Jo Swinson, minister for women and equalities, is right to emphasise that crash diets don't work in the long term and are potentially harmful. The majority of those who lose weight quickly not only regain it but end up heavier. But rather than attacking newspaper and magazine editors for their irresponsibility in encouraging this behaviour, she should be concentrating her efforts on dealing with the real culprits – the major food corporations.

This month, the National Child Measurement Programme reported that one-third of children are overweight by the time they leave primary school. This should have the food industry's attention. Instead, "big food" continues to engage in behaviour that undermines public health. Obesity expert Professor Robert Lustig has studied the toxic, addictive and appetite-driving properties of sugar on the body, leading to high blood pressure, cardiovascular disease and cancer. It's causing obesity in babies, giving teenagers diabetes. "Sugar is cheap, it tastes good and it sells. So companies have little incentive to change," he says. Sugar is the new tobacco.

Perhaps comparisons with the tobacco industry are instructive in other ways. Last month, in an unprecedented case, a US judge ruled that tobacco companies must spend their own money on a public campaign admitting that they lied about the risks of smoking. The fact that it has taken 50 years is a testament to how the industry was able successfully to defend its practices. Key to the strategy was buying the loyalty of scientists – planting doubt, confusing the public, giving ammunition to political allies and stalling government intervention.

The similarities with the food industry are chilling. Dr Steven Blair, one of the most published world leaders on the benefits of physical activity, openly declares that he has taken millions from Coca-Cola to fund his research. He repeatedly argues that calorie intake or excess sugar are not linked to obesity, despite rapidly growing scientific evidence to the contrary. Not all scientists make their financial ties to industry so transparent and Blair should be commended for doing so.

But for academics, it is the prestige of publication in high-impact scientific journals that can be the most powerful motivator. And who funds this research? Often the pharmaceutical and food industry. According to Dr Marion Nestle, one of the most powerful voices in food politics: "Sponsorship makes it more difficult to design a study that can give impartial outcomes. If you want good science, you cannot allow corporate sponsorship of research."

There is even a question mark over the true impartiality of the very organisations that we trust to give us dietary advice. The American Dietetic Association has received "generous support" from the likes of PepsiCo, Coca-Cola and Mars. The British Nutrition Foundation has a member list that reads like the Who's Who of the food industry, including Coca-Cola, Kellogg's, McDonald's, Nestlé and PepsiCo.

"Big food" also uses front groups such as the Centre for Consumer Freedom, a name deliberately designed to divert the public from industry connection. It denied the notion of food addiction, in response to a Newsnight report. This organisation, funded by food and restaurant companies, claims to be "dedicated to protect consumer choices and promoting common sense".

It is important to remember that in 1994 the CEOs of every major tobacco company in the US went before Congress and under oath said that the evidence linking smoking and nicotine to lung cancer was inconclusive.

At the American Sugar Alliance international sweetener symposium held earlier this year, Rhona Applebaum, chief scientific and regulatory officer for Coca-Cola, highlighted that food companies needed to fight off the industry's "detractors". She also stressed to sugar growers the importance of being "proactive" in talking to consumers about "eating sweetened products while also exercising to avoid obesity".

Obviously, I advocate the health benefits of exercise but policy-makers should be aware that an emphasis on physical activity alone is doomed to failure. When it comes to weight, what you eat is much more important than what you do. A child doing an hour of PE a day will be putting it all to waste if he eats a bar of chocolate, with crisps, a burger and chips, washed down with a sugary drink. You have to run half a marathon to burn off that many calories.

In times of austerity, we should be more vigilant of getting our money's worth but the very corporate institutions that got us into this mess are able to exert even greater influence. I was appalled to learn that the most popular boy band in the world, One Direction, and Beyoncé have recently landed multimillion dollar deals with Pepsi. In October, Coca-Cola and Nestlé paid a mere $50,000 and $150,000 respectively to sit on a global food policy board of a cash-strapped World Health Organisation.

If failure to regulate the banks was the prime reason for causing the biggest financial crash in half a century, then failure to regulate the food industry is leading to a world public health crisis of unprecedented and catastrophic proportions.

Simon Capewell, professor of clinical epidemiology at the University of Liverpool, agrees, saying: "The UK is proud of its many public health successes, including safe drinking water, sanitation, pollution control, seatbelts and smoke-free buildings. All these great achievements were underpinned by regulation, not cosy voluntary agreements with the guilty industries."

But there is a glimmer of hope. Senior members of all parties are taking this issue seriously. Mark Browne, a senior health adviser to Boris Johnson, told me that the mayor has made tackling child obesity his number one priority. I was also heartened to learn that the shadow health secretary, Andy Burnham, has called for legal limits on the levels of sugar and salt in food.

Earlier this month, the consumer group Which? declared that the government's responsibility deal that allows the food and beverage industry to "self-regulate" has failed in its pledge to encourage consumers to eat more healthily. It's high time for a independent, evidence-driven approach. The industry should either work with government, medics and consumers or be subjected to the same public humiliation the tobacco industry has faced in recent weeks. Otherwise, our health will continue to deteriorate, with increasing costs to the NHS and the taxpayer.