Body Mass Index attempts to estimate how much body fat you have.

If your BMI is below 19:
This indicates a lean BMI, which means you have a low amount of body fat. If you are an athlete, this can be desirable. If you are not an athlete, a lean BMI can indicate that your weight may be too low which may lower your immunity. If your BMI and body weight are low, you should consider gaining weight through good diet and exercise habits, to increase your muscle mass. If you are a trained athlete, your weight based on your measured percent body fat would be a better indicator of what you should weigh.

If your BMI is between 19 and 22:
This indicates the ideal, healthy amount of body fat, which is associated with living longest, and the lowest incidence of serious illness.

If your BMI is between 22 and 25:

This is still considered an acceptable range, and is associated with good health.

If your BMI is between 25 and 30:
You are considered "overweight" and should explore ways to lower your weight, through diet and exercise.  You are at increased risk for a vareity of illnesses at your present weight. .

If your BMI is over 30:
This indicates being overfat, and means your excess fat is putting you at risk for heart disease, diabetes, high blood pressure, gall bladder disease and some cancers. You should consider losing weight through changing your diet and exercising to decrease your amount of body fat.

Study says middle-aged spread can be a killer

December 31, 1997
Web posted at: 10:27 p.m. EST (0327 GMT)

BOSTON (AP) -- Is keeping down your weight a New Year's resolution? Here's some incentive from the world of medicine:

One of the biggest studies ever to look at the effects of weight on longevity concludes that thinner is definitely better at almost all ages, including well into middle age and beyond.

It found that being too heavy seems to shorten life expectancy up to about age 75. After that, being big doesn't seem to make much difference, unless people are really obese.

"The weight associated with the lowest mortality was quite low, even lower than I had hoped it would be," said nutritionist June Stevens of the University of North Carolina, the principal author.

The new work may help settle one controversy among diet experts: whether it's safe to put on a few pounds as we age. Until recently, it was assumed that a little weight gain was nothing to worry about. However, guidelines put out by the U.S. Department of Agriculture in 1995 came down against middle-aged spread. They said people in their 60s shouldn't weigh any more than those in their 30s.

The new study backs the USDA's stand on this. It suggests that staying trim -- even thin -- is healthiest as people go through their 40s, 50s and 60s.

The results support those who believe "it is not appropriate in federal guidelines to endorse the fattening of America," said Dr. JoAnn Manson, an endocrinologist at Harvard Medical School.

The study was based on American Cancer Society data on 324,135 men and women who were enrolled in 1960 and then followed up in 1972. It was published in Thursday's issue of the New England Journal of Medicine, along with an editorial urging doctors not to push people too hard to lose weight.

The study found that the people who live longest have body mass indexes between 19 and 22, which is quite thin. It is about equal to -- or a little under -- the 1983 Metropolitan Life Insurance table of ideal weights.

Body mass index, or BMI, is quickly becoming the standard way of talking about obesity, since it is an easy way to compare the fatness of people of different heights. BMI is body weight in kilograms divided by height in meters squared. 

A 5-foot-4, 118-pound woman has a BMI of 20. Fashion models generally have BMIs around 18.

Mortality seemed to increase significantly when people's BMIs reached 25, and it went up even more sharply when BMIs were over 30. A 5-foot-4, 145-pound woman has a BMI of 25. At 175 pounds, she has a BMI of 30. 

Figures from federal surveys show that 59 percent of American men and 49 percent of women now have BMIs over 25.

Among men who ranged in age from 30 to 44 at the start of the study, 2 percent of those with BMIs between 19 and 25 died during the 12 years of follow-up, compared with 5 percent of the men whose BMIs were over 30.

Among men between ages 60 and 75, 38 percent of the thin people died during the follow-up, compared with 44 percent of those who were significantly overweight.

While the study clearly suggests that staying thin is a healthy thing to do, it does not offer any direct evidence that a New Year's diet will lead to longer life.

Experts believe that weight loss eases high blood pressure and diabetes, but it's never been proved that those who take it off are as healthy as people who never put it on in the first place.

For this reason, Dr. Jerome P. Kassirer and Dr. Marcia Angell, the journal's top editors, cautioned doctors against pushing their patients too hard to lose weight, especially when they are only mildly obese.

"Until we have better data about the risks of being overweight and the benefits and risk of trying to lose weight," they wrote in an editorial, "we should remember that the cure for obesity may be worse than the condition."