The grim reality is that, as a nation, Americans are getting fatter. If you're skeptical, just take a peek at the "Fat Clock" on www.DietDetective.com. It shows in real time the total weight gain of all Americans — approximately 8 pounds per second. In fact, the average weight for a woman in the United States is about 166 pounds, and for a male it's about 191.

Weight matters: If you're obese, you're at increased risk for many chronic diseases, including type-2 diabetes, coronary heart disease, stroke, hypertension, sleep apnea and certain types of cancer.

What is to blame for this epidemic? Fast food? Television?

According to David B. Allison, a University of Alabama biostatistician, "It's not as simple as saying we need to change X and everything will be fixed; there are many factors involved."

According to an article in the International Journal of Obesity, there are factors aside from sedentary behavior and too much food that could be causing our weight gain. Here are a few that the researchers found might be packing on the pounds.

LACK OF SLEEP

How it makes you fat: It can increase hunger and appetite. Also, when you're tired, you're less likely to be able to make the healthiest food choices.

The fix: "Go to bed earlier, and aim for seven or eight hours of sleep," says Milton Stokes, of the American Dietetic Association. Set up your environment for sleep success. Make sure the temperature is correct and you have the proper bedding.

"If your mattress is more than 7 years old, examine if it's time for a new one. You could spend a third of your life in bed, so don't buy the cheap model," adds Stokes. Other tips: Have a regular bedtime. Get rid of the TV in the bedroom. And make your sleep environment quiet — aesthetically and in terms of noise.

AIR CONDITIONING AND HEATING

How it makes you fat: Yes, you read it right. There is something called the thermoneutral zone, which is the temperature at which we don't need to expend calories to stay comfortable. So the mere fact that we have air conditioning in the summer and heat in the winter could be increasing our belt sizes. For instance, if you're cold, and you turn up the heat, your body doesn't have to burn calories to keep warm. Research also suggests that being too comfortable may restrict blood flow, which can affect your weight.

The fix: Louis J. Aronne, a weight-control specialist at Weill Medical College of Cornell University, recommends not keeping your office or home at one temperature year-round because that can promote weight gain. Varying the temperature above or below the thermoneutral zone can increase energy expenditure.

ENVIRONMENT

How it makes you fat: Industrially produced substances that include DDT and PCBs are known as "endocrine disrupters." Research shows they may interfere with hormones and cause an increase in body fat.

The fix: Be more concerned about the chemicals in your food supply.

NOT SMOKING

How it makes you fat: Ever wonder why the French don't get fat? It may be because they smoke a lot. Research shows that smokers weigh less than nonsmokers. The nicotine in cigarettes has both thermogenic (calorie-burning) and appetite-suppressant effects. According to Stokes, ex-smokers are tempted to eat more, because the food tastes better and they often need something to do with the extra free time and with their unoccupied hands and mouths — so they eat. Also, when stress hits, where smoking used to help, food is often the replacement.

The fix: Obviously, this doesn't mean you should take up smoking — or refrain from quitting. Planning is key here. Come up with alternatives to fill the free time and for stressful situations. For instance, chew your favorite gum. Or, better yet, Stokes recommends taking a bike ride or a walk when you want to smoke. "If at work, get up from your desk and climb the stairs. Guzzle eight ounces of water. Suck on a lemon." Physical activity might work well because it helps control that increased appetite. Try a variety of tactics to see what works.

PHARMACEUTICALS

How they make you fat: Certain pharmaceuticals, including antipsychotics, antidepressants, anticonvulsants, antihypertensives, steroids, antidiabetics, contraceptives and antihistamines, can interfere with the hormones that regulate body weight and cause you to gain.

The fix: Whatever you do, don't stop taking your medication without consulting your physician. However, it's not uncommon that changing medications can help you lose enormous amounts of weight, says Aronne. Other suggestions: Keep a journal of your weight, and if it is creeping up, analyze why, suggests Stokes. You might need to reprogram your behavior and adjust your diet once you realize that your appetite is being stimulated by medication. Also, there are nutritionists who specialize in working with those on medication. To find out more, contact the American Dietetic Association (eatright.org).

MORE REASONS WHY WE'RE GAINING WEIGHT