本文以「肥胖（症）」議題為具體的現象，進而考察社會建構論、批判實在論與ANT三種取向，在身體與社會的關係、存有論觀點問題上的差異。本文以Crossley於2004年發表的〈肥胖是一個社會學議題〉文章作為批判實在論的肥胖研究代表，分析此文所提的「肥胖是社會事實」、「能量比科學」問題，並從社會建構論取向進行兩派的分析。辯論指出，批判實在論將肥胖症與能量比視為獨立於社會文化之外的「生物事實」，而社會建構論卻直指了「肥胖作為疾病」本身牽涉到特定社會群體的利益與醫療化的結果。社會建構論的問題，是將文化、論述（或語言）視為真正的「行動者」；批判實在論卻容易忽略身體與科學知識之社會建構性。本文最後以ANT的視角指出，「能量比的科學」與「肥胖身體」，應該於知識生產脈絡與行動者的異質網絡中進行檢視。肥胖身體是透過促成、展演而轉為「事實」與特定的存有。本文最後指出，三種取向的比較分析讓我們看到更多異質知識與政治介入的可能性。

By exploring the sociological issue of fatness/obesity, the author compares three different approaches-social constructionism, critical realism, and actor-network theory (ANT)-to analyze relationships and ontological differences between body and society. Crossley's (2004) article, ”Fat Is a Sociological Issue,” is analyzed in terms of the concept of energy ratios and 'obesity as a social fact.' It is argued that critical realism locates obese bodies and energy ratios as biological facts existing outside of socio-cultural contexts. In contrast, social constructionists approach obesity as a medical issue, an approach that is criticized as an example of a discourse replacing the actor. However, the realists' approach is also criticized as ignoring the construction of scientific knowledge. Based on the ANT ontology, I argue that the concept of energy ratio should be reexamined in terms of knowledge production and heterogeneous networks. I conclude that analyses involving the three approaches provide greater space for heterogeneous knowledge and socio-political interventions.