High fat mass in adolescence causes insulin resistance, which can lead to a “vicious cycle” of worsening insulin resistance and obesity by young adulthood and increased risk of type 2 diabetes.

These findings come from a study conducted in collaboration between University of Exeter, University of Bristol, Université de Montréal in Canada, University of Bern in Switzerland, Aarhus University in Denmark, and the University of Eastern Finland. The results are published in the Journal of Clinical Endocrinology and Metabolism.

Dr Andrew Agbaje from the University of Exeter led the study and said: “This is the first long-term evidence of the morbid danger of high total body and abdominal fat in the young population, with abdominal fat twice as dangerous as total body fat. To observe a vicious cycle of fat mass and insulin resistance between the ages of 17 and 24 years is extremely disheartening. Fat mass contributes 75-percent to the fat mass-insulin resistance vicious cycle, while insulin resistance contributes 25-percent. Therefore, preventing weight gain is the best way to break this cycle.”

Childhood and adolescent obesity is a global epidemic. Estimated by body mass index (BMI), obesity has been associated with several cardiovascular, neurological, and musculoskeletal diseases – as well as type 2 diabetes in adulthood. However, BMI is a poor measure of obesity in childhood and adolescence since it does not distinguish between muscle mass and fat mass.

Insulin resistance occurs when body cells fail to take up glucose from the blood in spite of a normal amount of insulin production, leading to overproduction of insulin called hyperinsulinemia. Insulin resistance is a precursor of type 2 diabetes already in youth, but long-term studies relating total body fat mass, abdominal fat, and muscle mass with the risk of insulin resistance in a large population of young people are lacking.

This new study used data from the University of Bristol’s Children of the 90’s cohort, also known as the Avon Longitudinal Study of Parents and Children. Altogether 3,160 adolescents – 1,546 males and 1,614 females – were included in the analysis. The adolescents were 15 years old at baseline and were followed up for nine years until young adulthood at age 24. Total body fat mass, abdominal fat, and muscle mass were measured with dual-energy X-Ray absorptiometry at age 15 and repeated at the ages of 17 and 24. Similarly, fasting glucose and insulin were measured from blood samples taken at ages 15, 17, and 24, and insulin resistance was calculated.

With extensive control for inflammation, lipids, blood pressure, smoking status, sedentary time, physical activity, socio-economic status, and family history of cardiovascular disease, it was observed that each 1kg cumulative increase in total body fat mass from mid-adolescence through young adulthood increased the risk of excessive blood glucose (hyperglycaemia) by four percent, abnormally high insulin level (hyperinsulinemia) by nine percent, and insulin resistance by 12-percent.

Each 1kg increase in abdominal fat had even more pronounced effects, increasing the risk of hyperglycaemia by seven percent, hyperinsulinemia by 13-percent, and insulin resistance by 21-percent. However, each 1kg increase in muscle mass reduced the risk of both hyperinsulinemia and insulin resistance by two percent.

It was also found that a high amount of total body fat mass at age 15 caused high insulin resistance by the age of 17. A high amount of body fat mass at age 17 caused high insulin resistance at age 24 years, and, simultaneously, high insulin resistance at age 17 caused high total body fat mass at age 24 years. This results in a vicious cycle which was consistent in both males and females, regardless of BMI.

Dr Agbaje continued: “However, there is good news – we recently established that sedentary time contributes 10-percent to the total body fat mass gained in youth years, which can be completely reversed by three to four hours a day of light physical activity. Although the increase in muscle mass lowers insulin resistance only by a small amount, its protective effect when combined with light exercise may be critical to reducing the risk of type 2 diabetes. This is why teenagers should be encouraged to take up light physical activity.”

This is something Dr Agbaje discussed on a recent podcast interview about the benefit of light exercise.

DEXA-based Fat Mass with the Risk of Worsening Insulin Resistance in Adolescents: A 9-Year Temporal and Mediation Studywas published in the Journal of Clinical Endocrinology and Metabolism.

Dr Agbaje’s research group (urFIT-child) is supported by research grants from Jenny and Antti Wihuri Foundation, the Finnish Cultural Foundation Central Fund, the Finnish Cultural Foundation North Savo Regional Fund, the Orion Research Foundation, the Aarne Koskelo Foundation, the Antti and Tyyne Soininen Foundation, the Paulo Foundation, the Yrjö Jahnsson Foundation, the Paavo Nurmi Foundation, the Finnish Foundation for Cardiovascular Research, Ida Montin Foundation, Kuopio University Foundation, the Foundation for Pediatric Research, and Alfred Kordelin Foundation.