Scientists are changing their minds about the best way to monitor body fat. Body Mass Index (BMI) has long been considered the gold standard for evaluating an increased risk of health problems due to unhealthy weight. However, researchers now think that this is far from the perfect measure. BMI is calculated as weight (kgs) over height (in metres squared). It is internationally accepted that a BMI of 18-25 is 'ideal,' 25-30 is 'overweight,' and over 30 is 'obese'. However, the BMI doesn't take into account the amount of muscle a person has and is less accurate in older people who lose muscle and bone and gain fat with age. It is also less accurate in Asian and Islander ethnic groups because their body fat percentage at various BMI's differs from that of Caucasians. If you are very muscled, this also leads to an inflated BMI, for example, Arnold Schwarzenegger apparently has a BMI of 34 which (mis)places him in the 'obese' category.
BMI fails to measure visceral or belly fat, which is more significant to your overall health risks of future diabetes heart disease and stroke. Visceral fat is the fat that lies deep inside the body wrapping around the liver and other major organs. The best way to measure it is by CT scan. This takes a picture of a slice through the body like a slice of salami and shows the amount and location of body fat. It's not possible to do a CT on everyone though, so luckily a tape measure gives a good indication of how much visceral fat a person has. The evidence is so compelling that some experts suggest that it's time to ditch the scales in favour of the tape measure.
Don't assume you're too fat around the middle - or just right - without measuring your waist. While most overweight people have excessive visceral fat, even people with a normal BMI can have an unhealthy waist circumference.
Measuring Your Waist
Measure your waist at its narrowest point as viewed from the front after exhaling. That's usually at the navel for normal weight people. If you are overweight, measure at the level of your elbows when your arms are at your sides. Pull the tape measure snug. Too tight is cheating! For white and black men, above 40 inches/94 cm denotes an increased health risk. For Asian men, it's greater than 37 inches/92cm. For white and black women, 35 inches/80 cm or more indicates increased risk; for Asian women, it's greater than 31 inches/78cm.
In a study by researchers at Pittsburgh University in 2006 abdominal fat was strongly linked to the “metabolic syndrome" regardless of whether they were normal or overweight. The "metabolic syndrome" is a grouping of risk factors such as high blood pressure and high cholesterol which can predict diabetes and heart disease. A Canadian analysis published earlier this year looked at 15 studies including more than 250000 people. It found that for every 1cm increase in waist circumference above the ‘ideal' your relative risk of having a cardiovascular event (heart attack or stroke) increases by 2%.
Types of Fats - Not-So-Hidden Dangers
Why is fat around the middle so dangerous for health, whereas deposits of fat on the thighs seem to be cardioprotective? In other words, why is being an apple is worse than being a pear? Fat cells were once thought to be inert inactive storage units containing a droplet of oil (the fat) that expanded in a person gaining weight and shrank in someone losing weight. Now scientists realise that it is much more complex than this. Fat cells are actually mini hormone factories that produce a range of substances. One of these is harmful fatty acids. Visceral fat is in the region of the body near a very large vein (the portal vein), which feeds the liver so fatty acids are thought to gain entry to the liver by this route setting off a chain of events that can lead to insulin resistance the precursor of diabetes. They also increase blood lipids including triglycerides and cholesterol. We tend to lay down more visceral fat as we age. This is partly related to our genes but also because as we age we tend to move less eat about the same (or more) and lose muscle mass due to the ageing process itself. The good news is that visceral fat can be lost most quickly and effectively by physical activity. Dieting alone for weight loss tends to result in the loss of subcutaneous or superficial fat. Exercise promotes the loss of visceral fat. Having more muscle has in turn been shown to positively enhances insulin sensitivity (insulin resistance=diabetes).
Article written by Ian Scarborough. B.Sci (Exercise Science) Post. Grad. in Science (Exercise Rehabilitation) Level One Strength and Conditioning Coach-ASCA MAAESS AEP