Glugging lots of sugary drinks won't just make you fat, it might also lead to changes in the brain that have been linked to cancer and Alzheimer's disease — at least in rats.
This finding comes from the first analysis of how sugary drinks affect proteins in the brain. It showed that 20 percent of the proteins produced in a brain region related to decision-making were different in rats that drank sugary drinks from those of rats that had been given water.
It is well established that drinking sugar-sweetened drinks is linked to obesity and diabetes as well as to increased risk of cardiovascular problems.
But the effects of sugar-rich drinks on the brain have received much less attention. "For many people around the world, soft drinks are their sole source of liquid, or at least they provide a very high proportion of their daily calories," says Jane Franklin of the behavioral neuropharmacology lab at Macquarie University in Sydney, who carried out the new analysis. "We know that soft drinks are bad for the body, so it's reasonable to assume that they aren't doing anything good for your brain, either."
To confirm that assumption, Franklin and her colleague Jennifer Cornish gave 24 adult rats either water or a solution of water containing 10 percent sugar — about the proportion you would find in a typical can of soda — for 26 days.
For the following seven days, both groups were given only water. At the end of that time, the rats that had drunk the sugary drink were significantly more hyperactive — spending lots more time moving around — than the control group. "Hyperactivity is a physical sign that something unusual is happening in the brain," Franklin says. It is probably a reflection of changes being made to return the system back to its pre-sugar state, after it had adjusted to prolonged sugar consumption, she says.
To find out what was going on, the team looked at the rats' orbital frontal cortex, the part of the brain that sits behind the eyes. An enzyme was used to snip proteins from this tissue into their constituent peptides. These fragments were then analyzed using a mass spectrometer, which identifies the peptides, and therefore the proteins, present. This was then compared to a database of the proteins you would expect to see in a healthy rat of this species.
Of the 1,373 proteins identified in both sets of rats, 290 were altered in those that drank sugary drinks but not those that drank water. Some of the proteins were present in greater numbers, and some in fewer numbers than expected.
"This is a lot more change than we anticipated," Franklin says, and is significantly more than the group saw in a similar analysis of caffeine in other brain areas.
While more work is needed to determine the exact effect of these changes, just under half of the altered proteins are known to be involved in the cellular function of the brain, including determining cellular life span, communication and DNA repair. Thirty percent of the changed proteins are linked with conditions such as cancer, Alzheimer's disease, Parkinson's disease and schizophrenia.
"The results are telling us that sugar exposure has the potential to alter a lot of diverse biological processes and play a role in neurological disorders -- much more than we expected," Franklin says. "We can't say from this work that these changes are causing the associated diseases, but it's a warning that we need to look more closely at the link."
The work was presented at November's conference of the Society for Neuroscience in San Diego.