The diet soda business is expanding almost as fast as American waistlines. Compared to 15 years ago, consumption of diet beverages in the U.S. is up 20 percent. Diet sodas are seen by many as a healthy alternative to sugary beverages, which have been linked to type 2 diabetes and cardiovascular disease. But how healthy are diet sodas? A new study, published in the American Journal of Clinical Nutrition, looked at how overall diet and consumption of diet sodas contribute to health. Researchers found that, while both diet and diet sodas can affect you, what you eat has a larger impact. Over a 20-year period, people who ate a “prudent” diet—more whole grains, fruit, nuts and seeds—had the lowest risk of developing metabolic syndrome, when compared to those who ate a “Western” diet of meat and poultry, fast food, pizza and snacks. Signs of metabolic syndrome include elevated blood sugar, high blood pressure, excess abdominal fat, and elevated triglycerides and low HDL cholesterol. All of these can put you at increased risk of heart disease, stroke, and diabetes. People who consumed both a prudent diet and diet sodas, however, only had a slightly higher risk of metabolic syndrome, 20 percent compared to 18 percent for the prudent eaters who didn’t drink diet sodas. The highest risk of metabolic syndrome—32 percent—occurred with people who ate a Western diet and drank diet sodas. This, says researchers, suggests that diet is really the driving factor behind health, although diet sodas do contribute. This may help explain previous mixed results on whether diet sodas are healthy. One study found that diet sodas had no affect on weight gain, while another found that drinking three or more diet sodas a day could lead to weight gain. What is clear is that eating a healthy diet is likely to have a far bigger impact on your health. If drinking the occasional diet soda helps you achieve that, then that could be a good thing.