When calculating macros, protein is the most controversial macro of all. What follows is my recommendation and opinion. I expect that some people will argue that I am wrong to recommend an amount above the bare minimum. You should make your own decision. I have provided some links to support why I believe what I do.

While we recommend the keto-calculator for most new low-carb dieters, I believe the lower end of the protein range recommended by it is too low. The primary focus should be on the preservation of lean body mass, even in preference to deeper levels of ketosis. Even if losing weight is faster or easier with deeper levels of ketosis, it is counter productive to health if that weight loss comes with lean-body-mass losses beyond the minimum possible. In spite of this, it is completely possible to stay below the upper-limit recommended by the calculator while eating enough protein to ensure maximum preservation of lean-body-mass.

Let's take me, for example.

I am a 34.5 year old male, 163 cm (5'4") tall, weighing 72.5 kg (159.5 lbs), with a body fat somewhere between 18% and 24%. Yes, that is a wide range, but there are huge margins of error when trying to calculate body fat percentage. Based on the keto-calculator, I can go as low as 73-79g of protein a day. The maximum protein recommended would be between 121-131g a day. Is the minimum safe range below this amount?

First, let's start here: How Much Protein is Enough?

This is an article that tries to establish a minimum amount of protein for ketogenic diets. It's fairly well sourced. The article recommends 1.2g per kg (of IBW) for women and 1.4g per kg (of IBW) for men. My one issue with it is that the recommendation is in grams per "Ideal Body Weight." That's a rather nebulous measurement. I did find a calculator for this at http://www.calculator.net/ideal-weight-calculator.html. Based on that calculator my ideal weight ranges from 59.3 kg to 62.1 kg.

That calculation suggests that my minimum should be between 83-87g a day, as an absolute minimum. This is well below the maximum suggested by the calculator. Of course, I prefer a slightly safer number. Do we have an amount that's known to preserve muscle mass during weight loss?

The Myth of 1 g/lb: Optimal Protein Intake for Bodybuilders

We're not body builders, but there are two studies which concern us here. Those are the ones done on athletes losing weight.

Walberg et al. (1988) found that 0.73g/lb was sufficient to maintain positive nitrogen balance in cutting weightlifters over a 7 day time period.

So these guys were literally running on a 1000 calorie deficit while drastically increasing their training volume. [...] the protein intake of 0.82 g/lb in the other group completely protected the subjects from muscle loss.

Again, we're dealing with total body weight. These are athletes, so let's use the IBW number again. Why? Because it's probably lower than current goal weights or anything else. Heck, even if you use lean-body-mass numbers, you'll be safe here.

0.73g/lb = 95-100g
0.82g/lb = 107-112g

If I used LBM (55.1 kg - 59.5 kg), I would get 88-95g or 99-107g respectively.

So what are we left with? We're still well below the upper range suggested by the keto-calculator (121-131g). My recommendation, use the keto-calculator but choose a value in the middle of the range (something that results in 1.6-1.8 g/kg should be fine).

This is further supported by one of the links from the keto-calculator itself.

Protein Intake While Dieting

After much toing and froing and research had been done it was eventually found that a protein intake of about 1.5 g/kg of lean body mass (LBM; note that researchers actually used Ideal Body Weight but this is a rough proxy for LBM) was necessary to spare LBM losses in a non-training obese individual consuming low calories.

If 1.5 g/kg is necessary, than 1.6 g/kg should be a safe minimum and account for possible errors in calculating lean-body-mass. Despite linking to this article, the keto-calculator recommends a minimum of 1.3 g/kg. This is another reason to not select the minimum.

Now, it should also be noted that the maximum protein range is not set as the level beyond which we know ketosis is affected. It is set as the level beyond which we know even the most extreme athletes receive no further benefit from more protein. Not getting any further benefit is not the same as having a detrimental affect. In the same manner, eating below that amount is not a guarantee that we're not reducing the depth of ketosis. There's a lot we don't know about protein intake and how each individual reacts. It is up to each individual to determine what level of protein intake relative to ketogenic level they would like to maintain. I strongly encourage that you don't choose the minimum recommended by the keto-calculator, and certainly not an amount lower than that.

My personal recommendation would be to use a number around the middle of the range recommended by the keto-calculator as a safe and easy to get minimum.