The safety of artificial sweeteners has been controversial for years, although the industry has assured us artificial sweeteners were both safe and a great way to maintain a healthy weight and avoid weight-related diseases, doubts remain.

A two-part study recently published in the journal Nature suggests that artificial sweeteners may actually increase the risk of metabolic diseases by reducing the body’s sensitivity to insulin.

In the first part of the study, researchers tested the effects of artificial sweeteners on mice. They found mice who had been exposed to artificial sweeteners in their water experienced elevated blood glucose levels.

A very small human study was also conducted involving seven lean and healthy volunteers, who did not normally use artificial sweeteners, showed that consuming the maximum “safe” amount for a week caused insulin resistance and changes in gut bacteria in four people and no changes in the other three people.