Food for Thought

Last week I learned something wild about our brains and bodies that has to do with the way we taste food. It turns out our body knows when we are eating something nutritive or when we are just eating junk. Okay, I know you’re freaking out right now because somehow your brain is keeping track of when you eat a kale salad vs. a fried chicken thigh – like Santa making his naughty vs nice list – but that’s not quite what I mean.

What I mean is that your brain knows when the food you’re eating contains calories or not. The crazy thing is that when your fed and happy, your brain doesn’t care whether you eat energy-rich foods or not and your preferences are dominated by flavor. However, if you find yourself stranded on a desert island going on a week without food, your brain is going to know whether you climbed that tree for the juicy, sweet coconut or whether you slammed that last Sweet-N-Low packet you’ve been saving in your pocket since your plane crashed.

This is research I heard about from Dr. Greg Suh at the Skirball institute in New York. He’s been giving fasted fruit flies the choice between real sugar, D-glucose, and “fake” sugar, L-glucose, which their bodies can’t metabolize. These two molecules taste equally good to the flies on a normal day, but after a few hours without fly food they begin to strongly prefer the D-glucose, the molecule that provides them with actual energy. This seems like a reasonable survival mechanism I suppose, given that when you’re starving it is imperative that you eat things that will keep your vitals functioning.

But what do I mean your brain “knows”? It’s not going to send you an email to tell you to cool it with the Diet Coke. But the neurons that respond to energy-rich foods are connected to other parts of your body that promote feeding. In the fruit fly this means that a calorie rich food will actually stimulate the proboscis to extend and the gut muscles to activate, promoting excretion. These actions are the response to the energetic food signal, and they don’t occur if you offer the fly the useless sugar (L-glucose).  

Dr. Suh believes he’s identified the same pathway in mice, which is a step closer to suggesting that something similar underlies human interaction with food. For me the question is now, how does our brain respond to “fake” food under other conditions? When we are hungry our brains know what’s good for us so surely they can tell the difference when we’re fed too. I’ll just have to follow Dr. Suh’s work to see where it leads. Here’s a link to his lab webpage in case you want to too: https://med.nyu.edu/skirball-lab/suhlab/