The carbon in food is not captured or emitted in any coherent sense here. The crops are grown (capturing the carbon in the first place) for the purpose of feeding people -- in the same way that modern American forestry for paper is functionally carbon neutral (ignoring transport and processing) because the trees are in equilibrium. The counterfactual of not eating the food results in fewer crops and basically the same atmospheric carbon dioxide.

Edit: if you only mean food transportation carbon, it seems impossible bananas are literally optimal per calorie.