Can reduction of calories in an aging adult help with brain function? It is proposed caloric restriction can have neuroprotective effects on the brain when employed in the aging population.
First let's define caloric restriction. Caloric restriction is specifically defined as a reduction in energy intake well below the amount of calories that would be consumed ad libitum (at one's pleasure). This is specifically set as ≥10% reduction in human studies and usually 20% or higher in rodent species. It appears that 25% caloric restriction below ad libitum intake is optimal in animal studies when looking at longevity factors.(Ravussin et al., 2015).
There are alternate strategies to caloric restriction including: 1.) intermittent energy restriction (IER), which involves eliminating (fasting) or greatly reducing (e.g., 500 calories per day) daily intake food/caloric beverage intake intermittently, for example 2 d/wk; and (2) time-restricted feeding (TRF), which involves limiting daily intake of food and caloric beverages to a 4- to 6-h time window.
How does Caloric restriction improve brain function? Caloric restriction reduces insulin resistance peripherally which improves insulins impacts on the brain/central nervous system. Insulin centrally (meaning in the brain) is involved with synaptogenesis (making nerve connections) and also with brain signaling (Witte, Fobker, Gellner, Knecht, & Flöel, 2009).
In addition, a common feature of many major chronic diseases is the abnormal/excessive accumulation of protein aggregates within and outside of cells; examples include intracellular α-synuclein in Parkinson’s disease and extracellular amyloid β-peptide and intracellular Tau protein in Alzheimer’s disease. Caloric restriction or related strategies may help improve the autophagy process in cell that clears out protein aggregates. (Mattson et al., 2014).
Perhaps this is a key preventative strategy for the onset of Parkinson’s disease and Alzheimer’s disease.
There is some concern about the behavioral and psychological effects of long-term caloric restriction. In long term >50% caloric restriction we see an increase in eating disorders. However in long-term studies such as the CALERIE study with moderate caloric restriction approximately 25% we actually see less depression and less pre-occupation or worry about weight. (Redman & Ravussin, 2011)
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