Some studies have suggested that diet soda lovers could face higher risks of diabetes and heart disease, but one recent US study of several diet drink consumers found that overall eating habits may be what matters most in the end.
Researchers, whose findings were published in the American Journal of Clinical Nutrition, used data on more than 4,000 people taking part in a long-term study of heart health and followed them for the next 20 years.
Of the study participants between the ages of 18 and 30 when it began in the mid-1980s, 827 subsequently developed metabolic syndrome - a cluster of risk factors for heart problems and diabetes including extra weight around the waist, unhealthy cholesterol levels, high blood pressure and elevated blood sugar.
The researchers, lead by Kiyah Duffey of the University of North Carolina at Chapel Hill, found that young adults who drank diet beverages were more likely than those who didn't to develop metabolic syndrome over the next 20 years. But the picture became more complex when Duffey's team considered the role of diet as well.
"Our results suggest that both overall dietary pattern and diet beverage consumption are important, to various degrees, for different metabolic outcomes," they wrote.
The lowest risk of metabolic syndrome was seen in people who drank no diet beverages and stuck to a "prudent" diet, one rich in foods like fruits, vegetables, whole grains and fish.
Meanwhile, people who also ate a prudent diet but did drink diet beverages had a somewhat higher rate of metabolic syndrome - but not by much. Over 20 years, 20 percent of those men and women developed metabolic syndrome compared to 18 percent of prudent eaters who didn't regularly have diet drinks.
Participants with the highest rate of metabolic syndrome, at 32 percent, were those who drank diet soda and downed the typical "Western" diet including lots of meat, processed foods and sugar.
Healthy eaters who steered clear of diet drinks had the lowest risk of developing metabolic syndrome even after things such as people's weight and exercise habits at the start of the study were considered -- more than one-third lower than Western-style eaters who did drink diet beverages.
"I really think it's overall diet that's important," Duffey said in an interview, noting that for those people looking to cut calories, replacing sugary drinks with diet versions will do that.
"But if the goal is a broader impact on your health, you need to consider the whole diet," she added.
Duffey stressed that the study was observational and can't prove that diet drinks have a negative effect on cardiovascular health, but several studies have found that people who regularly down diet soda are more likely than people who don't to have certain risk factors for heart disease and diabetes.
One of those studies released last month became the first to link the beverages to the risk of actual heart attacks and strokes.
There's some evidence from animal research that artificial sweeteners can end up boosting appetite and food intake, but nobody knows yet if that translates to humans.
The impact of diet beverages on cardiovascular health is still an open question, said Hannah Gardener, a researcher at the University of Miami Miller School of Medicine, who led the recent study linking diet beverages to an increased risk of heart disease.
"We're still a long way from making any public health guidance," she told Reuters Health.