Gut-brain Health Effects of PREbiotics in Older Adults With Suspected COgnitive DEcline

As people around the world are living longer, the number of individuals with dementia, particularly Alzheimer\'s disease (AD), is expected to triple by 2050. There\'s growing evidence suggesting that our gut health might play a role in the prevention of dementia. The connection between our gut and brain, known as the gut-brain axis, is becoming an important area of study. Research in animals has shown that different types of dietary fibre can improve gut health, brain function, mood, blood sugar level and the immune system and may even prevent certain harmful brain changes seen in Alzheimer\'s disease. Subjective Cognitive Decline (SCD) is a condition where individuals notice a decline in their mental abilities, and it can be an early sign of Alzheimer\'s disease. The goal of this clinical trial is to learn if dietary fibres can improve gut and brain health in older individuals, between the ages of 60 and 79 years, who notice problems in their mental abilities, and meet the criteria of SCD. Three different dietary fibres will be given, and researchers will compare three different fibres to a placebo product to see if there is a difference between the fibres and the placebo. The main questions it aims to answer are: 1. Does dietary fibre improve working memory? 2. Does dietary fibre improve other markers of brain function? 3. Does dietary fibre improve gut health? 4. Does dietary fibre improve the immune system and blood glucose levels? 5. Does dietary fibre improve mood? Participants will: * Consume dietary fibres twice a day, mixed in water, tea or coffee, for a period of 26 weeks * Have two functional MRI scans, and three additional study visits, where blood, urine and feces will be collected * Undergo a number of neuropsychological tests, aimed at evaluating brain function * Fill out questionnaires on their general health, mood, dietary habits, gut health * Wear smartwatches for one week, at the beginning and the end of the study