Research has found a link between diseases of the nervous system and the gut
Photo by Cognitive Cacophony (flickr)
by Maja Skrętowska
Alzheimer’s Disease (AD) is one of the main research topics in the western medical sciences. In the developed countries, it is one among the most costly diseases. The chase to find a cure is pacing ever faster as the population is ageing and people are living longer. Sadly, no farno cure has been found so far and prescribed drugs only modulate the course of AD, indirectly affecting the symptoms rather than the cause. Unsurprisingly, people turn to alternative medicine and non-pharmaceutical treatment with the hope to keep the disease at bay, and sometimes the effort bears fruits. Especially, cases of successful dietary interventions have gained interest among those affected by AD.
It has been known in the scientific world for a long time that diets have a mysterious link with diseases of the nervous system, but our understanding of this is fairly limited. However, with the advancement in research of the enteric nervous system (the one that controls your gastro-intestinal tract) and microbiota inhabiting our gut, we have come to understand more of these links. The food we eat can trigger microbiota to produce cytokines which enter circulation and then activate or suppress inflammatory processes, including neuroinflammation contributing to degeneration of neurons. Additionally, the development of our immunity will be largely influenced by the gut microbiota. It should not be surprising, as up to 70% of our lymphoid tissue is enrolled in defending the organism from the external pathogens in the intestine. What perhaps is more unexpected is the finding that the vagus nerve, connecting the central (brain) and enteric (gut) nervous systems has some control over our mood and carries signals back and forth between the two centres. As both of them use virtually the same neurotransmitters, the signal exchange is not only larger than we predicted, but also involves mood changes.
The importance of the vagus nerve underpins other theories about AD pathogenesis. It has been observed that a number of neurodegenerative processes emerge from abnormal protein folding, resulting in widely spreading malfunction through their prion-like properties. This means that for example a severed tau or synuclein protein found in some types of AD or Parkinson’s will act on properly folded proteins of the same type and misshapen them, spreading the pathology. Such proteins will amass in neurons, causing disruption in their regular cycle and leading to cell death. The transport of these endogenous prion-like proteins can possibly come through the vagus nerve from the gut to the central nervous system. As we see again, the experience of the gut could translate to the function of the brain.
In terms of what we feed our gut, of course an apple a day will not suffice. Diets that are spoken of in the context of neurodegenerative diseases are very restrictive and intrusive on a person’s life. This includes strict plant-and-fish-based meals or ketogenic nutrition, which limits carbohydrate and protein intake to the minimum. The latter has surprisingly been used not only in Alzheimer’s but also in certain untreatable cases of epilepsy or multiple sclerosis since the ancient times. Possibly, by way of enforcing fat-based metabolism, the usual energy production severed in the above-listed diseases is circumvented, empowering neurons to survive. However, as the exact origin of AD has not been explained, it is also very difficult to find a single diet yielding positive results at all times.
AD, just as many other neurodegenerative diseases, could well be an umbrella term of syndromes sharing similar symptoms. Although it is not certain that a single set of recipes will suffice to target each and every case, the observation of dietary habits brings us closer to dismantling at least some of the causes and thus gives some hope to those affected.
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