Overweight and obese adolescents chew differently

Researchers evaluated the link between excessive weight and masticatory behavior.

By Diego Freire  |  Agência FAPESP – Two articles that were published by researchers who were affiliated with the Federal University of São Paulo (UNIFESP) and the University of Campinas (UNICAMP) in São Paulo State, Brazil, show that overweight or obese adolescents chew differently than adolescents of normal weight, and more frequently display changes in facial muscles and behaviors that are detrimental to nutrition. The researchers also found that mastication differs between boys and girls.

The findings are from the research project entitled “Evaluation of salivary composition and masticatory function in overweight and obese adolescents”, which was conducted with FAPESP’s support. The principal investigator was Paula Midori Castelo, a professor at UNIFESP’s Environmental, Chemical & Pharmaceutical Sciences Institute in Diadema, São Paulo State, and the project also involved researchers at UNICAMP’s Piracicaba campus.

The study evaluated the eating habits and quality of masticatory function of 230 adolescents aged 14-17 years who resided in the city of Piracicaba.

The investigation was performed in two stages. The first stage included 115 normal-weight boys and girls. The second stage included only overweight or obese adolescents of both sexes. None of the selected participants had tooth decay or any other condition that affected oral health to the extent that it interfered with masticatory function.

“There’s a consensus among dentists and speech therapists that it’s important to eat and chew slowly and on both sides of the dental arch so that food is properly broken down and processed before deglutition, and to avoid habits that hinder its absorption, such as having a drink with a meal,” said Castelo, the lead author of both articles.

“In our tests we observed that individuals with overweight or obesity, a multifactorial chronic condition, displayed muscle function alterations and greater difficulty with chewing. All that can affect nutritional quality.”

According to the study, overweight and obese girls more frequently chew on only one side of the mouth, causing an imbalance in the temporomandibular joint, which is bilateral. Among other problems, this can cause structural changes on one or the other side of the dental arch as well as impair food bolus formation and nutrition.

“The tests didn’t determine whether the alterations are related to the causes of overweight and obesity or to its effects,” Castelo stated. “However, they help us understand which adolescent behaviors and eating habits need to be observed and corrected. Myofunctional alterations can entail skeletal and muscular imbalances, among other problems.”

The adolescents were filmed while chewing, and the recordings were analyzed by a speech therapist, who assessed their masticatory behavior and counted the number of chewing cycles on each side of the mouth.

Masticatory performance was also evaluated using color-changing chewing gum that was specifically designed for this purpose and made in Japan. Its initial color is green. As chewing proceeds, it gradually changes to red. The extent of the color change provides information on masticatory efficiency.

Bite force was measured using a gnathodynamometer. These tests showed that male adolescents chewed faster and more effectively than female adolescents.

“It’s often said that people who eat quickly don’t chew their food properly and swallow without breaking it down sufficiently, but males have more muscle mass and physical strength, so they can chew faster by applying greater force and process food more efficiently,” Castelo wrote. “Some differences, such as girls’ chewing more delicately, are also cultural.”

This does not mean that eating fast is invariably better. “When you masticate for a longer time, you tend to eat less because there’s time for the release of hormones that regulate satiety or hunger as food processing information is transmitted to the central nervous system,” Castelo stated. “If you chew fast, therefore, you may eat more, even if your bite force is adequate. The important thing is to observe masticatory behavior as a whole.”

Drinking during meals

The tests also involved the completion of a questionnaire on eating habits. For example, the adolescents were asked whether they usually had to cut meat and other food into small pieces to make it chewable, could easily bite an apple, could eat fruit unpeeled, etc.

Among the results was the finding that the eating habits of overweight and obese adolescents more frequently impair mastication and digestion, including the use of large amounts of sauce or gravy and drinking during meals.

“If you drink while eating or use lots of sauce, you end up chewing less and swallowing the food before it’s well masticated,” Castelo wrote. “This makes digestion more difficult and can have consequences that range from stomach discomfort to inefficient absorption of nutrients.”

The researchers plan to evaluate the adolescents’ salivary microbiota and the nutritional markers in their saliva.

“We took samples of saliva from the adolescents who participated in the study to investigate whether the microbiota related to their nutritional state, among other things, because other studies have shown that it may relate to intestinal tract microbiota,” Castelo stated.

The results of the study involving overweight and obese adolescents are presented in the article entitled “Chewing in adolescents with overweight and obesity: An exploratory study with behavioral approach", which was published in Appetite. It won a prize at the 33rd Annual Meeting of the Brazilian Society for Dental Research (SBPqO), which took place in September in Campinas, São Paulo State. In addition to Castelo, the article was coauthored by the following researchers: Aline Pedroni-Pereira, Darlle Santos Araújo, Kelly Guedes de Oliveira Scudine, Daniela Galvão de Almeida Prado, and Débora Nunes Alves Leite Lima.

The study of normal-weight adolescents, by Castelo and Pedroni-Pareira, Araujo, Scudine, Almeida Prado and Ana Claudia Rossi, is described in the article entitled “Assessment of the differences in masticatory behavior between male and female adolescents”, which was published in Physiology & Behavior and is retrievable from www.sciencedirect.com/science/article/pii/S0031938416302013.