By now, many of us have heard about “good” versus “bad” fats. But a new study, published in the journal Molecular Psychiatry, suggests that stress eradicates the positive effects of choosing good fats.

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Though opting for “good” fats is a smart health choice, researchers suggest stress cancels out the associated health benefits.

“It’s more evidence that stress matters,” says lead author Jan Kiecolt-Glaser, professor of psychiatry and psychology at Ohio State University in Columbus.

She says their study is the first to show how stress can cancel out the benefits of eating healthier fats.

The American Heart Association (AHA) provide guidelines for consuming fats and note that dietary fats are crucial for the body’s energy and cell growth. In addition, dietary fats protect the organs and keep the body warm.

However, certain fats are better than others. Saturated and trans fats are the ones that can raise bad cholesterol levels in the body, while monounsaturated fats and polyunsaturated fats can lower bad cholesterol levels. These have been deemed the “good” fats.

Fats from foods like fish, nuts, and vegetable oils are of the “good” variety. As a rule of thumb, the AHA note that the bad fats tend to be solid at room temperature (a stick of butter, for example), while the good fats tend to be liquid at room temperature.

Prof. Kiecolt-Glaser and colleagues were aware that diet and stress can change inflammation in the body, which is linked to heart disease, diabetes, and rheumatoid arthritis.

However, they wanted to examine the interaction between stress, diet, and inflammatory markers that they could measure in the bloodstream.

To carry out their investigation, the researchers conducted a study in nearly 60 women, 38 of whom were breast cancer survivors. The women were an average age of 53 years old.

On two different days, the participants visited the university and were randomly assigned to eat one of two breakfasts: biscuits and gravy with eggs and turkey sausage that was mostly made with saturated fat from palm oil, or an identical breakfast made primarily with monounsaturated sunflower oil.

Additionally, the researchers asked the women about their previous day’s experiences, using a Daily Inventory of Stressful Events questionnaire to conclude whether or not the woman was stressed.

The team discounted minor irritants, but they noted stressful situations – such as cleaning up paint a child had spilled on the floor or helping a parent with dementia who resisted help. Prof. Kiecolt-Glaser notes that they are “not life-shattering events,” but they are relatively stressful.

Of the women, 31 had at least one recent stressor at one of the two visits. Additionally, 21 had stressful experiences before both visits, while six women did not have any.

After taking blood samples from the women at multiple times, the team looked at C-reactive protein and serum amyloid A, which are two markers of inflammation. The researchers also evaluated two markers that predict a higher likelihood of plaque building up in the arteries.

After controlling for factors that could skew outcomes – such as pre-meal blood levels, age difference, abdominal fat, and physical activity – results showed that women who ate the saturated fat meal had higher readings in all four negative markers, compared with the women who ate the sunflower oil meal.

However, in the women who had stressful days, this difference vanished, and as such, eating a breakfast with “bad fat” was the same as eating one with “good fat.”

Interestingly, while stress raised levels of the harmful blood markers in the sunflower oil group, stress did not affect the readings for the women who ate saturated fat.

The researchers specifically chose the meal they used for the study because it mimicked a typical high-calorie, high-fat, fast-food meal. Both breakfasts had 930 calories and 60 grams of fat, which is very similar to a Big Mac and medium fries.

Study co-author Martha Belury explains that they know “a less-healthy meal is going to have adverse effects on markers of inflammation, but we wanted to look at this type of meal with different types of fat.”

She notes that research is increasingly pointing to reduced inflammation as a major benefit of eating healthier foods – including following the Mediterranean diet, which is higher in oleic acid from olive oil.

The investigators add that because inflammation contributes to disease over time, when stressed, we should still be careful about what we eat. They conclude:

These data show how recent stressors and a [major depressive disorder] history can reverberate through metabolic alterations, promoting inflammatory and atherogenic responses.”

This study further sends the message that moderation is key; making consistently healthy choices may help mitigate the effects of stress over time.

Read about how certain fatty acids could improve reading skills in schoolchildren.