Comment by Dr David Ashton MD PhD - Medical Director, Healthier Weight
Honorary Senior Lecturer, Cardiac Medicine Group, Imperial College, London
Last night’s BBC Panorama documentary – 'Fat Tax' – was bland to the point of banality. It said nothing new and failed to address the assumptions underpinning an idea which has surfaced several times over the last decade.
The argument offered is familiar but lame: 'junk food', rich in fat and sugar, is at the root of the obesity epidemic. If we introduced an additional tax on high-fat and sugar-rich foods, it would dissuade people from buying them, leading to a reduced calorie intake and weight loss. This argument – if one can call it that – is based on questionable premises and is simplistic to the point of absurdity.
Firstly, the association between obesity and dietary fat intake is, at the very least, controversial. There are many good scientific studies which show that diets high in fat are not the primary cause of excess body fat in society and that a reduction in fat intake is not the solution. In the USA, a substantial decline in the percentage of energy from fat consumed during the past two decades, has corresponded with a significant increase in obesity rates. In the European Youth Heart Study, there was no relation whatever between fat intake and weight change over a 6-year period.
Exactly the same can be said for sugar intake and obesity. Several large studies have reported no association whatever between total sugar intake and obesity. Other studies have examined the effect of high intake of sugar from sugary drinks and, again, found no association with obesity rates.
For years now, the press and media have talked about 'junk food' as if everyone knew precisely what it was. In fact the term has never been adequately defined and, from a scientific perspective, the phrase is meaningless. Long-term studies on dietary habits, health and obesity are notoriously difficult to perform, which is why we read contradictory findings in the press and media almost every week. For example, a recently published study found that slim children consumed significantly more junk food than their obese counterparts.
The problem is that we have no idea what constitutes a 'junk food'. In the absence of a definition, it follows that we have no idea as to which of the thousands of items filling the supermarket shelves would be candidates for a 'fat tax'. Moreover, since some fats are essential to life, would foods containing beneficial fatty acids be exempt and, if so, at what concentrations?
The idea of a 'fat tax' may sound attractive, but to those of who work in the field, it is an unworkable irrelevance based on no credible scientific evidence.