"I'll have a diet soda with my French fries and double bacon cheeseburger. Oh! And one of those apple things," he added, pointing to a pastry. The guy giving the order then looked at me as I waited my turn to order coffee at the highway restaurant rest stop. "Might as well save some calories, " he laughed as he patted his prominent abdomen. I nodded to him as I asked for my coffee to be sweetened with a packet of the blue non-calorie sweetener.
We all seem to do it: eat a high-calorie meal but drink a no-calorie beverage sweetened with something artificial, munch on a bag of potato chips along with a diet soda, dig into an obscenely rich dessert but add a non-calorie sweetener rather than sugar to our coffee or tea, and drink alcoholic beverages without concern for their calories but "freak out" if we discover we are drinking real soda, rather than the diet stuff.
But do we really think of our coffee sweetened with an artificial sweetener as diet coffee? If we add diet quinine water to a gin and tonic, is the drink now a diet drink? Is artificially-sweetened bottled cranberry juice or flavored iced tea a diet beverage? Do hard candies sweetened with a sugar substitute qualify as diet candies?
A petition just filed with the U.S. Food and Drug Administration by a California-based group, U.S. Right to Know, wants companies to stop using the word "diet" on products that use artificial sweeteners. The petition states that: "Consumers are using products -- Diet Coke and Diet Pepsi -- that are advertised to make us think they assist in weight loss, when in fact ample scientific evidence suggests that this is not true and (instead quite) the opposite may well be true." 
Interesting. Do people really believe that they will lose weight by drinking these products? I doubt that the man standing in front of me contemplating his snack of a double cheeseburger, fries and dessert thought that he would be three pounds lighter because he drank a diet soda. And I suspect that my not ordering a doughnut (although I wanted to) along with my coffee had more of an impact on my weight than putting that stuff from that blue packet in my coffee.
The writers of the petition reviewed the research literature on diet beverages and weight gain that seemed to confirm the need to remove the word diet from sugar-free beverages. Some studies such one published in the Yale Journal of Biology and Medicine in 2010 suggested that artificial sweeteners may contribute to weight gain,  and another in 2012 found that an association between artificially sweetened beverages and weight gain might exist in children.  But just because an association exists between two events doesn't mean there is a causative relationship between them. I have a relative who drinks copious quantities of a caffeinated diet beverage because she hates coffee and tea, but wants to consume caffeine throughout the day. She doesn't like the taste of the fructose-sweetened version of the caffeinated sodas; they taste too sweet to her. If I asked her whether she thought drinking so much diet soda would help her lose weight, her answer would be, "In my dreams."
However, might diet beverages indirectly cause weight gain? Might the man in front of me at the fast food restaurant justify ordering dessert because his beverage contained no calories? Do we have less guilt at gobbling up a rich dessert because there is no sugar in our tea? Do we reach for the sugarless chocolate ice cream in the freezer without a thought to its calories because it is artificially sweetened?
There is another, more biologically-subtle, reason why so-called sugar-free foods might cause weight gain. Many people have a natural and unavoidable craving for carbohydrates, especially in the afternoon and/or evenings. The craving arises from their brains and is related to the brain's need to make the neurotransmitter serotonin. Often the craving is accompanied by a small, but very real, deterioration in mood. Eating a carbohydrate, sweet or starchy, will restore serotonin levels and improve mood soon after the carbohydrate is digested. [4 ]If the craver attempts to satisfy this need to eat something sweet with something artificially sweetened, there will be no restoration of serotonin levels in the brain and no improvement in mood. So what happens? The craver may eventually give in to his or her craving, which was, of course, not satisfied by the diet beverage. Consequently, this person may scarf down a snack food that is sugary but also high in fat like a chocolate chip cookie, an ice cream cone, a candy bar, or a cupcake with three inches of frosting.
Perhaps if the craver satisfied the craving immediately by eating a low-calorie, mildly-sweet snack like graham crackers or licorice sticks rather than attempting to quell it with the diet beverage, the impulse to eat a fattening carbohydrate snack could have been curtailed.
It will be interesting to see what becomes of the petition. Since so many of us order a diet (fill in the blank) drink without giving a nanosecond's thought to the word diet on the label, it may be very difficult for us to get used to another name. We tend to use the work Xerox instead of copy as in, "I will Xerox this" or Kleenex rather than facial tissue as in, "I have a Kleenex." So I suspect we will continue to call artificially sweetened beverages diet, even though we know they are not.