Impact of AGEs on Metabolism & Cognition

Overview

A number of processed foods particularly those high in protein and based on whey protein are high in advanced glycation end products (AGEs). AGEs are the result of a chemical reaction between mainly sugar and protein when they are heated together (known as the Maillard reaction). Whey protein is routinely derived via high temperature processing methods which produce AGEs. AGEs are absorbed during digestion and high circulating concentrations of AGEs are associated with adverse health effects such as dementia and the metabolic syndrome. In this study we aim to firstly ascertain the habitual level of AGE intake in the diet via a dietary questionnaire and equate this to both metabolic health and cognition at baseline. Volunteers will then be given a milkshake with either a high or low AGE content on either a high or low fat background. AGEs are usually ingested as part of a processed food diet which can be high in fat and it is necessary to separate the effects of these two food types. We will test these effects in a young and older group of volunteers with low and higher levels of circulating AGEs respectively. Circulating levels of hormones, glucose and lipids in the blood will be measured as indicators of metabolic health. Cognitive tests will be carried out to assess the impact of AGEs on episodic memory.

This study will be a short-term, randomized, double-blind, cross-over trial. Volunteers will be younger (18-30 years) and older (55-75 years) men and women, normal and overweight (BMI\>19 to 29.9). N=24 in each age group. Medical screening for all study volunteers and neuropsychological screening will be carried out prior to study start. A small, pin prick, fasted blood sample will be taken to measure glucose and HbA1C levels to rule out type 2 diabetics. Anthropometric and body composition measurements will also be taken. Body weight and height will be measured using a scale and a stadiometer to the nearest 0.5 kg and 0.5 cm, respectively. Waist and hip circumferences will be measured and the waist-to-hip ratio calculated. Standard procedures will be followed for the anthropometric measurements and the average of three measurements taken. Neuropsychological screening may be repeated on another day if volunteers are borderline on their first visit as scores may vary by a couple of points depending on external events i.e. vounteers are having a bad day. Experienced staff will carry out abdominal fat measurements by manual determination of the area between the upper surface of the second lumbar vertebra, the lower surface of the fourth lumbar vertebra, and the lateral margins of the outer rib cage. If the Viscan is available we will use that to measure abdominal fat. Venous blood samples will be collected as appropriate for the hormones and metabolites to be tested and stored at -70 °C. The day prior to the challenge volunteers will visit the Human Nutrition Unit (HNU, RINH). They will be given a low AGE breakfast and be supplied with a low AGE lunch and dinner for that day and instructed not to consume anything else. After an overnight fast volunteers will receive a one-off dose of either high AGE (11.4 mgs) or low AGE (2.4 mgs) whey protein delivered in a either a low or high fat milkshake (400ml) blended with flavours and a consistent quantity of sugar. All ingredients will be commercially available and of food grade. Apart from differences in fat and AGE the content of shakes will be closely balanced for sugar and other components. All participants will be asked to answer two questionnaires one to determine their habitual intake of dietary AGEs and one to determine their level of physical activity. The different milkshakes will be tested with a minimum 7 day wash out period between tests. Volunteers will be randomised to each test group. After a 12 h overnight fast and a standardised intake the day prior to the tests, and no strenuous physical activity for 2 days previously, subjects will attend the HNU. Volunteers will be requested to provide a small urine sample for AGE analysis. An intravenous catheter will then be placed in an antecubital vein and flushed with saline between aspirations to keep the catheter clear. After a short resting period, a blood sample will be taken prior to the first memory test then a single milkshake will be consumed under supervision. Blood samples will be taken immediately before the milkshake ingestion (0 min) and after 30, 60, 90, 120, 150 and 180 and 240 min. Further computer based memory tests will be carried out at 30, 90 and 240 minutes. A urine sample will be requested at the end of the study before participants are offered lunch. Memory tests have been designed by Dr Ros Langston (University of Dundee) and Dr Kevin Allan, School of Psychology and will be carried out on lap tops specifically designated for this study. Blood and urine will be analysed for AGEs. Blood will also be analysed for glucose lipids and hormones. Dr Janice Drew will also analyse blood samples for gene expression of the SIRT-1/NAD+ complex indicative of the response of individuals to dietary challenge.