Mirror, mirror …

Two-thirds of Americans are overweight or obese, so the qualitative lines blur on what is considered normal weight.

An August 2010 Harris Interactive/HealthyDay poll found that 30 percent of overweight people believed they were normal size. Moreover, 70 percent of obese people felt they were merely overweight, including 39 percent who were morbidly obese. Interviewers asked respondents for their height and weight to calculate an accurate body mass index (BMI). Interviewers then asked them to describe whether they were obese, overweight or normal size.

“While there are some people who have body images in line with their actual BMI, for many people they are not, and this may be where part of the problem lies,” said Regina Corso, vice president of Harris Poll Solutions. “If they don’t recognize the problem or don’t recognize the severity of the problem, they are less likely to do something about it.”

More said excess weight is an exercise problem, rather than a food problem. Even though exercise has little impact on weight loss, 6 of 10 respondents believed their excess weight is a result of lack of exercise. About half that many – including only 27 percent of the morbidly obese – said they ate more than they should “in general.”

How fat happens

Conventional wisdom is that weight gain is a mathematical phenomenon. It requires 3,500 excess calories to produce a pound of fat. One’s metabolism supposedly is dictated by weight and activity. For example, an active 150-pound man should consume 2,250 calories. If he consumes an average of 1,750 calories a day for a week, he would lose one pound. If he eats a daily average of 2,750 calories for a week, he would gain a pound.

If only it were that easy. Weight gain and loss is highly individual and is the result of a complex set of factors.

One theory is that everyone has a genetically determined weight set point that can fall within a range of 20 to 30 pounds, depending upon nutritional and exercise habits. If a person attempts to go below that range, the body rebels by slowing its rate of metabolism and signaling its hunger.  The familiar lament of the yo-yo dieter – “I gained all my weight back, and then some!” – is a result of the metabolic change.

Some experts speculate the obesity rate is going to increase more slowly because the nation is reaching a sort of obesity saturation point. That implies that nearly everyone who is genetically meant to be obese is now there.

If one parent is obese, the child has a 50 percent likelihood of also being obese. With two obese parents, the risk rises to 80 percent. Obese children almost inevitably become obese adults. The link is likely to be cultural as well as genetic, because family members have similar eating and physical activity habits.

Genes clearly dictate who is the most vulnerable to excessive weight gain, but other factors determine whether weight gain actually happens. For example, the Pima Indians were originally from Mexico, where they were poor farmers without weight problems and the resulting chronic conditions. Those who moved to the United States adopted a different lifestyle. One-half of the Pima Indians in the U.S. now have diabetes and 95 percent of those are overweight.

Despite obesity’s complex causes, researchers continue to attempt to pin the epidemic on one cause.

An Australian researcher declared in 2009 that obesity has doubled in the past 30 years exclusively because of increased calorie consumption. Physical activity had a minor role, he declared, because physical activity levels had not changed much during that time. Children are consuming 350 more calories a day than children of three decades ago, and adults are taking in 500 more.

A Canadian researcher, however, blamed office-based jobs. According to his research, people are eating better and exercising more than they did three decades ago, so sedentary work must be the culprit.

In 1960, about 50 percent of the U.S. jobs required moderate physical activity. That has fallen to 20 percent. That translates to about 120-140 fewer calories expended daily per capita. That lack of activity closely tracks the nation’s weight gain over the past five decades.

It’s the “uh-oh” season for weight gain

Weight gain seems to sneak up on people during the holiday season. This leads to an inevitable New Year’s resolution to shed weight too quickly, leading to disappointment and self-recrimination.

Anyone who struggles to maintain an ideal weight understands the uphill battle. Only about 1 in 6 overweight Americans lose weight and keep it off. Women are better at it than men. However, being married makes it more difficult to keep an ideal for both sexes.

A review of 31 long-term studies involving tens of thousands of dieters offers grim news. More than 80 percent of dieters gain all of the lost weight back within two years, and very few kept it off for five years. One of the biggest barriers to weight loss is striving for an unrealistic body weight. The scientific community believes diets and medications realistically cannot produce more than a 10 percent weight loss. Some of the most respected health organizations – the Institute of Medicine, the World Health Organization, the U.S. Preventive Services Task Force, the National Heart, Lung, and Blood Institute – recommend that health-care providers ask patients to lose no more than that amount.

Linda Bacon, a professor of nutrition at City College of San Francisco and author of Health at Every Size: The Surprising Truth About Your Weight, runs a program to teach overweight people about healthy eating habits and the merits of physical activity. Bacon tracked 78 obese women aged 30 to 45 for two years. Half the group participated in her program and the other half were in a traditional weight-loss program. At the end, both groups essentially weighed the same. But the group in Bacon’s program lowered cholesterol and blood-pressure levels and had higher self-esteem.

Bacon contends that the body will do what it is supposed to do if people learn to enjoy physical activity and to stop eating when they are full. That may be the most sensible weight-control strategy during, and after, the holidays.