An FDA Guide To Dieting

An FDA Guide to Dieting

Introduction

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 portal 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.

Research indicates that obesity may be linked to the proportion of fat in the diet rather than to the amount of calories consumed.

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.

Set for Life?

This study supports the much-debated "set point" theory, which holds that inner mechanisms set a person's weight at a predetermined level and if anything is done to change the weight, the body will adjust to restore fat content to the set point.

"I regard body temperature, which stays around 98.6 degrees F, to be a set point. Weight doesn't have a set point in that sense," says Xavier Pi-Sunyer, M.D., director of the Obesity Research Center at St. Luke's-Roosevelt Hospital Center in New York.

If there is a set point for weight, it generally seems to move in one direction--that is, the body will not make adjustments to counteract a large weight gain but will fight efforts to lose the weight. "When a person gains weight and stays at that weight a while, the body will defend that weight. It becomes the new `set point'," explains Pi-Sunyer.

Aside from the action of LPL, the body uses other adaptive mechanisms when food intake is reduced. To cite just two of them: Dieting depresses the metabolic rate so that calories are burned more slowly, and as fat cells shrink, they become more responsive to the action of insulin and do not release their contents as readily.

"The body is very good at defending itself from the danger of underweight, but is not really equipped to handle overweight. Throughout the ages, people have not had a problem with having too much to eat. That's a modern problem," says Pi-Sunyer.

Though a definitive study has yet to be done in humans showing that weight gain becomes more likely after each successive diet (the so-called "yo-yo" syndrome), the Cedars-Sinai study strengthens this controversial hypothesis. However, in order to show conclusively that weight loss gets harder each time a person loses and regains weight, the subjects in the Cedars-Sinai study would have to be followed through several cycles of weight gain and loss to determine whether LPL levels kept rising after each diet.

Repeatedly losing and gaining weight may have other health consequences, according to a report in the June 27, 1991, New England Journal of Medicine. American and Swedish researchers analyzed weight fluctuations and later health problems over a period of 32 years in more than 3,000 women and men who participated in the Framingham (Mass.) Health Study. The researchers said that people who repeatedly lose and regain weight appear to have an overall higher death rate and to be at greater risk of heart disease and some cancers than those whose weight remains stable (even if overweight) or steadily increases.

Are All Calories Created Equal?

"The body will do what it was programmed to do even if that's not what you want it to do," notes Callaway. For this reason, restricting food intake to 1,000 or 1,200 calories in order to lose weight is "doomed to failure," he says. "For many people, going on one more diet isn't going to solve a weight problem in the long run."

Even well-established weight-loss programs are not individualized enough to account for genetics, past dieting attempts, and a person's activity level, he says.

While Pi-Sunyer agrees that putting everyone on the same prepackaged weight-loss regimen can be counterproductive, he believes that restricting caloric intake is an important weight-control tool. "You can easily cut caloric intake just by restricting the amount of fat and sugar you eat. This might be the only adjustment a moderately overweight person would need to make in order to lose weight."

Research indicates that obesity may be linked to the proportion of fat in the diet rather than to the amount of calories consumed, according to a survey of the diets and exercise habits of 107 men and 109 women reported in the September 1990 issue of American Journal of Clinical Nutrition. Researchers at Indiana University in Bloomington found that overweight subjects got 35 percent of their calories from fat and 46 percent from carbohydrates, compared to 29 percent of calories from fat and 53 percent from carbohydrates for their slender counterparts. A recent University of Vermont study suggests that limiting fat intake to about 20 percent of total calories enabled chronically obese patients who failed to lose weight on a variety of reducing programs to lose an average of 20 to 30 pounds over the course of a year.

Scientists used to think that all calories were created equal. That is, whether it came from fat, carbohydrates or protein, a calorie produced a certain amount of heat when the body burned it to fuel metabolic processes. Thus, according to "The Dieter's Law of Thermodynamics," mashed potatoes and milkshakes were no more culpable in promoting weight gain than pasta and peas--as long as caloric intake was limited to 1,000 or some other magic number.

Alas, further research has shown this to be an illusion. Calories from carbohydrates, fat and protein are used differently by the body. Virtually all fat calories are immediately stored in fat cells. Carbohydrates and protein are converted into glucose for fuel, with only those calories in excess of the body's energy needs being stored.

Compounding the problem, a gram of fat has 9 calories while an equal amount of carbohydrates or protein has 4. "For the same number of calories, a person can have a much bigger serving of a food that is primarily carbohydrate as one that is high in fat," observes Walter Glinsmann, M.D., associate director for clinical nutrition at the Food and Drug Administration's Center for Food Safety and Applied Nutrition. For instance, a 6.5-ounce baked potato has the same number of calories as 1.5 ounces of potato chips (about 225).

The type of fat in the diet is important as well. Currently, the National Cholesterol Education Program recommends that the diet be limited to 30 percent of calories from fat, with no more than 10 percent of those coming from saturated fats. "Unsaturated fats are precursors of such biologically active molecules as prostaglandins, which are involved in a variety of body processes, including blood pressure regulation and immune system function. Various types of fat have different roles in health maintenance and disease risk," says Glinsmann.

Exercise the Key

Rather than severely restricting caloric intake and depressing metabolic activity as a result, weight-loss specialists now advise moderate exercise as a means of achieving weight control. "A person not only burns calories while exercising, but if he or she is eating an adequate amount of food, calories will continue to be burned at a higher rate for up to several hours afterward," says Callaway.

