Obesity: what’s the genetic connection?

Experts believe that genetics account for about 25% to 40% of the tendency to be overweight. Information is provided about the ‘fat gene‘ and about why people who have lost significant amounts of weight tend to gain it back.

fat-gene“Let’s face it, Sharon. We’re doomed!”

Sharon looked at the lineup of old photos on the top of her grandmother’s mantle and worried that her cousin might be right. Sharon resembled many of Grandma’s deceased female relatives–at least facially–although she wasn’t as heavy as most of them. And for Sharon, the battle against obesity had never been easy. She exercised and ate sensibly, but it was always a struggle to keep a Healthy weight. Were her genes really her biggest enemy in the fight against fat?

Too Much Fat–Not Mirrors, But Measures

When it comes to body fat, how much is too much? First of all, mirrors and old photos are not the best yardstick. In fact, in some illnesses, facial swelling can cause an illusion of obesity by producing a chubby face on a very skinny body. For the true verdict on body fat, health experts use measurements.

The first of these, tables of weight and height (sometimes with age included) are used to arrive at healthy body weight. “Healthy” on these tables is determined by statisticians who compared the lifespan, health history, and body weight of thousands of people. According to these tables, anyone who weighs 20 percent or more above the “healthy” weight for his or her height and sex is considered to be overweight.

Body mass index (BMI), another indicator based on weight and height, is a second way to determine obesity. BMI is calculated by the weight (in kilograms) divided by the square of the height (in meters). According to health experts, a BMI above 30 (some argue for 27) is a sign of obesity. These figures are for adults.

In fully mature bodies, a third measure, the waist circumference, is used. A waist circumference more than 35 inches in a woman or 40 inches in a man usually means a high risk of weight-related problems.

But no matter what the yardstick for obesity, the bottom line is not numbers but health. Obesity is a serious risk factor for heart disease, high blood pressure, diabetes, and gallstones. It’s also been linked to colorectal cancer, to prostate cancer in men, and to cancers of the breast, uterus, and ovaries in women. Health experts estimate that 22 percent of today’s children and adolescents are overweight–an increase of 15 percent from the 1970s. So in spite of media hype about fitness, exercise, and healthy eating, today’s teens are actually heavier than their parents.

Does Fat Run in Families?

For the body, a little bit of body fat is like money saved for a rainy day–it’s stored energy designed to be tapped when times are hard and food is scarce. For our ancestors, storing fat quickly and efficiently may actually have given them a survival advantage over their skinny neighbors in times of poor harvest or plague. But are there really genes that make some human bodies fat-storing aces, or is storing fat a function of behavior?

For centuries, people have guessed that having large amounts of body fat might run in families. When scientists actually began to examine the evidence, they started with studies of identical twins, pairs of people born with exactly the same genes. These twin studies confirmed what families had guessed all along: Identical twins who were fed the same number of extra calories gained the same amount of weight, and their bodies deposited fat in roughly the same places. These, together with other family-based weight studies, lead experts to believe that genes account for 25 percent to 40 percent of the tendency to be overweight.

A Fat Gene

1But where is the fat gene, and how does it work? Can we change it, or maybe modify the body blueprints it contains?

Right now scientists are looking at several candidates for the “fat gene.” One, called Ob (for Obesity), was first discovered in mice who were bred to be genetically obese. Researchers later found a similar gene in humans. The Ob gene apparently contains the inherited directions for a protein called leptin that fat cells secrete into the blood. When this protein enters the blood, it travels to the brain where it shuts off the body’s appetite centers and helps a person stop eating. When the Ob gene is normal, this shut-off mechanism works just fine, but when the Ob gene is missing or defective, the brain doesn’t get the signal that enough is enough.

Although finding the Ob gene is an exciting breakthrough, is it the whole story? Probably not. Most overweight people have appropriate levels of leptin, suggesting that leptin deficiency is not the cause of their obesity. Another gene, one that codes for an enzyme called lipoprotein lipase (LPL) has also drawn the attention of obesity researchers. LPL is an enzyme that is produced by fat cells to store calories as fat. If there is too much LPL, fat storage is increased. Perhaps the LPL gene that regulates LPL will hold the answer to why some of us store more fat than others.

It Keeps Coming Back!

Health experts know that most people put back the weight they’ve lost. If genes account for only 25 percent to 40 percent of the reason why this happens, what other factors are to blame?

First of all, psychological factors, including the way that families deal with food issues, help to determine the role that food plays in our life. Children often learn to see cookies, candy, and other treats as rewards, or as ways to deal with stress or unhappiness. These unhealthy eating patterns, begun in childhood, can persist into adulthood. Unlearning these pattern–is substituting a hot bath or a long walk for a dish of ice cream–is part of the solution to obesity for many people.

Physical activity is another key. Researchers know that it’s not just our genes and our diet that make us obese; it’s the sedentary lifestyle that most of us are trapped in. Today’s teens’ parents, who were lighter as teens, didn’t have PCs and video games.

The Skinny on Fat

Obesity-GeneIf you have health concerns about obesity, check with the experts. Congress authorized the National Institutes of Health (NIH) to set up the WIN Network (Weight-control Information Network) to help all Americans get the skinny on fat absolutely free.

Fat Facts

* About one-third of American adults are overweight.

* Mississippi has the highest percentage of overweight residents (32%); Arizona has the lowest (20%).

* There has been an 8% increase in the number of overweight Americans over the last decade.

Focus on Females

* Girls accumulate the most body fat during their early teens. This is part of the body’s natural preparation for pregnancy and breast-feeding during the reproductive years.

* Girls who use dangerous diets to fight fat to the extreme may risk losing bone mass, may stop having regular menstrual periods, and may trigger lifethreatening nutritional problems.

Diet–What’s “Healthy” Anyway?

According to the U.S. Department of Agriculture, only 1 percent of teens eat a healthy diet.

A healthy diet should in Jude daily:

11 servings of grain
3-5 servings of vegetables
2-4 servings of fruit
2-3 servings of dairy products
2-3 servings of fish, meat, poultry, other proteins

The National Cholesterol Education Program suggests that a healthy diet means no more than 30 percent of calories from fats (no more than 10% from saturated fats). According to Department of Agriculture figures, U.S. teens currently get 40 percent of their daily calories from fats and added sugars.

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