Diabetes and heart disease may stem from fat you can't see

Becoming fat brings conspicuous changes to the shape of the human body, but pioneering research in the Department of Medicine at Flinders University, Australia is working on the theory that the obvious "spare tyre" may not be the major culprit in fat-related diseases.

In obese and overweight people, fat is deposited in different sites in the body. While large deposits of fat typically accumulate subcutaneously and around the internal organs, the Flinders research points to less easily detected deposits of fat lurking within muscles and organs as potentially important in increasing risk of diseases such as diabetes and heart disease.

Using a combination of magnetic resonance imaging (MRI) and spectroscopic measurements, researchers at Flinders are aiming to uncover the relationship between fat deposits in different parts of the body and the body's ability to utilise glucose.

Honours student Madeleine Phillips is conducting a pilot study that is employing these two techniques on 14 patients who have recently undergone gastric banding surgery as a means to lose weight. This elective laparoscopic procedure reduces the available digestive capacity by applying a band around the top part of the stomach, and the stomach's capacity can be further reduced through tightening the band by filling an inflatable silicon balloon with saline solution.

MRI scans and spectrographic measurements are taken before surgery and 12 weeks postoperatively to keep track of the change in the volume of fat in the respective areas in their bodies.

Along with blood pressure, the patients' fasting blood levels of insulin and glucose are also measured.

"There is a simple mathematical equation where you can determine insulin sensitivity from those two measures, and we are relating that to their weight loss," Ms Phillips said.

"In the end, we hope to able to identify a change in one fat depot that was most related to the change in insulin sensitivity."

Ms Phillips said the pilot study was testing techniques and methodology to pave the way for a larger-scale study.

She said MRI scans were proving ideal for the study of subcutaneous and visceral fat. As well as being non-invasive, the images clearly contrast fat against organs, enabling straightforward calculations of fat volume. More complicated spectroscopic analysis is required to identify fat peaks in organs and muscle, and is being undertaken by Ms Phillips' academic supervisor, Associate Professor Campbell Thompson.

The presence of fat in the organs and muscles is an alarm signal. Fat in the liver, for instance, is abnormal in healthy people, Ms Phillips said, and is seen as a precursor for serious liver disease.

"The occurrence of fat in the liver has traditionally been seen among those who consume alcohol in excess of recommendations, but is now a common finding in obese people."

Ms Phillips said the research was possibly the first in the world to explore the differential effects and health consequences of weight loss, and would play a part in helping to address the escalating level of obesity in Australia and the Western world with its attendant increase in chronic diseases.

Ms Phillips' collaborators in her research include Dr John Slavotinek and Robin Valentine in the Radiology Department and Professor Jim Toouli and Dr Lilian Kow in the Department of Surgery. The work is funded by a grant from Diabetes Australia Research Trust.

Ms Phillips said that while some sectors of science and medicine had been calling for urgent action on obesity for the last 30 years, they had met with little response.

"Maybe now that it's got to the extent it has, people will look at techniques such as banding as a real, viable option, and a necessity for these people," she said.

"Surgery like this is still widely seen as aesthetic, but in terms of health it is really fundamental."