A consultant psychiatrist friend, on his recent appointment to a new job, was so disgusted by the detrimental effect of the unchecked consumption of junk food on his patients' health that he successfully banned vending machines selling chocolates, fizzy drinks and crisps from the hospital grounds.

He wondered whether I – as a clinician – believed the consequences of eating junk food were as bad for our health as smoking cigarettes. "No, not as bad," I replied, "in many ways it's far worse!"

It is estimated that diet-related diseases are responsible for 35 million deaths worldwide, dwarfing smoking-related ones of 5 to 8 million. And while there have been tremendous advances in discouraging cigarette consumption, we haven't really started to act on obesity.

Last year, Cancer UK declared that obesity was the commonest cause of breast cancer in older women followed by alcohol and smoking. Only last week, we heard that there had been a significant increase in womb cancer for the same reason.

So what is the biggest culprit of the obesity epidemic and how do we combat it? According to Professor Robert Lustig, a child obesity expert at the University of San Francisco, it's sugar (including sweeteners) and processed carbohydrate. He describes sugar as being addictive and toxic and has called for a ban on the sale of sugary drinks to under-17s and a consumer tax on any substance with added sugar. This would be a good start.

Lustig explains that the consumption of these "food-like substances" leads to an increase in chronic insulin levels, the fat-making or energy-storing hormone. We are thus consuming empty calories, ie foods that not only provide no nutritional value but are quickly converted to fat. As we have not used these calories in a meaningful way, we feel hungry again and so the cycle continues.

In my opinion, the food industry is the main culprit for this catastrophic public health disaster. Given that the revenue of some of the big food companies is bigger than that of the GDP of more than 120 countries, you would hope that they would dedicate resources to make their products healthier. Instead, they have mastered the promotion of cheap junk food, especially to the most vulnerable and impressionable members of society – children.

A survey by the Children's Food Trust of more than 1,000 parents with at least one child aged between three and 15 revealed that the majority believed advertising had an effect on what their children asked for. Some 72% said they had bought fast food or other unhealthy products as a result of pestering by their child.

If we are going to really alter the statistics on obesity we need to concentrate on the next generation. The banning of junk food in schools needs to be enforced and headteachers have a major role to play. In some schools, the head will write a letter to parents forbidding children from bringing in such unhealthy snacks, but others are either too fearful, don't believe it will have an effect, or don't believe it's their responsibility. What is the point of a good education if the child who receives it becomes limited by premature bad health?

The demonisation of junk food must be supported by compulsory cooking lessons and food education promoting nutritious real food. I call on the Department for Education to introduce this into every primary school. This would be a step towards saving our future adults from the dangers of obesity; and hospitals banning vending machines that sell snack foods is long overdue. It horrifies me to see well-known high street brands getting away with the display of chocolates, crisps and fizzy drinks in prominent positions. It's perverse that institutions that represent health and wellbeing and treat the consequences of poor diet allow the sale of such products.

As big food profit margins rise, we get fatter and sicker. You will often hear two defences from big food corporations. The first: it's your choice what you eat; and the second: you need to exercise more. We have already demonstrated where the balance of power lies in regard to choice, but most worrying is that we are being misled by items of food that are marketed as healthy or low-fat when they are full of processed carbohydrates and sugar.

In response to the second point, a study by Professor Boyd Swinburn, presented at the European Congress on Obesity in 2009, concluded that excess food intake explains weight gain. This was backed by a spokesman for the American College of Cardiology, Dr Matthew Sorrentino, who said that 90% of weight loss is achieved by cutting calories, and 10% is achieved by significantly increasing physical activity. Soon, the Olympic Games will take place. Embarrassingly, McDonald's is the main sponsor. One would hope that the spectacle of the world's best athletes competing would have a positive influence on Britain's young and many in government claim that the Games will improve the health of the fattest nation in Europe.

I believe nutritionist and author Zoe Harcombe is more accurate when she says the sponsors of the Games will have more impact on what is consumed than what is done. Maybe more of us should listen to her advice which simply says, "eat real food".