Can What You Eat Prevent Depression?

Did you know that eating a lot of processed foods (most of the foods in the center aisles) may be related to developing depression? A study recently reported by BBC News and passed along to a fellow colleague at Harvard School of Public Health (thanks Rachael!) has reached this conclusion -- and I am apt to agree.

Take-Home Message
Eat a diet rich in whole foods (fruits, vegetables, unprocessed meats, natural fats, and whole grains) and forgo the traditional diet of refined sugars and wheat, artificial fats, and *deli* meat and cheese.

Why should you? 
Because you can might not just impact your waist line, but also your mental health.

Feeling tired? Out of sorts? Sad or blue?  These issues might be fueled by a poor diet! (Note: This isn't the case for everyone. And depression should be taken extremely seriously and referred to mental health professionals and skilled counselors when indicated.)

The Study (Epidemiology 101)
The study is pretty sophisticated in that it randomly assigned people to a diet full of whole foods, fruits, vegetables, and assigned other people to eat a diet comprised mostly of processed foods like refined grains, sweet desserts, processed meats, and the like.

Randomization is a really important aspect of public health (i.e. epidemiological) research, because it helps to tease apart the factors that are truly leading to a specific outcome of interest; in this case, the outcome is depression. Randomization helps to ensure that the two groups (if large enough) are identical in terms of their underlying characteristics, which means that differences in depression are less likely to be a result of underlying differences in health status or lifestyle factors associated with a particular risk factor; in this case, diet.

For example, if you just observe differences in depression by looking at the types of diet a person then you need to account for the fact that people with healthier diets might also be more physically active than people who have less healthy diets. In fact, studies show that people who are more physically active are less likely to have depression. So, in an observational (not random) study like this, it will be difficult to know whether the link between diet and depression is due to another factor, such as level of physical activity (called a confounder in public health lingo) or is a true association.

Indeed, that is what public health research is all about. Trying to figure out whether diet causes cancer or whether the two are merely related. If they are merely related, then changing one's diet might not have any impact on depression. If you want to design effective interventions then you want to tackle the causal factors -- not just those that are associated with a certain health outcome!

Can It Be Trusted?
Now, before I have convinced you that this study is "right" it is important to remember that no one study can definitively prove a causal link. Some certainly lend more support than others; however, in general, one needs to consider the entire body of literature.

So I took a look at the literature and after reading a few abstracts, there certainly is a growing case to be made for both diet's relationship with an array of mental health problems, including Alzheimer's disease and depression. One of the study authors, Archana Singh-Manoux, has published several articles on obesity and obesity-related factors (such as metabolic syndrome) on depression all from a huge British study called the Whitehall II Study. These other studies suggest possible ways that poor dietary patterns can influence depression (for example, through metabolic and chemical changes in the body and brain). Yet, even he acknowledges to the BBC that physical activity or other lifestyle factors might be explaining the diet-depression association.

What are your thoughts? Can you find evidence that supports or refutes the diet-depression link?