Low-Carb Diets May Dull Brains of Children, But Not Adults
Low-carbohydrate diets, where carbohydrates constitute anywhere from 5 to 30 percent of total caloric intake (approximately 25 to 150 grams each day), are all the rage right now. For many, they're a successful impetus to sustained weight loss and improved health. But there could be an unforeseen toll.
Because of the way that the human brain functions, low-carbohydrate diets may adversely impact cognitive ability. Does a low-carb diet really make you duller? To examine this question, let's first discuss its focus: the brain.
There's no reason to beat around the bush, your brain is a pig. Though idle enough when observed outside its home cranium -- all pink, squishy, and squelchy; kind of cute really -- the brain is a charged biological machine. In an unseen electrical storm that would rival even the mightiest lightning display, 86 billion neurons fire -- almost nonstop -- to create the mosaic of thoughts, emotions, and mental images that we call the mind. The whole operation is an immense power suck, ravenously consuming roughly 250 to 300 calories each day, 20-25% of a human's base energy expenditure.
As far as food goes, the brain is a fairly picky eater. Like a young candy-craving child, it prefers simple sugar molecules -- glucose to be specific -- and when the brain doesn't get glucose, it gets crabby and distracted. Since the body most easily creates glucose by metabolizing carbohydrates, it stands to reason that limiting carbohydrates could dampen cognitive function.
When consuming low-carb diets in the short term, this is certainly true. In a 2008 study, psychologists placed 19 women on either a calorie restricted low-carb diet or a calorie restricted high-carb diet for 28 days. Throughout the study, participants' memory, reaction time, and vigilance were tested at regular intervals. While those on the low-carb diet enjoyed a slight boost in vigilance, they suffered impaired reaction time and reduced visuospatial memory.
"The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory, and thinking," lead investigator Holly A. Taylor, a psychology professor at Tufts University, explained.
But the short-term isn't the long-term. Though the brain prefers to compute on glucose, after about four days of carbohydrate deprivation it sates about 70% of its hunger on ketone bodies, the byproducts produced when fatty acids are broken down by the liver. And by most accounts, the brain can run pretty efficiently on this fuel once it grows accustomed to it after a few weeks.
In fact, researchers have shown that low-carb diets can bring about improvements in cognitive functioning in both aged humans and rodents compared to traditional diets. Writing at Psychology Today, psychiatrist Emily Deans accounted for how this might happen.
"When we change the main fuel of the brain from glucose to ketones, we change amino acid handling," she says. This reduces the levels of glutamate in the brain, an amino acid and neurotransmitter that can cause harm in excessive amounts. Less glutamate leads to "a lower seizure risk and a better environment for neuronal recovery and repair."
In adults, low-carb diets have no adverse cognitive effects in the long-term. A well-executed, year-long study published to the Archives of Internal Medicine in 2009 found no difference in cognitive functioning for subjects consuming either a low-carb weight loss diet or a high-carb weight loss diet. Both actually enjoyed improvements to working memory and speed of processing, a result presumably attributed to weight loss.
Older and middle aged adults aren't dulled by low-carb diets, but what about children and teenagers? With still-developing brains, should they consume such diets? Here -- due to a dearth of long-term data -- the waters are murkier, but one study published in 2004 discerned some troubling results for low-carb diets. Reporting in Pediatric Research, researchers found that young rats fed a low-carb diet gained less weight than their peers on a regular diet (which isn't necessarily healthy during development). Moreover, they also had "significantly impaired visual-spatial learning and memory" and -- most disturbingly -- "significantly impaired brain growth."
Adults looking to lose weight may have their waistlines thinned and senses sharpened by low-carb diets, but those with still-developing brains should probably steer clear.
(Image: Low-carb meal via Shutterstock)