A diet rich in processed
carbohydrates, which are also high glycemic index (GI) foods, such as cakes,
pastries, macaroni and cheese, alone or coupled with a sedentary lifestyle,
promotes insulin resistance and is one of the quickest way to get the bulge. This is well known. Insulin resistance causes blood sugar and insulin levels to
stay high long after eating. And that's not all. High blood pressure, high
levels of triglycerides, and low HDL (good) cholesterol are all linked to
insulin resistance and increase the risk for diabetes, heart disease and
We also know from experience that
at times we crave for these high GI foods; it sort of becomes addictive. There
are three things to note here:
Foods high in glycemic index
are digested very quickly and in no time you are hungry again.
Since high GI foods are
deficient in fiber, you just end up with lot of empty calories.
High GI foods make you feel
good; they make you feel content.
Know that pleasant feeling and
wanting to reach out for more of those goodies? That craving is caused by
dopamine, a neurotransmitter in the brain that is released in response to
pleasure and rewarding activities. Just like some drugs and sex - high GI foods
that make you feel good increase the dopamine activity.
This is what a Boston Children's
Hospital research team led by David Ludwig set out to investigate. They wanted
to find out how food intake is regulated by dopamine-containing pleasure
centers of the brain.
'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
The study included 12 overweight
or obese men aged 18 to 35 years. They were given two types of milkshakes, both
with the same number of calories, macronutrients and taste, but one contained
rapidly digesting (high-glycemic index) carbohydrates and the other had slowly
digesting (low-glycemic index) carbohydrates.
Researchers measured blood
glucose levels and hunger, and observed brain activity during the four-hour
period after a meal using functional magnetic resonance imaging (fMRI). The
four-hour period after eating is important because this is the time frame which
drives our eating behavior at the next meal.
After drinking the high-glycemic index milkshake,
the participants experienced an initial surge in the blood sugar levels,
followed by sharp crash four hours later. This decrease in blood glucose was
associated with excessive hunger and
greater brain activity
centered in the right
, a critical brain region involved in addictive behaviors.
'These findings suggest that limiting
high-glycemic index carbohydrates like white bread and potatoes could help
obese individuals reduce cravings and control the urge to overeat,' says
Although the findings are not
different than those found in other such studies, there were two new aspects to
The researchers in this study
evaluated patients with an fMRI in the four-hour
after a meal
time frame, whereas previous studies have evaluated patients
with an MRI soon after eating
This study compared high glycemic index carbs to low glycemic index carbs
against high-calorie to low-calorie meals comparison made by previous studies.
They showed how high GI foods could alter brain function and promote
'Compared with an isocaloric low-GI meal, a high-GI
meal decreased plasma glucose, increased hunger, and selectively stimulated
brain regions associated with reward and craving in the late postprandial
period,' concluded the researchers.