Boosting BDNF Through Exercise

Fortunately, you can increase BDNF very easily by lacing up your hiking boots. Physical activity is the best-studied factor in this regard. 29 studies with more than 1000 subjects showed that single exercise sessions, regular exercise, and especially single exercise sessions within regular exercise increase BDNF levels. For example, just ten minutes of cycling at 70 percent of maximal capacity can significantly raise levels. The higher the exercise intensity, the greater the increase in BDNF levels. But even in older people with limited mobility, a physical therapy intervention with progressive dynamic resistance training appeared to increase blood BDNF levels.

So is BDNF one of the reasons exercise boosts brain performance? Yes, at least in rodents. Scientists have clearly shown that in rats and mice, blocking BDNF prevents the memory-enhancing effect of exercise, thereby proving BDNF’s role in mediating the positive effects of exercise. In humans, we can only test whether the degree of exercise-induced improvement in BDNF corresponds to the improvement in memory performance from the training. This answer is less clear, because that was the case in only four of the ten studies on the topic.

Boosting BDNF Through Calorie Reduction

Fasting is touted as a way to rejuvenate body and mind, but after just 18 hours of fasting, some people become noticeably irritable. Surprisingly, after a few days of fasting, people can sometimes become downright euphoric. BDNF could be partly responsible. I explore this phenomenon in my video see.nf/fastingbdnf. However, fasting is by definition not sustainable. Would a more modest calorie restriction work as well?

If we cut 25 percent of the calories from our daily diet, this has been shown to produce a 70-percent increase in BDNF after just three months. Over the same period, even about a 10-percent calorie reduction can improve memory performance. Is there something we can add to our diet to raise BDNF levels so we can benefit without having to starve?

Boosting BDNF Through Food

The results of calorie restriction studies can be skewed by changes in diet quality. For example, participants in one study who ate a low-calorie diet and had higher BDNF levels not only ate less, but also ate healthier—less saturated fat and sugar, but more fruits and vegetables. A single high-fat meal can lower our BDNF level within a few hours. We know it’s the fat, because scientists observed the same reaction when they injected fat intravenously into people. This would be one explanation for why increased saturated fat intake in a high-fat diet may contribute to brain dysfunction, including neurodegenerative diseases, long-term memory loss, and cognitive impairment.

In my video see.nf/foodbdnf I compare this with the Soviet fasting studies against schizophrenia. After the patients had fasted for up to a month, they were given a diet that excluded meat and eggs. When the scientists reported that the remarkable effects persisted years later, that applied only to the patients who had stuck with the diet. Those who dropped out relapsed. In contrast, the effect was that much greater the more closely patients followed the instructions. Since we know from a randomized controlled trial that avoiding meat and eggs can improve mental state within just two weeks, it is difficult to say what role the initial fasting played in the reported improvements.

In the video I cover all the foods that have been shown to increase BDNF. These include fruits and vegetables high in flavonoids, nuts, turmeric, and cocoa powder. For example, researchers randomly assigned older men and women to receive daily a chocolate drink with either high flavonoid content (the flavonoid content of about two and a half tablespoons of natural cocoa powder) or low flavonoid content (equivalent to about two tablespoons of alkalized cocoa). Those who consumed more flavonoids over weeks recorded a significant increase in BDNF levels and overall cognitive function. One food can increase BDNF after just a single meal: rye porridge.

Healthy young adults were given a late-evening meal randomly containing either whole-grain rye bread with intact kernels or regular white bread. Before breakfast the next morning, more than ten hours after the evening meal, their blood was drawn. Those who had eaten whole-grain rye bread the previous evening had a 33 percent higher BDNF level. Given the timing, it is likely that this is a microbiome effect, since blood butyrate levels were also 30 percent higher. As a reminder: Butyrate is a byproduct of gut fermentation of fiber and other prebiotics by good bacteria and increases BDNF expression in mice. Administering probiotics—the good bacteria themselves—does not appear to affect BDNF levels, so it may be better to feed the good bacteria we already carry within us.

Nurture Your Microbiome

BDNF is only one of the ways butyrate from fiber can contribute to brain health. On PET scans, older people with higher blood butyrate levels tend to have lower amyloid levels in the brain. In vitro, butyrate inhibits the neurotoxic clumping of beta-amyloid. In rats with memory impairments, it acts as a cognitive enhancer; in an experimental model with Alzheimer’s mice, butyrate substantially lowers amyloid levels in the brain and improves cognitive function—even at a late stage of disease. Butyrate can even prevent beta-amyloid from getting from the blood into the brain in the first place.

In “germ-free” mice raised in a sterile environment, the blood-brain barrier, which normally shields the brain from toxins in the bloodstream, was leaky. Butyrate maintains and repairs the barrier function of the gut, so perhaps the lack of good gut bacteria in the mice could explain the leaky brain. In fact, the scientists were able to show that it was due to butyrate: They restored the blood-brain barrier of the germ-free mice with butyrate or simply colonized their gut with fiber-eating bacteria.