Professor Philip James, director of the Rowett Research Institute, commenting on the White Paper The Health of the Nation, said that changing behaviour was very difficult to achieve.
'A thousand calorie a day diets do not work. People become obsessed with food.
'The brain is screaming for food. Even if people do manage to reduce by these methods they have to stay on a diet for the rest of their lives to maintain the weight,' he said.
His work at the Rowett, a major nutrition research establishment in Aberdeen funded by the Scottish Office, has convinced him that new strategies are needed for dietary behaviour and health. But the White Paper proposals will not work unless the Government tackles the food industry and agriculture to alter the balance and prices of foods offered to consumers, he said.
'In fact, consumers have been doing it right. We are buying more low fat produce and skimmed milk. But the total amount of fat in the diet has hardly changed.
'This means it is creeping in from somewhere else. We are getting it unseen as an additive in other food products and consumers do not have a hope of regulating the total of energy they derive from fat.'
The White Paper wants to see a reduction in the amount of fat we eat and a reduction in the number of men and women who are overweight. Professor James pointed out that people who stop smoking are likely to gain weight and that this had to be addressed 'particulary in younger women' if the smoking reduction targets are to be achieved.
The majority of the White Paper's targets and proposals interlink. Poor diet affects obesity and heart disease and smoking affects heart disease, strokes and cancer. Diet may affect cancer too. High blood pressure affects strokes; smoking causes lung cancer. Non-smokers tend to eat healthier food than smokers.
Gerry Shaper, Professor of Clinical Epidemiology, at the Royal Free Hospital, London and a specialist in the incidence of coronary heart disease, said that the greatest benefit of the White Paper may be for future generations.
'What we really need to make the big difference is a generation that grows up with clean arteries. We know that damage is being done in childhood. By the time people are 20 there is quite a lot of damage and by the time they are 40 there is a lot.'
He said that researchers can find a divergence in blood cholesterol levels - a predictor of heart disease - in children as young as 10. 'These differences can almost always be traced to dietary differences,' he said. Professor Michael Oliver, director of the Wynn Institute for Metabolic Research, London, also believes that a health education strategy may not be sufficient to change behaviour. 'Very full collaboration with agriculture and the food industry is needed.
'We need to know so much more. Death from coronary disease has been falling in the past 30 to 35 years but we do not really understand why. We have rather poor information about the incidence or otherwise of heart disease,' he said.
Professor Oliver said that many improvements in health due to lifestyle changes could be seen in the middle classes. 'But poverty itself is not the only cause of higher rates of ill health. Impoverishment may be more important. People living in difficult circumstances find it very hard to comply with the good advice. Obesity is a good example. It can be terribly hard to lose weight,' he said.