The government's new "sugar tax" is a bit of a mess. First of all, it's not a sugar tax—it's a tax on the sugar in soft drinks except fruit juices and those based around milk. Secondly, given that people can easily substitute into other sweet and calorific foods, a tax at the rate the government's proposing is expected to reduce calorie intakes by about 2 kcal each.
But I think that these are relatively minor concerns. After all, the government will probably follow up this baby step with more extensive measures, with a broader, more logical scope, and set at a higher level. The bigger issue is that a couple of papers in the latest issue of the International Journal of Obesity question the entire narrative that sugar is a unique, hellish, dietary evil.
Just as the diet-obsessed obsessively avoided fat in the 1980s (just read the book American Psycho—protagonist Patrick Bateman won't eat a single fried thing), those attempting to follow the best diet guidance avoid sugar today. The Harvard School of Public Health and the Swedish diet buraeu have set the trend. But what if the current anti-sugar crusade is just a rerun of previous dietary fads?
This seems at least possible, given these last two papers. The first, by Luc Tappy, argues that popular ideas about the especially bad nature of sugars in general and fructose in particular are based on misconceptions and misunderstandings:
In this closing perspective, the author exposes why targeting a single nutrient like sugar is in his opinion unlikely to be efficient in preventing obesity and metabolic diseases. He defends the proposal that the concept of fructose toxicity is based on major misconceptions of nutritional physiology. He specifically proposes that (1) sugar being a non-essential nutrient does not obligatorily imply that it has no beneficial effect; (2) alterations of blood triglyceride concentration and hepatic glucose production within the normal range may merely reflect adaptations to a fructose-rich diet rather than early markers of diseases; (3) overfeeding is a normal physiological response to exposure to an energy-dense, palatable nutrient rather than the consequence of ‘leptin resistance’; (4) we may presently overemphasize the role of biological regulations and of gene-related heredity when assessing the effects of fructose in particular, and the determinants of obesity in general.
The second, by Theodore Angelopoulos and James Rippe questions the validity and quality of most of the animal model studies that have been used to push the line that sugar is uniquely important in obesity or health (as opposed to over-eating in general). It says:
The effects of added sugars on various chronic conditions are highly controversial. Some investigators have argued that added sugars increase the risk of obesity, diabetes and cardiovascular disease. However, few randomized controlled trials are available to support these assertions. The literature is further complicated by animal studies, as well as studies which compare pure fructose to pure glucose (neither of which is consumed to any appreciable degree in the human diet) and studies where large doses of added sugars beyond normal levels of human consumption have been administered. Various scientific and public health organizations have offered disparate recommendations for upper limits of added sugar. In this article, we will review recent randomized controlled trials and prospective cohort studies. We conclude that the normal added sugars in the human diet (for example, sucrose, high-fructose corn syrup and isoglucose) when consumed within the normal range of normal human consumption or substituted isoenergetically for other carbohydrates, do not appear to cause a unique risk of obesity, diabetes or cardiovascular disease.
I am not an expert in nutrition, and I am not qualified to judge whether these papers are the best in the whole of nutrition. But the evidence on 'sugar is evil' seems far from clear. As such, even if the practical problems with the levy are solved, I don't expect the sugar tax to have many positive effects either on obesity or on health.