Hidden ‘skinny fat’ is worse for your health than flab – but how do you know if you’ve got it?

People can look slim but have visceral fat or VAT (visceral adipose tissue) around their organs. Photo / Sean S

Oh good, another hidden health risk to worry about. Researchers have found that higher levels of visceral (or belly) fat – the insidious, hidden kind that wraps itself around our internal organs – is associated with the dangerous proteins amylase and tau that disrupt brain function and lead to the sort of memory-loss symptoms associated with Alzheimer’s disease.

In the small study at the University of Washington, Seattle, it was established that of 56 middle-aged people, all of whom had a BMI of 32 or above (classified as obese), those with more visceral fat (measured using an MRI scan) had more of the deleterious proteins (established by a PET scan) that were observable up to 15 years before the onset in patients of Alzheimer’s symptoms.

Visceral fat is often described as “skinny fat”, because people who appear slim can still have it and, therefore, be at risk from Alzheimer’s.

So is there trouble ahead for you? Do you need a scan? Two expensive scans? And what is skinny fat, because don’t we have enough to worry about without this oxymoron?

What is ‘skinny fat’ and why is it bad for us?

Visceral fat or VAT (visceral adipose tissue) is more problematic for your health than subcutaneous fat, which is the stuff that lies outside your abdominal cavity, underneath your skin – the flab that gathers increasingly around your waist, bum, thighs, even face as you reach middle age.

Visceral fat, also known as “active fat”, has a variety of ways of attacking you. It produces inflammatory substances that can contribute to chronic inflammation of your body. It affects the function of your hormones, in particular blocking insulin, which can lead to glucose intolerance that, in turn, leads to Type 2 diabetes. Visceral fat can send your blood pressure rocketing and it will also adversely affect blood-clotting.

Research previously suggested that people with more visceral fat suffered measurable brain shrinkage (Hamer, Loughborough University), and now the Seattle study suggests that it creates chemical reactions within the body that will, in turn, create reactions in the brain producing harmful proteins. If you have visceral fat, it is time for some contemplation.

How to tell if you have visceral fat

The researchers in Seattle used magnetic resonance imaging to establish exact levels of subcutaneous versus visceral fat. But it is also possible to employ a CT scan to establish precise body composition. Both of these methods are very expensive, and possibly overkill for the idle worrier.

Two methods exist for the amateur investigator: take a measurement of the circumference of your belly, usually around your navel; and then compare this with your hip measurement, producing a ratio, at which point, Google it. Or you could try the drum test: basically, do you have a protruding belly which is almost hard enough, when tapped on, to produce a sound vaguely like a drum?

There is a third way, and this is a compromise between home investigations and full-on Harley Street procedures: get a DEXA scan. It’s cheaper than an MRI or CT, and almost as reliable, certainly much more accurate than BMI. It’s £175 (NZ$363) for what is basically a three-minute X-ray that will establish your exact body composition: lean mass (muscle), bone density and fat – subcutaneous and visceral with exact percentages. It will even illustrate the site of this fat in yellow blobs on a Rorschach-like image of your body.

Having said all of that, when I went for my own DEXA scan, and the operator and I were waiting for the computer to churn out all the horrifying data (8.6kg of visceral fat, thanks for asking), he said: “Oh yeah, I could tell you had loads of visceral fat as soon as you lay down on the machine. Your stomach was hard as a drum.”

Should you be tested for visceral fat?

Theoretically, it’s possible for you to look thin – svelte, hard-bodied even – but to conceal dangerous levels of visceral fat. A DEXA scan is most useful in identifying people who look pretty thin and fit but lack muscle mass. The other category that a DEXA scan can benefit is those people considered overweight or obese who are in fact quite fit. (A BMI will not distinguish between being overweight and having lots of muscle mass.)

A combination of BMI, measuring around your navel and doing the stomach tap-test can help you work out whether you have visceral fat.

For everyone else, a combination of BMI, measuring around your navel, and doing the stomach tap-test will generally suffice. The truth is, DEXA or no DEXA, the answers will typically be the same: you need to eat healthily and exercise more.

What we can do to lose visceral fat

Good news: visceral fat is easier to get rid of than subcutaneous fat. With exercise and a sensible diet, it is the first fat to come off. This is because it is the last to be created.

Peter Attia, the guru of middle-age health, uses the analogy of a bath. Everyone has a different-sized bath, which fills up with a certain amount of subcutaneous fat but then reaches a limit (everyone has a different limit; some people put on a lot of subcutaneous, others only a little). When you reach your limit, the fat then overflows into your abdomen and settles around your organs. In this sense, people with lots of subcutaneous fat are lucky; they may not have reached their limit - they may have no VAT.

The answer for everyone is the same: a calorie-controlled diet (heavy on the protein). Exercise more, especially brisk, sustained walking. In my case, I succeeded in halving my visceral fat in eight weeks, without going to extreme effort. Lots of walking, and definitely watching what I ate, but I confess I still drank a moderate amount of alcohol. Sixteen weeks later, the VAT has almost disappeared.