"For most people, cutting fat intake and adding moderate exercise can work as well as a commercial weight control program," says Pi-Sunyer. Exercisers are also more likely than sedentary people to keep weight off, whether they use a "do-it-yourself' diet or attend a program.

Unfortunately, weight maintenance is a universal failing of all weight-loss programs, regardless of how expensive or well-established. "If you're going to evaluate weight-loss success, you can't just look at the number of pounds lost. You have to look at long-term weight maintenance," says Callaway.

"Diet programs make money on the weight-loss phase, not the weight maintenance phase. At the time when people need the most help in controlling their weight, many programs cut them off," says Pi-Sunyer. By various estimates, as many as 85 percent of dieters put the weight back on within two years after weight loss.

"Perhaps weight-loss programs should be less focused on weight control and more focused on identifying individual risk factors and dietary patterns associated with obesity, and to modify them where possible," suggests Glinsmann.

"Obesity is not yet well understood," concedes Pi-Sunyer, "and all we can do right now is to tell people to exercise and to cut down on fat intake." However, while genetic predisposition towards obesity can be mitigated by exercise and sensible eating habits, some people will have to work a lot harder at keeping weight at optimal levels than others. "It's like jazz--there's a theme and rhythm and you've got to work within that framework, but you can improvise," says Callaway.

Product Bans and Controversies

In the wake of last year's House Committee on Small Business hearings on the $33 billion weight-loss industry, FDA and the Federal Trade Commission separately announced investigations into the safety and efficacy of diet pills and programs, and how they are promoted in advertising. FDA also moved to pull dangerous or ineffective products off store shelves.

In the fall of 1990, FDA proposed a ban on 111 ingredients in over-the-counter (OTC) diet products, including amino acids, cellulose, grapefruit extract, and kelp. The agency had given manufacturers of these products an opportunity to provide data from clinical tests showing they were effective in promoting weight loss, but did not receive adequate information to support advertising claims, according to William Gilbertson, Pharm.D., director of FDA's OTC Drug Review Program. "Many of these ingredients had been marketed before 1962 [when an amendment to the 1938 Food, Drug, and Cosmetic Act was passed requiring drugs not only to be safe, but also effective] and had never been evaluated for efficacy," Gilbertson explains.

He says that manufacturers wanting to market weight-loss drugs using the banned ingredients will have to get prior FDA approval--which means filing a new drug application and supplying data from clinical tests to support claims.

FDA also recalled Cal-Ban 3000, a heavily advertised diet pill containing guar gum (a vegetable gum that swells when it absorbs moisture, providing a feeling of fullness, according to advertising claims) after receiving a number of consumer complaints of adverse reactions. In a number of cases, the tablet caused gastric or esophageal obstruction, and one person died as a result of complications following surgery to remove the mass of gum blocking his throat.

The most widely used ingredient in OTC diet pills, phenylpropanolamine hydrochloride (PPA), an appetite suppressant that is chemically related to amphetamines, has been the subject of a decade-long medical dispute. Though clinical tests yielded conflicting results (often due to defects in study design), an FDA panel concluded in 1982 that enough data existed to support the efficacy of PPA in curbing the appetite to qualify it as an OTC weight-loss aid. However, a controversy developed over PPA's safety. The drug can cause small elevations of blood pressure at recommended doses, and there are a few reports of marked blood pressure elevation and intracranial bleeding associated with its use. Whether such events are truly drug-related and can occur at recommended doses is the subject of debate.

In May, FDA held a public meeting to explore such issues as whether PPA can cause such central nervous system damage as stroke when taken at (or over) the recommended dosage, whether the drug poses a health hazard to teenagers, and whether PPA is especially hazardous to those with eating disorders.

For its part, FTC has begun to look into advertising claims of 14 diet programs. "We are concerned with programs that go beyond promising weight loss and claim to be able to keep the weight off," says Richard Kelly, assistant director of FTC's division of service industry practices. Additionally, FTC is looking into whether diet companies are touting the safety of their programs while playing down such health risks as the development of gallstones or loss of muscle tissue. Kelly expects the FTC investigation to be completed by the end of the year.

FTC also monitors advertising claims for diet aids on an ongoing basis and takes legal action to get companies to stop making unfounded claims. Among the agency's recent targets: Fat-Magnet, a pill that claimed to break up into thousands of tiny "fat-attracting" particles that "flush" fat from the body, and Fibre Trim, a high-fiber supplement that its manufacturer claimed could aid in weight reduction.

FDA's ban of ineffective diet drugs could make future FTC action easier. "The FDA says these products are not efficacious, which is a good piece of evidence to have when we go to trial," says Judy Wilkenfeld, assistant director of FTC's advertising practices division.

Consumers can get a list of ineffective diet aids by writing to: FDA, HFE-20, 5600 Fishers Lane, Rockville, MD 20857.

About the Author

Ruth Papazian is a freelance writer in New York City specializing in health and medicine.

Document Source:

U.S. Department of Health and Human Services
Public Health Service
Food and Drug Administration, HFI-40
Rockville, MD 20857.
DHHS Publication No. (FDA) 92-1188
October 1991

[Rees AM (ed): Phoenix, Oryx Press, 1995, pp 343-346.]