Are Diet Sodas Harming Your Health? The Truth Behind Low-Calorie Drinks

Just because a beverage has the word “diet” on the label doesn’t mean it’s good for you. Researchers are linking low-calorie drinks to a variety of medical issues, from an increased waist circumference to stroke. Is this just another health scare? Medical Detective gets to the bottom of this bubbling issue... Choosing a diet drink over a high-calorie beverage feels good. Righteous even. But don’t pat yourself on the back just yet. In recent years, many studies have suggested that diet sodas might harm your health, without even shrinking your waistline. In July 2011, researchers from the School of Medicine at The University of Texas Health Science Center San Antonio found that diet soda is associated with a larger waist circumference in humans and aspartame raised blood sugar in diabetes-prone mice. So do diet sodas really cause osteoporosis, heart disease, kidney problems, weight gain and diabetes? That’s the $21-billion question – the amount Americans spend on low-calorie drinks annually. “There’s a connection between diet soda and negative health outcomes,” says Susan Swithers, Ph.D., a professor of psychological sciences at Purdue University who studies food intake and body weight. What’s not clear is whether the drinks are directly responsible for those problems, or if people with health issues or unhealthy behaviors just happen to consume more of them, she says. In other words, 59% of Americans who drink diet soda (according to a 2007 survey by the Calorie Control Council, a diet-food trade organization) should ponder the repercussions before gulping it down. Lifescript’s Medical Detective found that women who drink these beverages daily could have reason to worry. Here’s the truth about how diet soda can affect your health. Weight Gain It seems illogical that zero-calorie beverages could make you pack on pounds, but that’s what a three-year study by the University of Texas Department of Medicine found in 2005. For each diet drink participants had per day, they were 65% more likely to become overweight in the next 6-7 years, compared with those who didn’t drink them at all, UT researchers found. They were 41% more likely to become obese, defined as having a Body Mass Index (BMI) over 30, which for a 5’ 7” woman would mean weighing more than 190 pounds. One reason could be biological programming. Our bodies associate sweet tastes with an intake of calories, says Swithers, who researched the subject in a 2008 study at Purdue’s Ingestive Behavior Research Center. When you drink a diet soda with no calories, your body may get confused – either causing your metabolism to slow down or prompting a craving for more food to make up for the calories that never arrive, she says. Another factor: Our bodies associate solid foods, more than liquids, with satiation (fullness), says Ramachandran Vasan, M.D., professor and chief of preventive medicine and epidemiology at Boston University School of Medicine. Then there’s the “Big Mac, fries and a diet soda” theory. Wishful thinkers who believe they can have a high-calorie meal if they wash it down with a zero-calorie drink end up consuming more than they should. “People use diet sodas as an excuse to eat poorly,” Vasan says. Those who drink more low-calorie beverages tend to eat foods with more saturated and trans-fats, exercise less and eat fewer fruits and vegetables, he adds. Osteoporosis For many women, nothing refreshes after a workout like a diet drink. “Knowing I get to enjoy a diet soda after exercising motivates me,” says Maddie Warner, a 36-year-old Los Angeles artist. “I burn off calories and get a zero-calorie reward when I’m done.” But what’s the punishment? Possibly undoing that exercise’s benefit to her bones. About 44 million people, 68% of whom are women, are at risk for osteoporosis, a condition in which bones become extremely porous and vulnerable to fracture, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Middle-aged and older women who drank three or more 12-ounce servings of cola (either diet or regular) per day had almost 4% lower bone mineral density in the hip, according to a 2006 Tufts University study examining more than 1,400 women. That’s after researchers factored in conditions such as age, menopausal status, calcium and vitamin D intake, and alcohol and cigarette use. Women who drank non-colas weren’t affected. “I’m convinced that cola is a risk factor for bone loss in older adults, particularly women,” says study leader Katherine Tucker, Ph.D., professor and chair of the Department of Health Sciences at Northeastern University Bouvé College of Health