Cognitive Daily

I think I’ve mentioned here before that I’m a big fan of chocolate. I get upset when coffee shops in my area only bring out the chocolates in the afternoon. Who says you can’t have a chocolate chip cookie for breakfast?

Chocolate, combined with a cup of coffee, helps me work all the way through to the end of the day, when I’d otherwise be tempted to call it quits in the late afternoon. So naturally I was excited when Greta found a research report on the effect of chocolate on mood. Could there be scientific confirmation that chocolate helps you get through the day?

There has been plenty of research suggesting that many people eat in response to negative moods and stress, but there is less evidence that eating actually improves mood. Many of the studies done on emotional response to food have been poorly controlled. Others have shown that mood can improve as a result of nutrient consumption — but this impact may be delayed for some time. Michael Macht and Jochen Mueller wanted to know if eating chocolate could immediately improve mood.

They recruited 48 volunteers via classified ads, all of whom said they liked chocolate. The volunteers reported their mood (on a scale from 1 [negative] to 25 [positive]), then watched one of three short movie clips: A mourning scene from “The Champ,” the Meg Ryan orgasm scene from “When Harry Met Sally,” or a clip from a documentary about copper manufacturing. As you’d expect, the first clip had been previously shown to induce negative mood, the second, positive mood, and the third, no mood change. After viewing the clips, the volunteers reported their moods, and their moods had changed as predicted.

Then half the volunteers were given a piece of chocolate, and the unlucky second group got a glass of water. 1 minute later, they reported their mood once again. This was repeated for each clip (the clips were shown in a random order for each participant). So did chocolate have a different effect from water? Here are the results:

As you can see, the effect of chocolate depends on the type of movie the viewers watched. If the movie was sad, then eating chocolate led to a significant improvement in mood, significantly better than water. For a happy film, there was no improvement in mood, and the difference between chocolate and water was only marginally significant. For a neutral movie, there was no significant difference in the effect of chocolate and water.

The volunteers were also surveyed about their eating habits, and there was a significant positive correlation between those who were emotional eaters (who ate at times of stress) and mood improvement after a sad movie. In other words, emotional eaters get a big boost from eating chocolate, while people who exhibit dietary restraint do not (though since this is only a correlation, we can’t say why it’s happening).

The next question Macht and Mueller had was whether there was something about the chemical or nutritional properties of chocolate that improved mood after a sad movie clip, or it was simply related to the pleasurable taste of chocolate. They recruited 113 new volunteers, and this time, they surveyed them first about their preferred and least-favorite type of chocolate: Milk chocolate, or 70, 85, or 99 percent dark chocolate. Everyone was shown the sad clip, and then one group was given their preferred type of chocolate, another group got their least favorite type of chocolate, and the final group got nothing. Here are those results:

After one minute, the group eating their preferred (palatable) chocolate was in a significantly better mood. The group eating their least-favorite (unpalatable) chocolate was unchanged. But after three minutes, there was no difference between the palatable and unpalatable chocolate-eaters. So the initial improvement in mood is very likely due to the pleasant taste of chocolate, but after a few minutes, mood improvement may be more related to the nutritional or chemical properties of chocolate.

All in all, I see nothing here to change my current pattern of an afternoon dose of chocolate to motivate me to work through the day. Hooray for chocolate!

One important additional line of research Macht and Mueller would like to see done in the future:

Further studies should address the question of whether mood effects over longer periods of time may result from consumption of a greater amount of chocolate.

Sign me up!

MACHT, M., & MUELLER, J. (2007). Immediate effects of chocolate on experimentally induced mood states Appetite, 49 (3), 667-674 DOI: 10.1016/j.appet.2007.05.004

Comments

#1 Anne Marie
October 6, 2009

Consumption of water is not a good control – they should have had a separate group that was given a different kind of food item, or some kind of non-caloric item to chew on. All the first experiment shows is that consuming food improves mood. The second experiment is a bit more interesting with the palatable/non-palatable distinction, but it would be nice to have a group given a non-palatable non-chocolate food (brussels sprout?) to see if there is any effect after a few minutes of simply consuming calories. As it is, this study tells us nothing about the effects of chocolate on mood.
#2 Gregory Marton
October 6, 2009

