A number of governments have implemented sugar taxes in order to tackle the growing problem of obesity. The basic premise of these sugar taxes is to increase the price of sugar containing foods and beverages, with particular emphasis on soft drinks, in order to to discourage their purchase and consumption. There have been a number of estimates as to how effective such taxes could be but there is no real consensus on their effectiveness. However, evidence suggests that a threshold may exist and below this threshold smaller increases in price may not affect consumption. Many of the models that are used to predict the effects of the sugar tax are based on the reduction in energy that is predicted from the reduced consumption of the sugar in the drinks. For example, it has been estimated that a 20 % sugar tax would decrease consumption of soft drinks. Applying this to soft drink consumption data may lower daily energy intake by 34 to 47 calories among adults and 40 to 51 calories among children.
Decreasing sugar consumption may have beneficial health effects on body weight to a much greater degree than reductions in other macronutrients. This relates to the fact that sugar is able to cause an insulin resistant state, and this can be a primary driver of weight gain. It is clear that a energy from different macronutrients can have quite different effects on weight gain. The benefits of low carbohydrate diets for example, may come from the fact that such diets eliminate sugar. Consuming low carbohydrate diets at an energy intake equivalent to a high carbohydrate diet has been shown to cause more weight loss in the low carbohydrate diet group compared to the high carbohydrate diet group, and clearly this would not be possible if the total energy intake was responsible for the weight loss effect. The weight causing effects of sugar are therefore more that its energy content, and so reductions in sugar from soft drink consumption may underestimate health effects.
Authors claim that models show that such a reduction in energy would cause a reduction in weight over the long term, but are these models accurate? In order to answer this question it is important to consider how sugar is able to cause obesity. In terms of soft drinks, sugar is really referring to sucrose or high fructose corn syrup, two calorific sweeteners used in soft drinks. These molecules contain fructose, and it is the fructose that is thought to be detrimental to weight gain. This is because fructose is able to induce insulin resistance, and it is the insulin resistant state that is particularly damaging. Once insulin resistance has developed, energy is less efficiently utilised, and significantly this increases the storage of all energy as body fat, yet at the same time decreases the release of energy for exercise. In others words, sugar is more detrimental to weight gain, calorie for calorie, than other macronutrients, and therefore reductions in sugar consumption may have a larger effect that when just considering energy.
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