What are the claims?
There have been some claims that coconut oil could be used as a treatment, or even a cure, for Alzheimer's disease. However, there is currently not enough experimental evidence to back up these claims.
The claim is based on the theory that the neurones (nerve cells) in the brains of people with Alzheimer's disease are unable to use glucose to produce energy properly and therefore 'starve'. The theory is that coconut oil may act as an alternative energy source, but there is not enough scientific evidence to know for sure whether this is the case.
A clinical trial into the potential effects of coconut oil was originally being conducted in in the US. However, sadly this trial had to be discontinued as the number of people enrolled on the trial was not enough to give robust results. Without high-quality trials in people, it is not possible to understand whether coconut oil has any benefit for people affected by dementia.
Why do people think that coconut oil could help in Alzheimer's disease?
Insulin, the hormone responsible for regulating blood sugar and glucose, has been linked to changes in the brain associated with Alzheimer's disease. However, it is not clear exactly what role insulin has in the disease and the hormone has many different roles in the body alongside regulating glucose. This means that the changes associated with dementia could be unconnected to glucose metabolism. Brain cells do appear to have problems with their metabolism in Alzheimer's disease, but it is unclear whether this is a cause of the disease or is the result of other disease-related processes.
The idea that coconut oil could provide an alternative energy source for brain cells comes from the successful treatment of children with epilepsy with a ketogenic diet. In this diet, carbohydrates are strictly limited and replaced by high fat intakes, forcing the body to use fat as a primary energy source (a similar idea lies behind the Atkins diet). Coconut oil is used to allow a slightly higher level of carbohydrate intake, making the very strict diet slightly easier to follow, but still preventing the body using sugar from carbohydrates as the main energy source. This works only because the body is forced to metabolise fats.
The ketogenic diet must be incredibly strict because the body will always preferentially use glucose for metabolism. Therefore, simply adding coconut oil to the diet would not provide the neurones in the brain with an alternative energy source. The diet is also linked to very high cholesterol levels, which increases risk factors for stroke, heart disease and dementia.
There is also evidence to suggest that fats like coconut oil could indirectly result in increased levels of a protein called acetylcholinesterase. Current treatments for Alzheimer's disease are 'acetylcholinesterase inhibitors' and work by reducing the levels of this protein. An increase is associated with Alzheimer's disease, meaning that coconut oil could be detrimental to people with Alzheimer's disease. This is why it is important to ensure that any potential treatment is safe to use for people with Alzheimer's disease before it can be approved for widespread use.
Update (May 2017): The trial into coconut oil has sadly been discontinued due to difficulties recruiting enough people to take part.