Weight loss and appetite control

Monday 5 September 2011 8:48AM (view full episode)

Researchers in Brisbane investigated fat cells and the role they play in obesity.

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Norman Swan: Other Australian research is also showing how complicated weight and appetite control can be but is making some headway in finding ways that might help weight loss in individuals. The Mater Medical Research Institute in Brisbane has an international reputation for its work on the fat cell. Professor John Prins heads the Institute.

John Prins: Yes, so our interest is in the fat cell itself and we and other groups showed around 15 years ago that the fat cells in the body, just like most other cells in the body, turn over, so we get new fat cells all the time and old fat cells die all the time.

Norman Swan: It used to be thought that you were born with a certain number of fat cells and that's what you had for the rest of your life.

John Prins: Yes and that was how the genetic I guess influence on final weight used to be explained. We now know that that genetic influence is explained at a lot of levels including appetite and including how genetically inclined you are to get exercise etc.

Norman Swan: And even your taste for certain foods?

John Prins: Absolutely, food choice, where it's very clear that different individuals are subconsciously drawn to different kinds of food.

Norman Swan: So tell me more about this cell fat turnover, so it's not the fact that we've been born with a certain number of fat cells?

John Prins: No, and in fact our entire complement of fat cells turns over about every 10 years so we turn over about 10% of our cells every year, so it's relatively slow compared to for example skin or muscle cells.

Norman Swan: Which is why cancer of fat cells is quite rare.

John Prins: It probably is, exactly, but also why a cancer of fat cells is actually becoming a little bit more common as people become more obese, there's perhaps an indication, we don't know for certain, that the turnover of fat cells might be greater in obese individuals than in lean individuals.

Norman Swan: So what's the significance of fat cell turnover then for obesity?

John Prins: If you have excess fat, if you're obese or overweight, then there are two contributions to that. There's the number of fat cells you have and also the size of each individual fat cell of the average size. And we know that as an individual gains weight then the first thing that happens is that each of their cells gets a little bit bigger, just stores a bit more fat in each cell and then after a certain point is reached and we don't understand how this decision is made, you then acquire new fat cells. We also now recognise that it's the large fat cells that misbehave in terms of telling the brain what to do or telling muscle what to do. So ideally we would like to have a situation where you have smaller fat cells on average and perhaps even for the same weight if you have a larger number of smaller fat cells then you will be healthier. Fit fat individuals tend to have lots of small fat cells as opposed to larger sized individual cells.

Norman Swan: What studies have you done that suggest that is the case?

John Prins: We are interested in trying to understand how fat decides to recruit new cells. We know that in adipose tissue there's what we call stem cells which are just sitting there ready to develop into fully fledged fat cells at any time and we're very interested in how that's regulated. With a view to potentially if we can understand how it's regulated maybe developing some drugs or strategies which might be a dietary intervention which would reduce the number of fat cells that are produced.

Norman Swan: But you've just told me you don't necessarily won't want to do that.

John Prins: What we might like to do is balance then the size of the cells with the turnover of the cells so if we could understand why when a cell gets to a particular size it stops getting bigger but it recruits new cells then it's that complex interplay that we need to try and intervene with.

Norman Swan: And have you got any candidate interventions?

John Prins: We have discovered a couple of molecules or hormones that are very important in promoting the growth of new fat cells. And so our initial thoughts going back a decade or so were that we should just inhibit that hormone's action in fat cells and therefore we'd have less fat cells developing. But as you've said we've not come to realise that the residual fat cells might then continue to get very large which might not be in the very best interest of the organism. So now we're looking at a combination of approaches, perhaps looking at the factors that cause fat cells to die as well as causing fat cells to grow there'd be different factors we believe and it may be that you could encourage fat cells to die when they get to a certain size and encourage the growth of newer cells which will be smaller and that might be healthier.

Norman Swan: And what diets seem to affect this apart from the hormones?

John Prins: We don't know yet, certainly the body has to work harder to convert non- fat in the diet to adipose tissue.

Norman Swan: This is like protein; the route from protein to fat is quite circuitous?

John Prins: Yeah, that's right it's an expensive way to store fat. Obviously the body doesn't want to get into a situation where it can't utilise food that's available so the body is very good at inter-converting. But it's much happier in converting dietary fat into body fat and it does that very easily and very quickly.

Norman Swan: And what's this hormone that you've been looking at?

John Prins: The hormone that we're interested in which encourages the fat cells to divide and develop into new fat cells is called FGF1 fibroblast growth factor.

Norman Swan: Now everybody is going to be thinking liposuction where you remove fat cells, have you done any work on that?

John Prins: We haven't but there's a lot of work that's been done and to cut a long story short liposuction gives you a very short term cosmetic benefit but it doesn't actually improve your overall health because the remaining fat cells have still got those abnormal signals that they're sending to the brain and they are sending to other tissues. So it doesn't reduce your blood pressure, it doesn't fix your diabetes, it doesn't fix your cholesterol. And that's also probably because liposuction removes fat from under the skin and fat under the skin is relatively benign.

Norman Swan: So in other words you're not moving the abdominal fat?

John Prins: That's right, not moving the fat from inside the abdominal cavity or the tummy but you're also not removing the fat drop that's within the muscle cells or within the liver cells because they cause a lot of trouble as well.

Norman Swan: And does different fat in different parts of the body have different abilities to multiply, in other words will the fat cells regenerate?

John Prins: That's a tough question. We know that in response to either excess food or food restriction the first adipose tissue depot to change size is the one inside the tummy. It's very difficult in human studies of course to get access to that tissue in that sort of way but animal studies suggest that the turnover rate of the intra-abdominal fat cells is much higher than that of the subcutaneous.

Norman Swan: And what about brown fat, is there any relationship at all between brown fat and regular fat, the brown fat that generates energy for newborn babies?

John Prins: We now know that almost all adults still have brown fat and that it is...

Norman Swan: And lean adults probably have more than fat ones?

John Prins: They do and lean adults in a cold room have more than lean adults in a warm environment as well. It does contribute to the overall amount of energy that we burn if you like. The implication of that in terms of weight control has not been clearly shown yet in humans; it's an area of enormous research. And the other area of interest is that under some circumstances white fat can take on some of the characteristics of brown fat.

Norman Swan: Oh really?

John Prins: We may be able to encourage white fat cells to be a bit more brown in their approach to life and they might burn a little bit more energy off rather than store it.

Norman Swan: By sleeping in a refrigerator?

John Prins: Well a variation of that has actually been done by a Canadian group which is putting people in cold suits and observing them for a few weeks and seeing the amount of energy that they utilise or burn goes up.

Norman Swan: It sounds as if it might be easier to take on the food industry. Professor John Prins is Director of the Mater Medical Research Institute in Brisbane.


Professor John Prins
Mater Medical Research Institute,


Dr Norman Swan
Brigitte Seega

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  • D.S. :

    16 Sep 2011 11:51:08am

    Interesting program, but the idea that eating fat makes you fat was contradicted in an earlier program you did on 11 July this year, "A Menu for Weightloss". That research showed no correlation between the amount of fat consumed and weightloss - as counterintuitive as that sounds! It was more about the types of food consumed than about the fat content of those foods. ???