1128th General Monthly Meeting
Life, Death and the Pacemaker Theory
Prof. Tony Hulbert
School of Biological Sciences, University of Wollongong
Date: Wednesday, 4th August, 2004
Time: 7:00 pm
Venue: Institute Lecture Room 3, University of Sydney (building adjacent to Darlington Centre, City Road)
Metabolism is fundamental to life and the relative rate of this metabolism can vary more than 100-fold between different animal species. It's only recently that a mechanism has been proposed to explain it this variation. It's called the membrane pacemaker theory of metabolism, which proposes that the types of fats that make up cell membranes determines the metabolic rates of cells, tissues and consequently whole animals. Small species which have high metabolic rates have polyunsaturated membranes, while large species which have low metabolic rates have monounsaturated membranes.
Professor Hulbert will explain his theory which has important implications for some of the disease states that plague us such as depression, insulin-resistance and obesity.
Report on the General Monthly Meeting
Professor Hulbert delivered a thought-provoking talk about his work on the metabolic rates of different animals and what that might teach us about basic cellular function and how we could eat a healthier diet.
His work, with colleague Professor Paul Else, also of the University of Wollongong, has revealed large differences between reptile, birds and mammals. But even amongst mammals, there is a remarkable difference between species depending on their size. Small mammals have faster metabolic rates than do very large mammals. This variation makes it possible for all mammals to function at about the same body temperature even though the heat losses of a mouse are much more than those of an elephant (because of much more surface area per kilo of body weight.)
Through a series of meticulous experiments and observations, Hulbert and Else showed that this metabolic variation amongst mammals is a cellular phenomenon. But what in the cell was causing the difference? They showed that Sodium Pumps in the cell membrane operated at different speeds. Could it be the makeup of the membrane influencing metabolic rate?
Cell membranes are made of fats. Which fats are in our cells depends on two things; our genes and our diet. Most of us know that fats divide into Saturated, Monounsaturated and Polyunsaturated. But surprisingly, the only kind of fats our bodies can't make for themselves are Polyunsaturated fats. So if we don't have enough of one Polyunsaturated fat, we replace it with another.
Hulbert believes that the lipid composition of our cells is dictating their metabolic rate. If we don't get enough Omega 3 fats (from green vegetables and fish), our body replaces them with Omega 6 fats. These behave differently in the cell membranes, by slowing metabolic processes down slightly.
Back in the stone age our consumption of Omega 3 and Omega 6 fats would have been about equal. But now, the Omega 3's are swamped by ten times the Omega 6's in our diet. It seems that Soy Oil is now almost exclusively used in the United States as vegetable oil in processed foods. Is this Omega 6 blow-out causing our cells metabolism to slow? Hulbert speculated that any slow down would also affect our body cells' response to insulin - making us more insulin resistant. Could this imbalance in fats be part of the West's obesity and diabetes epidemic?
Hulbert will travel to the United States next year to work on the implications these findings may have for our growing health problems and to fine-tune a breath test which will measure the balance of fats in our bodies.