Over Weight: Causes and Health Risk

For most people, overweight and obese are not scientific terms, but loaded words that trigger anxiety and frustration. In our culture, weight gain is often noticed and generally perceived as an important change in an adult, usually for the worse. Yet, although these two terms are often used interchangeably, they do not mean the same thing. Obesity is a medical term for the storage of excess fat in the body but no single measure of excess fat is generally accepted in determining obesity. It is often defined as being 20 percent heavier than your “healthy weight” but according to what standard? A 250-pound football player may be overweight according to government weight tables, but may actually have a below average amount of body fat. Conversely, a person in a normal weight range who is out of shape could have small muscle mass and from the perspective of body fat be classified as obese.

The line between desirable weight and overweight, and between overweight and obese, is not clear cut, even for experts. Both overweight and obesity must be measured against some arbitrary standard, and the definition must take into account the amount of muscle mass a person has and where the fat is distributed on the body (excess abdominal fat is more of a health risk than fat on the hips).

By virtually any standard a great many of us have been getting fatter not only in the United States, but around the world. A report published in 1999 in the Journal of the American Medical Association (JAMA), which analyzed data from a national survey conducted by the Centers for Disease Control and Prevention (CDC); found that the prevalence of obesity among Americans rose by nearly a third from 12 percent to nearly 18 percent between 1991 and 1998. For this survey, obesity was defined as a body mass index, or BMI, of 30 or higher. Obesity increased in every state, in both sexes, and across all age groups, races, and educational levels. Another report, based on the Third National Health and Nutrition Examination Survey (known as HANES III), used a lower cutoff point for overweight a BMI of 25 or higher and concluded that more than half of adults in the United States are overweight or obese.

Health risks

Doctors have observed for many years that overweight and obesity are associated with disease. Studies also show that the risk for disease rises with increasing weight.

Coronary artery disease (CAD)

Obesity is associated with an increased risk for developing, and dying from, CAD because it may raise LDL (bad cholesterol) and lower HDL (good cholesterol). Diabetes and hypertension  both are also a contributing factors to heart disease mortality.

Hypertension

On average, overweight adults have a risk of hypertension three times greater than for normal-weight people.

Diabetes

Type 2 (non-insulin-dependent) diabetes can be delayed or averted by weight control. Diabetes is three times more common in people who are overweight.

Cancer

Studies have shown that certain cancers (of the colon and prostate in men, of the breast in postmenopausal women, and of the uterus in all women) are more prevalent in the obese than in the non-obese. One large, long-term study conducted by the American Cancer Society revealed those women who were 40 percent heavier than average had a 55 percent higher overall cancer risk than normal-weight women; for obese men, the cancer risk was about one-third higher than for normal weight men.

Causes of weight gain

Why do some people get fat and others don’t? The possibility of a genetic determinant was raised in press reports when researchers at Rockefeller University announced several years ago that they had mapped and cloned an obesity gene in mouse. The ob gene, as it is called, apparently produces a hormone that is secreted by fat cells and controls body weight. The researchers quickly cautioned that more investigation was needed, and that a fat gene in mice doesn’t necessarily mean that human beings are similarly encoded.

Certainly behavioral factors overeating and being sedentary are at work in causing people to be overweight. But other factors are involved as well. These include race, gender, and economic status as well as genetics. African-American men between the ages of 35 and 55 are more likely to be overweight than white men in the same age group, and African-American women 35 to 55 are almost twice as likely to be overweight as their white counterparts. For reasons not well understood, those who live below the poverty line, particularly women, are more likely to be overweight than people at the top of the economic heap.

The tendency to be overweight also appears to run in families though no one is certain to what extent this is a matter of eating habits or heredity. But a study some years ago in the New England Journal of Medicine by Dr. Albert Stunkard and his colleagues concluded, “”Genetic effects plays a significant role in defining fatness in grown-ups, whereas the family environment alone does not have any important effect.”

Dr. Stunkard studied 540 middle-aged adults who had been adopted as children. Their body mass index, which many experts consider the best method to define overweight, bore little relation to their adoptive parents’ index; instead, the daughters tended strongly to follow the pattern of their biological parents, particularly of their mothers, although the sons showed no such relationship to either set of parents. This again emphasizes the complex relationship of genetics and environment to obesity.

Heredity is not destiny

A genetic tendency toward being overweight does not doom a person to be fat any more than a familial tendency in the other direction guarantees thinness. Studies have shown that rats bred for thinness can still get fat on a diet of snack foods; animals genetically prone to be fat will get fatter on the same diet. But both groups lose weight if returned to a normal maintenance diet. Furthermore, even fat-prone rats can be saved from obesity if their physical activity is increased.

If you know that being overweight runs in your family, you can use the knowledge preventively. Because Americans, as a whole, live relatively sedentary lives and have plenty of food available to them, those looking to lose weight must make an effort to keep active and to eat a low-fat, high carbohydrate diet that is moderate in calories.

What is a healthy weight?

Clearly, medical science has more work to do on this whole vexing and confusing subject. Even the most famous weight table, which is based on the actuarial tables of the Metropolitan Life Insurance Company, may be misleading. Actuarial tables do show who lives the longest no argument there but only among people who buy life insurance. In this country only a select group can afford to carry life insurance and thereby show up on the actuarial tables in the first place.

The question “What is a healthy weight?” has no easy answer. Being obese is undeniably laden with risk. On the other hand, a study published in the International Journal of Obesity analyzed 19 other studies of mortality and body weight and concluded that being moderately overweight was not associated with increased mortality from all causes. It appears likely, then, that the health risks of carrying a few extra pounds may have been exaggerated. But where does overweight end and obesity begin?

Weight tables and other indices can only serve as an approximate guide to what you should weigh. The chart above, from the U. S. government, maps out the general weight ranges, plus two categories of overweight. If you take the government’s guidelines seriously, the permitted ranges may seem extremely wide. You do have to make some allowance for your bone structure and gender: though this single chart covers all people, women tend to have less muscle and bone than men and are generally shorter, so they should stick to the lower end of the ranges, while large-boned men will need to aim at the higher end.

Waist size and body shape. Another indicator of weight related health problems is waist size. A Dutch study published in 1998 found that this simple measurement may be as effective as more complex measures of obesity such as the body mass index. The study found that for women, a waist measurement of 34.5 inches signals a serious risk. For men, the cutoff point is 40 inches. People with apple shaped figures (fattest in the abdominal area) have lower HDL (“good”) cholesterol and higher LDL (“bad”) cholesterol than their thinner counterparts. They are at increased risk for heart disease, as well as stroke, hypertension, and diabetes.