Body fat and health: Less is more

Content provided by the Faculty of the Harvard Medical School

Body fat and health: Less is more

It’s getting harder all the time. Americans are getting heavier and heavier at the same time that researchers are reporting more and more benefits of being thin. Obesity has reached epidemic proportions; at present 30% of Americans are overweight, 30% of Americans are obese, and 5% are very obese. And doctors have added asthma to the list of diseases that are more common in overweight people. It’s a long list that already included diabetes, cholesterol abnormalities, heart disease, high blood pressure, stroke, osteoarthritis, gallstones, many cancers, and the disturbed sleep pattern called obstructive sleep apnea.

Given that a staggering two-thirds of American men need to lose weight, is it any wonder that diabetes and high blood pressure have increased at an alarming rate or that heart disease and stroke have stubbornly retained their positions as the first and third leading killers of Americans? But what if you are in the lucky 35% who have a normal weight — are you home free or do you still need to watch your weight?

There was a time when doctors thought that normal was good enough. But a study from Harvard suggests that, as with blood pressure and cholesterol, lower is better, even within the “normal” range.

Evaluating obesity

The issue is not body weight but body fat. That’s why the traditional insurance company height and weight charts have been largely abandoned. Researchers can measure body fat quite accurately with special tests such as bioelectrical impedance testing, magnetic resonance imaging, and underwater weighing. Despite their value, these methods are cumbersome and expensive, which is why they’re not widely available. But that doesn’t mean you have to rely on a peek in the mirror to see where you stand. Instead, you can use a yardstick to check your height, a scale to measure your weight, and a pencil (or calculator) to determine your body mass index (BMI), the body fat standard for population studies and personal risk assessment.

The BMI has been in use since 1869. Although it is less accurate in highly muscular men and in men over age 65, it has emerged as the best overall indicator of obesity and medical risk. To calculate your BMI, just follow four steps:

1. Measure your height in inches (without shoes) and your weight in pounds (without clothing).

2. Multiply your weight by 703.

3. Divide that number by your height.

4. Divide again by your height.

Or, if you are mathematically challenged, you can simply look up your BMI in “Body mass index” (see BMI chart above).

What should you weigh? Your tailor may have one answer, your insurance agent another, your wife a third. American doctors used to be guided by a standard that drew the line between normal and overweight for men at a BMI of 27.8. But, prompted by the rising tide of chronic illnesses related to obesity and the World Health Organization’s criteria, the U.S. Dietary Guidelines offered the following more stringent classification: Men with BMIs below 18.5 are underweight; 18.5–24.9 is considered healthy; 25–29.9 is moderately overweight; and 30 or above indicates obesity.

These criteria reflect a growing appreciation of the expanding burden of obesity in America. But a Harvard study examined the health impact of BMIs in the normal range.

The Harvard study

To evaluate the relationship between weight and health, researchers combined information from the Health Professionals Follow-up Study of 51,529 men and the Nurses’ Health Study of 121,701 women. All the volunteers submitted details about their diet, health habits, and medical histories as well as their height and weight. The scientists tracked the subjects for 10 years, noting the occurrence of illness and comparing those developments to each subject’s BMI.

The results were similar for men and women. They confirmed the dreadful impact of obesity, which was associated with a nearly twentyfold increase in the risk of diabetes as well as a substantial increase in high blood pressure, heart disease, stroke, and gallstones. In addition, the study confirmed that people who are overweight but not obese (BMI 25–29.9) also faced an increased risk of each condition, except that only men were at an enhanced risk of stroke and only women were excessively vulnerable to gallstones.

Within the overweight and obese ranges, there was a direct relationship between BMI and risk; the higher the BMI, the greater the burden of disease. All these findings jibe with earlier studies from around the industrial world. But the study went one step further, looking at the relationship between BMIs in the healthy 18.5–24.9 range and the risk of illness. It found that men and women with BMIs between 22.0 and 24.4 were significantly more likely to develop at least one of the weight-related illnesses than their leaner peers with BMIs between 18.5 and 21.9.

It’s sobering information and leads to the conclusion that although BMIs below 25 are healthy, BMIs below 22 are even healthier. But before you despair, consider additional aspects of this weighty question.

Other perspectives

Chronic illness is bad enough, but death is even worse. Doctors refer to the former as morbidity, the latter as mortality. The Harvard study says that you can lower your morbidity by getting your BMI below 22, but other research shows you don’t have to go quite that low to lower your mortality rate. A major study of 7,735 British men pegged the ideal BMI right at 22; above that very lean level, each 1-point increase was associated with a 10% increase in the risk of heart disease and in the overall mortality rate.

Other studies of men agree. In Japan, the ideal BMI was 22.5 and in Framingham, Mass., it was 22.6. In Norwegian men, the ideal BMI was 21.6 at age 20 but rose to 24.0 at age 70. And in a 1999 study of over one million American adults, the American Cancer Society found that men with BMIs of 23.5–24.9 had the lowest mortality rate.

None of this negates the Harvard study, but it does provide some wiggle room for men fighting the battle of the bulge. And even though mortality rates do rise above BMIs of 22–23, the rise doesn’t get steep until BMIs of 25–26. It’s not a reason to be complacent about your weight, but it does give you a bit more flexibility in setting your goals.

