Anyone who's ever taken a bite of a Reese's Peanut butter Eggs that are only sold during the Easter season knows that chocolate is a mood enhancer, but in case you thought it might just be the wonderful taste, there is actual empirical evidence that chocolate can elevate your mood. Specifically, eating chocolate appears to make individuals suffering from atypical depression and seasonal affective disorder (SAD) feel better. As a result, chocolate and carbohydrate cravings are common in atypical depression and SAD, perhaps as a form of self-medication1. Several hypotheses have been offered to explain this effect, the most well-known of which argues that eating chocolate helps to regulate serotonin levels. Since a low serotonin level is one cause of depression, it stands to reason that depressed individuals would crave foods that might increase their serotonin levels. Other explanations include (from the summary of the paper, linked below):
- corrects a deficiency in the regulation of mood
- is highly pleasurable
- is addictive
- is a means of coping during a negative mood.
An article by Parker et al. in the June issue of the Journal of Affective Disorders the various proposed explanations for the effects of chocolate on mood2. You can read a summary of the paper here. Parker et al. find each of the proposed explanations wanting. For example, the serotonin hypothesis suffers from two major problems. The first, and most obvious, is that the potential increase in serotonin level resulting from eating chocolate wouldn't occur fast enough to explain the immediate elevation in mood. The second is that chocolate's protein content is too high for the body to be able to get the building blocks of serotonin from it. Furthermore, they find in their review that while chocolate can produce a short-term elevation of mood, when people eat too much chocolate (as they often do when they are craving it), their mood soon drops below it's pre-eating level. So, chocolate doesn't make a very good anti-depressant, and it's not really clear why it produces temporary elevations in mood for some people.
On a related note, one of the papers cited in the Parker et al. review is particularly interesting, not so much because of the results, but because of the methods. Small et al3 had hungry participants eat squares of chocolate until they were full, and then keep eating. As they ate the chocolate, they rated how pleasurable the chocolate was, and underwent PET scans each time their ratings dropped 2 points on a 20 point scale (from -10, awful, to +10, delicious). The purpose of the study was to observe differences in brain activity for approach motivations (when they are hungry and want chocolate) and avoidance motivations (when they're so full they feel like they're going to puke), and they found such differences. If you're interested, when eating chocolate was still pleasurable, increased blood flow was observed in the caudomedial orbitofrontal cortex, subcallosal region, insula, striatum, and
1Wurtman, R.J., Wurtman, J.J., 1989. Carbohydrates and depression. Scientific American, 260, 68-75.
2Parker, G., Parker,
3Small, D.M., Zatorre, R.J., Dagher, A., Evans, A.C., Jones-Gotman, M., 2001. Changes in brain activity related to eating chocolate. From pleasure to aversion. Brain, 124, 1720-1733.
SAD? How would that work - something in chocolate acting as Zeitgeber (fixing the underlying cause), or something in chocolate upping the mood (fixing the symptoms)?
Anyway, I am a chocoholic and an SAD sufferer, so I guess I am self-medicating.
Judging by the review, there's no clear mechanism, and it doesn't really do anything long-term anyway.
I would like to start a neuroblog carnival. If I can get enough contributions, I'll post the first edition on my blog on 1sy July. Contributors would take turns editing and hosting editions of the carnival on their blog, which would initially be monthly.
I'd very much like you to be a regular contributor and co-host of this carnival. If you're interested in taking part, please email me up to 3 recent posts from your blog (firstname.lastname@example.org mo187 at yahoo dot com.) or post a comment on my blog.
Getting a depressed person to feel better has nothing to do with treating depression. Cocaine makes a lot of people feel better too, yet it is hardly a treatment for depression; in fact, it makes it worse, in the long run.
Treatment of depression should result in alleviation of vegetative symptoms: low energy, anhedonia, and the like. So while it is interesting that some depressed persons feel better when they eat chocolate, it probably tells us nothing of clinical utility (as Coturnix pointed out.)
Thus, this qualifies as basic, preclinical research. It tells us something about brain pathways.
As for the mechanism, I would suspect theobromine is the active agent, but there could be others that go along with it.
You have a serious Reese's Egg problem. However, I can concur with the chocolate=good aspect of the post.
I don't have a problem. I can stop eating them anytime I want!