Research Review:
Why junk food won't make you happy

By Helen Kollias, Ph.D.

Ever sit down with a big bowl of ice cream after a bad day? Or maybe even an entire tub of ice cream? Well, that might not be the best thing to do.

Now I know you’re probably saying that you know and pretty much everybody knows that eating a tub of ice cream isn’t good for you — and you’re right.

But poor eating habits may damage more than your waistline — they might affect your mental health too.

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Research question

The study in this week’s review looks at how diet and depression are linked. As the researchers suggest, eating a bowl of ice cream to feel better is probably counter-productive.

Akbaraly TN, Brunner EJ, Ferrie JE, Marmot MG, Kivimaki M, Singh-Manoux A. Dietary pattern and depressive symptoms in middle age. Br J Psychiatry. 2009 Nov;195(5):408-13.

Methods

With this study the researchers started off with a whopping 10,308 people, but over the 20 years of the study they lost a few participants and screened out a few people. In the end there were 3,486 people – still impressive!

All the participants were civil service workers from 20 London departments.

In phase 1 of the study (that happened between 1985 and 1988), the participants were given a clinical examination and a questionnaire that asked about things like healthy lifestyle factors, work characteristics, social support, and life events.

Measuring food

During phase 5 (between 1997-1999), the questionnaire looked at dietary patterns in the participants.

Everybody still involved filled out a Food Frequency Questionnaire that had a list of over 127 foods (the original questionnaire foods plus common UK foods). Beside each food they were asked how often they ate the given food. Participants could choose from a range of answers between “never” and “six or more times per day”.

The foods from the questionnaire were grouped into 37 food groups – holy cow, 37 food groups! Personally, I think that 10 food groups should cover everything.

From this grouping of the questionnaire answers the researchers grouped the participants into one of two groups:

Whole food pattern: those who had a high intake of vegetables, fruits and fish.
Processed food pattern: those who had a high intake of sweetened deserts, chocolates, fried food, processed meat, pies, refined grains, high-fat dairy products and condiments.

Measuring depression

Five years after the dietary phase, the researchers did the depression assessment phase, or phase 7 (from 2002-2004).

Here I’m going to point out the obvious – these studies take a long time. Relatively speaking there is not a lot of time to administer & analyze, but researchers spend a really long time waiting to see what happens – 20 years from beginning to end.

Assessment of depression was done with a short self-reporting scale called the Center for Epidemiologic Studies – Depression scale (or CES-D for short). Twenty items on the scale measure depression symptoms. CES-D asks how often certain symptoms occur using a four-point scale (0 – less than 1 day to 3 – 5 to 7 days).

Results

After everything was said and done, 416 of the 3,486 participants were depressed.

Those considered depressed were less likely to have a high intake of whole food – meaning that if you corrected for age, gender and energy intake those people who ate a lot of fruits, vegetables and fish were less likely to be depressed.

A brief statistical interlude – odds ratio

Odds ratio is used to figure out the chance of something happening between two groups. If the odds ratio is 1 then both groups have equal chance of a particular thing happening.

For example: Let’s compare the odds of Bob and Doug (two fictitious people) getting stuck in a snow storm in January.

Bob lives in Winnipeg, Canada (a place considered cold even by Canadians) and Doug lives in Las Vegas, USA.

Bob has a higher odds ratio of being stuck in a snow storm than Doug– so the odds ratio would be bigger than 1. Doug, on the other hand, is less likely to get stuck in a snow storm – so his odds ratio would be less than 1.

Processed foods and depression

Those participants in the study that had the highest reported consumption of processed food were more likely to be depressed than the people who ate whole food.

The odds ratio of depression in people who ate a lot of processed food was 1.58. (More likely.)
The odds ratio for someone eating a lot of whole food to be depressed was 0.64. (Less likely.)

Chicken or the egg

chicken-the-egg

So do depressed people eat processed food? Or does processed food trigger depression? Which came first? It’s a classic chicken and egg dilemma.

Luckily, there is an answer in this study – not so much with the chicken and egg.

Since, there was 5 years between the dietary phase and the depression phase questionnaire of the study, the researchers could figure out what came first.

During the dietary phase (5 years before the depression phase) of the study all participants self-reporting that they had depression were excluded (about 427 people). So anybody that was already depressed was out of the study and not included for the dietary and depression phases.

All the dietary analysis was done on people who started out relatively happy. 5 years later those eating a high processed food diet were more likely to be depressed.

Using this screening process you can safely say that depression didn’t trigger the increase in processed food (at least not initially). So, eating processed food increases your chances of becoming depressed – if all other things are equal – same gender, age, marital status, etc.

Another thing to show that depression didn’t cause dietary changes was looking at rates of depression (using a self-reporting scale of depression) 5 years before the dietary analysis. You see, rates of depression didn’t predict dietary pattern.

While the data seems solid enough, this doesn’t seem true to me. I know that my moods do impact my eating habits. In the very least, if I’m stressed because I’m very busy I’m less likely to eat what I’d like because of lack of organization. So I take this finding with a grain of salt – it just doesn’t seem right to me.

Conclusion

If you eat whole foods like fruits, vegetables and fish you are less likely to have depression than someone with a very similar profile to you who eats processed food.

Now if you didn’t have enough reasons to eat whole unprocessed food you can add mental health to the list.

The researchers take a few stabs at explaining why whole food would be protective for depression. They came up with a few:

High content of antioxidants in fruits & vegetables
High content of folate in vegetables – particularly coniferous (e.g. broccoli, cabbage, etc), green leafy vegetables (e.g. spinach) and dried legumes (e.g. lentils)
High content of long-chain omega-3 polyunsaturated fatty acids found in fish

All these nutrients have been linked to lower rates of depression.

The researchers also thought that the sugar in processed foods could be part of the reason for increased rates of depression.

Bottom line

While I don’t think this study definitively proves that diet causes depression instead of depression impacting nutrition, it does show that the two are clearly linked.

Now ask yourself: what do you have more control over? You can’t change: