If healthy eating is the norm for you, junk food – starchy, sugary, simple carb foods – likely has little appeal. In fact, eating it can probably make you feel really sick, really fast.
On the other hand, those who tend to eat mostly hyper-processed foods may find it hard to imagine any pleasure or satisfaction in eating lots of veg, lean meats, whole grains and other less processed fare.
We know this, of course, from experience, but research published recently in Frontiers in Psychology shows just how drastically dietary preferences can shift.
For the study, healthy rats raised on a healthy diet were switched for two weeks to a a diet
that included daily access to cafeteria foods, including pie, dumplings, cookies, and cake – with 150% more calories – the rats’ weight increased by 10% and their behavior changed dramatically. They became indifferent in their food choices and no longer avoided the sound advertising the overfamiliar taste. This indicated that they had lost their natural preference for novelty. The change even lasted for some time after the rats returned to a healthy diet.
The authors speculate that the diet changed the reward circuits of the rats’ brains, impairing decision-making – and that the same may hold true for other mammals, including humans.
But this isn’t the only dynamic that can drive food choices. Another recent study – published in Neuroscience Letters – suggests at least one physical way in which stress may push us toward unhealthy eating.
It involves glucocorticoids – hormones released when we’re stressed, some of which heighten the stress response and some which counteract it. They work by activating specialized receptors inside your body’s cells, including the oral taste cells for sweet, bitter and umami.
Comparing stressed and unstressed mice, the researchers found that the stressed mice had 77% more glucocorticoid (GC) receptors within their taste cells.
The results suggest that sweet taste perception and intake, which are known to be altered by stress, may be specifically affected via secretion of GCs and subsequent activation of GC receptors in taste cells.
“Taste provides one of our initial evaluations of potential foods. If this sense can be directly affected by stress-related hormonal changes, our food interaction will likewise be altered,” said [lead author M. Rockwell ] Parker.
Senior author Robert Margolskee added that because these receptors are found throughout the body, there may be other implications, as well – for instance, receptors in the pancreas further increasing sugar cravings.
Nor is it just humans whose dietary habits may be affected by other conditions. A study just published in mBio looked specifically at the bacteria involved in periodontal (gum) disease. What the researchers found is that those microbes behave a lot differently when you’re healthy than when you’re ill.
“The main thing that they change when they go from health to disease is that they change their metabolism,” [lead author Marvin] Whiteley said. In other words, a species of bacteria that ate one thing, fructose for example, can switch to a different kind of sugar to feed on if diseased.
You have to wonder: Does their change spur us, their hosts, to change our eating to suit their preferences? This study didn’t explore that, but in light of what we do know, it’s squarely in the realm of possibility.
And this study shows something else that’s always worth keeping in mind: that the issue is never a single type of microbe but the whole ecosystem of the human individual. The whole, as they say, is greater than the sum of its parts – a concept crucial to biological dentistry and medicine.
“What our study says is that it doesn’t really matter what bacteria you have, because the communities are acting very similarly,” Whiteley explained. “So a healthy community has this metabolism, no matter what the members are. And a diseased community has a very different metabolism, no matter what the members are. It’s this conservation of a metabolic community. ”
Whiteley compared what’s happening under our gums to an ecosystem in the African savannah. The interactions among ‘animals’ is key. “You have lions, and you have leopards, and wildebeest, and all of these animals that are there. If you look at it as a whole community, it kind of makes sense. But if you were to only take a one-acre plot out of the African savannah and look at it, it may not make sense because there may not be a lion in that one acre. So trying to understand interactions, you need to take a much larger, bigger context. And that’s what this study did,” Whiteley explained.
Image by Rodrigo Suarez, via Flickr