We have performed a number of studies indicating that most healthy humans maintain lean body mass and function during a ketogenic diet providing between 1.5 and 1.75 grams of protein per kg of ‘reference body weight’* (Phinney 1983, Davis 1990).
*Reference body weight is an arbitrary value for men and women based upon the medium frame values from the 1959 Metropolitan Life Insurance ‘Ideal Body Weight’ tables. (Met Life, 1959) Using these values allows for protein intakes to be based roughly on normal lean body mass rather than total body weight. Note: ‘reference weight’ is an arbitrary value used to estimate daily protein needs—it is not a weight
But in no case should dietary protein intake be reduced below 1.2 g/kg in the context of a well-formulated ketogenic diet. This range; 1.2 g/kg at the low end and 2.0 g/kg at the upper end, with a 1.5 g/kg mid-range moderate intake target, can be translated into daily consumption of protein-rich foods in ounces in the table below. Each ounce of protein-containing food contains about 7 grams of protein.
Read more on protein requirements here: https://blog.virtahealth.com/how-much-protein-on-keto/
Dr. Phinney on protein: