Kidney Transplant Low-AGE Diet Study

Kidney transplantation is the optimal treatment option for end-stage kidney disease. Cardiovascular disease is the leading cause of death in persons with kidney disease, even after receiving a kidney transplant. Advanced glycation end-products (AGEs) are compounds that form naturally in our bodies from the chemical reaction of sugars with proteins. If the concentration of AGEs becomes excessive in our bloodstream, they can cause damage to almost every tissue and organ in our bodies, which eventually may lead to an increased risk of cardiovascular death and ill health. AGEs are also found naturally in foods and the content of AGEs in foods is increased considerably by using cooking methods that require high temperatures, such as frying, roasting and grilling.

Skin autofluorescence (SAF) is a relatively new, non-invasive, validated and easy to perform technique that measures the skin accumulation of AGEs. It has been reported that kidney transplant recipients have significantly lower SAF levels when compared to persons receiving dialysis; however, these are higher than the general population.

Because of the adverse outcomes (e.g. increased risk of death) strongly associated with higher levels of SAF, several options focused on reducing the accumulation of AGEs have been proposed. One of these promising interventions is the reduction of dietary intake of AGEs. It has been suggested that cooking techniques that avoid very high temperatures such as poaching, steaming, stewing and boiling can significantly reduce the AGE content of food when compared to frying, broiling, grilling and roasting. Several studies conducted in healthy overweight and/or obese volunteers, persons with diabetes and in those with chronic kidney disease and performing peritoneal dialysis have reported that reducing dietary AGE intake is associated with a reduction in blood levels of AGEs, suggesting that a low AGE diet may also be associated with a decrease in SAF. Nevertheless, most of the evidence regarding diet modifications to reduce dietary AGE intake is of low quality and therefore further studies are required. Furthermore, this simple dietary intervention has not been previously study in the kidney transplant population. Therefore, if this proposed feasibility study is successful, we will use these findings to identify ways to design future larger research projects to improve the care of persons with a kidney transplant.

This is a feasibility study that will be conducted in two parts:

Part 1:

This will be a randomised controlled trial (RCT) aiming to recruit 40 participants with a functional kidney transplant. Participants will be assigned to either a low AGE diet (intervention group) or a standard diet for persons with a kidney transplant (control group). Participants will be followed-up for 6 months and will receive precise oral and written advice on how to follow the diets. This advice will be tailored to their needs and food preferences.Adherence to both diets will be evaluated by means of a 3-day food diary (2 weekdays and 1 weekend day) every month.

The purpose of the control group is to show what would normally happen to AGE levels in the skin and compare it with what happens to AGE levels in the skin when persons with a kidney transplant follow a low AGE diet. Therefore, this will show if the low AGE diet is really responsible of the observations.

Potential participants will be approached by the Chief Investigator (a member of the transplant team), during routine follow-up appointments. After the participants have read and understand the Participant Information Sheet (PIS), and had sufficient time (at least 24 hours) to consider their participation in this study, we will ask them to sign a consent form, which shows their willingness to take part. We will then collect information from their medical records or direct interview about their age, ethnicity, medical conditions, educational level, employment and smoking status, medication, alcohol history, and information about their transplant and kidney disease.

During the first study assessment, we will:

• Measure the accumulation of toxins (AGEs) in the skin using a safe, quick (less than five minutes) and painless technique called skin autofluorescence. This involves placing the forearm on a piece of equipment that shines a light on the skin and measures the amount of light that is reflected back.
• Take routine blood samples and blood pressure.
• Ask participants to complete a quality of life questionnaire (EQ-5D-5L), a 3-day food diary (2 weekdays and 1 weekend day) to assess energy, fat and protein intake and a validated food frequency questionnaire to evaluate dietary AGE intake.
• Assess nutritional status using the validated 7-point scale Subjective Global Assessment.
• Measure weight, height, mid-arm circumference, triceps skinfold thickness, handgrip strength and aortic pulse wave velocity (a measure of cardiovascular health).

These same procedures and measurements will be conducted at 3 and 6 months of follow-up.

Part 2:

Once the RCT (Part 1) has finished, 10 participants from the intervention group and 5 from the control group (ensuring as far as possible that the sample includes a diverse representation of the study population), will be invited to take part in interviews asking questions about the acceptability and tolerability of the intervention (low AGE diet), as well as feedback about the study process.

Potential participants will be given or sent an invitation letter and PIS, have the study explained to them and consented separately. The interview will take place at a time and location convenient to the participants and will take about 60 minutes.

Inclusion criteria

• Adults (>18 years) with a functioning (not on dialysis) kidney transplant.
• More than 12 months post-transplant.
• Able and willing to give informed consent.
• Skin Autofluorescence levels above the general population mean value for age.

Exclusion criteria

• Persons with dark skin colour (i.e. Fitzpatrick skin colour type 5-6).
• Persons with malnutrition (Subjective Global Assessment [SGA] score <5).
• Pregnancy or breast feeding or intending pregnancy.
• Active infection.
• Active rejection.
• Persons with learning difficulties.
• Prisoners.