Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7001, Australia.
Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T1Z4.
J Exp Biol. 2024 Apr 1;227(7). doi: 10.1242/jeb.246722. Epub 2024 Mar 27.
The physiological processes underlying the post-prandial rise in metabolic rate, most commonly known as the 'specific dynamic action' (SDA), remain debated and controversial. This Commentary examines the SDA response from two opposing hypotheses: (i) the classic interpretation, where the SDA represents the energy cost of digestion, versus (ii) the alternative view that much of the SDA represents the energy cost of growth. The traditional viewpoint implies that individuals with a reduced SDA should grow faster given the same caloric intake, but experimental evidence for this effect remains scarce and inconclusive. Alternatively, we suggest that the SDA reflects an organism's efficacy in allocating the ingested food to growth, emphasising the role of post-absorptive processes, particularly protein synthesis. Although both viewpoints recognise the trade-offs in energy allocation and the dynamic nature of energy distribution among physiological processes, we argue that equating the SDA with 'the energy cost of digestion' oversimplifies the complexities of energy use in relation to the SDA and growth. In many instances, a reduced SDA may reflect diminished nutrient absorption (e.g. due to lower digestive efficiency) rather than increased 'free' energy available for somatic growth. Considering these perspectives, we summarise evidence both for and against the opposing hypotheses with a focus on ectothermic vertebrates. We conclude by presenting a number of future directions for experiments that may clarify what the SDA is, and what it is not.
进食后代谢率升高的生理过程，通常被称为“特殊动力作用”（SDA），其背后的机制仍存在争议。本文从两个对立的假说角度来探讨 SDA 反应：（i）经典解释，即 SDA 代表消化的能量成本，与（ii）替代观点，即 SDA 的很大一部分代表生长的能量成本。传统观点认为，在相同的热量摄入下，SDA 降低的个体应该生长得更快，但这种效应的实验证据仍然稀缺且不确定。或者，我们认为 SDA 反映了生物体将摄入的食物分配到生长中的效率，强调了吸收后过程的作用，特别是蛋白质合成。尽管这两种观点都认识到能量分配的权衡和能量在生理过程中的动态分布，但我们认为将 SDA 等同于“消化的能量成本”过于简化了与 SDA 和生长相关的能量利用的复杂性。在许多情况下，SDA 降低可能反映了营养物质吸收减少（例如由于消化效率降低），而不是用于体生长的“自由”能量增加。考虑到这些观点，我们总结了支持和反对这两种对立假说的证据，重点是变温脊椎动物。最后，我们提出了一些未来实验的方向，这些实验可能会阐明 SDA 是什么，以及它不是什么。
