HIIT Workouts Turbocharge Exercise's Neuroprotective Power

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Brain-derived neurotrophic factor (BDNF) is a specialized protein that promotes neuroplasticity and neurogenesis (the birth of new neurons). Higher levels of BDNF are associated with better overall cognition and memory function.

BDNF also has neuroprotective benefits. Lifestyle choices that increase circulating BDNF levels may offset the risk of degenerative brain diseases associated with dementia and reduce age-related cognitive decline.

Some scientists refer to BDNF as "Miracle-Gro for the brain" because it helps neurons grow while keeping them strong and healthy. Researchers have known since the early 2000s that aerobic exercise increases circulating BDNF levels in both humans and mice. Recent animal studies have also shown that intermittent fasting boosts BDNF and increases hippocampal neurogenesis in the mammalian brain (Baik et al., 2019).

New human research (Gibbons et al., 2023) teases apart the influence of fasting versus high- or low-intensity physical activity on BDNF levels. Of these three interventions, vigorous, high-intensity workouts triggered the greatest increase in circulating BDNF. These peer-reviewed findings by researchers at New Zealand's University of Otago were published in The Journal of Physiology.

"BDNF has shown great promise in animal models, but pharmaceutical interventions have thus far failed to safely harness the protective power of BDNF in humans," first author Travis Gibbons said in a news release. "We saw the need to explore non-pharmacological approaches that can preserve the brain's capacity, which humans can use to naturally increase BDNF to help with healthy aging."

High-Intensity Intervals Boost BDNF More Robustly Than Prolonged Low-Intensity Cardio

For this study, participants visited an exercise physiology lab on different days. One day, each person did a prolonged "light" workout that involved riding a stationary bicycle for 90 minutes at a low-intensity level of exertion. On another day, each person performed six bouts of high-intensity interval training on the bike. Each episode of maximum effort lasted less than a minute, followed by a brief recovery period and five more high-intensity intervals.

After each workout session, the researchers compared circulating BDNF levels. They also had participants fast intermittently throughout these experiments and gauged if and how fasting affected BDNF in combination with different intensities of stationary cycling.

"Prolonged (90 minutes) light cycling exercise increased plasma- and serum-derived BDNF irrespective of being fed or fasted and seemed to be independent of changes in cerebral shear stress," the authors explain. "Six minutes of high-intensity cycling intervals increased every metric of circulating BDNF by four to five times more than prolonged low-intensity cycling."

Notably, the researchers found that just six minutes of high-intensity exercise releases significantly more BDNF than 90 minutes of prolonged low-intensity cardio. Based on these findings, Gibbons et al. speculate that six-minute bouts of vigorous exercise can help keep the brain healthy and may offset the risk of age-related neurodegeneration more efficiently than low-intensity physical activity.

Six minutes of high-intensity interval training (HIIT) throughout the week could also help to delay the onset of neurodegenerative disorders like Alzheimer's disease and Parkinson's more effectively than prolonged low-intensity cardio sessions.

6 Minutes of High-Intensity Exercise Causes BDNF to Skyrocket

To the best of my knowledge, this is one of the first human studies to pinpoint specific details about how different "doses" (frequency/duration/intensity) of cardiorespiratory physical activity increase BDNF and optimize exercise's neuroprotective power.

In terms of prescribing exercise as "medicine" to keep the brain healthy as we age, the latest (2023) research suggests that incorporating some high-intensity interval training into your weekly exercise routine is better than only doing prolonged low-intensity cardio.

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Although Gibbons et al. found that short bouts of vigorous, high-intensity exercise are a much more efficient way to increase BDNF compared to longer sessions of light, low-intensity exercise, the reason for these differences remains unclear. More research is needed to identify the neural mechanisms that make high-intensity workouts such an effective way to increase circulating BDNF.

Additionally, more research is needed to figure out how calorically restrictive diets and fasting can be harnessed in conjunction with different "doses" of exercise to upregulate the expression of BDNF.

Of note: When making lifestyle changes designed to improve brain health that involve a potentially dangerous combination of fasting and vigorous exercise, everyone should consult a primary care physician before doing anything radical.

"We are now studying how fasting for longer durations, for example, up to three days, influences BDNF. We are curious whether exercising hard at the start of a fast accelerates the beneficial effects of fasting," Gibbons concludes. "Fasting and exercise are rarely studied together. We think fasting and exercise can be used in conjunction to optimize BDNF production in the human brain."

Disclaimer: This blog post is not intended as medical advice. Always consult a healthcare provider or nutritionist before fasting or going on a calorie-restricted diet. If vigorous exercise isn't part of your weekly routine, consult with a primary care physician before doing any high-intensity interval training (HIIT).