The Evidence Supporting a Chocolate Diet: Correlation or Causation?

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A new study published in the journal Archives of Internal Medicine finds that chocolate consumption is associated with lower body mass index (BMI) [1]. In the news and across the web, reporters are touting this as evidence that eating chocolate lowers BMI.

Image credit: Assorted chocolates via Shutterstock

In the study, researchers asked a group of 1,018 participants how often they consumed chocolate. They then determined the BMI of 972 of the subjects (BMI is calculated as weight in kg divided by the square of height in meters). The investigators found that those who consumed chocolate frequently had a BMI of about one point less than those who did not consume chocolate frequently (in the study, a small but statistically significant difference). The scientists speculate that chemicals in the chocolate, including caffeine, boost metabolism.

While the results are certainly interesting, evidence of correlation is not the same as evidence of causation. Dieters, there’s no reason to rush out and buy chocolate. The results of the study show that those individuals who consume chocolate more frequently have lower BMI, but they don’t prove that consuming chocolate lowers BMI. To do the latter, the researchers would have had to take a group of subjects, randomly assign them to conditions (chocolate versus no chocolate), and then track change in BMI over time. If the chocolate eaters ended up with lower BMI than the non-chocolate eaters, this would be evidence of a causal relationship.

Correlations are funny things. For instance, there’s a strong positive correlation between ice cream sales and murder rate; the more ice cream sold, the more murders committed. However, there’s absolutely no evidence that eating ice cream leads to homicidal rage. The two variables are related to one another through a third variable: temperature. The hotter it is, the more ice cream people eat, and the more likely they are to fly off the handle.

Could eating chocolate lower BMI? Possibly. It’s possible that compounds in the chocolate increase metabolic rate, or that antioxidants in chocolate have some effect on fat storage. It’s also possible that people who choose to eat chocolate tend to eat a healthier diet in general, or have lower levels of stress (unrelated to the chocolate consumption), or are demographically similar in some other regard. Without more research, there’s no way to know. Unfortunately, therefore, as tempting as the idea of a “chocolate diet” may be, there’s no reason to believe that eating more chocolate will lead to weight loss.

References

1. Golomb et al. Association Between More Frequent Chocolate Consumption and Lower Body Mass Index. Arch Intern Med. 2012 Mar 26;172(6):519-521.
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