New thesis on the impact of dietary macronutrients on cognitive health among older adults

How the dietary ratio of carbohydrates versus fat impacts cognitive performance and dementia risk among older adults is poorly understood. A few promising pilot studies on ketogenic diets (very carbohydrate-restricted) have increased the interest for this area of research but it has been unclear whether it is motivated to also investigate moderate carbohydrate reduction in future randomized trials. We performed observational studies on older adults with risk factors for dementia to investigate the associations between their dietary macronutrient proportions and results on a cognitive test. Furthermore, we investigated whether APOE-genotype, an important risk factor for Alzheimer’s disease, modulated the associations between diet and cognition. The most common variant APOE3 is associated with normal Alzheimer risk while APOE4 increases and APOE2 decreases the risk. 

Which are the most important results?   

A lower proportion of carbohydrates compared to fat was associated with better cognitive performance in the whole group. Further analyses indicated that those results were driven by the sub-group APOE34/44, and analyses on BMI, blood pressure, and blood lipids did not indicate any disadvantageous associations with a lower carbohydrate/fat-ratio for those. APOE-genotype also modulated associations with cognition for protein, fiber and fat-subtypes. Our results are in line with published hypotheses that APOE4, compared to APOE3, may provide less adaptation to a high carbohydrate/plant-based diet. Furthermore, we found that insulin status modulated the results. One conclusion is that the cognitive field might prioritize randomized trials on moderate carbohydrate restriction, rather than strict ketogenic diets which may be more complicated and reach a more limited target group. 

How can this new knowledge contribute to the improvement of people’s health? 

Our results motivate that future diet research and guidelines shift focus from average dietary needs in the population towards distinct needs for certain sub-groups. APOE4 is over-represented in the Nordic countries where roughly 25% of the population—but 75% of Alzheimer patients—have that gene variant. Better understanding on how to optimize diet for that group could potentially improve their cognitive health in the future. 

What’s in the future for you? Will you continue to conduct research?

Yes! This is a very interesting area of research and fortunately we have received funding to follow up the results in a randomized controlled trial among patients with prodromal Alzheimer’s disease. It would also be interesting to use already collected data from various studies to replicate the findings and extend analyses to broader age groups and aspects of health.