Many of us have noticed that we become ravenously hungry when our blood glucose (BG) levels are falling rapidly. I have a graph showing this on page 255 of my book The First Year: Type 2 Diabetes.
This was an experiment in which I first ate some French bread and sugarfree jam (no sacrifice too great in the name of science) and hiked up a steep road near my house, while measuring BG levels periodically. Then I ate the same thing, again measuring the BG levels, but working at the computer. It’s clear that the exercise after eating had a large effect on my BG levels.
But the interesting thing is how ravenous I got at the point marked A, even though my BG level at that time was almost 200, hardly what I’d consider hypoglycemia (low blood sugar).
Now researchers are beginning to find the same thing. In a study done at Boston Children’s Hospital, researchers used brain imaging to study what happens when people eat high-glycemic foods or low-glycemic foods.
The glycemic index (GI) measures how quickly a food raises BG levels. A high-GI food raises BG levels quickly, and a low-GI raises them more slowly.
In the study, 12 overweight or obese men consumed milkshakes containing the same amount of carbohydrate, but with different glycemic indexes. They found that the high-GI milkshakes caused an initial surge in BG levels, followed by a BG crash about 4 hours later. The low-GI milkshake resulted in a lower peak.
This in itself isn’t news. What is interesting is that the BG crash was associated with ravenous hunger and activation of a brain region involved in addictive behaviors. In other words, high-GI carbohydrates can be addictive and cause hunger that makes you eat before you really need to.
This idea that high-GI carbohydrates, and for some people, even lower-GI carbohydrates, can trigger hunger is not news to many of us patients. People without a tendency to gain weight or develop diabetes may be able to cope with high carbohydrate loads, even loads of high-GI carbohydrates. They can secrete enough insulin so that their BG levels never go as high as mine did after eating a piece of French bread and sugarfree jam.
And when BG levels don’t soar, they don’t plummet either, so such skinny people can eat all the white rice and bread they want without a problem.
But those of us with a diabetic tendency are different. We find that carbohydrates do cause hunger, especially high-GI carbohydrates. And one benefit of a low-carbohydrate diet is that we don’t get these peaks and plummets, so we rarely feel hunger.
When it’s close to a mealtime, I get a vague sensation that I could eat something. But it’s nothing like the compelling signals telling me to "eat or else" that I got when I did that exercise test.
Now, at least, we have a study that confirms what we’ve known for a long time. Perhaps our doctors will believe it at last.