The goal of this clinical trial is to assess the effect of a vegetarian diet on innate immunity of patients with a recent acute myocardial infarction and healthy participants. Also, we will assess the willingness to adapt a more vegetarian eating habit. Study subjects will follow a vegetarian diet for five weeks, whereafter a stabilisation period of six weeks will follow. Then, participants will follow to the other dietary intervention for five weeks. Blood will be drawn at given time points to analyse inflammatory parameters.

We will perform a proof-of-concept study according to a prospective randomized open label blinded endpoint (PROBE) design. Patients with an acute myocardial infarction (AMI) and their healthy life partners / spouses will be randomly assigned to an immediate vegetarian diet or their habitual diet. Patients with AMI will be stratified for non-ST-elevation myocardial infarction (NSTEMI) or ST-elevation myocardial infarction (STEMI). The dietary intervention will start one week after the index event and will comprise a period of five weeks. After a stabilisation phase (six weeks), to assure normalisation of the inflammatory response secondary to the acute myocardial infarction, patients and their spouses will follow the other dietary intervention arm. Then, half of them will start directly with the other dietary intervention and half of them will start after a period of five weeks. Blood samples will be taken at the time points. Also, all participants will be asked to complete a questionnaire at baseline, after twelve weeks and at nine months follow-up. Infarct size as assessed by Cardiovascular Magnetic Resonance (CMR) imaging will be used to adjust cytokine levels.

Inclusion Criteria for patients:

• Acute myocardial infarction (STEMI/NSTEMI) with a clear culprit lesion on angiography and successful primary percutaneous coronary intervention (PCI) <1 week before randomisation
• Body mass index between 18.5 and 35 kg/m2
• Written informed consent

Inclusion Criteria for healthy volunteers (life partners / souses)

• Body mass index between 18.5 and 35 kg/m2
• Written informed consent

Exclusion Criteria for patients and healthy volunteers:

• Already on a vegetarian or vegan diet
• Previous myocardial infarction
• Diabetes Mellitus
• Medical history of any disease associated with immune deficiency (either congenital or acquired, including chemotherapy, chronic steroid use, organ transplant)
• Use of immunomodulatory drugs
• Vaccination less than one month before start of intervention
• Clinically significant infections within 1 months prior to start of intervention (defined as fever >38.5 degrees Celsius)
• Active malignant haematological disease
• Known eating disorder (e.g., Anorexia nervosa, Bulimia nervosa)

Exclusion Criteria for healthy volunteers

- Use of lipid lowering therapy

No individual participant data will be shared. Results will be published by the investigators in academic journals. Sharing of generated study data will be carried out in several different ways. We plan to make our results available to researchers and potential collaborators.