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May 02, 2005
How your brain makes you fat
And how maybe, with science's help, it might be able to make you thin
BARBARA WICKENS
The students in the combined grades 4, 5 and 6 cooking class at Ste Odile may not know it, but they're part of a grand experiment. They're participating in a pilot project, Les ateliers cinq épices, that sends dietitians to eight Montreal elementary schools. Their job: to teach kids how to cook foods that are lower in salt, fat and sugar than the highly processed snacks they're used to eating. Just as important is making sure that, as these youngsters bake yummy cookies and cut fruits and veggies into weird shapes, they enjoy their break from the regular classroom routine. As program director Manon Paquette puts it, "We're hoping to make healthy eating fun." The kids are, in effect, learning nutrition through stealth. And there's new evidence that they may even be rewiring their brains in the process.
Thanks to advances in neural imaging techniques, we can see the brain at work in a way that was not possible even a decade ago. And in light of mounting concerns about the increasing prevalence of obesity, this is good news. According to data released last week by the World Health Organization, 4.1 per cent of Canada's teenagers are obese (19.3 were found to be merely overweight). This makes the Canadians the fourth most obese teens in the world, behind Malta, the United States and Britain. The WHO, in fact, describes obesity as a global epidemic. And the traditional approach to weight loss -- hoping individuals can muster enough willpower to stick to a low-calorie diet and get a little exercise -- clearly hasn't worked. But by scanning the brains of the obese and the lean, science is coming to a new understanding about how the brain, body and food interact.
There is still much to be learned, but one thing already seems clear: humans are hard-wired to prefer, maybe even crave, the very foods that today cause us so many problems. No surprise, they're sweet, salty and/or high in fats and calories (the body's way of storing energy for future use). But new data is revealing that the brain is also more malleable than previously thought, even in adults. Lay down the right neural pathways and you can hook people -- especially those under 21, whose brains are still growing and maturing -- on a handful of crunchy carrots rather than a bag of nachos.
In North America, where 23,000-odd diet books have been published in the past three decades, the new research has far-reaching implications for parents, legislators and school administrators, not to mention the purveyors of fast food. Doctors, psychologists, nutritionists and others interested in weight control are just starting to use brain scans to answer such questions as: which regions are activated when you show someone food? Is the result different in obese and thin people? Where do cravings originate? Which part controls impulses? The knowledge gained from such testing, scientists hope, will be used to make and keep people healthy. If your brain can make you fat, maybe -- if you can push the right buttons -- it can also make you thin.
Earlier research had already mapped the vital organ's basic structures and developed crude maps of what went on where. But as technology improved, increasingly detailed pictures of the brain emerged. Positron emission tomography uses increases in blood flow associated with increased activity to give a sense of which brain cells are at work. But it takes radioactive markers to do this, and a PET scan can take up to an hour. Then in the mid-1990s, the introduction of functional magnetic resonance imaging even allowed researchers to peer into the brain while it was performing some sort of mental task. An MRI detects the minute changes in magnetism that indicate increased blood flow to active parts of the brain. Those spots, which appear as brighter colours on the image, are giving scientists a much clearer picture of what the human mind goes through when it calculates a mathematical formula, recognizes different words -- or contemplates a bar of chocolate.
The brain has yet to give up all its secrets. It has, after all, some 100 billion neuron cells extending through its different regions. Still, studies are indicating that brain chemistry strongly affects body weight. The neurons communicate with one another via a number of chemical messengers called neurotransmitters. One of these is dopamine, which is key to the brain's internal reward system. Thanks to dopamine's cheerful role in allowing us to feel pleasure, some researchers hope it can be enlisted in the fight against fat.
Dopamine is also known to be a culprit in cocaine and nicotine addiction, but as obesity researcher Marcia Levin Pelchat points out, "this brain circuitry did not evolve for the purpose of recreational drug use." It seems designed to ensure that basic functions like eating, drinking and reproducing are more likely to be repeated if they're pleasurable.
So does this mean food can be addictive? It may be for some overweight individuals, says Pelchat, a scientist at the Monell Chemical Senses Center in Philadelphia. A series of studies has shown that some people who overeat may have less dopamine in their system, or fewer receptors for it. The theory is that they might be eating more in an effort to boost the pleasure they derive from food. Pelchat recommends the development of new behavioural methods or drugs that can help these people enjoy a more normal reward from eating. What's the alternative, she asks: "Are we going to outlaw pleasure?"
