The common perception has been that having a higher percentage of body fat protects against the bone-wasting disease. But US researchers found that overweight women with lots of fat around their abdomens, as opposed to pear-shaped women with more fat on their hips and legs, were at greater risk of osteoporosis and other diseases.
Everyone knows that being overweight is unhealthy, but the key is where the fat is distributed. During the past 20 years researchers have learned that people with apple-shaped bodies (fattest in the abdomen) have a greater risk of heart disease, diabetes, and stroke than those with pear shapes (fattest in the hips, buttocks, and thighs). Some studies also suggest that post-menopausal women who store fat in the midsection and upper body may be at increased risk for breast cancer.
Men are more likely than women to store excess fat in the midsection and develop a beer belly, whether they drink alcohol or not. Women typically store fat lower on the body, which is less of a health hazard (some studies, in fact, have found that this kind of fat may even be protective in some ways). Because of these gender differences, sex hormones probably help determine where fat is deposited. Still, women can be apple-shaped, too, with all the risks that entails. After menopause, in particular, many women start to accumulate more fat around the waist. Heredity and activity level also affect your body's shape.
Why is it bad to be apple-shaped? Abdominal obesity increases the risk of having high LDL (bad) cholesterol, triglycerides (fats in the blood), blood pressure, and blood sugar, as well as insulin resistance and low HDL (good) cholesterol. This cluster of problems is now known as the metabolic syndrome, which in turn increases the risk of diabetes, coronary artery disease, stroke, and some cancers. Abdominal obesity has also been linked to elevated C-reactive protein (a sign of inflammation) and blood clotting abnormalities, both of which play a role in cardiovascular disease.
While fat in the hip/thigh region is mainly stored just under the skin, fat in the midsection is also stored deeper inside the body, in and around the liver and other organs. Fat cells deep in the abdominal area apparently behave differently than fat cells under the skin of the thighs and hips. In scientific lingo, these fat cells are more metabolically active. They may release different substances, for example, more fatty acids which could explain some of the adverse effects. They may directly affect the functioning of the liver. The potential increase in breast cancer risk may be due to estrogen production associated with abdominal obesity.
In a recent study, 50 overweight, pre-menopausal women with an average body mass index (BMI) of 30 were scanned for their distribution of fat and their bone mineral density.
Those with more visceral fat - which is located deep under the muscle tissue in the abdominal cavity - had lower bone mineral density, one of the tell-tale indications of osteoporosis.
There was no strong link between either total fat or subcutaneous fat - which tends to be stored on the hips and thighs - and bone mineral density.
Dr Miriam Bredella, a radiologist at Massachusetts General Hospital and assistant professor of radiology at Harvard Medical School, said: "We know that obesity is a major public health problem. Now we know that abdominal obesity needs to be included as a risk factor for osteoporosis and bone loss."
She added: "Our results showed that having a lot of belly fat is more detrimental to bone health than having more superficial fat or fat around the hips.
"It is important for the public to be aware that excess belly fat is a risk factor for bone loss, as well as heart disease and diabetes."
The study was presented at the annual meeting of the Radiological Society of North America in Chicago on Monday.
According to the National Osteoporosis Society, half of women over 50 and a fifth of men will break a bone during the remainder of their lives, mainly because of poor bone health.
Women tend to suffer from it in later life more than men because they tend to lose bone mass at a greater rate after the menopause.
Are You an Apple?
To evaluate your risk based on your fat distribution, determine your waist-to-hip ratio (WHR) as follows. Measure your waist at the navel, then your hips at the greatest circumference around the buttocks. Then divide the waist measurement by the hip size. A WHR greater than 1.0 for men and 0.8 for women indicates increased risk. That means that the circumference of a man's waist shouldn't exceed that of his hips; a womans waist should measure no more than 80% of her hips.
A simpler but accurate gauge is just to measure your waist: more than 40 inches in men, and 35 inches in women, is a sign of significant abdominal obesity and increased health risks, regardless of height. But those are not magic numbers: there's some evidence that risk starts to rise before those cutoff points.