Taking aim at belly fat

Published: August, 2010

Unlike fat parked on the hips and thighs, fat around the middle produces substances that can create serious health risks.

No matter what your body shape, excess fat isn't good for your health. But saddlebags and ballooning bellies are not equivalent. When it comes to body fat, location counts, and each year brings new evidence that the fat lying deep within the abdomen is more perilous than the fat you can pinch with your fingers.

In most people, about 90% of body fat is subcutaneous, the kind that lies in a layer just beneath the skin. If you poke your belly, the fat that feels soft is subcutaneous fat. The remaining 10% — called visceral or intra-abdominal fat — lies out of reach, beneath the firm abdominal wall. It's found in the spaces surrounding the liver, intestines, and other organs. It's also stored in the omentum, an apron-like flap of tissue that lies under the belly muscles and blankets the intestines. The omentum gets harder and thicker as it fills with fat.

Although visceral fat makes up only a small proportion of body fat, it's a key player in a variety of health problems.

As women go through their middle years, their proportion of fat to body weight tends to increase — more than it does in men — and fat storage begins favoring the upper body over the hips and thighs. Even if you don't actually gain weight, your waistline can grow by inches as visceral fat pushes out against the abdominal wall.

Where's the fat?

illustration of abdomen showing visceral and subcutaneous fat

Visceral fat lies in the spaces between the abdominal organs and in an apron of tissue called the omentum. Subcutaneous fat is located between the skin and the outer abdominal wall.

The trouble with visceral fat

Body fat, or adipose tissue, was once regarded as little more than a storage depot for fat blobs waiting passively to be used for energy. But research has shown that fat cells — particularly visceral fat cells — are biologically active. One of the most important developments [since the mid-1990s] is the realization that the fat cell is an endocrine organ, secreting hormones and other molecules that have far-reaching effects on other tissues.

Before researchers recognized that fat acts as an endocrine gland, they thought that the main risk of visceral fat was influencing the production of cholesterol by releasing free fatty acids into the bloodstream and liver. We now know that there's far more to the story. Researchers have identified a host of chemicals that link visceral fat to a surprisingly wide variety of diseases.

Subcutaneous fat produces a higher proportion of beneficial molecules, and visceral fat a higher proportion of molecules with potentially deleterious health effects. Visceral fat makes more of the proteins called cytokines, which can trigger low-level inflammation, a risk factor for heart disease and other chronic conditions. It also produces a precursor to angiotensin, a protein that causes blood vessels to constrict and blood pressure to rise.

Gut check

A tape measure is your best home option for keeping tabs on visceral fat. Measure your waistline at the level of the navel — not at the narrowest part of the torso — and always measure in the same place. (According to official guidelines, the bottom of the tape measure should be level with the top of the right hip bone, or ilium — see the illustration — at the point where the ilium intersects a line dropped vertically from the center of the armpit.) Don't suck in your gut or pull the tape tight enough to compress the area. In women, a waist circumference of 35 inches or larger is generally considered a sign of excess visceral fat, but that may not apply if your overall body size is large. Rather than focus on a single reading or absolute cut-off, keep an eye on whether your waist is growing (are your pants getting snug at the waist?). That should give you a good idea of whether you're gaining unhealthy visceral fat.

illustration of how to measure waist

From fat to disease

Visceral fat can be measured in a variety of ways. CT scans and full-body MRIs are the most precise, but they are expensive and rarely available, so investigators often use estimates based on waist circumference or waist size in proportion to height (see "Gut check"). To ensure that they're not just measuring overall obesity, researchers also check whether a person's waist circumference is higher than average for her or his body mass index (BMI).

Visceral fat is implicated in a number of chronic conditions, including these:

Cardiovascular disease. Several studies have documented this effect. For example, a large study of European women ages 45 to 79 concluded that those with the biggest waists (and those with the largest waists in relation to their hip size) had more than double the risk of developing heart disease. The risk was still nearly double even after adjustment for several other risk factors, including blood pressure, cholesterol, smoking, and BMI. Even in healthy, nonsmoking women, every 2 inches of additional waist size raised the risk for cardiovascular disease by 10%.

