Dr Fernando Gomez-Pinilla of the University of California, LA discussed the studies he had undertaken with rats on fitness training and cognitive decline.

Increased exercise in rat models was shown to increase their hippocampal levels of BDNF - brain-derived neurotrophic factor. BDNF is a protein that supports existing neurones, and encourages the growth of new neurones and synapses in the hippocampus, cortex, and basal forebrain - areas vital to learning, memory, and higher thinking. Increased exercise enabled the rats to learn faster and to recover more quickly from a traumatic brain injury.

It was also found that a diet high in saturated fats reduced
hippocampal levels of BDNF while supplementing with fish oils increased levels of BDNF. Like the exercise, the fish oil supplements speeded up recovery from traumatic brain injury. Combining exercise and good diet had a positive synergistic effect.

Dr Stephen Cunnane from the Université de Sherbrooke, Canada looked at brain function in the aging. In Europe 10% of over 65 year olds suffer from cognitive brain decline, as do 50% over over 85 year olds.

Genetic factors may be relevant in this decline but they are uncontrollable. However it seems clear that insulin resistance/type 2 diabetes, low fish intake and a reduced uptake of glucose (brain fuel) all affect the incidence of decline.

To keep all neurones and synapses in the brain fully operational requires a high input of fuel (glucose and metabolites - amino acids, glycerol and glycogen): it takes 74% of the total energy consumed by a new born baby, 23% of total energy consumed by an adult.

In omega 3 deficient animals the brain uptake of glucose is poor; there is 20% less glucose uptake in the brains of Alzheimer's patients than in normal brains. Is there a connection?
Insulin must play a role in glucose supply so insulin resistance impairs the ability to get glucose into the tissues, thus starving the brain of fuel.

It is possible that ketones (the substances made when the body, in search of energy/fuel/glucose, breaks downs fats to access it) may help to supply the brain with fuel but there is little evidence of this.
It is not clear whether the inability of the brain to access sufficient fuel is a vascular problem (not enough glucose is getting through) or neurone problem (they are unable to capture the glucose when it arrives). Nor is it known how fatty acids are actually transported into the brain.

Humans are not good at making DHA out of omega 3 fatty acids - we are most efficient as neo-nates but get worse as we get older. But if there is a sufficient dietary supply (fish) there is no need for us to convert it anyhow.

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