There is an unpalatable truth about the foods we crave: they are generally bad for us. Our evolutionary history has left us longing for sugars and fats, exactly the sort of energy-dense substances that stopped our ancestors from starving in lean times.

Those ingredients, now cheap and plentiful, are fuelling a worldwide rise in obesity and type 2 diabetes. The issue resurfaced in the UK last week with the publication of a report into public health, and on childhood obesity in particular. Now a bitter war has broken out between politicians and health experts on the merits of a tax on high sugar products such as soft drinks. I can understand the clamour — and such a move may shock us into cutting consumption — but a sugar tax does not quite hit the sweet spot.

In a high-income country, a levy substantial enough to deter abusers is likely to be unfair on those who exercise restraint. But it would also see the government flexing its fiscal muscles over an ingredient that is neither poisonous nor addictive; crowd out discussion of other undesirables such as saturated fats and salt; absolve manufacturers of the need to change their products; and, most worryingly, convey the impression that government can exonerate consumers from personal responsibility.

The World Health Organisation recommends that adults and children derive no more than 5 per cent of their total energy intake from free sugars (these include glucose, fructose, table sugar and those in honey, syrups and fruit juices, added by manufacturers or consumers). That amounts to six teaspoons daily, less than is found in most cans of fizzy pop.

Britons do a bad job of sticking to this: free sugars account for up to 15 per cent of the average person’s energy intake. Public health messages — as well as hollow industry pledges on reformulation — have failed to slim down that statistic. The report from Public Health England urged the following: banning supermarket promotions; reformulation (a tactic that worked for salt) and portion size reduction; restricting aggressive marketing; clear labelling; and removing the worst products from hospitals. But its suggestion of a 10-20 per cent excise tax was rejected by Prime Minister David Cameron.

If we still eat too much sugar despite knowing the risks, does that mean it is addictive? An EU-funded study on the neurobiology of eating put paid to that idea last year: sugar does not elicit the same neurological high as heroin or cocaine. The NeuroFAST consortium concluded that overeating was a behavioural addiction rather than a substance-based one. And while sugar is harmful when consumed to excess, it is clearly not a poison in the same way that nicotine and alcohol are.

If sugar is neither intrinsically toxic nor addictive, an alternative justification for a tax is that the ends justify the means. In which case, does it work? A meta-analysis published in 2013 concluded that a tax on sugar-sweetened beverages (SSBs) — in Mexico, some US states, Brazil and France — had cut demand for both sugary and diet drinks. This is encouraging but the effects on body weight, the key metric, are very modest, possibly because fizzy drinks are swapped for equally calorific fruit juices. It is possible that Britons would fare better but, for now, an SSB levy looks like tinkering around the edges.

We may also ask: why target only sugary drinks when we also gorge on sweets, chocolates, cakes, takeaways and booze? The food and drinks industry is absolutely guilty of peddling us products we do not need but that is true of most commerce. Meanwhile, the trickier issue of personal responsibility remains unaddressed. The singular focus on a sugar tax risks distracting us from thinking more intelligently about how to square our ancient cravings with modern life: eat less, eat better, drink more water and get off the sofa.