The Genetics of a Sweet Tooth
People with a Certain DNA Difference in the SLCa2 Gene Crave Sugar
Some people have trouble saying no to sweets. Now a group of scientists from Toronto Canada may have discovered part of the reason why.
In a study from May 2008, researchers found that people with a certain DNA difference in their SLCa2 gene ate more sugar than people with other versions. The researchers hypothesize that these folks may have brains that are less sensitive to the amount of sugar in the blood. Which means they may need to eat more sugar to feel full.
A Sugary Gene
Genes are simply recipes for making a protein. And proteins are the molecules that do most of the work in our cells.
The SLCa2 gene is no different. It has the instructions for making the GLUT2 protein.
GLUT2's job is to move glucose, the sugar our bodies use for energy, into cells. The researchers argue that GLUT2 is involved in feeling full from blood sugar levels. There are at least four reasons they think this:
- GLUT2 is found in the brain
- Mice without GLUT2 eat more food
- DNA differences in the SLCa2 gene have been linked to an increased risk for Type 2 diabetes
- Glucose does not stick very strongly to GLUT2
Taken together, all of these suggest that GLUT2 is involved in telling someone when he or she is full. The results of this study add further proof to this idea. The results suggest that one small change in GLUT2 causes some people to eat more sugar.
People with an Isoleucine (Ile) at 110 Eat More Sugar
Proteins are made up of amino acids all lined up in a row. The specific order of amino acids determines what a protein will do. And how well it will do its job.
GLUT2 is made up of 524 amino acids. Amino acid 110 is usually a threonine (Thr) but sometimes it is an isoleucine (Ile). The researchers set out to determine whether this difference has any effect on people's diet.
The researchers first looked at a group of 100 men and women who were in the early stages of getting Type 2 diabetes. In the group, 80 had a GLUT2 with Thr at position 110 and 20 had at least some of their GLUT2 proteins with an Ile at 110.
Some people have sweet
tooths because they
have an ile instead of a
thr at position 110 of
their GLUT2 protein.
The researchers looked at what these people ate over a three day period (visit 1). And then again over another three day period two weeks later (visit 2).
What they found was that the 20 people with the Ile at position 110 of GLUT2 ate more sugar than the rest of the group. In fact, they ate a lot more.
People with only Thr at position 110 ate on average 86 +/-4 grams of sugar per day on visit 1 and 82 +/-4 grams per day on visit 2. People who had at least some GLUT2 proteins with an Ile at position 110 ate on average 112 +/-9 grams of sugar per day on visit 1 and 111 +/-9 grams per day on visit 2.
This means that one group ate around 25 grams more sugar per day. That is quite a sweet tooth!
Of course this was an older group on the verge of getting Type 2 diabetes. What about a healthy, younger group? Would these people with an Ile at 110 of their GLUT2 also eat more sugar?
To answer this question, the researchers looked at a group of 587 young adults. In the group, 478 had a GLUT2 with Thr at position 110 and 109 of them had at least some of their GLUT2 proteins with an Ile at 110. The researchers looked at how much sugar these people ate everyday on average over a one month period.
On average, the Thr group ate 115 +/-3 grams of sugar per day. The Ile group ate 131 +/-5 grams of sugar per day.
Again, people with the Ile at 110 ate more sugar (around 15 grams/day). This is consistent with the idea that people with a sweet tooth sometimes have an Ile at position 110 of their GLUT2 protein.
People with the Ile at 110 Only Eat Extra Sugars
An important point is that the Ile folks didn't just eat more in general. They just ate more sugar.
The researchers looked at how much protein, fat, alcohol, and cholesterol each group ate. And they found no consistent difference between Thr and Ile people in any of these categories.
This research suggests that having an Ile at position 110 of the GLUT2 protein gives people a sweet tooth. The sweet tooth might come from a need to eat more sugar to feel full.
Of course this is still a small study. Researchers will need to look at many more people to confirm that it is this change that is responsible for these folks eating extra sugars. They will also undoubtedly create the DNA change in mice and see if they eat more sugar too. This last experiment will help prove that this single change is responsible for a sweet tooth.
What does knowing this kind of thing mean to patients and their doctors? It can let the patients know they crave sugar for a genetic reason. And the doctors can help these patients create a diet plan that takes into account their sugar craving. This might prevent a patient from becoming obese or developing Type 2 diabetes.