Effects of a High Carboxymethyl-lysine (CML) Diet on Absorption and Excretion Levels in Healthy Adults

Advanced glycation end products (AGEs) are a heterogenous group of compounds form mainly by the Maillard reaction. AGEs can be found endogenously and in some foods. Several AGEs have been characterized, but carboxymethyl-lysine (CML) is one of the most widely studied in foods. Several studies have demonstrated the association between advanced glycation end products and several pathologies. However, few studies have focused on studying the absorption and excretion processes of these glycation products. Therefore, the objective of the study is to evaluate the effect of carboxymethyl-lysine (CML) on the levels of absorption and excretion of CML, and in the microbiota of healthy adults. To achieve the objective, a randomized clinical trial will be carried out, which will consist of a 7-day washout period during which participants will receive general recommendations that allow them to stick to a diet with a low CML content, adherence to these recommendations will be evaluated through three dietary records. At the end of the washing period, participants will be randomly assigned to either a high-CML or to a low-CML diet for 5 days. Participants will receive the 5 corresponding meals (breakfast, lunch, snacks and dinner) during the 5 days of the intervention, these preparations will be elaborated by a catering company with indications and supervision by the research group. Participants will assist to the research center to receive the breakfast, lunch and snacks. After lunch the subjects will receive a package containing a snack for mid-evening and the dinner. Adherence to the diet during the intervention period will be evaluated through a dietary record of foods.

The intervention will be based on an isocaloric diet with a distribution of 55 to 63% carbohydrates, 12 to 15% protein, 25 to 30% lipids and less than 10% saturated fat.

The diet with high content of CML will have twice the amount that the low diet, but with similar amounts of macro and micronutrients.

A blood sample will be taken on the first day of the intervention to measure CML basal levels. In order to evaluate the levels of CML absorption, the serum collection will be performed on the second day and at the end of the intervention. To evaluate the levels of CML excretion 24-hours urine will be collected the day before the intervention and the day after the dietary intervention finished. To evaluate the effects on the microbiota subjects will take a fecal sample the day before and a day after the intervention. Measurement of CML in serum, 24-hour urine and food will be performed by Liquid chromatography tandem-mass spectrometry. DNA extraction from the fecal sample will be carried out by a commercial kit. Bacterial log10 number of copies will be determined by using q-PCR.