Tomatoes and French fries
The greatest benefit of a plant-based diet comes from the diet overall, not from any single food item. That said, these studies use a scoring system to reflect which items are healthy and which are not.
Diet was assessed every 4 years, starting in 1991, using a semiquantitative food frequency questionnaire that recorded the consumption of 131 foods and drinks during the previous year. The researchers determined the average frequency with which participants consumed each food. Eighteen food groups were sorted into three categories: healthy plant-based foods (whole grains, fruits, vegetables, nuts, legumes, vegetable oils, tea, and coffee), unhealthy plant-based foods (fruit juices, refined grains, potatoes, sugary drinks, sweets, and desserts), and animal-based foods (dairy, eggs, fish or shellfish, meat, and various foods of animal origin).
Healthy plant-based foods were given positive scores, while less healthy plant-based foods and the animal-based food groups were given negative scores. The consumption of each food group was classified into PDI using quintiles.
Women in the highest PDI quintile had a significantly lower risk for hypertensive disorders of pregnancy, compared with women in the lowest quintile. There was a negative dose-response relationship between PDI and risk of the disease. “A vegetarian diet isn’t necessarily healthier than a nonvegetarian diet if it’s made up of superfluous foods like French fries and soft drinks,” said Dr. Sotos-Prieto. “The difference lies in the quality of the plant-based foods. That’s what makes the difference between a healthy and an unhealthy diet.”
Give up meat?
Dr. Chavarro said that removing meat from his dinner menu 22 years ago was one of the hardest things he ever did. “Now, it’s no problem,” he said. But he understands that there are people for whom changing the diet by replacing animal products with nonanimal products is difficult. But meat need not be entirely abandoned.
“The women in the highest quintile aren’t necessarily vegetarian or vegan, but they consume much fewer animal-based foods than the others,” he noted. He added that vegetarian or vegan diets are not incompatible with a healthy pregnancy. “All vegans know how to get vitamin B12 from supplements.”
Diet or weight loss?
Much of the benefit observed in the study appears to be related to better weight control. The body mass index between dietary assessment and pregnancy accounted for 39% of the relationship between PDI and hypertensive disorders of pregnancy and 48% of the relationship between PDI and pregnancy-related hypertension.
“Part of the association seems to be explained by better weight control over long periods,” explained Dr. Chavarro. Women who adopted diets with more plant-based foods gained weight more slowly than those who consumed more animal-based foods. “They are different in terms of their weight trajectory over many years. So, part of the association that we observe is related to better long-term weight control. But the other half of the association is attributable to the diet itself and not necessarily to weight.” The authors suggest mechanisms of action such as endothelial dysfunction, inflammation, or blood pressure before pregnancy to explain the association.
Dr. Sotos-Prieto believes that this point is “extremely relevant.” In her opinion, it reveals that controlling weight at the start of pregnancy is important for pregnant women. Weight control may also improve other factors, like gestational diabetes. “I think preventive measures should focus on that. These results show that interventions are needed to increase the likelihood of going into pregnancy with an appropriate weight. And this includes modifying diet.”