Dietary Intervention Trial Targeting Metabolic Syndrome After Kidney Transplantation (DIETTX)

Kidney transplant recipients (KTR) have a considerably lower life expectancy as compared with the general population, primarily due to a high prevalence of cardiovascular diseases. KTR often develop an unfavourable cardio-metabolic risk profile characterized by weight gain, metabolic syndrome and post-transplantation diabetes mellitus (PTDM). In general, nutrition plays a key role in both the prevention and treatment of these cardio-metabolic derangements. However, in KTR most RCT's with a dietary intervention, failed to show significant improvement in cardio-metabolic health. This at least questions the efficacy of the diets of these intervention, which relied on general or diabetes guidelines, after kidney transplantation. KTR not only face a high cardio-metabolic risk, but also have a high risk for malnutrition and muscle mass depletion. More knowledge is required to determine the optimal diet and macronutrient composition for improvement of the cardio-metabolic risk factors in the context of the high malnutrition risk. In this regard, observational studies point towards the needs for a higher protein intake for better patient outcomes. Therefore, in this study, the investigators will examine if a high-protein, carbohydrate-reduced diet is more effective than a diet in line with the Dutch Dietary Guidelines for improvement of cardio-metabolic risk factors and for improvement of the body composition in KTR.

the high-protein, carbohydrate-reduced diet will consist of 1.2-1.4 g/kg/d protein, 26-20en% carbohydrates and +/- 50en% fatty acids, with mainly unsaturated fatty acids. This diet consist of mainly unprocessed, fresh nutrient-dense food-products. Ultra-processed foods and alcoholic beverages will be totally avoided. Salt consumption will not exceed 5-6 g/d. The diet is ad libitum and caloric restriction will not be applied. The diet will be followed for 6 weeks.

the diet according to the Dutch Nutritional Guidelines will consist of a protein intake of 0.8-1.0 g/kg/d and 50-60en% carbohydrates, and +/-30en% fatty acids, with restriction of saturated fatty acids <10en%. This diet consist of mainly unprocessed, fresh nutrient-dense food-products. Ultra-processed foods and alcoholic beverages will be totally avoided. Salt consumption will not exceed 5-6 g/d. The diet is ad libitum and caloric restriction will not be applied. The diet will be followed for 6 weeks.

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

change in circulating triglyceride concentrations, low-density lipoprotein cholesterol (LDL-C) and HDL-C (in fasting serum levels) in mmol/L.

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

change in insulin resistance measuring by the homeostatic model assessment of insulin resistance (HOMA-IR index, fasting glucose, insulin)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

change in fat and muscle mass measured by multi-frequency bio-electrical impedance analysis (BIA) BMI, weight

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

change in nutritional intake measured by nutritional intake biomarkers from 24-hour urine measurements (sodium, potassium, and urea excretion for calculating the protein intake by use of the Maroni equation)

before and after experimental diet (high-protein, carbohydrate-reduced diet - 6 weeks) / before and after active comparator (Dutch Nutritional Guidelines - 6 weeks) / wash-out period in between (6 weeks)

Inclusion Criteria: Age 18 years or older. Given informed consent. At least 6 months after kidney transplantation. Stable renal function with an estimated glomerular filtration rate (eGFR) > 30 mL/min. Raised systolic blood pressure (≥130 mmHg) and at least two more features of metabolic syndrome: central obesity (waist circumference ≥102 for men and ≥88cm for women), elevated triglycerides (≥ 1.7 mmol/L), reduced HDL-C (< 1.0 mmol/L for men and < 1.3 mmol/L for women) or on drug treatment for reduced HDL, elevated plasma glucose (≥ 5.6 mmol/L) or on drug treatment for elevated glucose9. Approval by nephrologist for participation in the study. Exclusion Criteria: Active medical illness, including rejection of the graft. Psychopathology or serious cognitive impairment. Necessity to follow specific dietary measures for health purposes that conflict with the study diets. Use of insulin or sulfonylurea (SU)-derivates. Language barrier. Pregnancy or lactating. Serum potassium > 5.0 mmol/L that requires dietary measures. Moderate or severe malnutrition (Patient-Generated Subjective Global Assessment (PG-SGA) stage B or C). In this case, patient will be referred to a renal dietician. Participation in other intervention trials.