The aim of this paper is to discuss issues that fall within the general concept of well-being, with special emphasis on approaches that have been used in studies of nutrition and behaviour. Following this, two specific studies are described in detail, the first examining high-fibre breakfast cereals and the second investigating effects of inulin. Studies of nutrition and well-being can be categorised in a number of ways. One method involves examining acute effects of nutrition on mood and cognitive functioning. Another method has been to examine cross-sectional associations between dietary habits and questionnaire measures of reported health. Examples are given showing that regular consumption of a high-fibre diet is associated with better-reported physical and mental health. The problem with such correlational studies is that it is impossible to infer causality. Intervention studies are necessary to achieve this and some examples of this approach are given. In the first study reported here, we examined whether consumption of high-fibre breakfast cereal led to an increase in energy. Such an effect was observed and plausible biological mechanisms underlying such results are described. A similar methodology has recently been used to examine the effects of inulin. In this case the results showed no negative side-effects of taking inulin but there were no beneficial effects of inulin on measures of well-being (both subjective reports and objective measures). Possible reasons for these effects are discussed.