While it's obvious that exercise is good for your body, new research is shedding light on why it's also good for your brain:

Physical activity is good for our brains. A wealth of science supports that idea. But precisely how exercise alters and improves the brain remains somewhat mysterious.

A new study with mice fills in one piece of that puzzle. It shows that, in rodents at least, strenuous exercise seems to beneficially change how certain genes work inside the brain. Though the study was in mice, and not people, there are encouraging hints that similar things may be going on inside our own skulls.

For years, scientists have known that the brains of animals and people who regularly exercise are different than the brains of those who are sedentary. Experiments in animals show that, for instance, exercise induces the creation of many new cells in the hippocampus, which is a part of the brain essential for memory and learning, and also improves the survival of those fragile, newborn neurons.

Researchers believe that exercise performs these feats at least in part by goosing the body’s production of a substance called brain-derived neurotrophic factor, or B.D.N.F., which is a protein that scientists sometimes refer to as “Miracle-Gro” for the brain. B.D.N.F. helps neurons to grow and remain vigorous and also strengthens the synapses that connect neurons, allowing the brain to function better. Low levels of B.D.N.F. have been associated with cognitive decline in both people and animals. Exercise increases levels of B.D.N.F. in brain tissue.

Additionally, it appears that there's a connection between this effect and ketones, the energy source produced when the body metabolizes fat for fuel. Ketones appear to have a secondary effect of promoting synthesis of B.N.D.F. in the brain.

The body uses ketones for fuel when blood sugar levels grow low, either through depletion of glycogen stores in the body or when eating a low carbohydrate diet. Advocates of the paleo diet and other low carbohydrate diets will find some suggestive data in this study.