Big FAT Lie
Thursday, 24 October 2002
Have we been wrong all these years?
For thirty years we’ve been told that when it comes to diet, fat is bad and carbohydrates are good. That’s why carbohydrates form the base of the food pyramid.
Yet over the same time, obesity has increased dramatically, as has the incidence of diabetes, heart disease and cancer. Could these all be connected?
Our diet is now lower in fat and much lower in sugar than it was 20 years ago, but it’s higher in carbohydrate. Australian research is showing that some carbohydrates are bad for our health. Have the health experts been wrong all these years? Catalyst investigates…
Narration: Woody Allen’s movie “Sleeper” set 200 years in the future, made some bold predictions about how wrong we could be in our current thinking of what makes a healthy diet.
You mean there was no deep fat? No steak? Or cream pies or hot fudge? Those were thought to be unhealthy – precisely the opposite of what we now know to be true. Incredible!
Narration: And what you are about to hear may make you think Woody wasn’t far wrong. This is a story about what makes you fat. And if you just said ‘fat’ – go to the bottom of the class. For thirty years or so we’ve been told that it’s the fat in these foods that’s making us fat. Now, a growing band of researchers is saying that’s not the case.
Dr David Ludwig: …..dietary fat is not a primary cause of the obesity epidemic and low fat diets are unlikely in and of themselves to be the cure……”
Narration: We have lowered our fat intake and increased our carbohydrate intake just as the experts told us to. The famous food pyramid put carbohydrates – bread, rice, pasta, potatoes and breakfast cereals there at the bottom – the food type we should eat most of. Yet, we continue to get fatter at an alarming rate. In the last 20 years, the number of obese adults in Australia has doubled and – more worrying – there are nearly four times the number of obese children.
Dr David Ludwig: There’s no question that the dramatic increases in prevalence of obesity in the United States, in Australia and throughout the world constitute a major public health crisis.
Narration: So, if fat isn’t making us fat what is? According to Jennie Brand-Miller author of The Glucose Revolution Life Plan – it’s carbohydrates. Not all carbohydrates but those that have a dramatic effect on our blood sugar levels. Traditionally, we’ve classified carbohydrates by their chemical structure –Jennie’s been investigating them from a completely different angle. She’s looking at their glycemic index – the way they affect our blood sugar.
Jennie Brand-Miller: Well in my research we’ve been able to show that the ones that produce the highest blood sugar responses or more correctly blood glucose responses”….. “that that’s a pathway which can lead to excess body fat in the animal studies that we’ve done and we’re getting early evidence that that’s also true in humans.
Narration: Conventional thinking has been that because the fat we eat has more kilojoules than carbohydrates do, dietary fat has been the main culprit in obesity. But Jennie believes that we’ve been ignoring the crucial human hormone, insulin, which is produced by the body when blood sugar levels are high.
Jennie Brand-Miller: Here we’ve got a typical human cell and here we’ve got what’s called a mitochondria, it’s the area in the cell which produces energy from the food that we eat. There’s either glucose and there’s fat both of them are competing for entry into the mitochondria. When there’s a lot of insulin around it drives glucose into the cell and displaces fat. that means only one thing. It means that you’re going to gradually accumulate more and more fat on your body if you’re insulin levels are always high.
Narration: To test the theory that our bodies can’t burn fat when our blood sugars are high, Jennie Brand-Miller’s group did a study of rats over 32 weeks – the equivalent of 30 years of a human life. There were two groups of rats. Both got exactly the same number of kilojoules, the same percentage of fat, fibre, protein and carbohydrate. But the carbohydrates were different – one was high glycemic index (or GI) and the other was low.
Jennie Brand-Miller: The high GI fed rats they very gradually accumulated fat until by the end of the 32 weeks they were about 16% heavier. That evidence is very powerful evidence that a high glycemic index diet even when it’s the same calories is actually producing a fuel mix which is conducive to gradual body fat gain.
Narration: Jennie Brand-Miller’s testing (on people this time) has shown that some carbohydrates like white bread, potatoes, rice and most breakfast cereals have a high glycemic index – which means they raise blood sugar levels very quickly – surprisingly even more quickly than table sugar. And that leads to the other mechanism that these researchers believe is making us fat – hunger stimulation. Basically, the more your blood sugar levels fluctuate, the more hungry you get.
Narration: At the Children’s Hospital in Boston, David Ludwig found that people who ate a high glycemic index breakfast ate 81% more food for the rest of the day, than those given a low glycemic index breakfast.
David Ludwig: Hunger is the brain’s message that calories are needed directing an individual to go out to eat and to restore blood sugar. So we think that one of the key physiologic mechanisms relating diet to hunger is what happens to blood sugar in the five hours after eating.
Narration: But here in Adelaide, at CSIRO’s Health Science and Nutrition Division, they’re not convinced that Glycemic Index is the answer. Peter Clifton put the theory to the test by putting volunteers on high and low GI diets.
Peter Clifton: We found the weight loss was exactly the same on both diets over eight weeks. So we had a four week initial stabilisation period…. and then they switched to high or low GI and the weight loss in the next eight weeks was exactly the same. It was pretty much as you predict by the energy content.
Narration: Clifton’s saying what most dieticians will tell you; to lose weight, you need to reduce the number of kilojoules you eat. And that means a diet. But Ludwig argues that long term weight loss is harder to achieve.
David Ludwig: Almost anybody can lose weight in the short term but for almost everybody that weight comes back after six months, a year or certainly two years.
Narration: Ludwig’s solution is that his patients shouldn’t count kilojoules, they should simply swap foods that are high GI for those with a low glycemic index.
David Ludwig: We tell our subjects or patients to eat as much as they want and to snack when hungry under the belief that low glycemic index foods will fill people up sooner and lead them to naturally decrease calories without an arbitrary or strenuous external restriction.
Narration: And here’s another reason to take notice of Glycemic Index. There’s now increasing evidence that a high GI diet could be behind many of our most common diseases.
Jennie Brand-Miller: You’re at increased risk of developing type 2 diabetes. You’re at increased risk of developing heart disease. Actual heart attack was one of the outcomes and now the studies are starting to show that you’re increasing your risk of different types of cancer including breast cancer, colon cancer and the latest is pancreatic cancer. And the mechanisms that are underlying those diseases, what we call the diseases of affluence seem to be the same, that they’re all related to what we call insulin resistance.”
Narration: It seems our obsession with dietary fat in the last few decades has blinded us to the problems associated with high GI. If these researchers are right, a high glycemic index diet isn’t just making us fat – it could be killing us as well.
Jennie Brand-Miller’s book is: The Glucose Revolution Life Plan
ASSOC. PROF. JENNIE BRAND MILLER
Human Nutrition Unit
School of Molecular & Microbial Biosciences
University of Sydney
ph. 612 9351 3759
fax. 612 9351 6022
Reporter/Producer: Karina Kelly