Q. I’ve been following a "Longevity Lifestyle" for several months and have done very well. I seem to have plateaued, however, and I’ve even gained a pound or two back. Someone told me to stop drinking diet sodas. That's one of the choices I've hung onto because I really don't want the extra sugar found in regular sodas. Any comments?

A. You know I do (smile). Puzzling to me is how people persist in believing that diet sodas will help them lose or maintain an optimum weight—even in the face of research that contradicts that supposition—and continue to drink them. On average, you can figure that a 12-ounce can of regular soda contains sugar to equal 150 calories—a hefty hunk if you're wanting to maintain optimum weight levels. So you don't want the extra sugar found in regular sodas and other soft drink. I agree. Since sugar does tend to increase your weight, some move to diet sodas that contain no sugar.

Problem: Diet drinks typically contain artificial sweetener, or you probably wouldn't be able to tolerate the taste otherwise. In general, when your taste buds sense sweetness they notify your brain that something sweet is coming—and sweet tastes typically contain calories. The brain releases insulin to digest those calories, which triggers a biochemical cascade (as Steven Susskind MD puts it) that promotes a sense of feeling full.

Artificial sweeteners still notify the brain—but the diet-soda sweet isn't followed up with the promised calories. Gradually the brain learns to ignore sweet tastes as a predictor of calories-to-come. Instead, the brain wants more and more food. Those who use diet sodas tend to eat more calories later in the day or the following day (if they don't outright binge on sweets or simple carbs) than they would if they didn't drink diet sodas.

In a study published in Physiology and Behavior, researchers followed healthy adults who either drank at least one diet soda daily or avoided drinking diet soda altogether. After measuring brain scan activity, researchers found that regularly drinking diet sodas inhibits activation in a key area of the brain that helps to regulate food intake. The more diet soda participants drank, the less their sweet sensors worked properly. The brain's ability to let them know they were full stopped working properly. A long-term study from the University of Texas found that diet soda drinkers' waists expanded five times more than those who did not drink diet sodas.

For this reason, drinking pure water as your beverage of choice and avoiding all sodas, regular or diet, is a component of a longevity lifestyle.