Higher visceral-fat volume also has a deleterious impact on several other heart disease risk factors. It's associated with higher blood pressure, blood sugar levels and triglyceride levels, and lower levels of HDL (good) cholesterol. Taken together, these changes, known as metabolic syndrome, create a serious risk for cardiovascular disease and type 2 diabetes.

Dementia. Researchers at Kaiser Permanente found that people in their early 40s with the highest levels of abdominal fat, compared with those who had the least abdominal fat at that age, were nearly three times more likely to develop dementia (including Alzheimer's disease) by their mid-70s to early 80s. Dementia was not associated with increased thigh size.

Asthma. In a large study of California teachers, women with high levels of visceral fat (a waist circumference of more than 35 inches) were 37% more likely to develop asthma than women with smaller waists — even if their weight was normal. The risks were highest for women who were both large-waisted and overweight or obese. The investigators believe that belly fat raises the risk of asthma more than other poundage because it has inflammatory effects throughout the body, including in the airways.

Breast cancer. A combined analysis of several studies found that premenopausal women with abdominal obesity (the largest waist size in proportion to their height) were at greater risk for breast cancer. Large waists were also linked to breast cancer risk among postmenopausal women, but that effect was not significant once BMI was taken into account.

Colorectal cancer. People with the most visceral fat have three times the risk of developing colorectal adenomas (precancerous polyps) than those with the least visceral fat. The relationship was found after many other risks were accounted for. The researchers also confirmed that adenomatous polyps in the colon are associated with insulin resistance, which may be the mechanism that increases the cancer risk.

How lose (and prevent) visceral belly fat

Where you tend to gain fat depends on your genes, your hormones, your age, your birth weight (smaller babies more readily add belly fat later in life), and whether you've had children (women who have given birth tend to develop more visceral fat than women who haven't).

As young adults, women on average have less visceral fat than men, but that changes with menopause. You can't change your birth weight or your genes, and you can't hold off menopause. But there are several ways you can minimize the accumulation of visceral fat. The good news is that because it's more readily metabolized into fatty acids, it responds more efficiently to diet and exercise than fat on the hips and thighs. Here are some approaches that may help:

Keep moving. Exercise can help reduce your waist circumference. Even if you don't lose weight, you lose visceral belly fat and gain muscle mass. Engage in at least 30 minutes of moderate-intensity activity most days, such as brisk walking or bicycling at a casual pace. Also create opportunities to add motion to routine tasks. For example, park farther from your destination and walk the rest of the way, take the stairs instead of the elevator, and stand while you talk on the phone.

Studies have shown that you can help trim visceral fat or prevent its growth with both aerobic activity (such as brisk walking) and strength training (exercising with weights). Spot exercises, such as sit-ups, can tighten abdominal muscles but won't get at visceral fat. Exercise can also help keep fat from coming back.

Eat right. Choose a balanced diet that helps you achieve and maintain a healthy weight. Avoid products that seem to encourage belly fat deposition, especially simple sugars like fructose-sweetened foods and beverages.

Don't smoke. The more you smoke, the more likely you are to store fat in your abdomen rather than on your hips and thighs.

Get your sleep. Too little is bad. A five-year study found that adults under age 40 who slept five hours or less a night accumulated significantly more visceral fat. But too much isn't good, either — young adults who slept more than eight hours also added visceral fat. (This relationship wasn't found in people over age 40.)

Mind your mood. Middle-aged women who show more hostility and had more depressive symptoms tend to have more visceral fat — but not more subcutaneous fat.

Forget the quick fix. Liposuction for cosmetic fat removal doesn't reach inside the abdominal wall.

Image: UserGI15994093/Getty Images

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