Will the COVID-19 pandemic decrease the FatMax?

to the editor: We read with interest the article of Frandsen et al. (6) concluding that maximal fat oxidation (MFO or FatMax) is not influenced by menstrual phase in young healthy women during exercise tests. However, physical activity (PA) seems to be positively associated with MFO, insisting on the central role of exercise intensity related to V̇o2max levels (2). Indeed, MFO is mediated by several factors, such as training status, exercise intensity and duration, sex, and nutritional intake (1). The sedentary lifestyle is a leading cause of evitable mortality, involving several types of cancer and numerous cardiometabolic diseases (10). The continuum between inactivity, overweight, and obesity is particularly well-known in post- industrialized countries where sedentary behavior, physical inactivity, and junk food are pandemic (4). Interestingly, the variation of DNA methylation in individuals exposed to different environments could explain the complex relation between epigenetic, genetic heritage, and exposome (5, 9, 11). During the past months, the world was forced to stay at home to avoid the spreading of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), involving more than 3 billion people in the adoption of a sedentary lifestyle (12). Increasing sitting activities and teleworking, the global quarantine has contributed to enhance the global inactivity of people. Evidence data has shown that inactivity deregulates lipid metabolism by the methylation of DNA related to epigenetic regulation (11). Thus, lipoprotein lipase (LPL) seems to be deregulated in skeleton muscles subjected to inactivity and long-time sitting, increasing the risk of death and cardiovascular disease (3, 7, 8). Considering the evidence that MFO is a regulator factor of lipid metabolism, it could be expected that inactivity related to a sedentary lifestyle decreased the MFO. Even if quarantine in the fight against COVID-19 is currently a necessity to avoid contagion, inactivity related to the COVID-19 pandemic will increase the metabolic risk of confined people, aggravating the accumulation of fat mass, insulin resistance, and metabolic syndrome in coming months. Further studies after the global quarantine of the COVID-19 outbreak will be needed to explore the complex relation between sedentary time and MFO.

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

AUTHOR CONTRIBUTIONS

F.D. and V.N. conceived research; V.N. analyzed data; F.D., Y.E., and V.N. drafted manuscript; F.D. and V.N. edited and revised manuscript; F.D., Y.E., and V.N. approved final version of manuscript.