Through a series of questionnaires and statistical analysis, the team found that two thinking-related skills - planning, and execution of those plans - were weakened in women whose stress was high, and those skill gaps were associated with higher total fat intake.

These two skills are known as executive functions, a set of multiple thinking processes that enable people to plan, monitor behaviour and execute their goals.

"People with a higher level of stress tend to have a higher intake of fat, too. If stress is high, we're so stressed out that we're not thinking about anything - and we don't care what we eat," said lead author Mei-Wei Chang, associate professor of nursing at Ohio State.

"That's why we focused on executive functions as a mediator between stress and diet. And with this baseline data, we have reasons to believe that designing an intervention around executive functions could improve dietary outcomes," she said.

"I would anticipate the results could be similar for non-pregnant women, because it's all about how people behave."

The study was published recently in the Journal of Pediatrics, Perinatology and Child Health.

The 70 women enrolled in the study had a pre-pregnancy body mass index of between 25 (scores between 25 and 29.9 are categorised as overweight) and 45 (scores of 30 and higher are categorised as obese).

The participants completed questionnaires assessing both overall perceived stress and pregnancy-related stress, as well as executive functions - specifically focusing on metacognition, or the ability to plan, and behaviour regulation, the ability to execute those plans. They also completed two 24-hour dietary recalls of their calorie intake and consumption of total fat, added sugar, and fruits and vegetables.

"We were really interested in the mediation role of executive functions. The mediator is what makes everything happen," Chang said. "We wanted to know: If we focus an intervention on executive functions, would that carry through to behaviour change in dietary intake?”

"Weight loss interventions often involve a prescribed diet or meal plan, and you are told to follow it. But that doesn't lead to behaviour change in the long term."

Statistical modelling showed that higher perceived stress was associated with a worsened ability to plan and monitor behaviour, and that pathway was linked to higher total fat intake. Similarly, higher levels of pregnancy-related stress were associated with a lower ability to plan, which in turn was associated with worsened ability to monitor behaviours related to carrying out the plan - and these factors were linked to higher fat consumption.

These pathways suggested that an intervention designed to lower stress would function as a starting point to improve the diet, and enhancing skills through coaching - emphasizing the ability to plan, including being flexible with planning, and behaviour monitoring, particularly when making food choices - would be key to changing eating patterns.

"You need to improve executive functions, and you also need to lower stress," Chang said. She and colleagues are now analysing data on the effectiveness of an intervention for the study participants that emphasized stress management and boosting executive function to promote healthy eating.

Executive functions are regulated by a specific region of the brain, and strengths or weaknesses in these skill areas are thought to be affected by a variety of physiological factors. Previous research has found that executive function deficits are more likely to occur in women who are overweight or obese than in women whose weight is categorized as normal.

"Executive function is not well-studied, and it is not related to intelligence. But people with low executive function are unable to make detailed plans and stick to them, and that's how they get into trouble," Chang said. "Metacognition and behaviour regulation must go hand in hand - that way you have a much better chance to control your behaviours, and then you will eat better."