Researchers have demonstrated that saliva can be used for early detection of the risk of diseases associated with surplus body fat, an advance that may lead to better methods to diagnose chronic obesity-related ailments.
The study, published in the journal Nutrition Research, identified uric acid in saliva as a reliable signature chemical to predict body fat percentages in teenagers.
"The idea is to enable saliva to be more widely used as an alternative biological sample for clinical analysis. The advantage of saliva is that it can be collected several times noninvasively and painlessly, like urine," said study co-author Paula Midori Castelo from Universidade Federal de Sao Paulo in Brazil.
Castelo said the level of salivary uric acid is a good predictor of body fat percentage even in adolescents considered healthy, although the link between these two factors is poorly understood.
According to the researchers, uric acid is the end-product of the metabolic breakdown of purines -- molecular bases that make up the genetic material.
They said it accumulates in the blood, and in much smaller proportions in the saliva.
Although uric acid acts as an antioxidant, the scientists said it can lead to a predisposition to develop hypertension, inflammation, and cardiovascular disease when its levels become too high in the blood and saliva.
As part of the study, the researchers collected saliva samples from 129 girls and 119 boys aged 14-17.
In addition to uric acid, they also measured the levels of several other substances, including cholesterol and vitamin D, the study noted.
The participants answered a questionnaire on their medical and dental history, and also underwent an oral examination to exclude those with cavities and/or gum inflammation.
"Cavities and periodontal disease are known to influence salivary parameters such as pH (acidity), electrolytic composition and biochemistry. Both relate to the secretion of substances that can change the composition of saliva," Castelo explained.
The remaining participants were also subject to anthropometric evaluation that included measures of height, weight, and body fat percentage, as well as skeletal muscle mass.
In the study, the scientists sampled the saliva of the participants at home after they had fasted for 12 hours.
They measured the levels of cholesterol, uric acid, and other substances.
On analysing the data, they found that adolescents with a high level of salivary uric acid also had a higher body fat percentage.
"The level of this compound in saliva proved to be a reliable indicator of body fat accumulation, even in adolescents who were not being treated for chronic disease," Castelo said.
"It could be the basis for an accurate noninvasive method of monitoring dietary health and achieving early detection of changes in nutritional state," he added.