Why belly fat is the worst kind

Scientists are changing their minds about the best way to monitor body fat.  Body mass index, or BMI-long considered the gold standard for evaluating an increased risk of health problems due to weight, is far from the perfect measure, according to researchers.

BMI  is calculated as weight (kgs) over height (M sq'd).  It has long been 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 BMIs differ from that of Caucasians.  If you are very muscled, it overestimates the BMI, eg Arnold Swartzengger apparently has a has a BMI of 34 which (mis) places him in the 'obese' category,

BMI also fails to measure visceral, or belly fat,and this is what is  more significant  to your overall health and risks of future diabetes, heart disease and stroke. than knowing one's BMI.

The best way to measure visceral fat, so called as it lies deep inside the body, wrapping around the liver and other major organs, is by a CT scan.  This takes a picture of a slice through the body, like a slice of bread, and shows the amount of 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. 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 fine- without measuring your waist.  While most overweight people have excessive visceral fat, even people with a normal BMI can have an unhealthy waist circumference.

Meausure yopur waist at it's narrowest point, as viewed from the front.  That's usually at the naval for normal weight people,  if you are overweight,meausre at the level of your elbow when your arms are at your sides.  Pull the tape measure snug.

For white and black men, above 40 inches denotes an increase health risk.  For asain men, it's greater than 37 inches.

For white and black women, 35 inches or more indicates increased risk; for Asian woman it's greater than 31 inches.

In a study by researchers at Pittsburgh University last year, abdominal fat was strongly linked to metabolic syndrome, regardless of whether they  were normal or over weight. 

The metabolic syndrome is a grouping of risk factors, such as high blood pressure and high cholesterol, that can predict diabetes and heart disease. Another study has shown that people with the most abdominal fat are 145% more likely to develop dementia than normal people,.

Why is fat around the middle so dangerous for health, whereas deposits of fat on the thighs seem to be cardio-protective, ie, 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 shrinking 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.  As visceral fat is in the region of the body near a very large vein which feeds the liver (the portal vein), these 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 presursor of diabetes.

It also seems to decrease the production of the hormone leptin, which signals satiety in healthy weight people, and produces a number of low level inflammatory substances which predispose to heart disease.  Fat has long been known to produce the female hormone oestrogen, which is one of the reasons very overweight men become 'feminised', ie have breast development and a reduction in potency.

The good news is that visceral fat can be lost, most quickly and effectively by physical activity.  Dieting alone for weight loss tends or lose more subcutaneous, or superficial, fat.

This is why many people find that their trousers fit better when they begin an exercise program even though they are not losing much weight.  The exercise needs to be vigorous enough  to just break a sweat and be done for 30 minutes a day

Whether an individual lays down much visceral fat as they age is related to their genes, but also because as we age we tend to move less, eat about the same (or more) and lose muscle mass.  This is why people tend to get bigger bellies and thinner legs as they age.