As brain chemicals go, dopamine is a pretty important player: it reaches into the brain's emotional centres, such as the hypothalamus, which is involved in memory, reward and learning; and rational centres such as the prefrontal cortex, where problem solving, planning and decision making occur. Willpower, a front brain function, is what helps a person resist immediate temptation -- I want these new shoes now -- in favour of a long-term goal, as in, I want my money in the bank to grow. But when it comes to food, the short-term almost always trumps the long-term, according to Antoine Bechara, a former Torontonian who is now associate neurology professor at the University of Iowa. And this may have something to do with our deepest ancestral instincts. Think of it this way the next time you grab a burger and fries at the nearest drive-through. Your conscious mind might register, I should've ordered a salad instead. But somewhere in its primordial parts your brain is cheering, Yippee! Mastodon meat! Tubers! Scarf 'em down quick before a sabre-toothed tiger comes by.
For millennia, our ancestors literally didn't know where their next meal was coming from. With food being scarce, and often requiring great effort to track down, the biggest bang for the hunter-gatherer's buck was a meal as high in calories as possible. This meant foods high in fats and sugars. Foods that fit the bill, like fruits and meat, were also rich in nutrients. Today, in the developed world at least, we have a cheap and plentiful food supply that's no farther than the nearest convenience store -- but not necessarily nutritious. While some fatty foods, such as olive oil, nuts, avocado and fish, can be part of a healthy diet, there's very little nourishment, for instance, in a candy bar. To make matters worse, we have too few reasons to exercise. In evolutionary terms, these are such new developments that our brains haven't had time to adapt.
Until recently, little effort was spent on trying to understand why people became fat. Wasn't the answer simple? They ate more calories than they burned off. Anybody who failed obviously wasn't trying hard enough. The equation hasn't changed, but that single-minded focus on willpower clearly has not worked. And considering that obesity puts people at greater risk for other serious ailments such as type 2 diabetes, heart disease and stroke, as well as some types of cancer, the potential costs to the health-care system -- not to mention the toll in human suffering -- are staggering. The time is overdue to take a more sophisticated approach.
That's exactly what happened in early April, when the faculties of medicine and business management at Montreal's McGill University brought together an unusual cross-section of scientists and health and marketing experts from North America and Europe to brainstorm. The challenge, according to conference chairwoman Laurette Dubé, a McGill marketing professor, was to examine whether it is possible to fight today's fat society by better understanding when, why and how people make certain food choices. "We have looked too much to the rational side," said Dubé. "No one serves a drink to an alcoholic and says the guy should resist."
Still, as one participant noted, understanding how the brain and body respond to food in a healthy person at a healthy weight, let alone in someone who is obese, "isn't rocket science, it's more complex than that." This complexity means that there will likely never be a single magic bullet for weight loss, but that a number of solutions may work. Some of the problems, it turns out, may be in your genes. There are at least 430 of them associated with obesity, says Diane Finegood, scientific director of the Institute of Nutrition, Metabolism and Diabetes, part of the Canadian Institutes of Health Research.
Some people may be more susceptible than others to putting on weight. Angelo Del Parigi wasn't specifically looking at that issue, but research he did at the U.S. National Institutes of Health in Phoenix, Ariz., may shed light on it. Using PET scans, Del Parigi studied the neurology of hunger and satiety -- medical jargon for "had enough." In the scans of both lean and obese people during and after a 36-hour fast, hunger showed up broadly in the hypothalamus and other limbic areas, while satiety was represented in the prefrontal cortex. However, the obese had a number of abnormal responses in both areas, which seems to indicate that they feel hungry more often and take longer to feel full. People who had lost weight, however, still showed abnormalities in their scans, indicating that even though their bodies were leaner, their brains remained "fat." Del Parigi said that neural responses to hunger and satiety may be a warning sign that someone is predisposed to obesity. One tantalizing question for further research, however, is whether the abnormalities caused the weight gain, or the weight gain caused the abnormalities.
Still, there is positive news in the fight against obesity -- in the form of clear evidence the palate can be re-educated to enjoy healthier foods. Over the past five years, Danone Canada quietly reduced the sugar content of its yogourt by 15 per cent. And, notes company president and CEO Louis Frenette, it accomplished this not only with no complaints, but sales in that period actually increased. Also, Dr. David Ludwig, director of the obesity program at Boston's Children's Hospital, said that youngsters who come from outside North America often find fast food distasteful. They have to learn to like it. And that presumably means others can learn how not to like it.
Iowa's Bechara has done research that also supports that contention. His studies indicate that the willpower to override impulses is influenced by what children are taught as they grow up. This suggests that if adults make eating healthy food a rewarding experience, children will develop a better ability to control their food impulses. Of course, he didn't study the particular kids in Montreal's Les ateliers cinq épices program. And there's no evidence that such early interventions will have an effect over a lifetime. But until researchers can tease more secrets from the tangle of neurons that make up our internal reward system, encouraging brains and taste buds to enjoy healthy food looks to be the best weapon yet in the battle of the bulge.
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