This is the first of a two-part series on weight loss. Look for the second installment Thursday.

They may taste sweet and have no calories, but health experts warn against drinking diet sodas.

“In our business, diet soft drinks are poison,” said Dr. Fernando B. Bonanni Jr., the director of the Institute for Metabolic and Bariatric Surgery at Abington Memorial Hospital.

In fact, people should avoid all artificial sweeteners in baked goods, drinks or other forms. Although there is no substitute for diet sodas, they aren’t worth it, he said.

“In general, people should avoid anything wrapped in cellophane, loaded with sodium, artificial sweeteners, or [anything that] has a shelf life longer than the planet Earth,” Bonanni said with a laugh.

He recommends drinking water—six to eight glasses a day.

“It is a natural diuretic and an essential component of our bodies. It helps curb hunger, and it is as healthy as you can get for a zero-calorie liquid. It also helps curb your appetite for carbohydrates,” he said.

If need be, drink sparkling water or club soda with citrus to get a soda feel.

Evidence continues to support Bonanni’s opinion of diet drinks. Science Daily recently reported two studies that link artificial sweeteners and diet sodas to weight gain.

“Epidemiologists from the School of Medicine at The University of Texas Health Science Center San Antonio reported data showing that diet soft drink consumption is associated with increased waist circumference in humans, and a second study that found aspartame raised fasting glucose (blood sugar) in diabetes-prone mice,” according to its website, www.sciencedaily.com.

Those studies came as no surprise to Bonanni, who cautions people from overreacting.

“First of all, the controversy surrounding sweeteners and diet soft drinks will never end, and nothing is ever as bad as it seems to be,” Bonanni said.

He said that some studies link obesity to diet soda, including the ones that have recently been discussed in the news. Bonanni cautions though, that consumers must understand a few fundamentals of diet soda before looking at data.

“First of all, those who drink diet drinks are more likely to be overweight and or diabetic. Diabetics are obviously avoiding sugar, and overweight people use it as a diet drink,” he said.

According to Bonanni, when you correct the data for overweight people and diabetics, the results of the studies are not as dramatic.

“The exact numbers are debatable, but the truth is, yes, there is still a relationship with lack of weight loss, weight gain and poor eating habits associated with diet soft drinks,” he said.

Regardless of these recent studies, Bonanni recommends people avoid diet sodas for several other reasons. For some, drinking a calorie-free beverage is an excuse to eat more calories in a meal.

“For example, people feel they are free to eat French fries because their soft drink has zero calories. Ask yourself why Burger King sells diet coke and 600-plus calorie burgers,” he said.

Another reason to avoid diet drinks is that sweeteners induce hunger, which can trigger many weight loss unfriendly mechanisms such as producing insulin and grehlin, which is the hormone that causes hunger, and an impaired insulin response, according to Bonanni.

“It is also widely believed that artificial sweeteners do not necessarily cause hunger, but do fail to trigger the satiety mechanism that natural sugars trigger,” he said.

Not to mention that all of those things enhance energy preservation by lowering the metabolism, producing insulin, impairing insulin response and storing carbohydrate energy into fat.

People who want to lose weight or maintain a healthy lifestyle should not drink diet soda. Natural sugar in low quantities is not harmful, but Bonanni said that people should not drink any calories. Leave the calorie consumption to food—healthy food, such as lean protein, vegetables and fruits.