By Laura Freeman
“Sugar is a very important component of the diet,” Munoz says. Its simple structure allows it to be broken down quickly by the body, providing an energy surge for athletes and combat troops. Sugar is also a cheap source of calories that is invaluable in times of food shortage. And eliminating carbohydrates such as sugar from the diet, Munoz says, forces people to “replace the calories with either protein or fat, which can cause heart, kidney, and other problems.”
When it comes to nutrition, “all extremes are bad for you,” Munoz says. “It’s really about balance. About 50 percent of the calories you take in should be carbohydrates, and up to around 10 percent of those can be from simple sugars. If you eat the right amount of calories and the right amount of calories are coming from sugar, then you will not have a problem.”
Of course, many of us find it hard to stick to those recommendations. This may in part be a problem of willpower, but it is also a question of genetics, argues Munoz. “I think the problem we are facing is that changes in our environment are happening too fast for our bodies to adapt,” he says. Where once our bodies had to be prepared for times of scarcity, now “food is everywhere, and it has been manipulated with added sugars and preservatives to make it more appealing.” Labor-saving devices such as automobiles, remote controls, and elevators make it hard to burn off excess calories, Munoz adds. His solution? “If our genes are not changing, we have to use our brains to protect our bodies from this toxic environment.”
That is not an easy task, he admits. “It seems that your taste sense gets used to higher and higher amounts of sugar, and people who want to cut down on their sugar intake have a hard time initially.” But the good news is that “eating has a very large behavioral component,” he says, “so people can learn how to forget their previous behavior” and scale back.
There is little doubt that our sweet-saturated diets are out of balance. But almost everything else about sugar science is shrouded in mystery or clouded by debate—or both. “Many of the current theories about sugar are controversial,” says Munoz, who is using his background in endocrinology, epidemiology, internal medicine, and clinical nutrition to study the health effects of the modern diet. “We are learning so many new things, but we have limited data.”
Take, for example, matters of taste. “We once thought that the taste function was very simple: to detect the flavor of substances such as food and poisons,” says Munoz. “We thought the tongue had receptors that were able to taste different foods, and that was it. But very recently we have discovered that taste is a more complex mechanism. Those receptors send signals to the brain, which releases hormones that actually change its chemical balance.” Although the exact pathways from tongue to mind remain unclear, sugar seems to trigger the release of chemicals in the brain, which explains the soothing power of ice cream after a rough day at the office.
But the tongue is not the body’s only taste tester. New research has shown that we have taste buds in the gastrointestinal tract, Munoz says. While we aren’t consciously aware of their reports, proteins in the small intestine can determine the type of food we’re eating and take action. When they sense a rise in glucose levels, for example, they signal the brain and other organs to register satiety.
Researchers have also discovered that our intestinal taste buds do not sense and respond to artificial sweeteners the same way they react to natural sugars. Unlike sugar, artificial sweeteners don’t signal the brain to register satiety. This could offer at least a partial explanation for recent studies demonstrating that drinkers of diet sodas are more likely to gain weight than people who drink regular, sugar-sweetened versions. “There is some speculation that taste sensors and hormones may be signaling the brain to expect calories,” says Munoz. When those calories don’t come—when a person drinks a zero-calorie soda, for example—the brain could be triggering the body to find them, leading to weight gain.
One constant in sugar studies is the importance of the hormone insulin, which helps the body use and store the energy it gets from food in the form of glucose. When the level of glucose in the blood rises after a meal, the body responds by releasing insulin from the pancreas. Insulin sweeps glucose into the liver, muscles, and fat cells, returning the bloodstream to equilibrium. But not all foods stimulate insulin in the same way. “If you eat a simple carbohydrate”—such as a doughnut—“your blood sugar is going to rise very quickly” and provoke an equally rapid insulin release, says Munoz. Complex carbohydrates such as pasta are made up of chains of carbohydrates, which the body must pull apart before they can be converted to glucose, so the rise in blood sugar is more gradual.
Problems with insulin production and function are the underlying cause of diabetes, but new research has implicated insulin in other conditions. “There are suggestions from epidemiological data that people who have Alzheimer’s also have problems with insulin resistance,” says Munoz. “And there is also evidence that people with diabetes have a higher incidence of Alzheimer’s. Some people are calling Alzheimer’s the diabetes of the brain.” This is because preliminary data from animal models indicates that brain cells can become resistant to insulin just like cells in the rest of the body. Insulin in the brain is not primarily concerned with glucose uptake, however. Instead, it plays an active role in the crucial tasks of learning and memory, which may explain some of the deficits in these areas experienced by Alzheimer’s patients.
As with most areas of sugar science, much more research is needed, Munoz cautions. “We are just beginning to learn about new mechanisms of taste, pathways, and hormones that regulate behavior and the very complex physiology of how energy is stored,” he says.
Even though we think we know it so well, sugar still has many secrets to keep.
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