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This Is Your Brain on Sugar

This Is Your Brain on Sugar

Picture of Kathleen  Page
So good, but so bad.

Editor's Note: The Children’s Health Matters blog features an occassional column with new insights offered by two of Children’s Hospital Los Angeles’ leading community-based research teams. This post is from Dr. Kathleen Page, assistant professor and practicing endocrinologist at USC's Keck School of Medicine and Children's Hospital Los Angeles.


The American diet is loaded with sugar, and it may surprise you that children are actually consuming a bigger proportion of their daily calories from added sugars than adults. According to recent estimates from the Center for Disease Control, children and adolescents consume about 16 percent of their daily calories from added sugars whereas adults consume an average of 13 percent of their calories form added sugars. Adolescent boys are the biggest consumers of added sugars, with about 440 calories of their daily intake coming from such sugars. The targeted marketing of sugary foods and beverages to children and adolescents may be contributing to these trends.

Added sugars are caloric sweeteners that are added to processed and prepared foods and drinks to make them taste better. A number of studies have linked added sugar consumption to weight gain, obesity, type 2 diabetes and cardiovascular disease. Many of these studies were observational — meaning they didn’t test cause and effect. However, two large studies published in New England Journal of Medicine in 2012 tested the effects of replacing sugar-containing beverages with non-caloric beverages on weight gain over time in children and adolescents. Both studies were double-blinded randomized controlled trials, the gold standard in clinical trial design.

In one of the studies, Ebbeling and colleagues randomly assigned 224 overweight and obese adolescents who were regular consumers of sugar-sweetened beverages to an intervention group, which received home delivery of non-caloric beverages for one year, or a control group, which did not receive any beverages. They found that replacing sugar-sweetened beverages with non-caloric beverages significantly reduced weight gain after the one-year intervention, and the effects persisted at the two-year follow-up among Hispanic adolescents. The second study included 641 normal-weight children between 4 and 12 years old and showed that replacement of a sugar-containing beverage with a sugar-free beverage significantly reduced weight gain and fat accumulation over the 18-month trial.

So we have evidence from both large epidemiological and randomized controlled trials suggesting that the consumption of added sugar-sweeteners contributes to weight gain in children and adolescents.

At the University of Southern California, we are exploring how sugar consumption affects brain pathways that control appetite and reward. Using sophisticated brain imaging techniques, we can see how people’s brains respond to specific nutrients (such as sugar) and to food cues (such as a picture of chocolate cake).

Recently, we performed studies to compare the effects of consuming two different types of simple sugars – glucose and fructose – on brain and hunger responses to pictures of high-calorie food cues.

We studied 24 healthy young men and women between 16 and 25 years of age who came in for brain scans in the mid-morning before they ate breakfast. On one occasion they consumed a drink sweetened with glucose and on another day they consumed a drink sweetened with fructose. We sampled their blood for hormones that help control appetite, and we performed brain scans while the volunteers looked at pictures of tasty foods (like pizza) or objects (like a lamp) and rated their hunger and desire for food. To see how motivated people were to eat high-calorie foods we gave the volunteers choices between being served tasty food immediately after the study or having money sent to them one month later.

When study participants consumed fructose, they had greater activity in brain reward areas, greater ratings of hunger and more desire for food when they looked at pictures of tasty foods, as compared to when they consumed glucose. Volunteers also had a greater willingness to give up money rewards to obtain immediate high-calorie foods after they consumed fructose compared to after they consumed glucose.

Our results suggest that consuming fructose relative to glucose activates brain reward regions and may promote eating behavior. We don’t yet know how the brain responds to combinations of glucose and fructose, such as sucrose (table sugar) or high-fructose corn syrup. While fructose is found naturally in fruits and vegetables, the biggest source of fructose in the American diet is added sugar sweeteners. That includes products such as soft drinks and processed sweets. Fruits and vegetables are packed with nutrients and fiber, which slow the absorption of sugar and help you feel full. In contrast, sugar-sweetened beverages are nutrient-poor and have a much higher quantity of fructose that the average whole fruit does.

The American Heart Association recommends that children limit their intake of added sugars to 3 to 4 teaspoons a day during early childhood, and between 5 and 8 teaspoons during adolescence. Similarly, the World Health Organization (WHO) recommends that adults and children consume less than 10 percent of their total daily calories as free sugars, and suggests a further reduction to less than 5 percent of total calories consumed as free sugars. (Free sugars are simple sugars added to foods and drinks, and sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates, according to the WHO.)

What are some practical ways to reduce added sugars from our diets? Decreasing the consumption of sugar-sweetened beverages, such as soft drinks, will go a long way. The average 12-ounce soft drink contains about 8 teaspoons of added sugar (about half of that is fructose). Not surprisingly, many processed baked goods, such as cookies and brownies, are high in added sugar. Sugar sweeteners are also hidden in a number of “healthy” foods, like yogurt, granola bars, cereals, salad dressing, and ketchup. So, it’s a good idea to check the labels on foods and drinks. The nearer the beginning of the ingredient list the sugar is, the higher the sugar content. Limit foods and drinks that contain more than 10 grams of sugar per 100 gram serving size. Try to eat a variety of whole fruits and vegetables, and include more fiber-rich whole grains, lentils, nuts, lean meats, fish, and plain yogurts (without the added sugar) in your diet.

A few tips: Swap out white bread for whole wheat breads; add berries, bananas or dried fruit to oatmeal or cereal; snack on air-popped popcorn, almonds, or string cheese; and drink water or low-fat milk instead of sodas and juices.

In addition to cutting down on our intake of added sugars, it’s important to remember that there are a number of other factors that play a role in the obesity epidemic, including lack of physical activity, excessive screen time, and bigger portion sizes. In today’s environment, we face many challenges that make it hard to maintain a healthy weight. Becoming more aware of what and how much we eat, and trying to cut back on sugar intake is one step that we can take to help improve health and prevent childhood obesity.

Photo by Travis Swan via Flickr.

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