Researchers have identified a potential new way to assess metabolic health using saliva instead of blood.
High insulin levels in the blood, known as hyperinsulinemia, can reveal metabolic problems long before obvious symptoms appear. It is already recognized as an important warning sign for future health issues, including Type 2 diabetes, obesity, and heart disease.
Now, researchers at UBC Okanagan say saliva may offer a much simpler way to spot that risk. Their study suggests that a saliva test can reflect insulin patterns linked to metabolic health, opening the door to a needle-free approach that could be easier to use in both research and routine screening.
Dr. Jonathan Little, a professor in UBC Okanagan's School of Health and Exercise Sciences, says the method could do more than replace a blood draw. It may also help identify early metabolic changes tied to obesity and related health risks, at a stage when blood sugar levels can still appear normal.
Published in Applied Physiology, Nutrition, and Metabolism, the study included 94 healthy participants across a range of body sizes. After fasting, each person drank a standardized meal replacement shake. Researchers then collected saliva samples and measured blood glucose with a finger-prick test.
"People living with obesity had much higher insulin levels in their saliva than those who were slightly overweight or had lower body weight—even though their blood sugar levels were the same," he says. "This suggests that saliva testing could be a simple, non-invasive way to identify people at risk of Type 2 diabetes before symptoms appear."
Detecting Diabetes Risk Years Earlier
Type 2 diabetes affects roughly 400 million people worldwide and is typically diagnosed when blood glucose levels become elevated. However, Dr. Little explains that underlying metabolic changes can begin much earlier.
Conditions linked to prediabetes, including insulin resistance and hyperinsulinemia, may develop 10 to 20 years before a formal diagnosis is made.
"If hyperinsulinemia can be detected before blood glucose levels start to rise, people at risk for Type 2 diabetes could be identified early, allowing for lifestyle changes and other treatments to be introduced long before glucose levels rise."
Early intervention is important because hyperinsulinemia is associated with an increased risk of several chronic diseases. These include Type 2 diabetes, hypertension, cardiovascular disease, stroke, and cancer. More recently, researchers have also connected the condition to obesity.
Co-author Dr. Hossein Rafiei says the goal of the study was to explore the possibility of creating a practical and non-invasive test for hyperinsulinemia. During the research, the team also observed a notable pattern after participants consumed the meal replacement drink.
Surprising Findings in Lean Participants
Previous research by Dr. Rafiei at UBC Okanagan showed that insulin levels detected in saliva closely track plasma insulin levels throughout the day after both high-carbohydrate and low-carbohydrate mixed meals.
"This suggests that saliva insulin may help distinguish between high and low plasma insulin responses, and could play a role in predicting the severity of hyperinsulinemia and possibly insulin resistance."
In the study, saliva samples were collected 30, 60, and 90 minutes after participants drank the beverage.
Dr. Rafiei notes that some participants with lower body weight also experienced large increases in saliva insulin after the meal. This pattern suggests they could face an increased risk of Type 2 diabetes even though they were not overweight and had normal blood glucose levels.
"The finding that some people who are lean have high insulin is intriguing," says Dr. Rafiei. "This indicates that saliva insulin may be more useful than measuring someone's weight or waist size."
Researchers also examined how saliva insulin levels related to waist circumference, body mass index (BMI), age, and sex. Among these factors, waist circumference showed the strongest relationship with saliva insulin levels.
"These findings suggest that waist circumference could be a more reliable indicator of hyperinsulinemia than age or overall body weight when using saliva insulin," he says. "Our results also suggest that saliva insulin may be better than blood glucose at distinguishing between those who are more metabolically healthy and those who are more likely to live with hyperinsulinemia."
Reference: "Saliva insulin concentration following ingestion of a standardized mixed meal tolerance test: influence of obesity status" by Hossein Rafiei and Jonathan Peter Little, 16 May 2025, Applied Physiology Nutrition and Metabolism.
DOI: 10.1139/apnm-2024-0532
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