The weight paradox is one that is created by societal misconceptions. It is best to be well informed, rather than depend on other people for information. Here is a comprehensive list of all the causes of obesity and even being overweight.

1.The calorie equation
The balance of calories stored and burned depends on your genetic makeup, your level of physical activity, and your resting energy expenditure (the number of calories your body burns while at rest). If you consistently burn all of the calories that you consume in the course of a day, you will maintain your weight. If you consume more energy (calories) than you expend, you will gain weight.

Excess calories are stored throughout your body as fat. Your body stores this fat within specialized fat cells (adipose tissue) — either by enlarging fat cells, which are always present in the body, or by creating more of them.

2.Genetic influences
To date, more than 400 different genes have been implicated in the development of overweight or obesity, although only a handful appear to be major players. Genes contribute to obesity in many ways, by affecting appetite, satiety (the sense of fullness), metabolism, food cravings, body-fat distribution, and the tendency to use eating as a way to cope with stress.

Genes are probably a significant contributor to your obesity if you have most or all of the following characteristics:

• You have been overweight for much of your life.

• One or both of your parents or several other blood relatives are significantly overweight. If both of your parents have obesity, your likelihood of developing obesity is as high as 80%.

• You cannot lose weight even when you increase your physical activity and stick to a low-calorie diet for many months.

Genes are probably a lower contributor for you if you have most or all of the following characteristics:

• You are strongly influenced by the availability of food.

• You are moderately overweight, but you can lose weight when you follow a reasonable diet and exercise program.

• You regain lost weight during the holiday season, after changing your eating or exercise habits, or at times when you experience psychological or social problems.

These circumstances suggest that you have a genetic predisposition to be heavy, but it is not so great that you cannot overcome it with some effort.

3.Environmental influences
Genetic factors are the forces inside you that help you gain weight and stay overweight; environmental factors are the outside forces that contribute to these problems. They encompass anything in our environment that makes us more likely to eat too much or exercise too little. Taken together, experts think that environmental factors are the driving force for the dramatic increase in obesity.

Environmental influences come into play very early, even before you are born. Researchers sometimes call these in-utero exposures “fetal programming.” Babies of mothers who smoked during pregnancy are more likely to become overweight than those whose mothers didn’t smoke. The same is true for babies born to mothers who had diabetes. Researchers believe these conditions may somehow alter the growing baby’s metabolism in ways that show up later in life.

4.The food factor
According to the Centers for Disease Control and Prevention (CDC), Americans are eating more calories on average than they did in the 1970s. Between 1971 and 2000, the average person added 168 calories to his daily fare, while the average woman added 335 calories a day. What’s driving this trend? Experts say it’s a combination of increased availability, bigger portions, and more high-calorie foods.

5.Portion inflation
Portion sizes for foods commonly consumed outside the home have increased over the years, and many experts believe this has contributed to overweight and obesity. Consider a typical fast-food meal that consists of a hamburger, French fries, and a soda. In 1955, consumers were offered only one portion size. Today they can select from multiple portion sizes.

6.The exercise equation
The government’s current recommendations for exercise call for an hour of moderate to vigorous exercise a day. However, fewer than 25% of Americans meet that goal. On the other hand, more people are exercising than in the late 1980s. According to a 2004 CDC report, the percentage of people who say they do no leisure-time physical activity (such as walking, golfing, or gardening) dropped from a high of 32% in 1989 to 25% in 2002.

7.The trouble with TV: Sedentary snacking
The average American watches about four hours of television per day, a habit that’s been linked to overweight or obesity in a number of studies. Data from the National Health and Nutrition Examination Survey, a long-term study monitoring the health of American adults, revealed that people with overweight and obesity spend more time watching television and playing video games than people of normal weight.

8.Stress and related issues
Obesity experts now believe that a number of different aspects of American society may conspire to promote weight gain. Stress is a common thread intertwining these factors. For example, these days it’s commonplace to work long hours and take shorter or less frequent vacations. In many families, both parents work, which makes it harder to find time for families to shop, prepare, and eat healthy foods together.

Sourced from: http://www.health.harvard.edu/staying-healthy/why-people-become-overweight

9.Health Conditions
Some hormone problems may cause overweight and obesity, such as underactive thyroid (hypothyroidism), Cushing’s syndrome, and polycystic ovarian syndrome (PCOS).

Underactive thyroid is a condition in which the thyroid gland doesn’t make enough thyroid hormone. Lack of thyroid hormone will slow down your metabolism and cause weight gain. You’ll also feel tired and weak.

Cushing’s syndrome is a condition in which the body’s adrenal glands make too much of the hormone cortisol. Cushing’s syndrome also can develop if a person takes high doses of certain medicines, such as prednisone, for long periods.

10.Medicines
Certain medicines may cause you to gain weight. These medicines include some corticosteroids, antidepressants, and seizure medicines.

These medicines can slow the rate at which your body burns calories, increase your appetite, or cause your body to hold on to extra water. All of these factors can lead to weight gain.

11.Smoking
Some people gain weight when they stop smoking. One reason is that food often tastes and smells better after quitting smoking.

Another reason is that nicotine raises the rate at which your body burns calories, so you burn fewer calories when you stop smoking. However, smoking is a serious health risk, and quitting is more important than possible weight gain

12.Age
As you get older, you tend to lose muscle, especially if you’re less active. Muscle loss can slow down the rate at which your body burns calories. If you do not reduce your calorie intake as you get older, you may gain weight.

13.Lack of Sleep
Research shows that lack of sleep increases the risk of obesity. For example, one study of teenagers showed that with each hour of sleep lost, the odds of becoming obese went up. Lack of sleep increases the risk of obesity in other age groups as well.

Sourced from: http://www.nhlbi.nih.gov/health/health-topics/topics/obe/causes