Medical Bulletin 26/ April/ 2024

A recent Sports Medicine – Open study conducted a randomized controlled trial to evaluate how varying carbohydrate intake and the glycemic index (GI) impact performance in endurance training regimens in men.

Carbohydrates are vital for endurance exercise performance, requiring optimal metabolic flexibility and glycogen stores. Muscles transition from fats to carbohydrates for ATP production as exercise intensity rises. High-carbohydrate diets with low glycemic index enhance metabolic flexibility and boost performance.

The 10-week study aimed to assess and compare the effects of the low carbohydrates and high fat diet on metabolic parameters, running economy (RE), peak running speed (PRS), and peak oxygen consumption. These parameters were assessed by measuring muscle energy stores, a five-kilometer time trial (TT) performance, and a graded exercise test.

The results revealed that the LOW-GI diet led to reduced energy intake, decreased blood lactate concentrations during exercise, higher values in the graded exercise test, maintenance of glycogen stores, and improved TT performance.Further, HIGH-GI improved performance at high intensities and increased muscle glycogen content. However, after 10 weeks, fat oxidation was impaired.

The findings suggested that relative to the LCHF or HIGH-GI diet, the LOW-GI diet could lead to beneficial changes in substrate oxidation during extended periods of exercise and improve endurance performance.

Reference: Moitzi, A. M., Krssak, M., Klepochova, R., et al. (2024) Effects of a 10-Week Exercise and Nutritional Intervention with Variable Dietary Carbohydrates and Glycaemic Indices on Substrate Metabolism, Glycogen Storage, and Endurance Performance in Men: A Randomized Controlled Trial. Sports Medicine - Open 10 ; 1-18. doi:10.1186/s40798-024-00705-9

A new study led by researchers in the Penn State College of Health and Human Development examined how a person's telomeres, sections of genetic bases that function like protective caps at the ends of chromosomes -were affected by caloric restriction.

The study was published in the journal Aging Cell.

Telomeres shorten with each cell replication, eventually leading to loss of the protective cap. This can result in damaged genetic information and impaired cell function or reproduction.

Longer telomeres indicate a younger cell compared to shorter telomeres. Thus, individuals of the same age may have different biological ages based on telomere length.

In the study, the researchers tested the telomere length of 175 research participants using data from the start of the CALERIE study, one year into the study and the end of the study after 24 months of caloric restriction.

The results showed that participants initially on caloric restriction lost weight and telomeres more rapidly than the control group in the first year. However, after stabilization of weight, caloric restriction slowed telomere loss compared to the control group in the second year. Ultimately, after two years, the telomere lengths of both groups were statistically similar.

"There are many reasons why caloric restriction may extend human lifespans, and the topic is still being studied. One primary mechanism through which life is extended relates to metabolism in a cell. When energy is consumed within a cell, waste products from that process cause oxidative stress that can damage DNA and otherwise break down the cell. When a person's cells consume less energy due to caloric restriction, however, there are fewer waste products, and the cell does not break down as quickly”

said Waylon Hastings, lead author of this study.

“This research shows the complexity of how caloric restriction affects telomere loss. We hypothesized that telomere loss would be slower among people on caloric restriction. Instead, we found that people on caloric restriction lost telomeres more rapidly at first and then more slowly after their weight stabilized"

Reference: Hastings, W. J., et al. (2024). Effect of long‐term caloric restriction on telomere length in healthy adults: CALERIETM 2 trial analysis. Aging Cell. doi.org/10.1111/acel.14149.

A study published in the journal The BMJ found that the lifetime risk of atrial fibrillation - a heart condition that causes an irregular and often abnormally fast heart rate - has increased from one in four to one in three over the past two decades.

Approximately 33.5 million people worldwide are affected by atrial fibrillation each year.

Atrial fibrillation (AF) can lead to various heart problems due to its irregular and rapid heart rate. It increases the risk of blood clots forming in the atria, which can result in strokes. The irregular rhythm can weaken the heart muscle over time, leading to heart failure and cardiomyopathy.

In the study, Researchers analyzed national data from 3.5 million Danish adults aged 45 or older with no prior history of atrial fibrillation over a 23-year period to determine AF development. They followed 362,721 individuals newly diagnosed with AF, without prior complications, until a diagnosis of heart failure, stroke, or heart attack. Factors like high blood pressure, diabetes, high cholesterol, heart failure, lung and kidney disease were considered.

The results revealed a rise in lifetime atrial fibrillation risk from 24% (2000-2010) to 31% (2011-2022), with men and those with heart issues experiencing larger increases. Heart failure was the most common complication (41% lifetime risk), followed by stroke (21%) and heart attack (12%). Men had higher risks of heart failure (44% vs. 33%) and heart attack (12% vs. 10%) than women, while stroke risk was slightly lower in men (21% vs. 23%). However, there was minimal improvement in heart failure risk and only slight decreases in stroke and heart attack risks over the study period.

“Our novel quantification of the long term downstream consequences of atrial fibrillation highlights the critical need for treatments to further decrease stroke risk as well as for heart failure prevention strategies among patients with atrial fibrillation”

said the study authors.

Reference: Nicklas Vinter, Pia Cordsen, Søren Paaske Johnsen, et al; Temporal trends in lifetime risks of atrial fibrillation and its complications between 2000 and 2022: Danish, nationwide, population based cohort study; The BMJ; https://doi.org/10.1136/bmj-2023-077209