In 2014, Americans spent $1.3 billion on brain-training programs that promise to sharpen thinking skills and improve memory. But a pair of walking shoes would have been a better investment.

That’s the opinion of memory researcher Randall Engle, PhD, of the Georgia Institute of Technology. “We want to think we can make ourselves smarter,” says Engle. “But if you look closely at the data, brain training has no real benefit. What really does seem to help the human brain is physical exercise.”

The best exercise for your brain? “Any regular aerobic activity that increases your heart rate,” Engle says. “It doesn’t have to be extremely intense. It’s more important to do it consistently. A brisk, half-hour walk may be all you need.”

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A fatal flaw in the studies

How could so many researchers and so many brain-boosting programs get it wrong? Engle says the design of many brain-training studies contains a fatal flaw that’s easy to overlook: Study volunteers who do the training programs interact a lot with the research team and build relationships, but the control group usually doesn’t.

“When participants take memory and thinking tests again at the end of the study to look for improvements, those who’ve gotten to know the staff — and who feel at home and comfortable — often perform better than they did the first time,” say Engle, who heads the Center for Advanced Brain Imaging at Georgia Tech.

"When a control group only comes in for testing at the beginning and at the end of a project, they don’t have those warm feelings. And they don’t do as well as the training group on the final tests. When we analyzed brain-training studies, this was the only factor that made a difference. When control groups spend time in the lab every day, they do just as well as brain-training groups on tests of memory and cognitive skills. I wish brain-training programs worked, but so far they do not.”

Criticism for the brain-training industry

Not everyone agrees with Engle’s assessment, of course. But in the fall of 2014, nearly 70 prominent American neuroscientists publicly criticized the brain-training industry’s claims that their products are based on solid science and increase brain power.

“No studies have demonstrated that playing brain games cures or prevents Alzheimer’s disease or other forms of dementia,” according to the statement from the Stanford Center for Longevity and the Max Planck Institute for Human Development, in Berlin. There is “little evidence that playing brain games improves underlying broad cognitive abilities, or that it enables one to better navigate a complex realm of everyday life.”

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How physical exercise sharpens your brain

For now, Engle says, the most powerful way to preserve or even improve memory and sharpen thinking skills is by getting regular exercise. Here's how it can help:

  • A bigger hippocampus. In one University of British Columbia study, regular aerobic exercise was associated with a bigger hippocampus. This brain region plays roles in learning and maintaining verbal memory.
  • More gray matter in key areas. When researchers from Finland’s University of Jyväskylä scanned the brains of 10 sets of identical twins, they found a surprising difference. One of the twins in each pair maintained a regular exercise routine, while the other had cut back in the years leading up to the study. Scans showed that the active twins had more gray matter in brain areas involved with coordination and motor control.
  • More robust white matter. In a University of Illinois at Urbana-Champaign study, physically-active older adults had healthier-looking white matter in the brain’s temporal lobes, which are involved with memory, language, and processing information we see and hear. White matter is made up of the fibers that connect brain cells, carrying messages between them.
  • More "Miracle-Gro." Other research shows that exercise increases levels of a protein called BDNF (brain-derived neurotrophic factor), which keeps brain cells healthy and seems to help maintain or even improve memory. Nicknamed “Miracle-Gro for the brain”, BDNF fosters the growth of new brain cells and new connections, called synapses, between them. It also helps keep brain cells alive, Harvard Medical School researchers report.
  • Healthier blood vessels. Exercise also keeps blood vessels in the brain healthy and can even build new ones, researchers from the Thomas Jefferson University Medicine College have reported. That won’t make you smarter, but could help you feel more alert and help you maintain thinking skills and recall as you age, the researchers note.

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So before you do that crossword puzzle, consider pulling out a pair of walking shoes and taking a brisk walk. Your brain — and your body — will thank you.

Sari Harrar is an award-winning health, medicine and science journalist whose work appears in Dr. Oz The Good Life magazine, Good Housekeeping, O--Oprah Magazine, Organic Gardening and other publications.