The fat body and the sporting body are conventionally understood as mutually exclusive, coming together only in sport-based weight-loss interventions. However, the sport of marathon swimming relies upon body fat as a performance advantage, and weight maintenance and gain are a common element of the training process. The concept of ‘heroic fatness’ offers (some) swimmers a means of negotiating this anomalous sporting embodiment, positioning swimming fat as an undesirable necessity, nobly, but provisionally, borne. The paper argues that this construction is made possible through the construction of swimming fat as fake and as separate from the self. However, the paper unsettles this ideal-type of heroic fatness through the identification of the exclusions upon which it relies, both in terms of gender, and in relation to those who are already fat at the start of training. This opens up the possibility of more ambivalent modes of fatness that run counter to both heroic fatness and its unheroic counterpart – the very ‘real’ fatness that is the target of instrumentalist sport-based weight-loss interventions.