When Pepsi announced last week it was dumping the artificial sweetener aspartame from its Diet Pepsi formula, it surprised many people that the soda giant would tamper with the recipe for such a successful product.

But there have been health concerns about aspartame for decades. The sweetener, which is sold under the brand names Equal and NutraSweet, has been linked to at least 90 symptoms, including headaches, dizziness, fatigue, weight gain, depression, and memory loss.

Pepsi's move may simply be one of economics.

It follows a 5.2 percent drop in sales of Diet Pepsi in 2014, and a survey found that aspartame is the main reason many consumers avoid diet sodas.

Studies questioning the safety of diet sodas have increased in number in recent years, finding they raise the risk of:

• Heart disease. Researchers from Columbia University and the University of Miami found that a single diet soda daily over a period of 10 years increased the risk of heart attack and stroke by 43 percent.

• Diabetes. A study published in the journal Nature found that diet sodas change the microbes living in the gut in a way that increases the risk of diabetes.

Researchers at Israel's Weizmann Institute of Science found that mice fed artificial sweeteners developed glucose intolerance.

They also found that people who regularly used artificial sweeteners, including aspartame and saccharin, had elevated levels of HbA1C, a measure of blood sugar. A study conducted at the University of Minnesota found that a single diet soda daily raised the risk of metabolic syndrome and diabetes by 36 percent.

• Weight gain. A study at the University of Texas Health Science Center at San Antonio found those who drank diet sodas were more likely to become overweight than those who drank regular sugary sodas.

For each can of diet soda consumed each day, the risk of obesity increased by 41 percent. After 10 years, those who drank two or more diet sodas a day increased their risk of obesity by 500 percent

According to researchers, aspartame can trigger or worsen many chronic illnesses including Alzheimer's, Parkinson's disease, chronic fatigue syndrome, and fibromyalgia.

One study found that aspartame became a brain toxin when combined with a common food coloring.

Other studies found that drinking two diet sodas every day could cause an increase in belly fat, and that the artificial sweetener, like sugar, actually increases blood glucose levels and leads to diabetes.

Still, the Food and Drug Administration insists aspartame is safe.

In February the agency's Dietary Guidelines Advisory Committee reiterated its stance, although it mentioned a "possible association" between aspartame and the risk of some blood cancers, such as non-Hodgkins lymphoma.

Pepsi will replace aspartame with sucralose — known as Splenda — a somewhat less controversial artificial sweetener, and Ace K, acesulfame potassium, a non-calorie sweetener that's 200 times sweeter than sugar.

Sucralose also has its detractors, however.

Studies show it reduces the "good" bacteria in the gut by 50 percent.

Changes in gut bacteria are linked to obesity and diabetes.

Studies have also shown that sucralose also limits drug absorption. Ace K contains methylene chloride, a carcinogen, and studies of lab animals have connected it to multiple types of cancer.

"Artificial sweeteners, including aspartame, are a disaster," says board-certified family physician Dr. David Brownstein, author of the Natural Way to Health newsletter. "They’re known to cause neurologic problems, autoimmune disorders, and probably cancer."