May 6, 2009

Food Smarts

Carbs, proteins and fats all affect the brain in different ways at different times of the day, leading researchers to wonder if how we think is a function of what we eat

By Helene Ragovin

If you’re reading this story after you’ve made a mid-afternoon trip to the vending machine for a candy bar, or grabbed a cheese stick from the fridge for your morning snack, you may be feeling happily sated. But what you ate may affect how well you remember this article.

“What we’re seeing are subtle changes in cognition,” says Kristen D’Anci, left, a research associate who works with professors Robin Kanarek, center, and Holly Taylor. Photo: Joanie Tobin

Psychology department researchers have been investigating the connections between nutrition and cognition for several years. Their findings show that carbohydrates, proteins and fats can affect mental functioning in different ways, depending on how and when they are eaten.

But, the researchers say, there’s no need for most Americans to dramatically fine-tune their nutrient intake in the quest for mental prowess.

“It’s important not to obsess about what you’re eating,” says Kristen D’Anci, G96, a research associate who works with professors Robin Kanarek and Holly Taylor. “What we’re seeing are subtle changes in cognition. It’s not the kind of thing that’s going to prevent someone from winning a Nobel Prize.

“It’s also not what you eat at each meal; it’s what you eat over the course of a day, a week or a year that contributes to brain structure and brain health,” D’Anci adds.

Kanarek and Taylor have examined, among other things, the effects of different breakfasts on the cognitive performance of 9- to 11-year-old children; the effects of sweet snacks on learning and attention in young boys and college students; and the effects of low-carbohydrate weight-loss regimes on the cognitive behavior and mood of adult dieters.

“The underlying idea behind the research is that the brain is fueled by glucose,” Taylor says. Glucose, a simple sugar, is the brain’s primary energy source. During digestion, carbohydrates are broken down into glucose, which enters the bloodstream to be used by the brain. “We’re looking at what people consume, and how the brain’s uptake of glucose affects cognition.”

Brainy Breakfasts

In the breakfast study, published in 2005 in Psychology & Behavior and funded by Quaker Oats, elementary school children were fed either instant oatmeal, cold cereal or no breakfast at all. While similar in calories, the two breakfasts had different amounts of carbohydrates, protein, fat and fiber, which contribute to their glycemic scores. Oatmeal has a lower glycemic score than the cold cereal used in the study, which means that its carbohydrates are digested and absorbed into the bloodstream more slowly.

As expected, the children who ate breakfast performed significantly better on a series of cognitive tests than those who had no breakfast at all. But among the breakfast-eaters, the children who ate oatmeal performed better on spatial and short-term memory tests administered an hour later. Taylor, Kanarek and their co-authors theorized that “due to compositional differences in protein and fiber content, glycemic scores and rate of digestion, oatmeal may provide a slower and more sustained energy source, and consequently result in cognitive enhancement compared to low-fiber, high-glycemic, ready-to-eat cereal.”

The researchers are now interested in measuring the effects of different breakfasts on how children perform these same tasks at various times throughout the morning.

In two separate studies looking at the effect of snacks on learning, memory and attention, Kanarek, Taylor and their colleagues offered test subjects either sugar-sweetened candy or low-calorie artificially sweetened snacks at different times of the day. In the first study, published in Psychology and Behavior in 2001, school-age boys received the snacks after an overnight fast and were then tested on a variety of tasks involving memory and attention.

The children who ate the sugary snack were better able to stay on task for an extended period of time. In the second study, published in the same journal six years later, boys and college undergraduates were given their snacks in the afternoon; the high-sugar snack generally improved performance on tasks involving memory, but had a mixed effect on attention. Funding for both studies came in part from the Mars candy company.

The researchers hypothesize that the different results may be a consequence of whether the snack is consumed after an overnight fast or shortly after a meal.

Don’t Hold the Carbs

The most recent work—published in March in the journal Appetite—touched on America’s obsession with weight loss, and garnered attention for its conclusion that strict low-carbohydrate diets led to some degree of memory impairment and self-reported confusion.

For three weeks, two groups of women followed two different weight-loss plans, either a diet that prohibited or strictly limited carbohydrates, or a balanced, reduced-calorie diet recommended by the American Dietetic Association. After the first week of the low-carb diet, during which the women ate no carbohydrates whatsoever, they performed significantly worse on memory-related tasks.

“What we saw was very clear and specific on memory performance,” D’Anci says. “When we restricted the carbohydrates, the women were less able to remember locations on a map, which is a visual and spatial task, either immediately or a week later.” The low-carb dieters’ short-term memory was also impaired, D’Anci adds.

However, “as soon as we re-introduced even a small amount of carbohydrates, their memory functioning returned to the original level,” Taylor says. The carbs they added were in the form of fruits, vegetables and whole grains.

That said, the low-carb group did show better “vigilance attention”—that is, they were able to pay closer attention during a long-term repetitive task—while on the diet. “That is consistent with studies that have shown that a basically high-protein diet does help with sustained attention,” D’Anci says.

It’s not entirely surprising that the no-carbohydrate diet had a different effect on memory than it did on attention. “Those are different kinds of functions,” Taylor says. “From brain-imaging studies, we know that the processing of memory and attention takes place in different parts of the brain. We know there are different neurotransmitter systems at work.”

The long-term impact of the work, Kanarek says, lies not in providing diet tips to college students seeking a leg up on their exams or to ambitious executives trying to score the best deal at the negotiating table.

“I think in this country, most people have enough to eat. While a given snack or lunch may have a small effect on behavior, it’s not a major effect,” Kanarek says. But “where it may have a major effect is in populations that have some sort of nutritional insult.”

That particularly applies to children and others in developing nations where food scarcity is an issue, or to nutritionally vulnerable groups in developed nations, such as the elderly, dieters or those with eating disorders.

Helene Ragovin can be reached at

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