The science behind Neuroceutik
Regulation Of Food Intake
Food intake regulation is a good example of a behavioral response. Many theories have tried to explain how the brain controls food intake and is responsible for hunger and satiation mechanisms.
The lipostatic hypothesis suggests that the size of fat deposits in the organism is connected to the neuronal or hormonal control of appetite.
Temperature changes affect the degree of appetite, possibly by affecting energy storage.
Thus, in humans, a cold environment stimulates appetite, where as a warmer environment diminishes appetite.
Changes in plasma amino acid patterns and the uptake of amino acids into the brain after food ingestion, provide signals that allow for the regulation of appetite.
Both the catecholamines and serotonin neurotransmitter systems are known to be involved in appetite regulatory mechanisms. The control of their synthesis by the availability of their amino acid precursors suggests that appetite regulation may be achieved by this mechanism.
The effects of nutrition on behaviors linked to human mental and psycho-affective activity are numerous and complex.
It is important to remember that macro nutrients and micro nutrients are essential to the brain's good functioning.
Moreover, as amino acids play an obvious role as precursors of neurotransmitters, it must not be over looked that they are closely tied to vitamins and minerals. It is clear that a healthy and balanced diet contributes to the stable maintenance of the brain's vital functions
The Brain Distinguishes Between Nutrients
It is through this system that the brain can distinguish a carbohydrate meal from a protein meal. Carbohydrate consumption increases plasma trytophan relative to competing neutral amino acids.
This happens because the release of insulin, which occurs after carbohydrates are consumed, causes the rapid uptake of amino acids by tissues, except tryptophan. When amino acids pass through the brain capillaries, tryptophan has an uptake advantage. As a result, tryptophan and serotonin levels increase in the brain.
The opposite happens to serotonin in the brain when proteins are consumed.
Proteins are relatively low in tryptophan but are high in the amino acids that compere for their uptake into the brain. Thus, a protein rich meal decreases the plasma tryptophan and the brain is informed that protein is consumed
Another neurotransmitter, dopamine, the immediate precursor of noradrenaline, is derived from the amino acid, tyrosine.
However, its synthesis is not directly influenced by plasma and brain concentrations of tyrosine, as it is for the relationship between tryptophan and serotonin.
The synthesis of noradrenaline from dopamine is limited by the biochemical properties of the synthesis enzyme (dopamine-B-hydroxylase) and by the location of this enzyme in the nerve cells.
Consequently, an increase in the dopamine content does not necessarily correspond to an increase in the noradrenaline content on a neuroanatomical and neurophysiological basis. In certain regions of the brain such as the cortical areas, the synthesis of dopamine is almost exclusively used for the synthesis of noradrenaline whose role as a neurotransmitter is dominant.
The Key Link Between Brain Function and Diet, Lies in Neurotransmitters
Since the 1950’s, it has been demonstrated that neuro transmitters such as catecholamines and serotonin play a significant role in several physiologic alstates.
Serotonin has been associated with the sleep cycle and noradrenaline with awake and vigilant states. Neuro transmitters are also involved in thermoregulation (maintenance of body temperature), the mechanism of hunger and satiation, and the process of learning and memory.
Neuro transmitters exert their actions in nerve endings after being released into the synapses - the spaces between cells. The pre-synaptic cell, which releases neurotransmitters, communicates with receptors on the post-synaptic cell. As a result, path ways throughout the brain serve as communication lines controlling brain function.
A neurotransmitter never acts alone. It is always in a metabolic or physiological relation with other neurotransmitters. The neuro-anatomical systems (motororlimbic systems) serve as support and as intermediaries for the transmission of information.
Serotonin and catecholamines are affected by food intake. Synthesized in the brain, they are formed when the amino acids, cryptophan and tyrosine, undergo an initial transformation (hydroxylation) by two different enzymes sharing the same nutrient cofactors (pteridine, vitamin C and iron). After hydroxylation, both amino acids are then decarboxylated by a vitamin B6 dependent enzyme to form the neurotransmitters dopamine and serotonin.
This step in the conversion of amino acids into neuro transmitters is metabolically significant because it assures a biochemical balance between the synthesis of dopamine (D A) and serotonin (5- HT).
Tryptophan will provoke an increase of serotonin and a decrease of dopamine, whereas dihydroxyphenylalanine (used, for example, in the control of Parkinson' s disease) will generate an increase of dopamine, and a decrease of serotonin.
This is only one example of a biochemical balance generated in the brain that allow neurotransmitters to receive and organize information.
Under normal concentrations of tryptophan and tyrosine in the brain, the hydroxylases, which are the rate limiting enzymes in both path ways, are not saturated by the substrates, tryptophan and tyrosine.
This means that diet induced changes in blood amino acid concentrations will influence the brain's synthesis of these two important neurotransmitters.
This simple relationship between the diec plasma and brain neurochemistry allow the brain to gather information on diet composition and the metabolic state of the body and use this information to regulace many of its functions.