Just in time for my Easter dinner of Slim Jims and Mickey Ds (kidding! I ate grassfed steak and potatoes with spices and kerrygold in honor of Walter Willett) comes this downer of a news article: Link Between Fast Food and Depression Confirmed.
That science daily piece is based upon a study newly published in Public Health Nutrition, Fast-food and commercial baked goods consumption and the risk of depression. Now Public Health Nutrition sounds like one of those buttoned-up nutrition journals filled with good intentions and soy, so let's see what the quality of the work is, shall we?
All right, so this is a revisit of the SUN study. I'm pretty sure I have some SUN study stuff around here somewhere, oh, here. Basically it is an epidemiological visit to sunny Spain, where nearly 9000 university graduates were followed for about 6 years, answering questions about diet and subsequent health.
And guess what? If you fill your plate with empty industrial fast food calories (weirdly, they call fast food "sausages, pizza, and hamburgers" in this study, which certainly can be fast food, but also not so fast…) and "commercial baked goods" including "muffins, doughnuts, croissants, and other commercial baked goods." Okay. Though I've probably eaten more homemade muffins than commercial ones, can't ever remembering making my own doughnuts or croissants, so they've got me there.
So all the folks did not have diagnosed depression at baseline, and over the years, several hundred began taking antidepressants or were diagnosed with clinical depression by their doctors. And, three guesses as to how diet correlated with the diagnoses????
That's right, a linear, dose-dependent correlation between the amount of "fast food" at baseline and depression. The "fast food and commercial baked goods" eaters were more likely to be young, and more likely to not eat other, more delectable foods, such as olive oil, fish, nuts, and vegetables (*cough* Mediterranean diet *cough*). The fast food shovelers were also more likely to smoke and to work more than 45 hours a week (not recommended!).
If you recall, all those studies listing relative risk of whatever (such as every statin study ever written) are all hiding something. In general you end up with headlines such as "A 49% increase of DEATH DEATH DEATH" but in actuality the risk of death goes from 1% to 1.49% which is hardly exciting. I had to edit this next part after Jonathon's comment because I carelessly reported the numbers incorrectly the first time around. I have several excuses having to do with poor time management and sleep deprivation, but no good excuses because I am not typically so careless… anyway, the percentage of change of the magnitude of the association varied as we went farther and farther from the original dietary measurement, discounting all the folks who had been diagnosed in the months prior to the last measurement of depression… these variations were from 1% or so to 14% or so for commercial baked goods. The absolute numbers were 493/8964 people diagnosed with depression, or about 5% (this number is low compared to the general population, but many folks were excluded from the sample due to already having a diagnosis of depression prior to the study, which skewed this sample toward healthier folks with later onset of depression symptoms). The hazard ratios aren't that impressive, but the trend is linear and significant for the fast food consumption.
The discussion is also interesting. The authors suggest that those who eat more fast food and baked goods have a higher trans fat consumption (likely true), and therefore poorer glucose control and poor glucose control (staggered they mention trans fats and not saturated fats here!! Do these folks actually read the nutrition literature?) Then, even more surprisingly, the authors have a cogent discussion of how high glycemic carbohydrates (found in abundance in commercial baked goods) will increase plasma tryptophan and increase serotonin uptake into the brain and thus decrease depressive symptoms (blah blah blah)… but these effects seem to have been studied only short term, and that long term, inflammation and pro-inflammatory cytokines are more associated with fast food-style diets and these are more likely to be important to longer term depression.
Phew, I was beginning to think these researchers were way too sensible when they went into a discussion of how high-fat, ketogenic diets can disrupt cognition (pray tell me how likely it is a fast food diet is highly ketogenic?)
And, let's not pull punches on the major weakness of this study. Diets were only assessed at baseline, and follow up occurred up to 8 years later. That's a lot of unknown eating to account for. I also thought the previous study of trans fats wasn't that helpful because it seemed that college graduates in Spain didn't have that much variation in how they ate. Meaning hardly anyone ate that much vegetable oil, and trans fats were mostly from dairy, as opposed to an American sample, where trans fats can make up a scary percentage of calories.
Still, correlations being what they are, if you are the sort of person to be quaffing from the drive-thru, you are also apparently far more likely to be the sort of person to be diagnosed with a clinical depression. Confounders galore, but there you have it. Now, back to my Slim Jims.