Obesity

Causes

The balance between calorie intake and energy expenditure determines a person's weight. If a person eats more calories than he or she burns (metabolizes), the person gains weight (the body will store the excess energy as fat). If a person eats fewer calories than he or she metabolizes, he or she will lose weight. Therefore, the most common causes of obesity are overeating and physical inactivity. Ultimately, body weight is the result of genetics, metabolism, environment, behavior, and culture.

Genetics. A person is more likely to develop obesity if one or both parents are obese. Genetics also affect hormones involved in fat regulation. For example, one genetic cause of obesity is leptin deficiency. Leptin is a hormone produced in fat cells and in the placenta. Leptin controls weight by signaling the brain to eat less when body fat stores are too high. If, for some reason, the body cannot produce enough leptin or leptin cannot signal the brain to eat less, this control is lost, and obesity occurs. The role of leptin replacement as a treatment for obesity is under exploration.

Overeating. Overeating leads to weight gain, especially if the diet is high in fat. Foods high in fat or sugar (for example, fast food, fried food, and sweets) have high energy density (foods that have a lot of calories in a small amount of food). Epidemiologic studies have shown that diets high in fat contribute to weight gain.

A diet high in simple carbohydrates. The role of carbohydrates in weight gain is not clear. Carbohydrates increase blood glucose levels, which in turn stimulate insulin release by the pancreas, and insulin promotes the growth of fat tissue and can cause weight gain. Some scientists believe that simple carbohydrates (sugars, fructose, desserts, soft drinks, beer, wine, etc.) contribute to weight gain because they are more rapidly absorbed into the bloodstream than complex carbohydrates (pasta, brown rice, grains, vegetables, raw fruits, etc.) and thus cause a more pronounced insulin release after meals than complex carbohydrates. This higher insulin release, some scientists believe, contributes to weight gain.

Frequency of eating. The relationship between frequency of eating (how often you eat) and weight is somewhat controversial. There are many reports of overweight people eating less often than people with normal weight. Scientists have observed that people who eat small meals four or five times daily, have lower cholesterol levels and lower and/or more stable blood sugar levels than people who eat less frequently (two or three large meals daily). One possible explanation is that small frequent meals produce stable insulin levels, whereas large meals cause large spikes of insulin after meals.

Physical inactivity. Sedentary people burn fewer calories than people who are active. The National Health and Nutrition Examination Survey (NHANES) showed a strong correlations between physical inactivity and weight gain in both sexes.

Medications. Medications associated with weight gain include certain antidepressants (medications used in treating depression), anticonvulsants (medications used in controlling seizures such as carbamazepine [Tegretol, Tegretol XR , Equetro, Carbatrol] and valproate [Depacon, Depakene]), some diabetes medications (medications used in lowering blood sugar such as insulin, sulfonylureas, and thiazolidinediones), certain hormones such as oral contraceptives, and most corticosteroids such as prednisone. Some high blood pressure medications and antihistamines cause weight gain. The reason for the weight gain with the medications differs for each medication. If this is a concern for you, you should discuss your medications with your physician rather than discontinuing the medication, as this could have serious effects.

Psychological factors. For some people, emotions influence eating habits. Many people eat excessively in response to emotions such as boredom, sadness, stress, or anger. While most overweight people have no more psychological disturbances than normal weight people, about 30% of the people who seek treatment for serious weight problems have difficulties with binge eating.

Diseases such as hypothyroidism, insulin resistance, polycystic ovary syndrome, and Cushing's syndrome are also contributors to obesity. Some diseases, such as Prader-Willi syndrome, can lead to obesity.

Social issues: There is a link between social issues and obesity. Lack of money to purchase healthy foods or lack of safe places to walk or exercise can increase the risk of obesity.

Preventing Obesity in Infants

The longer babies are breastfed, the less likely they are to become overweight as they grow older. Breastfed babies are 15 to 25 percent less likely to become overweight. For those who are breastfed for six months or longer, the likelihood is 20 to 40 percent less.

Preventing Obesity in Children and Adolescents

Young people generally become overweight or obese because they don't get enough physical activity in combination with poor eating habits. Genetics and lifestyle also contribute to a child's weight status.

There are a number of steps you can take to help prevent overweight and obesity during childhood and adolescence. (They'll help you, too!) They include:

Gradually work to change family eating habits and activity levels rather than focusing on weight. Change the habits and the weight will take care of itself.
Be a role model. Parents who eat healthy foods and are physically activity set an example that increases the likelihood their children will do the same.
Encourage physical activity. Children should have an hour of moderate physical activity most days of the week. More than an hour of activity may promote weight loss and subsequent maintenance.
Reduce time in front of the TV and computer to less than two hours a day.
Encourage children to eat only when hungry, and to eat slowly.
Avoid using food as a reward or withholding food as a punishment.
Keep the refrigerator stocked with fat-free or low-fat milk and fresh fruit and vegetables instead of soft drinks and snacks high in sugar and fat.
Serve at least five servings of fruits and vegetables daily.
Encourage children to drink water rather than beverages with added sugar, such as soft drinks, sports drinks and fruit juice drinks.

Preventing Obesity in Adults

Many of the strategies that produce successful weight loss and maintenance will help prevent obesity. Improving your eating habits and increasing physical activity play a vital role in preventing obesity. Things you can do include:

Eat five to six servings of fruits and vegetables daily. A vegetable serving is one cup of raw vegetables or one-half cup of cooked vegetables or vegetable juice. A fruit serving is one piece of small to medium fresh fruit, one-half cup of canned or fresh fruit or fruit juice, or one-fourth cup of dried fruit.
Choose whole grain foods such as brown rice and whole wheat bread. Avoid highly processed foods made with refined white sugar, flour and saturated fat.
Weigh and measure food to gain an understanding of portion sizes. For example, a three-ounce serving of meat is the size of a deck of cards. Avoid super-sized menu items particularly at fast-food restaurants. You can achieve a lot just with proper choices in serving sizes.
Balance the food "checkbook." Eating more calories than you burn for energy will lead to weight gain.
Weigh yourself regularly.
Avoid foods that are high in "energy density" or that have a lot of calories in a small amount of food. For example, a large cheeseburger and a large order of fries may have almost 1,000 calories and 30 or more grams of fat. By ordering a grilled chicken sandwich or a plain hamburger and a small salad with low-fat dressing, you can avoid hundreds of calories and eliminate much of the fat intake. For dessert, have fruit or a piece of angel food cake rather than the "death by chocolate" special or three pieces of home-made pie.
Crack a sweat: accumulate at least 30 minutes or more of moderate-intensity activity on most, or preferably, all days of the week. Examples include walking a 15-minute mile, or weeding and hoeing the garden.
Make opportunities during the day for even just 10 or 15 minutes of some calorie-burning activity, such as walking around the block or up and down a few flights of stairs at work. Again, every little bit helps.