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These Genes Make Me Eat Too Much

New Research Shows that Some People Have a Genetic Predisposition to Overeat

by Dr. Barry Starr, Stanford University

Researchers at SUNY, Buffalo may have identified one of the reasons some people need to overeat to enjoy their food. It has to do with how their genes make their brains work.

People eat for a lot of different reasons. One reason, of course, is to get the nutrients they need to stay alive. But most people also just enjoy eating.

In the brain, a feeling of joy often comes from the release of a neurotransmitter called dopamine. The brain knows that this neurotransmitter has been released when dopamine binds to proteins called dopamine receptors. So dopamine plus dopamine receptors equals that good feeling you get from a great meal.

The researchers at SUNY, Buffalo found that people who overeat tend to have fewer receptors than people who don't overeat. The idea is that people with fewer receptors need more dopamine to get enjoyment from the food. And the way to get more dopamine is to eat more.

Of course even if this is true it doesn't mean these folks get a free ride on their weight. It is still important that they don't become fat. It is just much harder for them than the folks with more dopamine receptors.

A Genetic Change that Makes it Easier to Overeat

How does someone end up with fewer receptors? Through their genes of course. To understand how this all works, we need to dig a bit deeper into what a gene is and how genes vary between different people.

Genes are really just the instructions for making a protein. And proteins are the things that do most of the work in a cell.

For example, the instructions for making dopamine are found in a gene. Same thing with dopamine receptors.

It is important to realize that we all share most of the same genes. What makes each of us unique is that we have different versions of a few of our genes.

For example, brown and blue-eyed people both have an OCA2 gene. It is just that blue-eyed people have a different version of the OCA2 gene than do brown-eyed people.

The same thing goes for dopamine receptor genes. Some people have gene versions that make them have more dopamine receptors. And some people have versions that make them have less.

To complicate things a bit, there are actually a number of different dopamine receptor genes (as well as different versions of each). For today's story, we'll just focus on one dopamine receptor—the dopamine D₂ receptor (DRD₂).

There are at least two different versions of the DRD₂ gene—A1 and A2. People with the A1 allele tend to have fewer receptors than A2 people.

Previous studies had shown that people with the A1 allele tend to weight more. And since dopamine is involved in enjoying food, the thought was that these people needed to eat more to get the same reward from eating. But no one had ever carefully tested this idea. Until now.

More Information

• Scientific journal article
  
• Why am I always hungry and therefore overeat? Is there a genetic component to our appetites?
  

How They Figured It Out

The researchers set two tasks for 74 people. The first task involved a taste test where people could eat as little or much of the food in front of them as they wished. The second task involved figuring out how much work someone was willing to do for extra food.

In the first task, participants were told they were part of a taste test for six different snack foods. The portions were quite large. The investigators then left the room and observed how much of the food each person ate.

What they found was that people who had fewer dopamine receptors ate more. This is consistent with the idea that these people need to eat more to enjoy their food.

The second task involved clicking a computer mouse to get food. Basically, a participant would get a food reward by playing a slots game on a computer. As time went on, "winning" became more and more difficult. In other words, over time people needed to work harder to keep getting food.

Obese people with fewer dopamine receptors went for longer than did obese people with more dopamine receptors. Again this is consistent with people with fewer receptors needing more food to enjoy eating it.

These results suggest that people with fewer dopamine receptors tend to overeat because they need more food to get their hit of dopamine. If further research proves this connection, scientists may be able to come up with a way to control weight by targeting the dopamine system.

Medicines probably won't result in fewer receptors. But they might be able to decrease the amount of dopamine someone makes.

One day people may be able to control their diet by controlling their levels of dopamine. Maybe the right pill can make someone get as much joy from a block of tofu as they do from a slice of cheesecake.

More Information

• Why am I always hungry and therefore overeat? Is there a genetic component to our appetites?
  

Content provided by the Department of Genetics, Stanford University.