Sciences in Boston. The culprit is phosphoric acid, a flavoring agent that increases blood acidity, she says. It’s a major component in many types of soda, but cola tends to have more. Phosphorus itself is an important bone mineral, but excess amounts may lead to bone loss because the body tries to neutralize excess acid by taking calcium from bones. Some experts also believe that people replace calcium-rich beverages like milk with diet sodas, leading women to take in lower levels of the bone-building nutrient. “Your calcium requirements increase after age 50,” says osteoporosis expert Robert Heaney, M.D., a professor of medicine at Creighton School of Medicine in Omaha, Neb. Women of any age should have 3 servings of dairy products per day for optimal calcium intake, whether they drink soda or not, he advises. Heart Disease A controversial February 2011 University of Miami study showing that people who drank artificially sweetened beverages daily had a 61% higher rate of heart attack and stroke than those who didn’t. Some nutrition, diet and vascular disease experts question the value of the findings because the study of 2,564 soda drinkers (63% were women) didn’t determine a direct relationship between diet soda and stroke. Also, the study was small, and soda consumption was self-reported by participants, according to detractors. Still, Northeastern’s Tucker finds the results compelling. “People know if they drink diet soda or not,” she says. “The behavior is clear.” Those who consume diet sodas daily typically have a higher BMI and are more likely to have diabetes, a risk factor for heart disease, notes Ralph Sacco, M.D., the University of Miami’s chairman of neurology and senior author of the report. Because this is such a serious issue, a larger study will shed more light on reasons for the heart disease connection, he says. But based on current research, Tucker is firmly in the anti-soda camp. “Why not drink a glass of iced tea or sparkling water?” she says. Metabolic Syndrome Think limiting consumption gets you off the hook? Even drinking just one glass of diet soda per day puts you at risk for metabolic syndrome, a 2007 Boston University study found. This syndrome is a cluster of risk factors for heart disease and diabetes, including large waist circumference, high levels of triglycerides (blood fats), low levels of HDL (good) cholesterol, high blood pressure and high-fasting blood sugar. About 23% of adult women have the syndrome, according to an extensive research study called the National Health and Nutrition Examination Survey III. Even factoring in levels of saturated fat and fiber in the diet, total calories consumed, smoking and the level of exercise among participants, the link between diet soda and metabolic syndrome was clear, says Boston University’s Vasan, author of the four-year study. But once again, it was difficult to determine cause and effect. Researchers don’t know if there’s a biological pathway in diet soda that causes problems, says Vasan, or “a behavioral pattern – that people who drink diet soda [also] eat more fast food.” Kidney Problems If you drink two or more diet sodas daily, you could double your risk of decreased kidney function, according to results from the Nurses’ Health Study, one of the largest and longest-running investigations of factors influencing women’s health. (It surveyed 3,000 nurses over 11 years.) Your kidneys serve several important purposes, including filtering waste products from blood and regulating blood pressure. Kidney function decreases a bit with age, says researcher Julie Lin, M.D., an assistant professor at Harvard Medical School and kidney specialist at Brigham and Women’s Hospital in Boston. But in this study, the “rate of kidney function loss was three times faster in women who drank diet soda compared with aging alone.” The link between the two is unclear, however, because “diet soda ingredients are proprietary – so we don’t know exactly what’s in them,” Lin says. One theory: Diet sweeteners could lead to kidney scarring, she says. Further studies need to be done to corroborate that theory. So what should you do when you feel the urge for a refreshing drink? “If you can’t avoid soda, drink it in moderation – less than one a day,” Vasan says. “If you can’t do that, exercise more regularly and have your blood checked.” Diet soda lover Warner is OK with that. “I’ll cut back, but I won’t give it up,” she says. “I don’t think I could ever cut it out entirely.” Are You Diet Soda Savvy? Most people assume it's what they're eating that packs on the pounds. But it might be what's at the other end of your straw, not fork, that's really to blame.