Height.
I don't know. 1 egg (7 g) for breakfast, 2 oz chicken (15 g) for lunch, 3 oz beef (22.5 g) for dinner is 44.5 g protein. Because I also eat nuts once a day and some vegetables are a source of protein too, I'm exceeding the upper limit of my 27 - 45 g protein intake a day. When I first started the low carb diet, I didn't think I was getting enough protein!
Digging through my books, I found this in Chapter 6: Determine Your Personal Protein Threshold in Jimmy Moore's book, Keto Clarity (2014)...
"What can you do to determine your protein threshold? Ketogenic experts have varying opinions about what the ideal protein intake is. Many have guessed that 1 to 1.5 grams per kilogram of body weight is the right amount but this could bring on gluconeogenesis in many people. Dr. Ron Rosedale, and expert in nutritional and metabolic medicine, advises that those who want to be in ketosis consume 1 gram of protein per kilogram of ideal body weight (based on your body mass index; a good calculator is available online at http://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm) and then subtract 10 percent. Meanwhile on my Ask the Low-Carb Experts podcasts, renowned protein expert Dr. Donald Layman suggested limiting protein intake to no more than 30 gram per meal and no more than 140 grams per day. To figure out what amount of protein works best for you, though, there is no perfect formula. Just as with carbohydrates, it comes down to a process of trial and error.
I'm a pretty tall guy at six foot three, and I started out at around 120 grams of protein daily to see how I would do. When I wasn't seeing the ketone production and other health effects I was looking for, each week I dropped my daily protein intake by 10 grams, until I discovered that ketones started to increase to beneficial levels at about 80 grams of protein a day. Now that may not seem like very much protein--there are 6 grams of protein in just an egg, for example--but it is what I needed to do in order to produce ketones in my body. Moderating my protein intake turned out to be a critical factor in my success on a ketogenic diet."
What's interesting is that if I use the BMI calculator - (using above link) - my "normal" weight range is 108 to 145 pounds - (the higher weight is my current weight). I'm small boned, so 120 pounds might be a good weight for me. Following Rosedale's formula using ideal weight, not lean body mass weight, results in 49 grams protein a day - (120 lbs. = 54 kilograms; 54 kilograms - 10% = 49 grams protein per day) or 37 grams if using the 0.75 g per kilogram formula.
Volek and Phinney write in their book: "Current guidelines recommend 0.8 grams/day of protein per kilogram of body weight for adults, with more for children, adolescents, and pregnant women." Following that guideline, my protein intake would be 53 grams per day - (145 lbs. = 66 kg; 66 kg x 0.8 g = 53 kg).
Recommendations can be adjusted based on the person's activity level.
So I guess we're on our own to figure this out, though Rosedale's recommendation takes into consideration limiting protein intake to avoid activating mTor which can lead to the development of cancer.
After sampling different ideas about this, I think Jimmy Moore's idea of reducing protein intake daily until
"ketones started to increase to beneficial levels" is interesting for those who want to lose weight.