Protein is one of the 3 macronutrients (well, 4 if you count alcohol).
It is required for: (this list is not exhaustive)
muscle building - actin and myosin
growth, development and transportation of nutrients via lipoproteins and cellular protein receptors
metabolic reactions through enzymes which are made up of protein components
cellular/tissue repair and regeneration
wound healing - specifically arginine and glutamine
blood clotting - the branched chain amino acids, leucine, isoleucine and valine
hormone production/function - insulin, glucagon, HGH, etc.
cellular/organ structure - elastin, keratin and collagen
hydration status and electrolyte balance - albumin and globulin
immune health - antigens and antibody production
source of energy at 4 calories per gram
Proteins are made up of an amino group, a side chain and a carboxyl group which form what's called an amino acid.
Amino acids can be linked together through peptide bonds to form various structures called primary, secondary, tertiary and quaternary structures.
There are 20 different amino acids, 9 of them being essential which means we must obtain them in our diet because our bodies can't synthesize them through chemical reactions.
The big question is EXACTLY HOW MUCH PROTEIN DO YOU NEED DAILY?
The best answer I can give is it depends... and the best target protein intake for you can be determined by a registered dietitian like myself or a qualified nutrition professional.
When I calculate protein intake for a client or patient here's what I factor into that equation: BMI, age, gender, previous dieting history, activity level, comorbid conditions, hydration habits, kidney health and fitness/physique goals.
But for those of you that just want the numbers and the science, here's the best information I found from the ISSN for healthy, exercising individuals:
The International Society of Sports Nutrition (ISSN) provides an objective and critical review related to the intake of protein for healthy, exercising individuals. Based on the current available literature, the position of the Society is as follows:
An acute exercise stimulus, particularly resistance exercise, and protein ingestion both stimulate muscle protein synthesis (MPS) and are synergistic when protein consumption occurs before or after resistance exercise.
For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day (g/kg/d) is sufficient for most exercising individuals, a value that falls in line within the Acceptable Macronutrient Distribution Range published by the Institute of Medicine for protein.
Higher protein intakes (2.3–3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods. (my personal opinion: protein intake at this ratio can get very high depending on the individual and I would not recommend using this ratio unless you're working with a nutritional professional).
There is novel evidence that suggests higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals (i.e., promote loss of fat mass).
Recommendations regarding the optimal protein intake per serving for athletes to maximize MPS are mixed and are dependent upon age and recent resistance exercise stimuli. General recommendations are 0.25 g of a high-quality protein per kg of body weight, or an absolute dose of 20–40 g.
Acute protein doses should strive to contain 700–3000 mg of leucine and/or a higher relative leucine content, in addition to a balanced array of the essential amino acids (EAAs).
These protein doses should ideally be evenly distributed, every 3–4 h, across the day.
The optimal time period during which to ingest protein is likely a matter of individual tolerance, since benefits are derived from pre- or post-workout ingestion; however, the anabolic effect of exercise is long-lasting (at least 24 h), but likely diminishes with increasing time post-exercise.
While it is possible for physically active individuals to obtain their daily protein requirements through the consumption of whole foods, supplementation is a practical way of ensuring intake of adequate protein quality and quantity, while minimizing caloric intake, particularly for athletes who typically complete high volumes of training.
Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS.
Athletes should consider focusing on whole food sources of protein that contain all of the EAAs as they are required to stimulate MPS.
Pre-sleep casein protein intake (30–40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis.
But what do studies say about protein intake and kidney health?!
We place a demand on our kidneys with everything really! And protein is definitely something to consider when is comes to managing our kidney health. This is typically something we don't worry about when we are younger but it's important to understand that "high dietary protein intake can cause intraglomerular hypertension, which may result in kidney hyperfiltration, glomerular injury, and proteinuria." - JASN August 2020.
When our bodies metabolize protein, one byproduct is urea and is measured as blood urea nitrogen (BUN). "High circulating BUN levels, by enhancing protein carbamylation and generating reactive oxygen species, lead to increased oxidative stress, inflammation, endothelial dysfunction, and cardiovascular disease." However, BUN levels can also be influenced by hydration status so it's important for medical professionals to look at the whole picture when assessing kidney health in relation to protein intake.
If you look at this chart summary, you'll see how variable the outcomes are in prospective and observational cohorts when looking at protein intake on kidney health. It looks like you could conclude what this following study found:
A 2021 study done in The American Journal of Clinical Nutrition looked at high protein intakes and how it affected kidney function.
In those with compromised kidney function:
A lower dietary protein intake (0.6 - 1.0 kg actual body weight per day) was not associated with mortality.
A dietary protein intake of ≥ 1.4 g/kg actual body weight per day was associated with higher mortality.
In those with normal kidney kidney function:
A low dietary protein intake of <0.6 g/kg actual body weight per day was associated with higher mortality.
Higher dietary protein intake of upwards of 1.4 g/kg actual body weight per day was not associated with death.
Basically.... if you have compromised kidney function, which is classified as having a low GFR (glomerular filtration rate), then you should restrict your protein and how much depends on what your GFR is. Your GFR is a measure of how well your kidneys filtration works.
And for those with healthy kidneys, a higher protein diet (one above 0.6 g/kg actual body weight and upwards of 1.4g/kg) was not associated with mortality risk, meaning its generally safe.
Another study done in Advances in Nutrition found that "in the short term, higher protein intake within the range of recommended intakes for protein is consistent with normal kidney function in healthy individuals." Granted the study population was n=26 which is very small but this does support the previous study in saying higher protein intake for healthy individuals is generally safe in the short-term.
What do I use as a clinical dietitian?
The RDA and WHO recommend a minimum requirement of 0.8 g/kg of body weight per day or 10-35% of your daily calories coming from protein.
The most common range I use in a clinical setting is 1.0 - 1.2 g/kg for general population adults regardless of age and 1.2 - 1.5 g/kg for those with increased needs.
The most common range I use with lifestyle clients is 1.5 - 2.0 g/kg. These clients usually are weight training 3-4 times per week and either have a daily step goal or are doing intentional cardio for caloric deficit purposes.
My thoughts on BCAA supplementation: This supplement is overly used and overly marketed as something you can use to simply flavor your water! But, it's not needed if you are meeting your personal protein needs.
My thoughts on protein supplements/powders: These can be helpful for someone who struggles to meet their personal protein requirements. I typically reach for vegan proteins because most of the time the ingredients are better and it's easier on your digestive system. My personal favs:
1UP Nutrition Vegan Protein - code BUFFBUNNY saves you $$
I hope this article was helpful and insightful for you!
If you are needing nutrition coaching, please reach out or apply to work with me in the "Coaching Plans" tab. You can also see everything I offer on that page and the "Nutrition Therapy" page as well!