It's no secret that overweight and obesity are big problems in the United States. At present, two-thirds of all Americans need to lose weight, and the number of overweight children and adults is growing at an alarming rate.

And it's no secret that obesity is bad for health. Excess body fat raises levels of LDL ("bad") cholesterol and triglycerides while also lowering HDL ("good") cholesterol levels. Obesity impairs the body's responsiveness to insulin, raising blood sugar and insulin levels. But obesity does more than produce bad numbers: it also leads to bad health, increasing the risk of heart attack, stroke, hypertension, diabetes, gallstones, cancer, osteoarthritis, obstructive sleep apnea, fatty liver, and depression. All in all, obesity is a killer; in fact, obesity and lack of exercise are responsible for about 1,000 American deaths each day, and if present trends continue, they will soon overtake smoking as the leading preventable causes of death in the U.S.

Obesity affects men and women about equally. But you may be surprised to learn that men bear a particular burden, since obesity takes a special toll on male hormones, sexuality, and prostate health.

Am I overweight?

A look in the mirror can give you a clue, but to find out if your weight puts you at risk for genitourinary disorders, you need a more precise assessment.

At present, the gold standard is the body mass index, or BMI. You can calculate your BMI by multiplying your weight in pounds by 703 and then dividing by your height in inches squared or by dividing your weight in kilograms by your height in meters squared. Or, if you're like most of us, you can skip the math and use an online calculator.

The BMI gives a reasonable estimate of overall body fat. A BMI between 25 and 30 puts you in the overweight category, while a reading of 30 or more says you're obese. But the BMI doesn't tell you how your fat is distributed. Scientists know that while no excess body fat is good, abdominal fat is the most harmful variety. So to find out if you are at risk, simply measure your waist at your navel; for men, risk begins to rise at waist circumferences above 37.5 inches, and troubles mount over 40 inches.

Obesity and testosterone

Testosterone is the major male hormone. As such, it's responsible for the deep voice, large muscles, and strong bones that characterize our gender, for development of the male reproductive organs, for sperm production and libido, and for the typical male pattern of beard growth. After being converted to dihydrotestosterone, the hormone also spurs growth of the prostate, which is a much less welcome sign of manhood for older gents.

Testosterone levels surge at puberty and peak in early adulthood, and then after a few years of stability, the hormone begins a slow drift downward in early middle age. Because the drop in testosterone averages just 1% a year, most older men retain normal levels. But anything that accelerates the decline can nudge some men into testosterone deficiency.

Obesity lowers testosterone levels. For example, a 2007 study of 1,667 men ages 40 and above found that each one-point increase in BMI was associated with a 2% decrease in testosterone. In addition, a 2008 study of 1,862 men ages 30 and above found that waist circumference was an even stronger predictor of low testosterone levels than BMI. A four-inch increase in waist size increased a man's odds of having a low testosterone level by 75%; for comparison, 10 years of aging increased the odds by only 36%. All in all, waist circumference was the strongest single predictor of developing symptoms of testosterone deficiency. And if you doubt these two American studies, just consider Australian research that found almost one in every seven obese men could benefit from testosterone replacement, a rate more than four times higher than in nonobese men.

Erectile dysfunction

Although men with erectile dysfunction (ED) often blame testosterone, hormonal disorders account for only 3% of ED. But even with normal testosterone levels, men who are obese have an increased risk of ED. For example, a Harvard study found that a man with a 42-inch waist is twice as likely to develop the problem as a gent with a 32-inch waist. Brazilian research also linked abdominal obesity to ED, but only in men older than 60. And a California study reported that having a BMI of 28 (overweight but not obese) increased a man's odds of developing ED by over 90%.

Establishing a link is one thing; finding a way to improve erectile function, another. But a Massachusetts study found that weight loss can indeed improve things for overweight men with ED. Similar results were reported by Italian scientists who randomly assigned 110 obese men with ED to a diet and exercise program or to simply continue their usual care. After two years, more than 30% of the men in the diet and exercise group had corrected their ED without medication, compared with less than 6% in the group that received their usual level of medical care. Men who lost the most weight enjoyed the greatest benefit.

