How much protein do I need per day?

The spread is not disagreement between experts so much as four answers to four different questions. An RDA is the intake judged sufficient to meet the requirement of nearly all healthy adults - a floor for adequacy, deliberately set above the median requirement so that almost nobody falls short. It was never proposed as an optimum.

The sports-nutrition figures address a different goal. The joint position statement from the Academy of Nutrition and Dietetics, Dietitians of Canada and ACSM puts athlete intakes generally at 1.2 to 2.0 g per kg per day. The ISSN's 2017 position stand states that 1.4 to 2.0 g/kg is sufficient for most exercising individuals to build and maintain muscle mass, and notes higher intakes during energy restriction.

PROT-AGE addresses age: at least 1.0 to 1.2 g/kg per day for healthy people over 65, more for those who are active, and 1.2 to 1.5 where acute or chronic illness is involved. The same paper names kidney disease as the case where intake stops being a calculator question and becomes a clinical one.

For per-meal figures the ISSN publishes 0.25 g per kg of body weight, or an absolute 20 to 40 g, ideally distributed every three to four hours. And for context on the upper end: the IOM's own AMDR allows protein anywhere from 10 to 35 percent of total energy, which at 2,500 kcal a day is 63 to 219 g. The full table by body weight is on how much protein per day.