Mediterranean diet reduces effects of stress in animal model

Eating a Mediterranean diet may provide a relatively easy way to help lessen the physiological effects of stress and promote healthy ageing, according to a new study.

Not only does stress have negative effects on work and personal relationships, it also increases the risk of many chronic conditions, such as heart disease and Alzheimer’s disease, and is associated with higher mortality rates. According to the American Psychological Association, Americans report some of the highest perceived levels of stress in the world — and that was before this year’s pandemic and presidential election.

With this in mind, researchers at Wake Forest School of Medicine conducted what they claim is the first preclinical trial to measure the effects of long-term consumption of a Western diet versus a Mediterranean diet on stress under controlled experimental conditions. Their findings were published in the journal Neurobiology of Stress.

“It is very difficult to control or reduce stressors in our lives,” said Professor Carol A Shively, principal investigator of the study. “But we do know that we can control our diet, and previous observational studies have suggested that lower perceived stress is associated with high fruit and vegetable consumption.

“Unfortunately, Americans consume a diet rich in animal protein and saturated fat, salt and sugar, so we wanted to find out if that diet worsened the body’s response to stress compared to a Mediterranean diet, in which much of the protein and fat come from plant sources.”

The researchers studied the effects of the chronic stress of low social status and the acute stress of being socially isolated for 30 minutes in 38 middle-age animals that were fed either a Mediterranean or Western diet. The diets were formulated to closely reflect human diets, with protein and fat derived largely from animal sources in the Western group and primarily from plant sources in the Mediterranean group. To determine the diets’ effect on stress responses, the scientists measured changes in the sympathetic and parasympathetic nervous systems and in the adrenal gland hormone cortisol, in response to acute and chronic stress.

The sympathetic nervous system is involved in the ‘fight or flight’ response and regulates bodily functions such as heart rate and blood pressure. The parasympathetic nervous system has opposite effects that help the body return to a calmer state. Cortisol, the body’s main stress hormone, helps the body access resources needed to fight or flee.

Compared to animals fed a Western diet, those fed the Mediterranean diet exhibited enhanced stress resilience as indicated by lower sympathetic nervous system and cortisol responses to stress, and more rapid recovery after the stress ended. Prof Shivley said, “Our study showed that the Mediterranean diet shifted the balance toward the parasympathetic nervous system, which is good for health. By contrast, the Western diet increased the sympathetic response to stress, which is like having the panic button on all the time — and that isn’t healthy.”

As the animals aged over the 31-month study, which is equivalent to about nine years in humans, the research group noted that sympathetic nervous system activity increased. However, the Mediterranean diet slowed the ageing of the sympathetic nervous system. The findings thus suggest that adoption of a Mediterranean-like diet may provide a relatively simple and cost-effective intervention to reduce the negative impact of psychological stress on health and delay nervous system ageing, Prof Shively said.

Image credit: ©stock.adobe.com/au/Alexander Raths

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