Your physical and psychological environments definitely affect appetite and hunger, sometimes leading you to eat more than normal, sometimes less. You’re more likely to feel hungry when you’re in a cool place than you are when you’re in a warm one. And you’re more likely to want high-calorie dishes in cold weather than in hot weather.

Just think about the foods that tempt you in winter — stews, roasts, thick soups — versus those you find pleasing on a simmering summer day — salads, chilled fruit, simple sandwiches. This difference is no accident. Food gives you calories. Calories keep you warm.

Making sure that you get what you need, your body even processes food faster when it’s cold out. Your stomach empties more quickly as food speeds along through the digestive tract, which means those old hunger pangs show up sooner than expected, which, in turn, means that you eat more and stay warmer and . . . well, you get the picture.

Everybody knows that working out gives you a big appetite, right? Well, everybody’s wrong (it happens all the time). Yes, people who exercise regularly are likely to have a healthy (read: normal) appetite, but they’re rarely hungry immediately after exercising because:

• Exercise pulls stored energy — glucose and fat — out of body tissues, so your glucose levels stay steady and you don’t feel hungry.

• Exercise slows the passage of food through the digestive tract. Your stomach empties more slowly and you feel fuller longer. Caution: If you eat a heavy meal right before heading for the gym or the stationary bike in your bedroom, the food sitting in your stomach may make you feel stuffed. Sometimes, you may develop cramps.

• Exercise (including mental exertion) reduces anxiety. For some people, that means less desire to reach for a snack.

Severe physical stress or trauma — a broken bone, surgery, a burn, a high fever — reduces appetite and slows the natural contractions of the intestinal tract. If you eat at times like this, the food may back up in your gut or even stretch your bowel enough to tear it.

In situations like this, intravenous feeding — fluids with nutrients sent through a needle directly into a vein — give you nutrition without irritation. Taking some medicines may make you more (or less) likely to eat. Some drugs used to treat common conditions affect your appetite.

When you use these medicines, you may find yourself eating more (or less) than usual. This side effect is rarely mentioned when doctors hand out prescriptions, perhaps because it isn’t life-threatening and usually disappears when you stop taking the drug.

Some examples of appetite uppers are certain antidepressants (mood elevators), antihistamines (allergy pills), diuretics (drugs that make you urinate more frequently), steroids (drugs that fight inflammation), and tranquilizers (calming drugs). Appetite reducers include some antibiotics, anti-cancer drugs, anti-seizure drugs, blood pressure medications, and cholesterol-lowering drugs.

Of course, not every drug in a particular class of drugs (that is, antibiotics or antidepressants) has the same effect on appetite. For example, the antidepressant drug amitriptyline (Elavil) increases your appetite and may cause weight gain; another antidepressant drug, fluoxetine (Prozac) usually does not.

The fact that a drug affects appetite is almost never a reason to avoid using it. But knowing that a relationship exists between the drug and your desire for food can be helpful. Plain common sense dictates that you ask your doctor about possible drug/appetite interactions whenever a drug is prescribed for you.

If the drug package the pharmacist gives you doesn’t come with an insert, ask for one. Read the fine print about side effects and other interesting details — such as the direction to avoid alcohol or driving or using heavy machinery.

Eating Disorders

An eating disorder is a psychological illness that leads you to eat either too much or too little. Indulging in a hot fudge sundae once in a while is not an eating disorder. Neither is dieting for three weeks so that you can fit into last year’s dress this New Year’s Eve.

The difference between normal indulgence and normal dieting to lose weight versus an eating disorder is that the first two are acceptable, healthy behavior while an eating disorder is a potentially life-threatening illness that requires immediate medical attention.

Although many recent studies document an alarming worldwide increase in obesity, particularly among young children, not everyone who is larger or heavier than the current American ideal has an eating disorder. Human bodies come in many different sizes, and some healthy people are just naturally larger or heavier than others.

An eating disorder may be present, though, when:

• A person continually confuses the desire for food (appetite) with the need for food (hunger)
• A person who has access to a normal diet experiences psychological distress when denied food.
• A person uses food to relieve anxiety provoked by what he or she considers a scary situation — a new job, a party, ordinary criticism, or a deadline.

Traditionally, doctors have found that treating obesity successfully is difficult. However, recent research suggests that some people overeat in response to irregularities in the production of chemicals that regulate satiety (your feeling of fullness).

This research may open the path to new kinds of drugs that can control extreme appetite, thus reducing the incidence of obesity-related disorders such as arthritis, diabetes, high blood pressure, and heart disease. Some people relieve their anxiety not by eating but by refusing to eat or by regurgitating food after they’ve eaten it.

The first kind of behavior is called anorexia nervosa; the second, bulimia. Anorexia nervosa (voluntary starvation), the eating disorder that sidelined Mary-Kate Olsen in 2004, is virtually unknown in places where food is hard to come by. It seems to be an affliction of affluence, most likely to strike the young and well-to-do.

It’s nine times more common among women than among men. Many doctors who specialize in treating people with eating disorders suggest that anorexia nervosa may be an attempt to control one’s life by rejecting a developing body. In other words, by starving themselves, anorexic girls avoid developing breasts and hips, and anorexic boys avoid developing the broad wedge-shape adult male body.

By not growing wide, both hope to avoid growing up. Left untreated, anorexia nervosa can end in death by starvation. A second form of eating disorder is bulimia. Unlike people with anorexia, individuals with bulimia don’t refuse to eat. In fact, they may often binge (consume enormous amounts of food in one sitting: a whole chicken, several pints of ice cream, a whole loaf of bread).

But bulimic people don’t want to keep the food they eat in their bodies. They may use laxatives to increase defecation, but the more common method they use for getting rid of food is regurgitation. Bulimic people may simply retire to the bathroom after eating and stick their fingers into their throats to make themselves throw up.

Or they may use emetics (drugs that induce vomiting). Either way, danger looms. The human body is not designed for repeated stuffing followed by regurgitation. Bingeing may dilate the stomach to the point of rupture; constant vomiting may severely irritate or even tear through the lining of the esophagus (throat).

In addition, the continued use of large quantities of emetics may result in a life-threatening loss of potassium that triggers irregular heartbeat or heart failure, factors that contributed to the 1983 death of singer Karen Carpenter, an anorexic/bulimic who — at one point in her disease — weighed only 80 pounds but still saw herself as overweight.

One symptom of anorexia and/or bulimia is the inability to look in a mirror and see yourself as you really are. Even at their most skeletal, people with these eating disorders perceive themselves as grossly fat. As you can see, eating disorders are life-threatening conditions.

But they can be treated. If you (or someone you know) experience any of the signs and symptoms just described, the safest course is to seek immediate medical advice and treatment. For more info about eating conditions, contact the National Eating Disorders Association, 603 Stewart St., Suite 803, Seattle, WA 98101; phone 800-931-2237; e-mail info@NationalEatingDisorders.org.