Do We Know What We Do not Know? A Response to Celine Bonnet.

Food taxes increase prices of food or food ingredients in order to stimulate consumers to change their eating behaviour and finally to level up population health. Their aim is to tackle the high rates of obesity and other lifestyle diseases. As Bonnet argues, often food taxes are set up out of an economic perspective (1). To change consumer behaviour is one thing, to level up people’s health is a complex matter. Evidently, to evaluate the most accurate measures, governments require rigorous consideration (2). People have to go along a process, through different stages and challenges (3–6). In ‘Food taxes: a new holy grail?’, we start from the questions ‘Will it work?’ and ‘Do we want it?’ (7). But even prior to that, we also need to demarcate the borders of ‘unhealthy food’. Overall, as stated by Bonnet (8), sweet drinks, junk food, savoury and sweet biscuits are considered as ‘unhealthy products’, Lobstein and Davies propose ‘nutrient profiling’ (9); nevertheless today, there is no consensus on what is unhealthy food. As a consequence, European countries like France, Hungary and Denmark, implement food taxes to decrease the consumption of unhealthy food, but each of them taxes different ingredients. At least this is confusing. Do we have to increase our consumption of fat, or sugar, or salt? And how is this related to physical activity? Many questions remain. As Bonnet underpinned, food taxes tend to be effective, but do their positive effects counterweigh the negative ones (10,11)? Food taxes have the most unpredictable and negative consequences; they are regressive, their social and cultural value is not pondered, for they undermine freedom in lifestyle choice; not to speak of their unpredictable economical consequences (11–13). If food taxes are supposed to be effective when it comes down to health, we need to rely upon evidence-based arguments from a medical, political and economical point of view (5,12,14). To stipulate only one aspect; many studies are based upon outcome variables different from health, e.g. consciousness, behaviour (2); an effect on behaviour may differ from a health effect (15– 17). Next to that, also public acceptation of food taxes is crucial in this. In a democratic society, it is important to involve people in decisions (18), in order to convince people. Food taxes should be part of a global health strategy (19); if not, they are doomed to fail or people will only look after substitutes which may even be more unhealthy. Sometimes it is good to know what we do not know. Ethical issues Not applicable.