Thursday, February 21, 2008

What if Morgan Spurlock were a mouse?

If you give a mouse a Big Mac, does he get fat? If the Morgan Spurlock documentary “Super Size Me” is any indication, it’s highly likely.

So here’s a scientific study that answers that question, although that was a small part of the study. A group of scientists the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, Germany used mice to study the differences between humans and chimpanzees. More specifically, they looked at the effect of diet on gene expression. The paper is here.

They took four groups of genetically identical mice and fed each group a different diet.

One group got the Mouse Diet: standard mouse chow.

A second group got the Chimpanzee Diet: fruits, vegetables, and yogurt usually fed to chimpanzees at the Institute.

The third group got the Scientist Diet: the food served in the Institute’s cafeteria.

A fourth group got the Morgan Spurlock Diet: straight from McDonald’s.

The most scientifically significant result had to do with gene expression. Each human, mouse, or chimp has a genome, a set of genes with the DNA blueprint that dictates which proteins that animal will make. The thing is, not all of the genes are used all of the time in every cell. You don’t want your heart to grow a mustache, for example, or your earlobes to be made of bone. The key is to make the right proteins at the right time in the right place. That’s gene expression.

Humans and chimps and mice have different genomes, different blueprints. But they’re not really all that different. What adds to the differences between species is the way the genes are expressed. The mystery is what causes these differences in gene expression.

The researchers at the Max-Planck Institute hypothesized that diet could affect how genes are expressed. What they found was that the livers of mice fed different diets expressed the genes in their livers differently. What was really cool was that 117 genes expressed differently in mice fed the chimp diet vs. the human diets were the same genes that are expressed differently in chimpanzees vs. humans. That means that diet affects how we express genes and is part of what makes humans different from chimps.

Notice that I said “human diets.” For the most part, the Scientist Diet and the Morgan Spurlock Diet produced the same results. (I wonder what they serve at that cafeteria.)

There were two differences. One was that, although gene expression in the livers of mice fed both human diets was pretty much the same, the Scientist Diet didn’t affect gene expression in the brain. The Morgan Spurlock Diet did. Fast food changes your brain. Scary.

The other difference was that after two weeks on the Morgan Spurlock Diet, the body weights of the mice were significantly greater.