“On average, a person spends about 10% of a meal’s total energy on TEF (thermic effect of food), but this varies considerably, depending on the composition of the meal. As the percentage of dietary carbohydrate
increases, the number of calories given off as body heat after a meal
increases. In contrast, as the fat in the diet increases, heat production
declines.”

Reed, GW and Hill, Jo. Measuring the Thermic Effects of Food, American
Journal of Clinical Nutrition, 63w 1996, pp 164 – 169

And there was me thinking it was just because I’d lost a thick layer of
insulating lard.

Zan