Effects of Alpha-lactalbumin Intake on Metabolic and Cognitive Functions in Elderly

Overview

Aging modifies the metabolic pathway of the neurotransmitter serotonin by reducing the synthesis rate and increasing the breakdown rate of serotonin, possibly related to the observed enhanced sensitivity of the serotonergic pathway. Since serotonin plays a prominent role in neuropsychological functions such as anxiety, mood and memory, the enhanced sensitivity of the serotonergic pathway in aging can probably explain the fact that elderly are more vulnerable to develop cognitive deficits and depressive symptoms. Serotonin synthesis in brain is regulated by its precursor tryptophan (TRP). Because tryptophan is an essential amino acid, modifying the availability of tryptophan through dietary intake, can directly influence central serotonin metabolism and consequently affective and cognitive processes. The aim of this study is to test the hypothesis that an acute intake of whey protein with high levels of TRP such as alpha-lactalbumin can stabilize the metabolism of serotonin and subsequently enhance metabolic and cognitive functions in healthy older adults. The acute effects of this dietary protein will be investigated in subjects with mild cognitive impairment (MCI), or dementia, compared to control subjects in order to examine whether healthy older subject with MCI benefit more from the intake of alpha-lactalbumin and/or whey. The investigators will investigate if this meal can optimize serotonin metabolism by elevating plasma TRP levels and plasma TRP appearance and enhance splanchnic TRP extraction. In addition, the effects on mood and cognitive functions will be examined.

The study involves for all subjects 3 test days (approximately 8 hours each). On this test day the investigators will examine the acute effects of a protein meal. Subjects will receive a mixture of alpha-lactalbumin and/or whey and/or casein, carbohydrates and amino acid stable isotopes to investigate protein and amino acid kinetics (assigned to alpha-lactalbumin or whey or casein group on test day 1, then switch on test day 2 and 3). The subjects will receive these stable isotopes by infusion in their blood and by oral intake (e.g. simultaneously with protein meal). For study purposes, blood will be drawn approx. 25 times during 8 hours on the test day, altogether about 100-120 ml of blood will be drawn on the test day.