The explanations for physical and psychological desire for foods are still a mystery; however, there are some questions we can answer.

Q. What is the difference between a craving and hunger?

A. Physiological hunger generally comes on slowly and may be accompanied by physical symptoms like a growling stomach; you may also have stomach pains and feel unfocused or a little dizzy. Your body is telling you it needs fuel — you need to eat. These feelings disappear after eating and do not recur for several hours. But hunger is not completely physiologically driven — there are biological, sensory and cognitive components, says Richard Mattes, a professor of nutrition at Purdue University in West Lafayette, Ind.

A craving, on the other hand, pushes you to eat even when your body doesn't need more fuel. If you are "hungry" one or two hours after eating a good meal, you're probably experiencing a craving.

"A craving is different from hunger in that it is directed to a specific food, taste or texture," says Mattes. "A craving results in more radical behavior — the motivation to follow the sensation is stronger.

"There are two schools of thought: those who think cravings reflect biological signals and those who think they're behaviorally driven. And there's no consensus."

Do we all have cravings? Well, almost all of us. A report in the journal Appetite has stated that cravings for foods are extremely common: 97 percent of women and 68 percent of men report episodes of cravings.

Q. True or false: Waiting 15 to 20 minutes before you go for seconds will curb your appetite?

A. True. According to Hollie Raynor, a staff psychologist at The Miriam Hospital's Weight Control & Diabetes Research Center in Providence, R.I., it takes "about 15 to 30 minutes to feel full. This is because the feeling of fullness has receptors in the stomach, hormones, gut and intestines — which take time to occur."

Q. True or false: The best advice for a craving is just let it pass.

A. Both. A craving lasts about 20 minutes. If you can wait it out, it will pass.

Check your hunger level: If it's been at least four hours since you last ate, you're probably experiencing hunger. Otherwise, you're probably having a craving.

Are you reaching for food because you're bored, lonely or anxious? Then target the "need." Many experts suggest drinking a glass of water. Often, we mistake thirst for hunger. Other experts suggest submitting to the craving but keeping it under control.

Q. True or false: Your body knows when it's nutrient-deficient and craves the nutrients you need.

A. False. "It is not clear at this time if cravings are biological, cognitively driven, learned or a combination of the three," says Raynor. "However, food cravings for most people are not related to nutritional deficiencies."

As Mattes points out: "Cravings are based on custom. When people are stressed or depressed, for whatever reason, they gravitate toward foods that are associated with better times and happier sensations. Pregnant women might crave chocolate, depressed people might crave ice cream. But if there were some biological need, if chocolate were really special, there would be universal cravings, not culturally specific cravings," Mattes argues.

Q. True or false: If a pill could make us feel full, we would all lose weight and keep it off.

A. False. How many times have you been completely full after a huge steak and then eaten dessert just because someone put it in front of you?

The scientific journal Neuroscience & Biobehavioral Reviews reported that the most important reason people stop eating is because they become tired of the food, not because they are full. In other words, if you're enjoying the taste, you'll keep on eating even if you're full. "The more options and variety, the more a person will eat," says Raynor.

In fact, "One of the reasons pharmacological solutions have not been effective long-term is the individual's disconnection from feelings of hunger and fullness. Just having a full stomach is not enough to stop eating; many people eat for emotional or other reasons," says Martin Binks, psychologist and director of behavioral health at the Diet & Fitness Center at Duke University Medical Center.

Charles Stuart Platkin is a nutrition and public-health advocate. Write to info@thedietdetective.com.