Because the human brain is only 2% of the body’s volume but consumes over 20% of its energy, it is particularly vulnerable to changes in metabolism.
Therefore this study, led by Stony Brook University professor Lilianne Mujica-Parodi, PhD, a Professor in the Department of Biomedical Engineering with joint appointments in the College of Engineering & Applied Sciences and Renaissance School of Medicine at Stony Brook University, aimed to discover how diet could influence the neurobiological changes associated with ageing.
The team focused on the presymptomatic period during which prevention may be most effective and found, using neuroimaging of the brain, that quite early on there is breakdown of communication between brain regions, typically in the late 40's, and that destabilisation correlates with poorer cognition and accelerates with insulin resistance.
They conducted targeted experiments which showed this biomarker for brain ageing to be reliably modulated with consumption of different fuel sources: glucose decreases, and ketones increase, the stability of brain networks. This effect was replicated across both changes to total diet as well as after drinking a fuel-specific calorie-matched supplement.
The findings, published in PNAS, are significant because if it is possible to increase the amount of energy available to the brain by using a different fuel, it may be possible to restore the brain to more youthful functioning through diet, according to Dr. Mujica-Parodi.
"What we found with these experiments involves both bad and good news," she said. "The bad news is that we see the first signs of brain ageing much earlier than was previously thought. However, the good news is that we may be able to prevent or reverse these effects with diet, mitigating the impact of encroaching hypometabolism by exchanging glucose for ketones as fuel for neurons.
"We think that, as people get older, their brains start to lose the ability to metabolise glucose efficiently, causing neurons to slowly starve, and brain networks to destabilise.
"Thus, we tested whether giving the brain a more efficient fuel source, in the form of ketones, either by following a low-carb diet or drinking ketone supplements, could provide the brain with greater energy. Even in younger individuals, this added energy further stabilised brain networks."
To conduct their experiments, brain network stability was established as a biomarker for ageing by using two large-scale brain neuroimaging (fMRI) datasets totalling nearly 1,000 individuals, ages 18 to 88.
Destabilisation of brain networks was associated with impaired cognition and was accelerated with Type 2 diabetes, an illness that blocks neurons' ability to effectively metabolise glucose.
To identify the mechanism as being specific to energy availability, the researchers then held age constant and scanned an additional 42 adults under the age of 50 years with fMRI. This allowed them to observe directly the impact of glucose and ketones on each individual's brain.
The brain's response to diet was tested in two ways. The first was holistic, comparing brain network stability after participants had spent one week on a standard (unrestricted) vs. low carb (for example: meat or fish with salad, but no sugar, grains, rice, starchy vegetables) diet.
In a standard diet, the primary fuel metabolised is glucose, whereas in a low-carb diet, the primary fuel metabolised is ketones. However, there might have been other differences between diets driving the observed effects.
Ketones for the brain
Therefore, to isolate glucose vs. ketones as the crucial difference between the diets, an independent set of participants was scanned before and after drinking a small dose of glucose on one day, and ketones on the other, where the two fuels were individually weight-dosed and calorically matched. The results replicated, showing that the differences between the diets could be attributed to the type of fuel they provide to the brain.
Additional findings from the study included the following: Effects of brain ageing emerged at age 47, with most rapid degeneration occurring at age 60. Even in younger adults, under age 50, dietary ketosis (whether achieved after one week of dietary change or 30 minutes after drinking ketones) increased overall brain activity and stabilised functional networks.
This is thought to be due to the fact that ketones provide greater energy to cells than glucose, even when the fuels are calorically matched. This benefit has previously been shown for the heart, but the current set of experiments provides the first evidence for equivalent effects in the brain.
"This effect matters because brain ageing, and especially dementia, are associated with 'hypometabolism', in which neurons gradually lose the ability to effectively use glucose as fuel. Therefore, if we can increase the amount of energy available to the brain by using a different fuel, the hope is that we can restore the brain to more youthful functioning. In collaboration with Dr. Eva Ratai at Massachusetts General Hospital, we're currently addressing this question, by now extending our studies to older populations," said Mujica-Parodi.
Additional research with collaborators at Children's National, under the direction of Dr. Nathan Smith, focuses on discovering the precise mechanisms by which fuel impacts signalling between neurons.
In collaboration with Dr. Ken Dill and Dr. Steven Skiena, at Stony Brook, Mujica-Parodi's team is also working on building a comprehensive computational model that can incorporate our understanding of the biology, from individual neurons to whole brains to cognition, as it develops.
The research is currently funded under a new $2.5 million National Science Foundation BRAIN Initiative "Frontiers" grants awarded to Stony Brook, as well as by the W. M. Keck Foundation, which originally funded the team in 2017 with a $1 million seed grant designed to jump-start "pioneering discoveries in science, engineering, and medical research.
Mujica-Parodi. L. R., et al
"Diet modulates brain network stability, a biomarker for brain aging, in young adults"