This was a double-blind, randomized, crossover study. A great design to answer their research question: Does stress cause us to gain weight? I like crossover studies because they use the same study subjects as controls which does away with some confounding. The control group in a parallel design (not crossover), could be made up of more younger or older or heavier or smokers, etc., any of which can confound your results.
Daily Stressors, Past Depression, and Metabolic Responses To High-Fat Meals: A Novel Path to Obesity, Biological Psychiatry, 13 July 2014
Weighty Issue: Stress And High-Fat Meals Combine To Slow Metabolism In Women, Ohio State University Press Release, 14 July 2014
They found that the more stressors women had on the day prior, the less fat they burned after a single high-fat meal (930 calories/60 grams fat) the following day. Women also had slower metabolisms in general the next day (“lower postmeal REE” or Resting Energy Expenditure).
Conclusion: The cumulative 6-hour difference between one prior day stressor and no stressors translates into 435 kJ, a difference that could add almost 11 pounds per year. These findings illustrate how stress and depression alter metabolic responses to high-fat meals in ways that promote obesity.
Participants burned about 100 fewer calories during the 7 hours after eating the meal than they would have if they weren’t stressed. They had higher insulin levels too, a hormone which promotes fat storage. They were fed either a meal high in saturated fat or monounsaturated fat (high-oleic sunflower oil). Both of these meals resulted in decreased metabolism. I wonder how a low-fat, high-carb meal would have affected metabolism under these circumstances.
“We suspected that the saturated fat would have a worse impact on metabolism in women, but in our findings, both high-fat meals consistently showed the same results in terms of how stressors could affect their energy expenditure,” said Martha Belury, a co-author of the study.
A history of depression led to higher triglycerides:
“In women who had stress the day before and a history of depression, triglycerides after the meal peaked the highest,” [lead author] Kiecolt-Glaser said. “The double whammy of past depression as well as daily stressors was a really bad combination.”
Researchers supplied this video:
If stress affects metabolism, slowing it in this case, this becomes yet another variable to account for in dietary studies. That is, if you’re going to adjust for calories, smoking, weight, alcohol intake, income, education and other socioeconomic factors, etc., you may also want to adjust for prior-day stressors.
What we eat may be easier to control:
Most of the reported stressors were interpersonal in nature: arguments with co-workers or spouses, disagreements with friends, trouble with children or work-related pressures.