Also quoted from the article linked:
On average, a person uses about 10% of their daily energy expenditure digesting and absorbing food, but this percentage changes depending on the type of food you eat.
Protein takes the most energy to digest (20-30% of total calories in protein eaten go to digesting it). Next is carbohydrates (5-10%) and then fats (0-3%).
So if I eat 200g of protein a day (which is not unusual for me, I’m heavy), that’s 800 kcal from protein, of which ~200 will be burned just digesting it. Someone on a low protein diet might eat 50g of protein, for a calorie content of 200 kcal, of which they would burn 50kcal in digestion. So a net difference of 150kcal burned in digestion compared to ingesting the calorie difference in fat (as an extreme example). So maybe a 5% difference in calories burned in digestion is a realistic difference between a high and low protein diet?