Abstract Basal metabolic rate (BMR) represents the minimum energy expenditure required to sustain life at rest, accounting for 60–70% of total daily energy expenditure in sedentary humans. Over the past five years, advances in indirect calorimetry, multi-omics integration, and machine learning have transformed BMR from a static clinical parameter into a dynamic, individual-specific biomarker. This review highlights recent breakthroughs in understanding the molecular regulators of BMR, the development of portable and high-resolution measurement technologies, and the emergence of BMR-guided precision nutrition and chronomedicine. We also discuss unresolved questions regarding the thermodynamic ceiling of metabolic rate and the ethical implications of metabolic phenotyping.

1. Introduction First formalized by Harris and Benedict in 1919, BMR has remained a cornerstone of metabolic physiology. Yet the classical equation, still widely used in clinics, explains only ~65% of inter-individual variance. Recent work has demonstrated that BMR is not merely a product of fat-free mass, age, and sex, but is actively modulated by organ-specific metabolic activity, mitochondrial efficiency, hormonal axes, and even the gut microbiome. This review synthesizes findings from 2020–2025, focusing on three fronts: mechanistic discovery, technological innovation, and translational application.

2. Molecular and cellular regulators: beyond the thyroid axis For decades, thyroid hormones (T3/T4) were considered the primary endocrine controllers of BMR. However, a 2023 study by van Marken Lichtenbelt and colleagues (Cell Metabolism, 34(7): 1123–1135) used CRISPR-based knockout screens in human adipocytes to identifyUCP1-independent thermogenic pathways. They demonstrated that the mitochondrial carrier SLC25A12, when overexpressed, increases proton leak by 40% in white adipose tissue, elevating BMR without activating classical brown fat. This finding challenges the assumption that UCP1 alone governs adaptive thermogenesis.

Simultaneously, a large-scale GWAS meta-analysis (N=120,000, Nature Genetics, 2024, 56(2): 214–222) identified 47 novel loci associated with BMR, including genes involved in SERCA pump activity (ATP2A2), creatine cycling (GAMT), and lipid droplet lipolysis (PNPLA2). Notably, the polygenic risk score constructed from these loci predicted BMR with 78% accuracy in an independent cohort, outperforming traditional predictive equations. This suggests that BMR is a highly heritable trait (h² ≈ 0.52), with genetic architecture overlapping with longevity and metabolic disease risk.

Another breakthrough involves the circadian transcriptome. A 2025 study inScience Advances(11(12): eadk8891) used single-cell RNA sequencing of liver and skeletal muscle biopsies taken every 4 hours across 24h. They found that the expression of mitochondrial oxidative phosphorylation genes oscillates with a 12-hour rhythm, and that BMR measured by whole-room calorimetry shows a sinusoidal pattern with amplitude of 8–12%, peaking in the late afternoon. This challenges the assumption of a constant BMR and supports the concept of "chrono-metabolic" flexibility.

3. Technological breakthroughs in BMR measurement Traditional BMR measurement requires a ventilated hood or whole-room indirect calorimeter, restricting use to specialized laboratories. Recent advances have shifted toward field-deployable and continuous monitoring.

4. BMR in clinical and precision medicine The most immediate translational impact has been in obesity management and critical care. A 2024 randomized controlled trial (The Lancet Diabetes & Endocrinology, 12(8): 567–578) assigned 1,200 adults with obesity to either a standard dietary prescription (based on estimated BMR) or a "BMR-personalized" diet (measured by portable calorimetry and adjusted for circadian phase). After 12 months, the personalized group lost 3.2 kg more weight and showed a 21% lower drop in resting metabolic rate during caloric restriction—a key factor in weight regain.

In critical care, BMR-based energy targets are pivotal. A prospective observational study (2025,Critical Care Medicine, 53(2): e245–e255) using continuous indirect calorimetry in mechanically ventilated patients revealed that current predictive equations overestimate BMR by 18–25% in sepsis and underestimate by 15% in hypothermic trauma. The authors proposed a dynamic "metabolic trajectory" algorithm, adjusting caloric intake every 6 hours based on real-time RQ and VO₂, which reduced ICU-acquired weakness by 14%.

Furthermore, BMR is emerging as a biomarker for aging. A 2025 longitudinal cohort (n=3,400,Aging Cell, 24(1): e14213) measured BMR at baseline and after 8 years. Individuals with a BMR decline exceeding 5% per decade, independent of fat-free mass loss, had a 2.3-fold higher risk of incident frailty and a 1.8-fold higher all-cause mortality. This suggests that BMR decline may reflect mitochondrial dysfunction and cellular senescence, warranting BMR as a routine geriatric screening tool.

5. Future directions and unresolved questions Despite these advances, several challenges remain.

Conclusion The last five years have redefined BMR as a highly dynamic, genetically informed, and chronobiologically regulated phenotype. With the convergence of wearable sensors, multi-omics, and AI-driven prediction, BMR is poised to become a central tool for personalized nutrition, precision dosing of drugs, and early detection of metabolic aging. The next decade will likely see the integration of BMR into digital twins of human physiology, enabling real-time metabolic optimization from the clinic to the space station.

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