A third of the U.S. population is now overweight, making it just a matter of time before normal-size people are actually in the minority. Americans have so ballooned in size, government safety regulators worry that airline seats and belts won't restrain today's men who average 194 pounds and women who average 165 pounds in the event of a crash.

Not everyone agrees that obesity is always a health problem. You can be overweight and still have normal blood pressure, blood sugar, HDL cholesterol and other metabolic markers if you exercise, say some, pointing to U.S. Surgeon General Regina Benjamin, who hiked the Grand Canyon in 2010 despite her extra poundage.

But others say fitness and exercise will not reverse the health effects of obesity. The British medical journal The Lancet recently reported that rising obesity in the U.K. will cause an extra half a million cases of heart disease, 700,000 cases of diabetes and 130,000 of cancer by 2030. And the overweight and obese are 80 percent more likely to develop dementia writes Kerry Trueman on AlterNet.

And there are other obesity "negatives." The obese are less likely to be employed, earn less than people of normal weight and "have more days of absence from work, a lower productivity on the job and a greater access to disability benefits," reports the Paris-based policy group Organisation for Economic Co-operation and Development.

Obesity raises Medicare, Medicaid and private insurance costs and affects national security, writes David Gratzer on KevinMD.com, "since thousands of recruits are turned away from military service because of failed physicals and poor overall health." It also shortens "the lifespan of millions of decent Americans who deserve better," he writes.

Yet eating too much and exercising too little, considered the root of obesity, are not the only probable culprits. Here are some other factors that are often overlooked.

1. Depression and Depression Drugs

Classic depression is characterized by a decrease in appetite, weight loss and general despondency. But in 1994, "atypical depression" debuted, a subtype of depression characterized by an increase in appetite and weight gain (as well as oversensitivity to rejection by others). Unfortunately, both types of depression are often treated with popular antidepressants like Prozac, Zoloft, Lexapro and Paxil and antipsychotics like Seroquel, Zyprexa and Risperdal, all of which can pack on the pounds.

To keep the weight gain from affecting Pharma sales, the pro-pill site, WebMD, tells patients that keeping the pounds off is their responsibility since only "healthy eating and exercise help control your weight gain." But it also counsels if the pill weight gain is "so strong that it simply can't be offset by any amount of calorie restricting or even exercise," the psychoactive medication "to help overcome your depression is far more important." To whom?

2. Artificial Sweeteners

Artificial sweeteners, found in soft drinks, many diet foods and an astounding number of children's cereals for unclear reasons, may do more harm than good. While marketed and perceived as helping people avoid calories, they can have two insidious side effects: because they are sweet they encourage sugar craving and sugar dependence just like salty foods train people to crave salt, says research in the Yale Journal of Biology and Medicine.

And, because sweetness is "decoupled from caloric content," they fail to satisfy the sweets reward system and actually further fuel "food-seeking behavior," wrote the researchers. See: giving hungry dog rubber bone. One artificial sweetener, Splenda, also has molecular similarities to endocrine disrupter pesticides, say food safety advocates.

3. Antibiotics

Noting that the average child in the U.S. and other developed countries "has received 10–20 courses of antibiotics by the time he or she is 18 years old," microbiologist Martin Blaser published some disturbing suggestions in the journal Nature last year. By killing "good" bacteria with important roles in the body, "Overuse of antibiotics could be fuelling the dramatic increase in conditions such as obesity, type 1 diabetes, inflammatory bowel disease, allergies and asthma," he reports.

Yes, obesity. Mice given low-dose antibiotics that mimic farm use and high-dose antibiotics that mimic infection treatment in children exhibited preliminary "changes in body fat and tissue composition," says Blaser. Mice developed as much as a 40 percent increase in fat and a 300 percent increase in fat when given a high-fat diet too, extrapolated Alice Wessendorf on the research. Denmark researchers found eerie parallels in humans. Babies given antibiotics within six months of birth were more likely to be overweight by age 7.