A better control would have look, texture, and taste, like chocolate, but no cocoa. It’s certainly doable. That’s blinding on one side, which would keep the subjects’ expectations of the mood change out of the picture. It may become important to double-blind: to keep the experimenters’ expectations from being possibly communicated to the subjects. Without that, horses can count.
#3 Lilian Nattel
October 6, 2009

Count me in on the chocolate experiments as long as I’m not in the water group.
#4 Jadehawk
October 6, 2009

A better control would have look, texture, and taste, like chocolate, but no cocoa. It’s certainly doable.

white chocolate with brown food coloring? or something completely un-chocolate-like (what would have the shape and consistency of chocolate, but not actually be chocolate-related?)
#5 Linda
October 6, 2009

But if I think I feel better, does it really matter if I REALLY feel better?
#6 Harlan
October 6, 2009

I’m very skeptical. It’s way too easy for the participants to just decide to respond the way they expect the experimenters want them to respond. Happens all the time, and pretty tricky to control for. If I were a reviewer on this paper, I’d likely have rejected it.
#7 Xenia
October 6, 2009

Wouldn’t the consumption of a greater amount of chocolate lead to feelings of guilt and thus counteract all the yummy goodness? Or am I just projecting?
#8 Karthik Durvasula
October 7, 2009

1) “They recruited 48 volunteers via classified ads, all of whom said they liked chocolate”
So, they took people who like chocolate and then tested if it improved their mood.

2) When they gave people chocolate of the kind they didn’t like, it didn’t have any effect.

It seems to me the proper controls should include in their descriptions things that people like to eat apart from chocolate. And then see if chocolate has any more of an effect.

This is really a poorly controlled study, in my opinion.
#9 Carl Lumma
October 7, 2009

Dude, it’s just theobromine (of which chocolate is the only significant source in the Western diet). I’ve seen so much speculation about PEA (not orally available) and caffeine (not much in chocolate)… and now this. Yes it improves mood, it’s freakin’ theobromine (if you’re eating something with real cocoa content).
#10 IanW
October 7, 2009

Never mind the choco-late – how about some choco-early?!
#11 Rachel Cotterill
October 7, 2009

I’d definitely like to sign up for the next stage of the trial!

Based on personal experience, I find that dried fruit works just as well as chocolate at cheering me up – but based on even wider experience (and medical trials…) there’s an awful lot of evidence for the placebo effect in so many different areas, so I’d probably attribute it to that. It would be very hard to design a scientific study of chocolate-versus-placebo….

It might be interesting to test whether there’s any mood improvement in people who don’t like chocolate. Or – more generic – whether “your favourite treat” has more or less effect than someone else’s favourite.
#12 karthik durvasula
October 7, 2009

@ Rachel Cotterill: your question is already answered in the study discussed above. There is an effect of chocolate one likes vs. chocolate one don’t like. (presumably, the chocolate one doesn’t like is liked by someone else.)

Re: placebo effect: absolutely, that’s what i was hinting at in my comment. I wouldn’t be at all surprised to see the same findings for ANYTHING that you like. even, food or no food! lol!

There is a tonne of such studies floating around that tell us close to nothing, but it makes the newspapers more fun to read.

Dunno how they get funding for stuff like this. Makes me wonder about the research aptitude of the grant reviewers at these funding agencies.
#13 Kathy Howe
October 8, 2009

There have been numerous studies about the effect of chocolate on mood…..it is evident based on the popularity of chocolate that people do turn to chocolate during stressful times.
#14 Dave Munger
October 8, 2009

Karthik:

I suppose it’s up for debate whether this study was worthwhile, but in any case the study would not have been very expensive — around a thousand dollars to pay the participants, plus with the cost of the chocolate. It’s certainly not a million-dollar experiment like many drug trials or other studies.

Karl:

If it’s just the theobromine, then why does the preferred chocolate improve mood more than less-well-liked chocolate?
#15 karthik durvasula
October 8, 2009

@ Dave: you forget the personnel cost, the lab (?) cost, and more than anything the wastage of time that can be spent conducting more illuminating studies (than poorly controlled ones like these) with the same resources .

But, I guess u are right. If they have the money and time, who am I to stop them. Let them roll in a little choco-loving.