Thanks to a study carried out by the Catholic University of Leuven (KUL), it appears that what we used to think of as pigging-out is in fact more a case of self-medication and neurochemistry.

The study was led by Lukas Van Oudenhove (pictured), a psychiatrist with a particular interest in the stomach and its relationship with the digestive tract. It’s not as strange an alliance as it sounds: the gut contains so much neural material – more than the spinal cord – it’s sometimes referred to as the “little brain”. Your gut has about 100 million nerve cells. The association between brain and belly is part of our language: we have “a gut feeling” about something or are “gutted” when things go wrong. At the same time, we “digest” information or find an excuse “hard to swallow”. You might start the day feeling “down in the mouth” and finish up feeling like “crap”. The whole alimentary tract is a ripe source of metaphor.

More concretely, the adrenalin peak that occurs when you’re, say, waiting to see the dentist may cause a dry mouth and sweaty palms, but also a churning in the stomach and even a certain looseness in the bowels. That’s a case of the mind influencing the body: Your knowledge of what’s going to happen in the dentist’s chair affects parts of the body not normally under conscious control.

In the KUL study, published this month in the Journal of Clinical Investigation (JCI), the whole mind-body interaction is turned on its head: The results clearly show that the body can also have a direct effect on the emotions.

The study took 12 healthy volunteers and subjected them to four 40-minute sessions in an fMRI scanner on different days. Later, they were shown photos of people with sad or neutral expressions and played either sad or neutral music.

Ten minutes in, comes the special part of this study. The subjects have already been fitted with nasogastric tubes and now they receive either a saline solution or a solution of fatty acids, such as are found in the sort of foods we’re usually counselled to consume in moderation, or not at all.

The subjects have no idea what they’ve ingested, but the gut knows: Those who had registered increased activity in the emotional centres of the brain – like the thalamus, hypothalamus and cerebellum (see diagram) – on being subjected to sad impulses, underwent a reduction of those emotions, in some cases by more than half. Those who received the saline solution showed no effect. In other words, fatty foods reduce sadness in the brain, even when you don’t know you’ve consumed them. And the effect shown is far higher than any results achieved by best-selling anti-depressants like Prozac.

Self-medicating with frietjes

“We already knew that taste and smell are really important in determining the reward value or the mood-altering properties of foods,” explains Dr Van Oudenhove. “But we showed for the first time that, even if you bypass all sensory stimulation, food can still have an influence on vulnerability to sad moods. That’s the novel thing here.”

The phenomenon of comfort food has been well researched, with the category divided by one study in 2006 into four areas: nostalgic foods, indulgent foods, convenience foods and physical comfort foods. The KUL’s finding is simple but revolutionary. It shows that the latter category, being outside conscious control, could be the most important.

In contradiction to the ruling Cartesian paradigm that states that the mind controls the body, this study shows that, in some cases at least, the body is controlling the mind. The body is sparking a neurochemical appetite for fatty food, over and above the normal desire people have for comfort foods.

Could people who indulge in comfort foods be unconsciously self-medicating, in the same way that pregnant women eat foods that satisfy “cravings” in response to an unconscious demand from their bodies for certain minerals or vitamins? This has been known to happen even if the idea of eating such things as ash, baking powder and even soil is unappetising, or even repulsive, to them.

“It’s hard to tell what aspects are all in play; it could be there’s a sort of homeostatic urge,” says Van Oudenhove, referring to the body’s need to restore a balance, in much the same way as cats or dogs eat grass when feeling unwell.

An editorial by scientists from the National Institute of Diabetes and Digestive and Kidney Diseases in the US accompanies the publication of the study results in the JCI, pointing out the study’s limitations – the small sample size and the lack of any demonstration of the mechanism of “gut-brain signalling”, as Van Oudenhove calls it.

“That’s the next thing to look at,” he tells me, accepting the criticisms of his peers. “Before rushing to apply the findings in other patient populations, we need to confirm the findings in a larger sample. We need to look at gender differences, personality features and the way the people involved think about eating. Only then can we look at how these results apply to patients with conditions like depression, obesity and eating disorders.”

Responsibility still key

For Greet Vansant, an expert in social medicine and nutrition at KUL, the findings of the Van Oudenhove study don’t, for the time being, suggest a new approach to the problem of obesity, which has reached epidemic proportions in the Western world.

“We have to learn to unravel the mechanisms of the way people react to food in certain ways,” says Dr Vansant. The notion that the urge to consume “comfort food” might come from the body itself rather than the mind, “doesn’t change our advice. The notion of comfort works hand-in-hand with obesity. While comfort may be a drive, we have to help people change their comfort methods. Why eat chocolate when you could eat an apple, or go for a walk, or do something active?”

While “we’re certainly not about to advise people to eat chocolate when they’re feeling down,” she says, “we’re also not going to ban it because it has its place in the food pyramid. That would have the opposite effect to the one we’re looking for. People just have to take responsibility for what they consume.”

www.jci.org/articles/view/46380