Since the 1970s, the number of new food products available to consumers in developed countries has increased dramatically. For any one type of food, there are often many different brands and varieties, from diet or “lite” versions through to indulgent “luxury” brands. Some of these products contain low-calorie sweeteners and fat substitutes, which means that within a single food category, calorie content can vary considerably.
It is well known that developed countries have a problem with obesity and that this is linked to changes in the food environment, such as larger portion sizes and the increased availability of calorie-dense foods. However, until now, there has been little consideration of the impact of eating different brands and varieties of the same food item.
Psychological research has established that, over time, we learn to associate the flavour of a food with its energy content. For example, sweetness or creaminess are common signals that a food contains calories. This learning is important because it comes to determine how and what we eat. However, complex dietary environments, where there are numerous brands and varieties of the same food, might compromise this learning – and this could result in over-consumption.
Studies with non-human animals provide initial support for this theory. Rats that are repeatedly exposed to low-calorie sweeteners go on to eat more food, gain weight and become obese. This is thought to be because they fail to learn an association between sweetness and the presence of calories.