An 8 ounce banana has 200 calories and 51 grams of carbohydrate. An equivalent serving of vanilla ice cream has 38 g of carbs, slightly more calories and a buttload more protein. Lower fat, but that difference will be offset by whatever fat is added by the nut butter, not inconsequential.
Given that excess carbs and high glycemic index of ingredients are thought to be the prime contributors to abdominal fat deposition, NOT necessarily dietary fat, I'd bet the difference between this recipe and a bowl of real ice cream is negligible.

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