Grabbing a jam-smothered bagel for breakfast or sipping away on sugary sweet tea in the afternoon might be worse for you than you realized. According to a new study published in the American Journal of Clinical Nutrition, such highly refined carbohydrates may actually make you hungrier and stimulate cravings for more of the same by the time your next meal rolls around.
In the study, researchers from Harvard Medical School and Boston Children's Hospital fed a small group of overweight men one of two special milkshakes that were identical in calories and equally sweet-tasting. The difference was that one was made with rapidly digesting, high-glycemic carbohydrates and the other was made with slowly digesting, low-glycemic carbs.
The men who consumed the high-glycemic shakes experienced a rapid rise in blood sugar followed by a major roller-coaster-style drop four hours later, associated with increased hunger levels. That wasn't so surprising. This was: MRI scans of those men revealed that the areas of their brains linked to cravings and addictive behaviors (the nucleus accumbens) lit up like a pinball machine four hours after finishing the shakes. (The control shake made with low-glycemic carbs did not spark the same reaction.)
"Beyond reward and craving, this part of the brain is also linked to substance abuse and dependence, which raises the question as to whether certain foods might be addictive," says lead researcher Dr. David Ludwig of Boston Children’s Hospital.
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One small study may not be enough to confirm that consuming high-glycemic carbs drives a person to overeat. Possible food or sugar addictions is still relatively new research territory. So is the idea of using a measure of different foods' impact on blood sugar – their glycemic index – to promote weight loss or help control appetite. It's important to understand how to use that yardstick properly, as well as its limitations, when determining your own Fiftysomething Diet.
The GI Controversy
High-glycemic foods, which create a rapid rise in blood sugar, include such staples as white rice, white bread and potatoes, as well as certain fruits like watermelon. Low-glycemic foods include more complex carbohydrates, like apples, kidney beans and lentils. They are absorbed more gradually by the body, with less rapid spikes or drops in blood sugar, and they generally deliver more fiber, along with essential vitamins and minerals.
Diets based on the glycemic index suggest that you consume foods with "low GI" rankings to help keep your blood sugar, and appetite, balanced. The thinking is that this strategy should promote weight loss and reduce the risk of contracting illnesses like diabetes and maybe Alzheimer's disease as well.
But some health experts disagree, sometimes quite strongly, about the usefulness of a GI-based diet strategy, even just for blood sugar control. "The biggest problem is that the GI looks at single foods and the real issue is what happens with meals," diabetes expert Marion Franz recently told Eating Well magazine. A high-GI potato, for example, becomes a low-GI meal if you add a pat of butter, because the added fat helps slow the absorption of the potato's carbohydrates. Managing such sometimes counterintuitive complexities, Franz says, is too confusing to make a GI-based diet useful for most people.
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Ludwig, who often advises a low-GI diet for patients in his Boston clinic, disagrees. He concedes that low-GI diets might not work for everyone, but believes the best candidates are people who carry more fat around their waists – those with larger bellies or what's often called an "apple" body shape – because they tend to produce higher quantities of insulin. "Apple-shaped people who have done poorly on traditional low-fat diets," Ludwig says, "may do especially well on a low-glycemic-load diet."
Where Should Your Diet Land?
While experts debate the usefulness of the glycemic index as a diet tool, they do come together behind two simple, fundamental nutrition strategies that emphasize the importance of eating the right carbs in the right amount. First, carbohydrates that are less processed or refined are probably better for your overall health and keeping hunger in check. Second, a healthy diet is never about adding or subtracting just one food, but changing your style of eating. Consuming an occasional higher-glycemic food like white pasta, white bread or even sugar can be OK as long as you pair them with lower-glycemic foods that can blunt the rapid blood sugar rise, such as proteins, fiber and healthy fats like olive oil, nuts or avocado. That could be as simple as spreading some peanut butter on that morning bagel or sipping that sweet tea slowly while eating a healthy lunch.