Despite the basic truth of the cardinal rule of nutrition—you are what you eat—some caveats have been discovered in recent years. For instance, it’s not just what we eat, but it's when we eat, what we drink, and what other habits we’re engaging in on a daily basis. And a new study in the journal Molecular Psychiatry finds that our stress levels may actually undermine our healthy food choices. In fact, a stressful day can apparently make a healthier food choice—in this case, the addition of a healthy oil—look like it’s junk, physiologically speaking. This is not license to eat junk food when you’re stressed or depressed, but rather, it’s another cue to take our mental health more seriously than most of us actually do.
In the new study, from The Ohio State University, the team had a group of middle-aged women, some of whom were breast cancer survivors and others not, eat one of two breakfasts. The meals both included eggs, turkey sausage, biscuits and gravy. These aren’t the healthiest breakfasts to begin with, but some were also high in saturated fat—in the form of palm oil—and some were higher in unsaturated fat—sunflower oil. The women ate one of the two meals on two different occasions and came into the lab for blood work, and to report on events in their lives that might affect their mental health. Stressful events included a variety of naturally occurring stressors, like having to clean up paint a child spilled all over the floor to caring for a parent with dementia.
As you’d expect, the women who ate the meals higher in unsaturated fat had better levels of four different markers of inflammation than women who’d eaten those higher in saturated fat. But for the participants who reported stressful events the day before the assessment, there was no benefit of eating the healthier oil. “Putting it another way,” the authors write, “for a woman with no prior day stressors, outcomes were higher after the saturated fat meal than after the sunflower oil meal. But if a woman had prior day stressors, the differences disappeared—because the stressors heightened responses to the sunflower oil meal, making it look more like the responses to the saturated fat meal.”
Why stressors would affect how our bodies respond to food is an interesting question. One possibility is that the boost in inflammation that comes from stress might act to counteract the effect of healthier oils, since it essentially mimics the physiological effects of unhealthy fats. (Unhealthy foods, like certain fats, processed food and excess sugar seem to raise inflammation in the body.) The study also found that women who were stressed and ate the unhealthier meal didn’t have any further increase in the inflammatory markers, which the authors suggest that this may be due to some sort of ceiling effect for these markers. But that doesn't mean we can eat whatever we want when we're stressed. It seems to mean, on the contrary, that we should take our stress levels seriously, and do what we know helps us de-stress, since both chronic stress and bad food choices seem to accrue over time.
One limitation of the study is that both of the meals were pretty unhealthy. This was actually done intentionally, to mimic a real-world Western meal, with healthy or unhealthy added fats. But what's less clear is how the situation might work with truly healthy meal—vegetables and fish, for example. Looking at how stressful events might (or might not) counteract the effects of really eating healthy, rather than just swapping oils, would be the next step. And what's also clear is that the types of stress many of us deal with every day can offset the smaller healthy choices, like switching oils—so it may be that a more global shift in our eating habits is necessary to withstand everyday stressors.
While the researchers are still figuring all this out, it's probably best to do what we already know—to eat well and take care of our mental health, among other things. It's true that food choices are critical for health, but so are all the other things we do every day. So it's not just "we are what we eat," but it's all of the other choices we make, physically and mentally, that contribute to our overall health.