The end of the Soviet era and the restoration of Estonia's independence significantly reshaped people's life experiences. These social changes also affected young people's physiology. "A person's core health and physiological indicators largely depend on what they themselves do and how they behave," explained Jaanus Harro, a professor of psychophysiology at the University of Tartu and co-author of the study.

"A person's actions and behavior, in turn, may depend on what is happening in society at large and when society changes, people's behavior often changes as well," Harro added. An effort to determine the extent of that impact led to the new research. The scientists used data from a study of Estonian children launched in 1998, comparing young people born in the early and late 1980s. The average age gap between the groups was just six years.

According to Harro, the study sample was exceptionally representative. Using a randomization algorithm, researchers selected 25 schools in the city and county of Tartu and invited all ninth- and third-grade students to participate. About 80 percent of those invited took part. To accurately assess diet, all participants kept food diaries and completed follow-up interviews. "The fact that the sample is nearly complete and very few were left out gives a unique opportunity to compare birth cohorts," Harro emphasized.

Doctoral student Urmeli Katus and nutrition specialist Inga Villa began analyzing the data. Initially, they examined the impact of gene variants on body composition. Soon, however, they identified an unexpected metabolic difference. The differences emerged in areas the researchers had not planned to examine: body composition and glucose metabolism.

Compared with the older group, the younger group consumed fewer carbohydrates. They also had a lower body fat percentage. Nevertheless, their metabolism behaved differently. "Toward the end of adolescence, at age 18, glucose levels were significantly higher in the younger cohort, which actually consumed fewer carbohydrates," Harro said.

The metabolic picture changed as participants grew older. "The difference disappeared by age 25, but then it emerged that the younger cohort had higher insulin levels, which could, of course, reduce glucose levels," the researcher said. Doctors took blood samples in the morning on an empty stomach. The results therefore reflected the body's general baseline state rather than an immediate response to food. "So it is not only what people eat that has changed; their metabolic response has also changed to some extent," Harro concluded.

The changes reflect the body's complex adaptation processes. The human body always strives to maintain internal balance. Harro explained: "Over the course of evolution, our bodies have developed into fantastic homeostatic systems that respond to changes in the external environment in order to keep the internal environment relatively stable." Health is thus determined by the close interplay between genes and the environment. The same gene variants can produce opposite outcomes under different living conditions.

Metabolism plays a critical role in coping with stress. Animal studies show a clear link between metabolism and stress. "How organisms respond to stress appears to depend on the nature of their carbohydrate metabolism," Harro said.

Reaching precise causal conclusions will take more time. Current statistical approaches tend to treat everyone as the same. "In my view, we have not made very much progress in mapping causal relationships, partly because we handle our statistical data analyses as if all people were the same," Harro acknowledged. In practice, however, people have different metabolic types and adaptive pathways.

The study was published in the journal Nutrition, Metabolism and Cardiovascular Diseases.

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