Quantifying the Ability of Fasting and Exercise to Increase BDNF Expression
Upregulation of BDNF is a useful goal, as it produces greater neurogenesis in the brain. Neurogenesis, the production of new neurons from neural stem cells, and their integration into neural circuits, is important in memory, learning, and the resilience of the brain to damage and aging. Increased levels of BDNF may also improve metabolism and reduce inflammation in brain tissue. BDNF levels decline with age, but evidence suggests that BDNF expression can be boosted via calorie restriction and exercise. Researchers here compare these approaches for effectiveness, finding that short bursts of high intensity exercise produce the best outcome.
The specialised protein named brain-derived neurotrophic factor (BDNF) promotes neuroplasticity (the ability of the brain to form new connections and pathways) and the survival of neurons. Animal studies have shown that increasing the availability of BDNF encourages the formation and storage of memories, enhances learning, and overall boosts cognitive performance. These key roles and its apparent neuroprotective qualities have led to the interest in BDNF for ageing research.
To tease apart the influence of fasting and exercise on BDNF production researchers compared the following factors to study the isolated and interactive effects: (a) fasting for 20 hours; (b) light exercise (90-minute low intensity cycling); (c) high-intensity exercise (six-minute bout of vigorous cycling); and (d) combined fasting and exercise. Twelve physically active participants (six males, six females aged between 18 and 56 years) took part in the study. The researchers found that brief but vigorous exercise was the most efficient way to increase BDNF compared to one day of fasting with or without a lengthy session of light exercise. BDNF increased by four to five-fold (396 pg/L to 1170 pg/L) more compared to fasting (no change in BDNF concentration) or prolonged activity (slight increase in BDNF concentration, 336 pg/L to 390 pg/L).
The cause for these differences is not yet known and more research is needed to understand the mechanisms involved. One hypothesis is related to the cerebral substrate switch and glucose metabolism, the brain's primary fuel source. The cerebral substrate switch is when the brain switches its favoured fuel source for another to ensure the body's energy demands are met, for example metabolising lactate rather than glucose during exercise. The brain's transition from consuming glucose to lactate initiates pathways that result in elevated levels of BDNF in the blood. The observed increase in BDNF during exercise could be due to the increased number of platelets (the smallest blood cell) which store large amounts of BDNF. The concentration of platelets circulating in the blood is more heavily influenced by exercise than fasting, and increases by 20%.
I think it is the lactate from the exercise. Lactate also stimulates growth hormone release if at the same time you also have low blood glucose, low insulin, high ghrelin (you are hungry).
You can make a ton of lactate with blood flow restriction training which has been shown to increase GH something crazy like 270x. BFR training has also been tested in humans for stimulating BDNF.
BFR might be better for old people because as shown in this study Reason posted, how many old people are you going to get to do 6 all out 40 second sprints at their VO2max? BFR gets you there with light loading.