I often hear the question, “how much protein is best?” but that depends for whom. Different people have a different protein needs. A healthy man or woman seeking to build muscle has a different protein need than an older adult wanting to reduce the risk of sarcopenia (muscle loss) or someone simply wanting to prevent deficiency. The amount of protein someone needs depends on many factors, including whether a person is growing, pregnant or lactating (breastfeeding), or has been sick or just had surgery. Even for those who aren’t in these special circumstances, protein needs may be calculated to prevent deficiency, to sustain exercise or to preserve muscle mass in older adults, and each of these calculations are different.
Protein needs are calculated as grams of protein per kilogram of body weight of the person, and not as a percentage of daily calories (energy). As explained below, 40% of calories as protein may be safe for one person and be in excess for someone else. For this reason, protein must to be calculated as grams of protein per kilogram of body weight.
Basic Needs – the Recommended Daily Allowance (RDA) for Protein
The Recommended Daily Allowance (RDA) for any nutrient is the average daily dietary intake level that is sufficient to meet the needs of 97-98 % of healthy people. It is important to keep in mind that the RDA is not the optimal requirement, but the absolute minimum to prevent deficiency.
The RDA for protein for healthy adults is calculated at 0.8 g protein / kg of body weight . A sedentary 70 kg / 154 pound man needs a minimum of 56 g of protein and a sedentary 60 kg / 132 pound woman needs a minimum of 48 g protein per day.
Protein Needs for Active Healthy Adults
For those who are physically active, the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine recommend a protein intake of 1.2—2.0 g protein / kg per day to optimize recovery from training, and to promote the growth and maintenance of lean body mass.
Protein Needs for Older Adults
There have been several position statements issued by those that work with an aging population indicating that protein intake between 1.0 and 1.5 g protein / kg per day may best meet the needs of adults during aging [3,4].
For the average, healthy 70 kg / 154 pound sedentary man this would be daily protein intake of 70 -105 g per day and for the average, healthy 60 kg / 132 pound sedentary woman this would be a protein intake of 60-90 g protein per day.
Range of Safe Intake
As I wrote about in an earlier article, according to Dr. Donald Layman, PhD, Professor Emeritus, of Nutrition from the University of Illinois, the highest end of the range of safe intake of protein is 2.5 g protein/ kg per day.
For the average 70 kg / 154 pound sedentary man this would be a maximum daily protein intake of 175 g per day and for the average 60 kg / 132 pound sedentary woman, this would be a maximum protein intake of 150 g/ day.
Someone eating on occasion above their safe range is a different scenario than someone eating above or at the very high end of that range on a regular basis. The body has a flexible capacity to tolerate higher protein intake on occasion, but regularly eating too much protein can result in protein toxicity.
Maximum Amount of Protein the Body can Safely Process
[Special thanks to Richard Morris, research biochemist from Canberra, Australian for the information contained in this section.]
When protein is eaten, the body needs to get rid of the ammonia that results and this is done by turning the ammonia into urea and excreting it in the urine.
The disposal rate of ammonia isn’t able to be calculated because ammonia is literally given off by the lungs and skin, and tracer studies suggest that the disposal rate is higher than the rate that urea appears in urine. This means that there are probably several reservoirs for ammonia (such as urea building up in circulation before filtration in the kidneys) and this ‘elastic’ or flexible capacity for ammonia enables us to survive high protein days interspersed with low protein days.
The rate limit for maximal disposal of urea through urine is 0.53 g of N per kilo of 3/4 body weight, as a proxy for lean body mass. The ratio of molecular weights between a nitrogen atom and the average molecular weight of amino acids is a factor of 6.05x, so the effective rate limit for maximal disposal of urea through urine is .53 x 6.05 = 3.21 g of protein/kg lean body mass. If someone were to eat above that amount of protein for too long, they will have filled their ‘elastic’ (flexible) reservoirs with urea, and would then be at risk of ammonia intoxication.
This calculation for determining the maximum amount of protein based on urea clearance requires know a person’s energy consumption (in kcals / calories), as well as lean body mass (LBM). Note that this is lean body mass, not total body weight. Lean body mass is essentially one’s total body weight minus the amount of fat they have.
Lean body mass can be assessed using a DEXA scan, or estimated by using relative fat mass (RFM). The amount of fat someone has can be estimated from total body weight (taken on a scale), minus their estimated RFM as described in this article.
Once we know a person’s lean body mass, we can use the equation (3.21 g of protein / kg lean body mass) to determine the maximum amount of protein they can eat on an ongoing basis while being able to safely dispose of the ammonia via urea through urine.
Here are some examples of calculations;
A 100 kg man (220 pounds) with 20% body fat would have 80 kg lean mass, so would have a maximum protein ceiling of ~256g/day (based on the maximum amount of ammonia disposal of 3.21 g of protein / kg of lean body mass). Assuming his energy consumption is 2500 kcal/day, 256 g of protein is ~41% of total energy.
A 60 kg woman with 25% body fat, would have 45 kg of lean mass, so would have a maximum protein ceiling of 144 g/day. Assuming her energy consumption is 2000 kcal/day, 144 g of protein would be 29% of total energy as protein. The maximum amount of protein that this woman could regularly eat based on the disposal rate of ammonia in urea is only 29% of energy as protein.
Since the amount of protein one can eat is tied to the amount of lean body mass, what if this woman were leaner, say at the very lowest end of the body fat range? Could she eat 40% protein on an ongoing basis and excrete all the resulting ammonia as urea in her urine?
The same 60 kg woman at only 10% body fat would have 54 kg lean mass, with a maximum protein ceiling of 173 g protein / day. Assuming her energy consumption is the same 2000 kcal/day, 173 g pro/ day would be 35% of total energy as protein.
While this woman can safely have a higher percentage of energy as protein because she has more lean body mass, the maximum amount of protein based on disposal of ammonia is still only 35% of energy as protein.
It is important to note that 10% body fat for a woman is at the very low end of essential fat range and could result in amenorrhea (loss of menstrual cycles).
To know if a diet has adequate protein, one needs to ask ‘adequate for whom’. If you are an older adult trying to preserve muscle mass to avoid the increased risk of falls that comes with sarcopenia (loss of muscle mass) then your protein needs will be very different than if you just want to make sure your protein intake is adequate, or if you are about to train for a half-marathon.
When evaluating diets and whether they have adequate protein, they should at least meet the bare minimum requirements of the RDA. Then, ask yourself if the diet has enough protein to sustain someone who is physically active or enough for an older adult? Finally, make sure that the amount of protein is within the safe upper limit and does it exceed the maximum level of amount of protein based on the disposal of ammonia in urea in the urine.
If you are unsure how much protein you need, and how much and what type of fats and carbohydrate are most suitable for you, then please reach out for assistance.
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- National Academies Press, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (2005)
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance [published correction appears in Med Sci Sports Exerc. 2017 Jan;49(1):222]. Med Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852
- Fielding RA, Vellas B, Evans WJ, Bhasin S, et al, Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology, and consequences. International working group on sarcopenia. J Am Med Dir Assoc. 2011 May;12(4):249-56
- Bauer J1, Biolo G, Cederholm T, Cesari M, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013 Aug;14(8):542-59
- Rudman D, DiFulco TJ, Galambos JT, Smith RB 3rd, Salam AA, Warren WD. Maximal rates of excretion and synthesis of urea in normal and cirrhotic subjects. J Clin Invest. 1973;52(9):2241-2249. doi:10.1172/JCI107410
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