The shape of man

Studies that use the BMI to evaluate how obesity affects health give appropriate weight to the importance of body fat — but they don’t say anything about how that fat is distributed. Although excess fat is never good, some types of body fat are worse than others. Unfortunately, men tend to put on fat where it is most harmful, around the abdomen and trunk.

To determine if you have too much of the worst fat, calculate your waist-to-hip ratio. First, with your abdomen relaxed, measure your waist at its narrowest, which is usually at the navel. Next, measure your hips at their widest, usually at the bony prominence. Finally, divide your waist size by your hip size to learn your ratio.

Waist size (inches) = ratio Hip size (inches)

How does your ratio translate into health risk? The risk of heart attack and stroke increases progressively in men with ratios above 1.0 (for women, the danger begins at 0.8), and the risk is substantial. For example, men with ratios above 1.0 have twice the death rate of those with ratios below 0.85. And according to the Health Professionals Follow-up Study, men with ratios above 0.98 are 2.3 times more likely to suffer strokes than men with ratios below 0.89. That’s a big effect from just a few inches.

The waist-to-hip ratio is a powerful predictor of a man’s risk for heart disease and stroke. But an even simpler index is the waist circumference itself. A waist size larger than 40 inches increases a man’s risk for complications, and a 46-inch waist increases risk substantially. And if heart attack and stroke are not enough to convince you of the value of a narrow waist, consider an earlier finding of the Health Professionals study: Abdominal obesity increases the risk of impotence. A man with a 42-inch waist is twice as likely to develop erectile dysfunction as a man with a 32-inch waist.

Your waist-to-hip ratio will help you interpret your BMI, telling you if you need to shape up. But don’t try to simply reduce your waistline. Americans spend countless millions on plans and gadgets to “spot reduce,” but it’s a waste. The only way to reduce your abdominal fat is to reduce your entire body’s adipose tissue. It’s true that plastic surgeons can do what abdominal crunches can’t, but although operations like liposuction and apronectomy (“tummy tuck”) can improve your profile, a 2004 study shows that liposuction will not improve your metabolism or your health. Moreover, no operation can remove the deeper fat around the abdominal organs, where it counts most (visceral obesity). And in most cases, patients regain the pounds that have been removed surgically.

There is no quick fix, but there is a slow fix, and it involves the same program that’s so good for other aspects of your health.

Your agenda

First, set your own goals. A BMI of 22 and a waist-to-hip ratio of 0.85 would be great, but they’re not in the cards for many men. For the short to intermediate term, at least, pick the best weight that you were able to sustain for a year in adulthood or get out your yearbook to estimate your weight at college graduation or at the age of 25. If you achieve that goal but it’s still too high, you’ll have plenty of time to set new targets based on the medical studies you’ve been reading about.

Second, be patient but persistent. A crash diet is like a yo-yo; what goes down fast is likely to come back up nearly as quickly. Adopt the healthy habits you need slowly and gradually. Aim to lose a half to one pound a week; it may not sound like much, but over the course of six months to a year, you’ll make great gains. But don’t expect steady, linear progress. Your determination to avoid that rich cookie is bound to crack from time to time; even if it doesn’t, your weight will fluctuate without apparent reason. Don’t get down on yourself and give up; like the stock market, weight control is a long-term investment.

Third, realize that diet and exercise are the hand and glove of weight control; nearly everyone who wins at the losing game does both. To lose weight, you’ll have to reduce the number of calories you eat. With nine calories a gram, fat is the most calorie-dense nutrient. Try to get your dietary fat down below 30% of your daily calories, and favor healthful fats such as the ones found in olive oil, fish, and nuts — but don’t overdose on them, because they have as many calories as the saturated fats and trans fatty acids you should avoid.

As you reduce your consumption of fat, substitute filling, vitamin-rich, high-fiber foods such as whole grains, vegetables, and fruits. And don’t get hung up on carbohydrates; it’s wise to cut down on simple sugars and other rapidly absorbed carbohydrates, but don’t deprive yourself of the many benefits of whole grains and other carbs with a low glycemic index (see “But according to Dr. Atkins...”).

Even if you cut down on fat and calories and boost your dietary fiber, you’ll find it nearly impossible to maintain weight loss without exercise. That means doing something for your body nearly every day. A brisk, daily 30-minute walk is great for your health, but to really take the pounds off, consider picking up your pace or extending your walk to 45 minutes or an hour. And don’t forget to do some strength training two or three times a week.

Finally, remember that every little bit helps, no matter what your BMI. For example, one study found that a 10-pound weight loss can boost HDL (“good”) cholesterol by 2 points, another that an 18-pound weight loss can lower blood pressure by 12 points —even though the subjects were still obese. The numbers may sound small, but they add up to big reductions in cardiovascular risk — and that’s the important result, not the numbers on your scale or the notches on your belt.

Realistic goals, real rewards

Some wag once said that you can’t be too rich or too thin. The Harvard study says nothing about the former but supports the latter. Still, you don’t have to be really rich or terribly thin to reap real rewards. Buy a lottery ticket if you are so inclined, then enjoy the many riches of the world, and the people, around you. Set realistic goals for your weight and work patiently to achieve them, then enjoy the real health benefits and personal satisfaction that come from even modest weight loss, especially if it’s accompanied by a regular exercise program.

Last updated:	August 21, 2006