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Sugar versus Fat

New research suggests it’s not just sugar or fat that is the sole villain, but a combination of the two that has a detrimental impact on our health. MiNDFOOD weighs up the latest thinking on how to change our diets for the better.

Sugar versus Fat

Sugar v Fat was the provocative title of a recently aired BBC documentary, which followed identical twin brothers Alexander (Xand) and Chris van Tulleken – both doctors – as they changed their diets for one month. Chris followed an extreme low-fat diet, consuming vegetables, fruit, cereal, chocolate and sugary drinks,  while Xand took on an extreme low-carb regime (primarily meat, eggs and cheese and no sugar). Who would fare better?

Sugar is currently blamed for the rising global obesity epidemic because consuming too much sugar stimulates the production of more insulin. This allows the body to convert sugar into fat, which may be stored. We’re clearly eating too much – sugars are hidden in many processed foods. Meanwhile, we’ve been told for years that fat is bad – processed trans-fats, and saturated (solid) fat in particular, due to its links with high cholesterol and an increased risk of heart disease. 

But of course it’s not that simple. For starters, not all saturated fatty acids are bad. For example, the saturated fat in coconut oil, which is high in lauric acid, gets the healthy tick.

“We have maligned saturated fat as a class, and only late in the game are coming to realise that not all saturated fatty acids are created equal,” says Dr David Katz, founding director of Yale University’s Prevention Research Center. 

In a recent meta-analysis of data from 72 studies involving more than 600,000 participants, researchers from the University of Cambridge found no overall association between saturated fat consumption and heart disease, though researchers recommend further study.


One thing is clear. The message of reducing fat intake has not had an impact on the rising rates of obesity, and now the finger is being pointed at sugar. The World Health Organization has proposed that sugars should make up less than five per cent of our total energy intake, compared with the current recommendation of less than 10 per cent. 

In his book Fat Chance: The Bitter Truth About Sugar, paediatrician Dr Robert Lustig calls sugar addictive and toxic. Foodstuffs that raise insulin levels in the body too high are the problem, says Lustig. “We need to de-sweeten our lives. We need to make sugar a treat, not a diet staple.”

When high-fat foods were blamed for making us overweight, manufacturers tumbled over each other to produce low-fat products. But to make them palatable, they added sugar, causing much greater problems, according to Lustig.

Does that mean fat is now off the hook? It would seem that way if the recent Time magazine cover headline “Eat Butter” is to be believed. Not surprisingly, this news was met with excitement – after all, butter tastes good. And there is the clue right there. Taste. It’s what researchers are now saying has led us down the obesity path.


While filming Sugar v Fat the twins conducted an experiment in London and New York, offering trays of assorted free doughnuts to members of the public. The glazed ring doughnuts, not the ones topped with icing or filled with cream, were the most popular. Why?

Associate professor Paul Kenny of The Scripps Research Institute may have the answer. Kenny’s research has shown that rats have an off-switch when it comes to eating sugar or fat on its own, but not when the two are combined. In particular, the 50-50 sugar-fat content of cheesecake that a group of rats ate in his experiments tasted so good that the rats’ brains’ pleasure chemicals took over, overriding the natural hormones that regulate intake by alerting the brain that the body has had enough calories. 

Glazed doughnuts, like cheesecake, have around a 50-50 sugar-fat content, too. Put simply, the combination of fat and sugar supercharges the brain’s reward system overpowering its ability to tell us to stop eating. And it’s a manufactured combination that can’t be found in nature.

“It’s much like what happens with drug addiction. You don’t need heroin, you don’t need cocaine. It has no nutrient value. It doesn’t do anything for you except make you feel good,” Kenny says.

Elaine Rush, professor of nutrition at the Auckland University of Technology, agrees. “It’s that bliss point that keeps getting talked about. There are no naturally occurring foods that contain fat and sugar in those quantities. So it’s something we have made, like a drug,” Rush says. “Taste is the biggest driver of what people eat across the world. If it tastes good, we eat it.”

The food industry knows this. When researching his book Salt Sugar Fat, investigative journalist Michael Moss was astonished by the “targeted” effort by food companies “to hit the magical formulation”. In an interview with Time, Moss says the optimum amount of sugar in a product is known as the “bliss point”, and for fat its “mouth feel”.

 “That’s the warm, gooey taste of cheese, or the bite into a crisp fried chicken that you get. It rushes right to the same pleasure centres of the brain that sugar does, but fat is carrying twice as many calories, so it is more problematic from an obesity standpoint.”

Salt, another component of processed foods, is the other miracle ingredient the food industry is hooked on, according to Moss. It provides flavour but also serves as a preservative and masks a lot of off-notes in flavours, says Moss. However, salt is also associated with high blood pressure.

Another major issue, says Rush, is alcohol. She cites a National Nutrition Survey (2008) that found the alcohol calories (five per cent of total calories) consumed in New Zealand are equal to the calories from non-alcoholic beverages. The same amount again is consumed as sugar and sweets. 

“Alcoholic drinks are nutrient-poor and if we’re looking at sources of excess energy that could be modified, fat, sugar and alcohol are things we should be discussing but often alcohol doesn’t enter the conversation,” she says.


So, what did the van Tulleken twins’ experimental diets prove? 

“I thought I’d got the better deal: I could eat meat, fish, eggs and cheese,” Xand wrote in the Daily Mail. “But take away carbohydrates and the joy goes out of meals. Remove all fruit and veges – they all have fibre – and you get constipated.”

Xand was never hungry, but he felt lethargic. Meanwhile, Chris never felt full and was constantly snacking, but he was more alert because the carbohydrates he was eating were producing glucose, which is the primary fuel for the brain.

The focus should be on the whole diet, rather than sugar and fat, says Rush, which is also a key message of Sugar v Fat.

“Constipation is the other elephant in the room,” says Rush. “It’s associated with bowel cancer. Things shouldn’t sit around in the bowel too long. Eating more fruit and veges helps prevent bowel cancer. We should be looking at the whole functioning of the body when we talk about nutrition.

“Fat and sugar are nutrients that provide energy that we need and there are all sorts of other nutrients we need, too, such as protein and vitamins. The focus should be on whole foods.

“Half of your plate should be vegetables, quarter good carbohydrates like potatoes or carrots, and quarter protein. That’s the sort of volume balance we should be looking at, and the shopping basket should be like that too.”


Ultimately, sugar and fat are sources of energy. We need both to survive. Glucose is the primary fuel for the brain, which consumes 60 per cent of the sugars in your blood. Fat from food is broken down into fatty acids, essential for brain, nerve and cell function, which can travel in the blood and be stored in fat cells. The problem is when there is too much glucose or fat.

The body has an unlimited capacity for storing fat and turns dietary fat into body fat more easily than sugar. Too much glucose activates insulin, the hormone that controls blood sugar,
and when that happens the body turns sugar into fat.

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