Thread by @nick_krontiris

The findings of this one suggest that BDNF responses to low-intensity endurance exercise are mediated by increased circulating platelets, and increasing exercise duration, and to a greater extent, intensity, is required to liberate free, unbound BDNF in circulation.

- Intermittent fasting and exercise provide neuroprotection from age-related cognitive decline.

- A link between these two seemingly distinct stressors is their capability to steer the brain away from exclusively glucose metabolism.

- This cerebral substrate switch has been implicated in upregulating brain-derived neurotrophic factor (BDNF), a protein involved in neuroplasticity, learning and memory, and may underlie some of these neuroprotective effects.

- Switching the brain’s fuel source from glucose to either ketone bodies or lactate, i.e. a cerebral substrate switch, has been shown to promote BDNF production in the rodent brain.

- This study investigated how circulating BDNF is affected by: (1) fasting for 20 h, (2) light, prolonged exercise, (3) short duration, high-intensity interval exercise, and (4) combined fasting and exercise.

Findings:

- Despite a shift in energy substrate delivery to the brain, fasting for 20 hours did not affect peripheral circulating BDNF at rest, or BDNF responses to exercise.

Note that fasting for 20 hours reduced circulating glucose by 0.7 mmol/l, insulin by 110 pmol/l and increased βHB by 0.5 mmol/l.

- Increases in circulating BDNF within 30 minutes of beginning light exercise were due exclusively to exercise-mediated increased platelet concentration, which itself appeared to be accounted for by plasma volume contraction.

- Prolonged (90 minute) light cycling exercise was sufficient to increase plasma-derived BDNF, which represents an unbound, bioavailable source of BDNF independent of elevated platelet concentration.

- 6 minutes of high-intensity cycling intervals increased every metric of BDNF by 4- to 5-fold more than prolonged exercise did.

- There was no relationship between cerebral shear stress and BDNF release during exercise or in the isolated, larger-magnitude shear-altering interventions.

Altogether, these data may suggest that BDNF responses to exercise are mediated by increased circulating platelets, and either increasing exercise duration or particularly exercise intensity are required to liberate free, bioavailable BDNF...

...while fasting for days, plural, may be required to increase BDNF.

Fasting for 20 h does not affect exercise-induced increases in circulating BDNF in humans

doi.org/10.1113/JP2835…

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