Obese individuals are at increased risk from a range of metabolic diseases, including insulin resistance, dyslipidaemia and hypertension. Adipose tissue is an important endocrine organ, secreting a range of inflammatory mediators, including tumour necrosis factor alpha and interleukin 6. Circulating concentrations of these cytokines are increased in obesity and may contribute to the pathogenesis of metabolic diseases. The present review considers the evidence linking inflammation and obesity-related disease. The data show that an inflammatory phenotype, measured by serum sialic acid concentration, identifies individuals with insulin resistance, dyslipidaemia and hypertension. Serum sialic acid concentration increases progressively in obese individuals with none, one or multiple features of the metabolic syndrome, independent of BMI. Supplementation with long-chain n-3 polyunsaturated fatty acids has shown anti-inflammatory effects in studies of both healthy populations and in models of chronic inflammatory conditions. The effect on insulin sensitivity has been varied, with both positive and negative effects. This variability may relate to the metabolic characteristics of the study population; individuals with high background inflammation may derive greater benefits from n-3 polyunsaturated fatty acid supplements, suggesting a possible interaction between diet and phenotype. Future research is needed to fully evaluate the role of anti-inflammatory strategies in the dietary management of obesity.