Scientists talked about the connection of walnuts with improved mood
Daily consumption of 40 grams of walnuts for eight weeks was associated with an improvement in overall mood in healthy young people. At the same time, the participants' levels of substances reflecting the metabolism of serotonin and the processing of food compounds by intestinal microorganisms changed. Such results were obtained by researchers at the University of Barcelona. How the experiment was conducted, what a mood change means and why the tests do not prove an increase in serotonin in the brain — in the Izvestia material.
Why scientists are interested in walnuts
Walnuts contain unsaturated fatty acids, including plant-based omega-3 fatty acids, dietary fiber, tryptophan, and polyphenols. These components are involved in various biological processes, so researchers are studying the possible connection of the product with the emotional state.
Tryptophan is an amino acid from which the body forms serotonin. This neurotransmitter is involved in mood regulation. However, the presence of tryptophan in the product does not yet allow us to predict how its use will affect the functioning of the nervous system.
The new work combines two areas: assessment of the emotional state and measurement of exchange products. The scientists tested whether changes in mood when eating nuts are accompanied by changes in biochemical parameters.
How the experiment was set up for 18 weeks
The study recruited 36 healthy adults aged 20 to 35 years. Five people dropped out, so 31 participants completed both experimental parts. The average age was 24 years, and about 90% of the participants were women.
The study did not include people with nut allergies, acute or chronic illnesses, smokers, or taking medications or dietary supplements. The participants also did not have to follow restrictive diets or work shifts. Thus, the scientists studied a fairly narrow group of healthy young people.
The experiment was randomized and cross-sectional. Some participants started with a daily intake of 40 grams of walnuts at dinner, while others started with a period without nuts and products made from them. Eight weeks later, a two-week break followed, after which the conditions were reversed.
The study lasted a total of 18 weeks. Each person went through both a period with walnuts and a control period without them. This design allows you to compare the condition of the same participant in different conditions. This helps to take into account individual characteristics that could make it difficult to compare two separate groups.
In both periods, the nutritionist gave standard recommendations on the Mediterranean type of diet. Therefore, the results relate to the inclusion of nuts in a specific food context.
What exactly was considered an improvement in mood
The emotional state was assessed using the Profile of Mood States (POMS) questionnaire. In addition to the overall indicator, the researchers analyzed individual mood characteristics, as well as perceived stress, well-being, and food cravings.
During the period of eating walnuts, the overall indicator of mood disorders was on average 4.85 points lower than in the control period. For this indicator, the decrease corresponds to a more favorable emotional state.
The result was statistically significant. At the same time, 4.85 points are the difference on a specific scale, not the percentage of improvement in mood or an assessment of how much happier each participant has become.
A change in the average also does not mean that all people have the same reaction. To assess the practical significance of the effect, its reproducibility and how noticeable it is in everyday life are important. The study was conducted among healthy participants. It did not test whether walnuts could treat depression or other mood disorders.
Why conclusions about anger and fatigue are more cautious
In the initial analysis, the indicators of anger and fatigue also decreased. However, these differences did not retain statistical significance after adjusting for multiple comparisons. Such an amendment is needed when scientists check many indicators at the same time. The more comparisons there are, the higher the chance of getting a separate positive result by chance. Additional statistical verification helps to reduce this risk.
Therefore, the improvement of the overall mood indicator cannot be automatically extended to every emotion. Data on the reduction of anger and fatigue require more careful interpretation.
The researchers did not find significant differences in friendliness, energy, perceived stress, and well-being. The overall result was favorable, but the changes did not cover all the measured aspects of the emotional state.
What did the serotonin metabolism tests show?
In addition to the questionnaires, the scientists analyzed the first morning urine samples. They measured 5-hydroxyindoleacetic acid (5-HIAA), the main product of the breakdown of serotonin. The level of 5-HIAA increased during the period of nut consumption. Its increase was associated with a lower overall indicator of mood disorders.
"We observed not only an improvement in mood, but also changes in biomarkers," said Maria Izquierdo-Pulido, professor of nutrition and Food sciences at the University of Barcelona, the head of the study.
In the report on the work, she explained that such indicators help to study possible biological mechanisms of the detected effect. However, 5-HIAA in urine reflects the metabolism of serotonin at the body level as a whole. This indicator can be influenced by nutrition, intestinal processes, the formation of serotonin outside the brain and the excretion of substances by the kidneys.
The study did not measure serotonin in the brain and did not directly assess the functioning of the central serotonin system. Therefore, the growth of 5-HIAA cannot be interpreted as evidence that walnuts increased the activity of serotonin in the nervous system. The found connection helps to formulate a hypothesis for the following studies. She does not yet explain what mechanism led to the mood change.
How do intestinal microorganisms fit into this picture?
When eating nuts, the levels of urolithins A and B also increased. These substances are formed when intestinal microorganisms process certain food polyphenols. An increase in urolithins was accompanied by an increase in 5-HIAA. Thus, the researchers found consistent changes in the two groups of exchange products.
This allows us to study the possible relationship between the processing of nut components by the intestinal microbiota and serotonin metabolism. But changing the indicators together does not establish a sequence of reasons. The urolithins could reflect the consumption of nuts and the activity of the corresponding metabolic processes. Additional experiments will be required to prove that they influenced mood through the serotonin pathway.
"The biological mechanisms require further study," the authors emphasize in the conclusions of the work.
They assume that changes in metabolites may reflect nutritional, microbial, or peripheral metabolic reactions.
What happened to stress and food cravings
The level of cortisol in urine did not significantly differ between periods. This is consistent with the absence of detected differences in perceived stress, although the laboratory indicator and the subjective assessment characterize different aspects of the condition.
Scientists have also studied food cravings. In the initial analysis, two indicators decreased: the expectation of relief from negative experiences after eating and feelings of guilt associated with food cravings or giving in to them.
But after adjusting for multiple comparisons, these differences also ceased to be statistically significant. Therefore, the study does not provide sufficient evidence to claim that walnuts reduce emotional overeating or guilt after eating.
Body mass index, body fat percentage, and physical activity did not significantly differ between the periods. At the same time, the quality of the diet during the period of nut consumption was slightly higher. These results help to describe the conditions in which mood changes were observed. They do not allow attributing all the detected shifts to a single substance in the product composition.
What can we conclude about walnuts and mood
The study showed that eight weeks of daily consumption of 40 grams of walnuts was accompanied by an improvement in overall mood and changes in some metabolites in healthy young adults.
At the same time, no significant differences were found in stress, well-being, and positive mood characteristics. The analyses also did not establish that the observed effect was related to a change in serotonin in the brain.
The amount of 40 g describes the mode of a particular experiment. The study did not determine the minimum effective serving, did not compare different doses, and did not establish a universal norm for improving mood.
The main scientific interest of the finding is in the combination of changes in the survey index with measurable metabolic shifts. This provides an opportunity to explore in more detail how common foods and their processing in the body can be associated with an emotional state.
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