Type 2 diabetes risk. A large national study completed in 2007 showed that people who drank one or more servings of diet soda each day had a risk of developing Type 2 diabetes 67% greater than those who did not drink diet soda. The researchers who conducted the study noted that these findings do not indicate that drinking diet soda causes diabetes. Although no clear role for diet soda in the development of diabetes was found in the study, the researchers suggested that drinking sugar-free soda might have an indirect effect on diabetes risk by leading to weight gain or by affecting the action of insulin. (The possible effects of diet soda on weight gain are discussed below.)
Kidney disease. A study presented in 2009 found an association between drinking diet soda and impaired kidney function. Of the 3,000 women in the study, including 730 with diabetes, those who drank at least two diet sodas daily experienced twice the rate of kidney function decline. This result was consistent after controlling for factors such as age, caloric intake, weight, and diabetes status.
Metabolic syndrome. Two recent large studies showed that drinking one or more servings of diet soda per day was associated with a 35% greater risk of developing metabolic syndrome. As in the study showing an elevated risk of Type 2 diabetes, the researchers did not find any evidence of cause and effect between drinking diet soda and metabolic syndrome, and they did not know what role artificially sweetened sodas might play in the development of this condition.
Weight maintenance. Much of the controversy surrounding low-calorie sweeteners focuses on whether they are truly beneficial for weight control in people with or without diabetes. Some researchers believe that drinking diet soda may in fact stimulate appetite and increase cravings for carbohydrate, leading to weight gain and possibly setting the stage for Type 2 diabetes and metabolic syndrome. Another theory is that people who drink diet soda could gain weight by eating more high-calorie foods since they believe they are “saving” calories by drinking diet rather than regular soda.
However, these theories have not been proven, and they are contradicted by other studies showing that people who drink diet soda consume, on average, 15% fewer calories than those who drink regular soda and are more successful at long-term weight maintenance.
Very little is known about the ways in which different low-calorie sweeteners might affect blood glucose control and weight management. Some research has shown that saccharin, aspartame, and acesulfame K may all increase appetite, though the findings are not conclusive. Studies are also beginning to suggest that each sweetener could produce unique effects in the body.
Aspartame has long been among the most controversial of artificial sweeteners, and there is continuing debate — both in the scientific community and among consumers — about its safety, as well as its effectiveness in producing and sustaining weight loss. Although very few studies have examined the role of aspartame in blood glucose control, a recent one found that people with diabetes who drank one or more servings of aspartame-sweetened soda a day tended to have a higher HbA1c level (an indicator of long-term blood glucose control) than those who didn’t.
Another study showed that sucralose — but not aspartame — stimulated the release of a hormone in the digestive tract known as GLP-1. This hormone helps the body regulate signals of hunger and fullness, or satiety, affecting appetite. Thus, it may be possible that the various artificial sweeteners in diet sodas affect hunger and satiety in very different ways.
Much attention has been given recently to stevia, one of the newer sweeteners used in soft drinks. Stevia is unique among low-calorie sweeteners in claiming that it may help regulate blood glucose. Although some studies have shown a favorable effect of stevia on blood glucose control as well as on blood pressure, overall results have been inconclusive. While the highly purified stevia extracts now being sold in beverages and single-serving packets appear to have a very low potential for toxicity or adverse reactions, stevia in its natural form may cause headaches, dizziness, and diarrhea in some people. Consuming large amounts of whole-leaf or less-purified extracts of stevia may also cause interactions with insulin or with blood pressure medicines. People who take these drugs should therefore be cautious when consuming such stevia products (currently sold only as dietary supplements) and probably limit their intake to modest amounts.