The less animal products a person eats, the lower his average body mass index is and the less extroverted he is. An association with depressed moods, as found in other studies, could not be confirmed. A large-scale study at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in collaboration with University Hospital Leipzig has now examined how being vegetarian is related to the body and the psyche – regardless of age, gender and education level – in nearly 9,000 people. .
It turned out that the rarer the proportion of animal foods in a person's diet, the lower their body mass index (BMI) and therefore their body weight. One reason for this could be the lower proportion of heavily processed foods in the plant diet. “Products that are too rich in fat and sugar are particularly fattening. They stimulate the appetite and delay the feeling of satiety. If you avoid animal foods, you consume less of such products on average,” explains Evelyn Medawar, lead author of the underlying publication. In addition:vegetarian food contains dietary fiber and has a positive effect on the microbiome in the gut. This is another reason they might fill you up sooner than those made from animal ingredients. “People who eat mainly plant-based foods may therefore consume less energy,” adds Medawar. In addition to a changed sense of satiety, lifestyle factors such as more sport and greater health awareness can also play a decisive role.
For BMI, it also seems to make a difference which animal products a person feeds on. If it is mainly so-called primary animal products, namely meat, sausage and fish, the person usually has a higher BMI than someone who mainly eats secondary animal products, namely eggs, milk, dairy products, cheese and butter. In the first case, the correlation is statistically significant.
Medawar uses an example to illustrate what this could mean for nutrition:“A person with an average lower BMI of 1.2 points either completely avoids certain animal products, such as primary ones, and follows a vegetarian diet. Or continues to eat meat and fish, but less often. Whether diet is ultimately the cause of lower body weight or whether other factors are responsible cannot be deduced from the data. A follow-up study in collaboration with the University Hospital Leipzig will now shed light on this.
Nutrition and personality
The researchers also found that vegetarian or vegan diets are also related to personality. Especially with one of the top five personality factors, extroversion. People who mainly eat plant-based foods have been shown to be more introverted than those who primarily ate animal products. “It's hard to say what the reason is for this,” says Veronica Witte. "It could be because more introverted people tend to have more restricted eating habits or because they are socially segregated because of their eating habits." Here too, further studies should follow on how people identify with the characteristics of their diet.
However, they could not confirm that a plant-based diet is associated with a tendency toward neurotic behavior, as other studies suggested. “Previous analyzes had found that more neurotic people were generally more likely to avoid certain food groups and to behave more restrictively. We focused solely on avoiding animal products here and were unable to observe any correlation," explains study leader Veronica Witte.
In a third part, they finally focused on whether a predominantly plant-based diet is more often associated with depressed moods. Here, previous studies had also suggested a link between the two factors. “We couldn't detect this correlation,” says Witte.” It's possible that in previous analyses, other factors had clouded the results, including BMI or salient personality traits known to be associated with depression. We accounted for it," said Witte, explaining a possible reason for the different results. In addition, the plant-based diet is now more common and more accepted and no longer restricted to a particular group.
The scientists had investigated these connections within the so-called LIFE project, a broad study in collaboration with the University Hospital Leipzig. They determined personal nutrition through questionnaires in which participants were asked to fill in how often they had eaten the individual animal products in the past 12 months - from "several times a day" to "never". The personality traits such as extroversion and neuroticism were assessed by means of a so-called personality inventory (NEOFFI), while depression was assessed by means of the so-called CESD test, a questionnaire that records various symptoms of depression.