4. Endocrine Disrupters

Antibiotics are not the only widely used substances that may be associated with a host of human problems. Chemicals called endocrine disrupters, found in everything from canned foods and microwave popcorn bags to cosmetics and carpet-cleaning solutions, are linked to breast cancer, infertility, low sperm counts, genital deformities, early puberty and diabetes in humans and alarming mutations in wildlife.

Many are aware of the endocrine disrupter BPA (Bisphenol A) banned in baby bottles and sippy cups in Washington state but given a pass by the FDA in March. But few realize that similar endocrine disrupters are found in flame retardants like phthalates and PBDEs, thermal receipts given out at stores and in "antibacterial" dish detergents and toothpaste, like Tricoslan found in Colgate's Total. Endocrine disrupters may also be linked to obesity. Pregnant women with high levels of PFOA, one disrupter, were three times as likely to have daughters who grow up to be overweight, reported the New York Times' Nicholas Kristof in May.

5. Start 'em Young Marketing

Bad eating is learned young and unfortunately some of the worst messages come from TV, parents and school. In a study in the journal Pediatrics, 4- to 6-year-olds who tasted identical graham crackers and gummy fruit snacks with and without cartoon characters "significantly preferred the taste of foods that had popular cartoon characters on the packaging."

Researchers who studied 500,000 California middle- and high-school students found those with schools near fast-food outlets were heavier. And another study of kids 12 to 19 found not one child ate a diet meeting all five of the American Heart Association’s criteria. Even though almost a third of U.S. children and teens are overweight, 84 percent of parents believe their children are at a healthy weight, say researchers, which compounds the problem.

6. Hooked on Cookies…and Chips, Pizzas and Ice Cream

For some overweight people, overeating is an actual addiction. Like alcoholism, food addicts are "preoccupied with their drug (food). Whether they are thinking about their next meal, trying to suppress their cravings, planning their diet, feeling guilty about their last binge [or] hoping to find the strength to say no to that dessert or second helping," writes Arya M. Sharma on KevinMD.com.

Like alcoholics, they dream their troubled relationship to food can miraculously heal, perhaps if their brain readjusts its "setpoint" or they spend "an hour in the gym each day," says Sharma. The increase in food addiction might correlate with the decrease in family meals, indicates some research. Studies by the National Center on Addiction and Substance Abuse reveal that food and other addictions are less likely to develop in children of families who eat together three times a week. Who remembers family meals?

7. Lifestyle Factors

There's another habit we learn (or don't learn) while growing up that can contribute to obesity–a strict bedtime, which few adults or children observe anymore. After just six nights of getting only four hours sleep, healthy young volunteers showed signs of prediabetes, reports the Chicago Tribune.

Other studies show sleep-deprived adults are more likely to be fat, regardless of how much they exercise and what they eat. Why? Researchers hypothesize that sleep deprivation changes levels of the hormone ghrelin (that tells the brain to eat), leptin (that tells the brain we're full) and the stress hormone cortisol. There's even another lifestyle contribution to obesity: room temperature. ABC News reported that air conditioning can add weight by sparing the body the need to regulate temperature, which is a mechanism that burns fat.

8. Government Duplicity

Is the government really helping people to slim down and avoid foods that pack on pounds and invite the risk of heart disease? High-saturated-fat foods like cheese? Not according to a New York Times expose in 2010. A USDA group with 162 employees called Dairy Management, mostly funded by farmers, is shamelessly committed to getting people to double and triple their cheese intake to replace profits from falling milk sales.

According to the Times, Dairy Management has supported Pizza Hut, Taco Bell, Burger King, Wendy's and Domino’s in "cheesifying" their menu options, putting dairy farmers' profits before consumer health. "If every pizza included one more ounce of cheese, we would sell an additional 250 million pounds of cheese annually,” rhapsodized the Dairy Management chief executive in a trade publication. Dairy Management received $5.3 million from the USDA during one year, for an overseas dairy campaign, which almost equals the total $6.5 million budget of USDA's Center for Nutrition Policy and Promotion. That's the group that tells people not to eat high fat milk and cheese!