Vegetarianism is healthy, but how vegetarian do you need to be?
Experts already know that diets that emphasize plant-based over animal-based foods — such as vegetarian or vegan diets — can decrease the risk of obesity.
However, scientists do not yet know how strictly these diets need to be followed to reduce the risk of becoming overweight or obese later in life.
The Centers for Disease Control and Prevention (CDC) report that, in the United States, obesity is highest among middle-aged and older adults.
Around 40 percent of 40–59-year-olds and 37 percent of adults aged 60 and over are obese, compared with about 32 percent of those aged 20–39.
Analyzing data from the Rotterdam Study
A team from Erasmus University Medical Center, based in Rotterdam, the Netherlands, examined long-term health information collected as part of the Rotterdam Study. The data included 9,641 adults with an average age of 62 years who took part in this ongoing population-based study.
In particular, the researchers were interested in the participants' diet, body mass index (BMI), waist circumference, weight in relation to height (fat mass index), and body fat percentage.
The team created a scoring system to categorize the amount of plant-based foods the participants consumed compared with the amount of animal-based food they consumed.
In this system, the participants received points for eating nuts, fruits, and vegetables, and were deducted points for eating meat, dairy, and fish. So, the higher an individual's score, the more closely they adhered to a plant-based diet.
Plant-based diets and BMI scores
The team found that people with the highest scores on the index were more likely to have a lower BMI over the long-term. This association still held true after accounting for factors that could have influenced the results, such as total energy intake, levels of physical activity, and socioeconomic background.
Participants with a score of 10 on the index had significantly lower average BMI and fat mass index scores compared with participants that scored zero on the index. Higher scores were also linked with lower waist circumference and lower body fat percentage.
The study suggests that these associations are stronger in people aged 45–65 than those over 65.
Crucially, the researchers explain that there were various ways that participants could achieve the higher scores without necessarily becoming entirely vegan or vegetarian. For instance, swapping 50 grams of red meat for 200 grams of vegetables each day would give someone a high score.
It is important to bear in mind, however, that these findings can only demonstrate a link between a high plant-based diet and reduced likelihood of being overweight or obese. The results do not prove cause and effect.
"Our study suggests that a more plant-based and less animal-based diet beyond strict adherence to vegan or vegetarian diets may be beneficial for preventing overweight/obesity in middle-aged and elderly populations."
Lead study author Zhangling Chen
She continues, "In other words, eating a plant-based diet to protect against obesity does not require a radical change in diet or a total elimination of meat or animal products."
"Instead," Chen adds, "it can be achieved in various ways, such as moderate reduction of red meat consumption or eating a few more vegetables. This supports current recommendations to shift to diets rich in plant foods with low consumption of animal foods."