Never Say Diet?

by Food and Drug Administration (FDA)

Like millions of her fellow Americans, talk show host Oprah Winfrey has known the thrill of weight loss and the agony of watching the pounds creep back on. Some three years after losing 67 pounds on a liquid formula diet, Oprah lost her battle to stay a size 10 and has sworn off dieting forever.

Considering that weight-loss programs, pills and potions typically slim the wallet but not the dieter, Oprah may be on to something. And, with research pointing to genetic and metabolic differences between stout and slim people, obesity experts are now debating whether dieting can achieve permanent weight loss.

Defining Obesity

Obesity is associated with such health problems as diabetes, gallstones, hypertension, and heart disease. Obesity is also linked to colorectal cancer and to breast, uterine and ovarian cancer in women and prostate cancer in men. But how many extra pounds does it take before a person crosses the line from overweight to obese? It depends on whom you ask: The definition of obesity is currently in a state of flux.

Traditionally, obesity was defined as 20 percent or more above an optimal weight for height derived from actuarial statistics that correlated with lowest death rates. Now, some health experts say that the weight-for-height yardstick is both imprecise and overly restrictive.

Recent research suggests that more important than the amount of extra weight a person carries is where it is located. "Rather than weight-for-height, obesity should be defined in terms of waist-to-hip ratio," says C. Wayne Callaway, M.D., associate clinical professor of medicine at George Washington University in Washington, D.C., and a leading authority on obesity.

Waist-to-hip ratio can be calculated by dividing the number of inches around the waistline by the circumference of the hips. For example, someone who has a 27-inch waist and 38-inch hips would have a ratio of 0.71. A woman whose ratio is 0.8 or higher would be at high risk of weight-related health problems, as would a man whose ratio is 0.95 or above.

Numerous studies show that fat in the hips and thighs is less health-threatening than abdominal fat. While other fat cells empty directly into general circulation, the fatty acid contents of abdominal fat cells go straight to the liver, by way of the portil vein, before being circulated to the muscles. This process interferes with the liver's ability to clear insulin from the bloodstream. As blood levels of insulin increase, muscles and other cells become insulin-resistant, and blood glucose levels rise as a result. In response, the pancreas cranks out more insulin, prompting the autonomic nervous system (which controls heart rate, blood pressure, and other vital signs) to produce norepinephrine, an adrenalin-like chemical that raises blood pressure. This sets the stage for the development of diabetes, hypertension, and heart problems.

Callaway also points out that weight tables do not take age-related weight gain into account (as people age, fat cells become less metabolically active, so one can weigh more and still be healthy) and "arbitrarily" assign lower weights to women at a given height than to men. "There is no evidence showing that women live longer if they weigh less than men of equal stature," he says.

To be a more useful indicator of health risks, experts advocate broadening the definition of obesity to meet three criteria: weight for age and height rather than for gender and height, waist-to-hip ratio, and presence of such weight-related health problems as hypertension.

Food or Fate?

As researchers try to figure out why some people get fat and others don't, it is becoming increasingly apparent that obesity has a variety of causes — heredity, environment, metabolism, and level of physical activity — and, therefore, no single "cure."

Adipose tissue (fat cells) stores energy in the form of fat to meet the body's energy needs when other sources, such as glucose, are unavailable or depleted.

The body has an almost limitless capacity to store fat. Not only can each fat cell balloon to more than 10 times its original size, but should the available cells get filled to the brim, new ones will propagate. As the body stores more fat, weight and girth increase.

A number of studies have shown that genetics may be the most important determinant of how much you weigh. Some people are more prone to weight gain than others even when caloric intake is the same, according to a study of 12 pairs of identical male twins aged 19 to 27 conducted at Quebec's Laval University and reported in the May 24, 1990, issue of the New England Journal of Medicine. After eating an extra 1,000 calories six days a week for 100 days, some of the twins gained 9 pounds apiece while others gained as much as 29 pounds each — in some twin pairs, the extra calories were stored as fat while others used up the excess calories by building muscle tissue. The twins in each pair gained the same amount of weight and in the same places, suggesting that as yet unidentified genetic factors influence the amount of weight gain and its distribution.

The same issue of the New England Journal of Medicine also reported on a study comparing the body mass of 673 pairs of identical and fraternal Swedish twins who had been raised together or apart to determine how much influence heredity had over obesity (identical twins have the exact same genetic makeup whereas fraternal twins do not; twins who were raised together were subject to the same environmental influences while those who were raised apart were not). Even if they had grown up together, the fraternal twins were less likely than the identical twins to share a similar pattern of body weight whereas identical twins — even when raised apart — did not vary significantly in weight. The researchers concluded that genetic factors, apart from diet or lifestyle, strongly influence how much a person weighs.

Previously, researchers at the University of Iowa found evidence of a recessive obesity gene (the child needs one copy of the gene from each parent to have the tendency towards overweight). A study of 277 schoolchildren and their families showed a pattern of obesity that followed the classic model for recessive inheritance.

However, it is likely that a number of genetic mechanisms exert influence on weight, among them genes that dictate metabolism and appetite. One that is being investigated actively is the gene that codes for lipoprotein lipase (LPL), an enzyme produced by fat cells to help store calories as fat. If too much LPL is produced, the body will be especially efficient at storing calories.

LPL is partly controlled by reproductive hormones (estrogen in women, testosterone in men), so gender-based differences in the activity of the enzyme also factor into obesity. In women, fat cells in the hips, thighs and breasts secrete LPL, while in men the enzyme is produced by fat cells in the midriff region. Fat cells in the abdominal area release their contents for quick energy, while fat in the thighs and buttocks are used for long-term energy storage. Thus, a man can often pare his paunch more readily than a woman can shed her saddlebags.

LPL also makes it easier to regain lost weight, according to a study conducted at Cedars-Sinai Medical Center in Los Angeles and reported in the April 12, 1990, issue of the New England Journal of Medicine. Nine people who lost an average of 90 pounds had their LPL levels measured before dieting and after maintaining their new weights for three months. The researchers found that levels of the enzyme rose after weight loss, and that the fatter the person was to start with, the higher the LPL levels were — as though the body was fighting to regain the weight. They believe that weight loss activated the gene producing the enzyme. This may be one reason why it is easier for a dieter to regain lost weight than for someone who has never been obese to put weight on.

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