People gain weight when the body takes in more calories than it burns off. Those extra calories are stored as fat. The amount of weight gain that leads to obesity doesn't happen in a few weeks or months. Because being obese is more than just being a few pounds overweight, people who are obese have usually been getting more calories than they need for years.

Genes - small parts of the DNA that people inherit from their parents and that determine traits like hair or eye color - can play an important role in this weight gain. Some of your genes tell your body how to metabolize food and how to use extra calories or stored fat. Some people burn calories faster or slower than others do because of their genes.

Obesity can run in families, but just how much is due to genes is hard to determine. Many families eat the same foods, have the same habits (like snacking in front of the TV), and tend to think alike when it comes to weight issues (like urging children to eat a lot at dinner so they can grow "big and strong"). All of these situations can contribute to weight gain, so it can be difficult to figure out if a person is born with a tendency to be obese or overweight or learns eating and exercise habits that lead to weight gain. In most cases, weight problems arise from a combination of habits and genetic factors. Certain illnesses, like thyroid gland problems or unusual genetic disorders, are uncommon causes for people gaining weight.

Sometimes emotions can fuel obesity as well. People tend to eat more when they are upset, anxious, sad, stressed out, or even bored. Then after they eat too much, they may feel bad about it and eat more to deal with those bad feelings, creating a tough cycle to break.

One of the most important factors in weight gain is a sedentary lifestyle. People are much less active today than they used to be, with televisions, computers, and video games filling their spare time. Cars dominate our lives, and fewer people walk or ride bikes to get somewhere. As lives become busier, there is less time to cook healthy meals, so more and more people eat at restaurants, grab takeout food, or buy quick foods at the grocery store or food market to heat up at home. All of these can contain lots more fat and calories than meals prepared from fresh foods at home.

I'm sure everyone has noticed the increase in weight problems and obesity over the past 20-30 years, yet genes have not changed one bit in that time. There have always been large people, but nothing like the numbers we see today. And look at the diabetes rates. Since genes haven't changed, it has to be cultural.

Like you mention, the lack of exercise is a big factor, but also the huge portion sizes in restaurants, the super-sizing, and the fact that they put high-fructose corn syrup in absolutely everything, and that is supposed to be one of those "addictive" type flavor enhancers. Also, you then shoot out a lot of insulin to get the cells to accept all that sugar, then fat storage increases.

I know menopause does not help and we do naturally gain some weight, but menopausal women in the earlier part of the 20th century were not typically obese or very overweight.

And I do blame food manufacturers (well, I can't blame Big Pharma and the medical industrial complex for everything, LOL), because they will put anything in the food that is cheap and "addictive" if it will line their pockets.

I wish they'd at least give us the option of real sugar from sugar cane, instead of the corn syrup. At least that is less harmful weight-wise (or so some experts say).