Stress and food: experimental and quasi-experimental evidence

In one study, department store workers ate more unhealthy foods
when they were working more demanding shifts. Is such a study likely to be
an experiment, a quasi-experiment, or a correlational study?
Credit: 22January/Shutterstock

A Washington Post journalist integrated several health psychology studies in an article about the relationships between stress and eating. For many people, stress and anxiety is associated with weight gain. The journalist summarized several examples of studies that support, and help explain, this link. Read them and think about whether they are  experimental or quasi-experimental. 

Here's the first study the journalist described (we'll call it Study A):

In laboratory studies, scientists have found that administering synthetic versions of cortisol to people causes them to eat substantially more calories than people who are given a placebo. That’s in part because cortisol reduces your brain’s sensitivity to leptin, also known as the satiety hormone, which regulates your appetite and makes you feel full.

a) There are two variables in this study. What are they? What are their levels? For each variable, decide if it is measured or manipulated. 

b) Do you think this was an experiment or a quasi-experiment? Explain your reasoning.

Here's the next one, which we'll call Study B:

In one study of department store workers, people ate more sugar, saturated fat and overall calories when they had to work long, demanding shifts compared with when they worked less stressful shifts with lighter workloads.

c) There are two variables in this study. What are they? What are their levels? For each variable, decide if it is measured or manipulated. 

d) Do you think this was an experiment or a quasi-experiment? Explain your reasoning.

Here's another, which we'll call Study C:

Even stress from activities we enjoy can lead to overeating. In one study, researchers followed ardent football fans in different cities. They found that fans whose NFL teams lost on Sunday consumed more calories and saturated fat the next day. Fans whose teams won ate less food and saturated fat the following day. The scientists found similar results when they looked at the dietary patterns of French soccer fans.

e) There are two variables in this study. What are they? What are their levels? For each variable, decide if it is measured or manipulated. 

f) Do you think this was an experiment or a quasi-experiment? Explain your reasoning.

So far, the evidence suggests that stress in one's life might lead people to eat more of types of foods that are not good for us. Here's a final study that was designed to test a way to prevent stress from affacting our eating habits. We'll call it Study D:

In a study published last year, [researcher Janet] Tomiyama and her colleagues recruited 100 adults with elevated stress levels and split them into two groups. Everyone was trained to do a daily, six-minute stress reduction exercise called progressive muscle relaxation, which involves tensing and relaxing your muscles from toes to head. You can find an example of it here. This deep relaxation technique has been shown in studies to reduce stress and anxiety.

But members of one group were assigned to eat a serving of fresh fruit such as sliced pineapple, honeydew and pears, about five minutes into each of their daily progressive muscle relaxation sessions. After one week of this, the researchers found that eating just the fruit alone made the participants feel less stressed and put them in a better mood. By pairing the fruit with a relaxation exercise, their brains began to view the fruit as something that reduced their stress levels — essentially turning the fruit into comfort food.

g) There are two variables in this study. What are they? What are their levels? For each variable, decide if it is measured or manipulated. 

h) Do you think this was an experiment or a quasi-experiment? Explain your reasoning.

i) Bonus question: Study D included an element of classical conditioning, which you probably learned about in Introductory Psychology. Can you identify the conditioned stimulus and conditioned response in this example? 

j) Rank the four studies (A, B, C, and D, above) in terms of which ones you believe have the strongest evidence (based on their methodology).