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Global Translational Medicine Letter to editor

when applied rigidly, have limitations. For example, they about 1 kg of fat gain over 28 days – approximately four
often fail to predict how macronutrient composition (e.g., times less than the theoretical prediction of 4 kg. These
3
low-carbohydrate or high-protein diets) affects energy findings highlight the dynamic and adaptive nature of
expenditure, fat oxidation, and storage efficiency. This metabolism, demonstrating that neither mass balance
limitation underscores the need for a more integrative nor energy balance models alone can fully capture the
approach. complexities of weight regulation.
The interdependence between nutrient mass (mass By combining mass balance for nutrient flow and energy
balance) and energy content (energy balance) becomes balance for metabolic regulation, a robust framework for
particularly evident when considering how they interact understanding obesity can emerge. Such a framework
to regulate body weight. While nutrient mass determines acknowledges that while nutrient mass determines physical
the physical input and output of body weight, the energy weight change, the energy derived from these nutrients
derived from this mass dictates how it is processed, stored, governs the metabolic pathways that dictate their ultimate
or excreted. For instance, 1 g of carbohydrate or protein fate – storage, oxidation, or excretion.
provides approximately 4 kcal, whereas 1 g of fat provides In conclusion, the manuscript provides valuable insights
9 kcal. These differences in caloric density illustrate why into the role of nutrient mass in obesity but would benefit
equal masses of macronutrients can lead to vastly different from a more nuanced discussion of the interplay between
metabolic outcomes. mass and energy. Recognizing their interdependence could
A caloric surplus of 500 kcal/day would theoretically help bridge the gap between traditional energy-centric
result in a fat gain of approximately 65 g/day, or about 2 kg approaches and emerging mass-focused paradigms, fostering
over a month. This estimate is based on the energy density a deeper understanding of obesity and its management.
of body fat, where 1 g of fat tissue corresponds to roughly Addressing these aspects would strengthen the manuscript’s
7.7 kcal (accounting for water and other components). scientific rigor and enhance its practical relevance.
However, this calculation assumes no compensatory
metabolic adjustments and that all surplus energy is stored Conflict of interest
as fat with 100% efficiency. In reality, the process is far The author declares no conflict of interest.
more complex and influenced by various factors. Notably,
some of the surplus energy may contribute to lean mass References
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Volume 4 Issue 1 (2025) 143 doi: 10.36922/gtm.8079