Currently, aspartame is the most common diet soda sweetener.
You’d think with decades of experiences with sweeteners and a number of controversies around them, we would have a better understanding of how they affect our bodies. A few recent studies highlight how little we know. One of the problems with studying the potential effects of diet soft drinks in people, is that it is nearly impossible to prove causality in problems that accumulate over the years. Many studies can only draw associations.
A study published in Stroke looked at nearly 2,900 adults for stroke risk and another 1,500 adults looking at dementia risk. They adjusted for the known major risk factors for these diseases (such as age, sex, smoking and physical activity). The hazard ratio for diet soda drinkers was nearly three times greater for both ischemic stroke and dementia. This made the news and some people got the impression that diet soda increases your risk of stroke or dementia by three-fold. But really, this is just an association, proving causality would be a much harder task.
Other studies have examined how diet sodas affect our metabolism, risk of diabetes and weight. A few studies have shown that drinking diet soda daily increases the risk of diabetes, and one study shows the risk is incrementally higher with every soda consumed. Another study found that overweight people who switched to diet soda didn’t have any weight loss compared to those who stayed with sugary soda.
We’ve spent so much time vilifying sugary soda—not that I’m promoting it—but we’ve failed to recognize that diet soda might not be any better. Why? One study found that overweight diet soda drinkers ate 90 to 200 more calories per day than non-diet soda drinkers.
One researcher hypothesized diet soda creates a psychological reason to reward yourself with something else high in calories. Meaning, you saved so many calories on a diet soda, why not have a doughnut? In the finance world, this is called penny wise, pound foolish. Let me be the first to say soda wise, pound foolish.
But it could be more than basic psychology. A very recent study examined whether our satisfaction of eating something sweet is linked to the actual number of calories it contains. By using fMRI, researchers can “see” what part of the brain is active when someone feels “rewarded” (ingesting something they like). The researchers created a series of drinks with varying amounts of sweetness and calories by using a mix of tasteless sugars and calorie-less sweeteners. The expectation was that drinks high in sweetness and in calories would create a greater response in the brain. But it turned out that really sweet drinks with few calories and high- calorie drinks with little sweetness didn’t have the largest response. The mid-range drinks with a match of sweetness and calories (about 75 calories) had the biggest response.
In other words, our physiological response to a drink is dependent both on the calories of that drink and our perception of its sweetness. This could be the reason why diet soft drink consumers don’t actually lose weight – they never feel completely satisfied or satiated from a sweet, zero-calorie soda.
These studies might guide soft drink makers to create low-calorie sodas that make us feel more satiated, but even then, we’d be better off with just water.
Salvatore Iaquinta, M.D., is a head-and-neck surgeon at Kaiser Permanente. He is also the author of The Year They Tried to Kill Me.
