A flurry of media attention followed England’s Chief Medical Officer Sally Davies’s recent admission that a sugar tax may have to be considered to try to reverse the overweight and obesity that now afflicts a third of UK children.

Such a tax might reduce consumption, the theory goes, by reducing demand for energy dense foods because they would be less affordable. Or it might reduce supply because competition would encourage manufacturers to make their products healthier.

But could additional taxes on specific foods actually reduce obesity? Would the public swallow them? Would food manufacturers? What of unintended health consequences? And might such taxes disproportionately sting the poorest, entrenching (health) inequity further?

To consider these unknowns, the British Nutrition Foundation (BNF) invited five speakers from academia and industry to St Thomas’s Hospital in London for a symposium on 7 April 2014, which was also streamed live online.

And, on food taxes, pretty unenthusiastic the speakers were too. Scepticism is necessary: we have insufficient evidence because food taxes for public health ends have barely been tried in the real world.

Richard Tiffin, director of the centre for food security at the University of Reading and a coauthor of a recent BMJ paper, told the symposium that economic modelling had found that a tax on saturated fat would reduce the relative risk of obesity “only marginally” and that a 20% tax on soft drinks would reduce the number of obese adults by a disappointingly low 1.3%. But modelling may have neglected crucial yet unidentified or misunderstood factors, he accepted.

Delegates heard from several speakers many of the reasons why the food industry does not want additional taxes on food—lack of evidence, increased administrative burden, potential inconsistent treatment of imported products, and so on. Job losses were mentioned.

Kate Halliwell, nutrition and health manager at the trade association the Food and Drink Federation, said that annual turnover for the sector was £76bn and spoke of its desire for “healthy and sustainable” growth.

But growth in energy consumption is the problem, and no speaker mentioned the pressure from shareholders against any intervention that might threaten profit.

“No country has seen any health benefits from food taxes,” said Christopher Snowdon, director of lifestyle economics at the libertarian think tank the Institute for Economic Affairs (IEA). He spoke about the withdrawal after just 15 months of Denmark’s tax on specific products high in saturated fat. But this doesn’t prove that the concept is fatally flawed.

The BNF, which convened the event, is a charity that takes funding from sources including industry, and the seminar’s programme credited such multinationals as Coca Cola, Danone, DuPont, Nestle, Kellogg, PepsiCo, and Unilever.

It was surprising given this disclosure then that none of the speakers followed suit by voluntarily mentioning the sources of their research funding in their talks—let alone any other competing interests—and neither did their biographies in the symposium’s programme.

Appraisal of research requires knowledge of context, which must include funding. We know that research funded by industry can be prone to bias, so much in some cases that the BMJ will no longer publish research funded by big tobacco.

Tiffin revealed at the end of the symposium that his university had taken “an awful lot of money” from the food industry but said that the current work was research council backed. Snowdon too denied any competing interests, saying that neither he nor the IEA had received money from the food industry. (The BMJ has no evidence to suggest that any of the speakers withheld information about any conflicts of interest affecting their disdain for food taxes.)

Sara Stanner, science programme manager at the BNF, told The BMJ that the foundation had invited other academics who might have been more enthusiastic about such taxes, but that they were unable to attend. She also said, “Although time is probably too limited to ask speakers to present their conflicts of interest at the end of presentations, we can certainly [in future] include this within the delegate packs.”

Speakers were keen to point out how taxing unhealthy products such as cigarettes is a different matter because fat and sugar, they argued, are nutrients essential for life. But huge individual servings of drinks that contain dozens of teaspoons of sugar each are not essential. Millions of children are being poisoned by energy overconsumption. Why shouldn’t such unnatural products be considered as toxic?

The symposium focused on how a tax might affect individuals’ rather than corporate behaviour, but this rhetoric implies that obese children and adults are simply making “bad choices.” But who would choose to make themselves ill?

Simon Capewell, professor of clinical epidemiology at the University of Liverpool, recently told the Independent, “We say there is no personal choice. At the moment, a mother can walk into a supermarket with a choice of four tomato soups—with three, or four, or five teaspoons of sugar in them. She has a choice of thousands of ready meals—with five, or six, or even nine teaspoons of sugar.

“The government should stand up and protect children; we think that responsible companies should stand up and protect children.”

And what of the fortune that industry spends on marketing and advertising these goods? And what about access—the so called obesogenic environment that we have created—where unnaturally energy rich foods can be bought cheaply, any time, anywhere.

If you hadn’t already guessed, food companies favour voluntary solutions to the obesity epidemic, which Halliwell said enable change faster than regulation. But if that’s the case, then what’s stopping them? The future health of millions of children and adults may depend on radical and speedy action now.

The seminar “Food taxes—what role might they have in the battle against obesity?” was held on 7 April 2014.

We’ll soon be publishing a Head to Head debate on whether sugar should be taxed.

Richard Hurley, deputy magazine editor, The BMJ.