Reproductive function

Obesity takes a toll on sexuality, and it may also impair fertility. American research has linked obesity to low sperm counts and reduced sperm motility; German scientists reported similar findings in men between 20 and 30.

Kidney stones

ED can cause great psychological pain for men and their partners. Kidney stones are much less personal but cause much more physical pain. Stones strike men twice as often as women, and obesity increases a man's risk.

A Harvard study of 45,988 men ages 40 to 75 found that high BMIs and large waist circumferences are both linked to an increased risk of kidney stones. Men who gain more than 35 pounds after age 21 are 39% more likely to develop stones than men who remain lean. Men who weigh more than 220 pounds are 44% more likely to have stones than men who weigh less than 150 pounds. These American results don't explain the reason for the link, but research from Europe and Asia shows that overweight people dump excess amounts of calcium and other chemicals into their urine, where the chemicals form stones.

Benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) becomes more common as men get older. It also becomes more common as men gain girth.

A Harvard study of 25,892 men found that waist circumference was strongly associated with a man's risk of developing BPH symptoms. Men with waists of 43 inches or larger were 2.4 times more likely to need surgery for BPH than men with waists smaller than 35 inches. The Harvard research did not implicate BMI as an independent risk factor, but a Baltimore study did. And scientists in Baltimore and China provide an explanation; they used ultrasounds and MRIs to measure the prostate gland and found that men with bigger bellies have bigger prostates.

PSA levels

The prostate gland is known for scientific puzzles and paradoxes. Here's another: prostate-specific antigen (PSA) levels rise as the prostate gland enlarges, and although obesity appears to grow the prostate, it also lowers the PSA level. According to the 2001–2004 National Health and Nutrition Examination Survey of Caucasian men ages 40 and older, each five-inch increase in waist circumference results in a 6.6% decline in blood PSA levels. But unlike many prostate puzzles, this one has a solution. A study of 13,634 prostate cancer patients found that men with higher BMIs had lower PSA levels, not because their prostates produced less PSA, but because obesity increases blood volume, so PSA is more diluted in the blood.

Prostate cancer

Because obesity lowers PSA levels, it can make it harder for doctors to use PSA measurements to detect prostate cancer in overweight guys. That's a numbers game caused by an artificial lowering of PSA. But obesity also has an adverse effect on the biology of prostate cancer.

Research from around the world shows that extra body fat increases a man's risk of developing prostate cancer. An American Cancer Society study of 404,576 men demonstrated the link: being overweight increases a man's risk by 8%, being obese boosts risk by 20%, and being severely obese increases risk by 34%. And that's not all. Obesity increases the odds that prostate cancer will spread beyond the gland, and it also makes relapse after treatment more likely. In addition, obesity boosts a man's chance of developing urinary incontinence after a radical prostatectomy operation.

Why is obesity such bad news for prostate cancer? Overweight men tend to put off medical care and they have lower PSA levels, so delayed diagnosis is part of the explanation. But obesity also alters the metabolism of sex hormones, which could affect the growth of prostate cancer. Most important, perhaps, obesity increases the body's production of growth factors such as insulin and insulin-like growth factor 1 (IGF-1). Both increase the rate of cell multiplication, and high blood levels of IGF-1 have been linked to an increased risk of prostate cancer, colon cancer, and other malignancies.

Why weight?

In today's America, being overweight is the norm — but it's not normal. In fact, this common problem is one of the things that make diabetes, high blood pressure, stroke, heart attack, and arthritis so common. And if that's not bad enough, it also increases the risk of male maladies, ranging from erectile dysfunction to BPH and prostate cancer.

It's hard to shed excess pounds, but it is possible. There is no quick fix, but there is a slow fix: adjust your diet to take in fewer calories and ramp up your exercise to burn off more calories. It's the manly thing to do, and the time to start is now.

When it comes to improving your health, don't weight.

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