Background: Health-related claims (HRCs) are statements to be found on food packets that convey the nutritional quality of a food and/or its impact on a health outcome. It is unknown whether HRCs improve, hinder, or have negligible effects, on diet and/or health. Aims: To estimate the impact of HRCs on dietary choices; measure the prevalence of HRCs in five European countries, and the nutritional composition of foods carrying HRCs; compare nutrient profile models aimed at regulating HRCs; and model the impact of HRCs on non-communicable disease (NCD) mortality. Methods: This thesis reports on a systematic review of the impact of HRCs on dietary choices; a survey of HRCs on pre-packaged foods available to purchase in the UK, Germany, the Netherlands, Spain, and Slovenia; analyses of the nutritional quality of foods that carry HRCs and foods that do not; and the development of a model to predict the current impact of HRCs on NCD mortality in the UK, and the impact of using a nutrient profile model to regulate the use of HRCs. Results: Foods carrying a HRC are 75% (OR 1.75, 95% Confidence Intervals [95% CI] 1.60, 1.91) more likely to be chosen than identical foods without a HRC. In the five countries surveyed, 26% (95% CI 24%, 28%) of foods carry a HRC and these foods, on average, have a more favourable nutritional composition than foods without a HRC. Modelling suggests that removing HRCs from food labels would result in an additional 2808 deaths per year (95% Uncertainty Intervals -2993, 7392), and that regulating the use of HRCs with a nutrient profile model (such that only foods that pass the model can carry a HRC) would also be detrimental to health. However, the uncertainty intervals associated with these results are large and cross zero. The largest contributor to this uncertainty is the insufficient statistical power of the food composition data. Discussion: Regulation of HRCs in the EU is the focus of much debate. Current EU law requires the development of a nutrient profile model for their regulation. In ...