One in four Germans suffers from metabolic syndrome. Several of four diseases of affluence occur at the same time in this ‘deadly quartet’: obesity, high blood pressure, lipid metabolism disorder and diabetes mellitus. Each of these is a risk factor for severe cardiovascular conditions, such as heart attack and stroke. Treatment aims to help patients lose weight and normalize their lipid and carbohydrate metabolism and blood pressure. In addition to exercise, doctors prescribe a healthy, low-calorie diet. Medication is often also required. However, it is not fully clear what effects nutrition has on the microbiome, immune system and health.