With some experts now putting sugar in the same category as alcohol and tobacco when it comes to damaging our health, there's growing concern about what exactly constitutes good food. For nutrition expert and author of the best-selling 'Hard To Stomach', Dr John McKenna, however, it's simply a matter of science.
Science, he believes, raises disconcerting questions over a number of commonly held assumptions about what's good for us. Take sugar. These days everyone knows it's is fattening. Yet, says McKenna, that wasn't always the case. Back in the mid-seventies, he points out, there was a belief that fat in the diet was a cause of heart disease.
This led food manufacturers to reduce the fat content of various products – which in turn made the foods less tasty – so they added sugar. And that, believes McKenna, was a fatal mistake.
Ordinary table sugar, he explains, is made up of glucose and fructose. Since the 1950s, says McKenna, we've known that fructose generates fat production in the body.
"Fructose is the 'bad guy' of sugar, and glucose is the 'good guy,' he explains. "Obesity wasn't an issue until the 1970s, when food manufacturers took fat out of foods and replaced it with a high-fructose sugar called 'high-fructose corn syrup'."
The problem is, he explains, that when you have a lot of fructose in the body, glucose becomes an "accomplice". In other words, while fructose generates fat, glucose generates the insulin which in turn drives the storage of fat in the body.
"Fructose is now being labelled by some doctors as a poison," says McKenna. "It goes to the liver and behaves much as alcohol does. It's responsible for giving you a fat tummy and for the storage of fat in different organs in the body. All of this fat produces oestrogen, which can also result in man boobs in men. It can also cause cancer because certain cancers are oestrogen-dependent."
At the same time, McKenna declares, we have been advised to increase starch in the diet through a generous intake of carbohydrate-rich foods, such as potatoes, porridge, bread, rice and pasta – foods which, he points out, make up the base of the iconic Food Pyramid, the public health bible for healthy eating. Starch, he explains, contains glucose.
"If you eat a lot of fructose, you generate fat production and if you eat a lot of starch – which contains glucose – it raises your insulin levels. The fat in the bloodstream generated by fructose is then "pushed" into the cells by the increased insulin levels, and stored as . . . fat. And this," he says, "is the basic problem with obesity."
Another factor in all of this, says McKenna, who has spent the last 25 years practising nutrition in different parts of Africa, Ireland and the UK, is the modern 'dwarf' wheat, which, he explains, has generally replaced the traditional tall wheat of his childhood.
Dwarf wheat, McKenna maintains, contains more starch than the old-fashioned wheat. The modern wheat we're eating produces significantly more glucose than the old-fashioned plant.
"There is a worrying interplay between the fructose and glucose in this equation. The Government is telling us to reduce our intake of sugar, but it's not saying to reduce our starch intake.
"Many Irish people are eating a lot of sugar while at the same time the Food Pyramid is advocating the consumption of a large quantity of starchy foods, like bread, cereal, rice and pasta.
"If you have a population which is eating a lot of sugar and combining this with a heavy intake of starchy foods, you're compounding the problem."
McKenna also criticises the Food Pyramid because of its recommendation that our intake of animal fat should be reduced.
"Our cells are mostly fat and protein. Telling people to reduce or cut out animal fat does not make sense from a scientific perspective. The two most important foods to give a child are fat and protein. However, it's recommended that saturated fat in the diet be reduced because it's believed that this causes heart disease. We now know that's not the case. That's why I disagree with the food pyramid.
"I'd put saturated animal fats such as butter, eggs and red meat at the bottom of the food pyramid because that's what our bodies are made up of and that's what they need."
However, Ruth Charles paediatric dietitian with the Irish Nutrition and Dietetic Institute argues the point:
"Starch is a natural compound occurring in nature. The starches we're asking people to eat in the food pyramid are natural. Wheat was one of the first grains we ever encountered as human beings," she says.
And although Charles acknowledges that wheat has been identified as a food to which some people experience intolerance, the evidence is, she says, that we are intolerant, not to wheat as a grain but to its processed form as a filler or thickener, for example in burgers, as a coating on chicken nuggets or as a thickener to soup:
"That's not the same as eating a slice of wholegrain bread or a wholegrain cereal like Weetabix," she says, pointing out that past generations never ate chicken nuggets or packet soups or ready-made gravy.
Human beings are genetically programmed to tolerate the starch in wheat, she insists, and while the Food Pyramid may not be for everybody, it is essentially a teaching tool:
"The food pyramid is really suited to teaching individuals. It's aimed at trying to get people to move away from the op group of fats, for example, in fried processed foods, sweets or biscuits. The Food Pyramid is an educational tool; a public health tool to teach the public the basics. It's not wrong," she says.