Protein requirements differ depending on age, sex, activity level, and a multitude of other factors. Generally, most adults should consume 1.2 to 2.4 grams of protein per kilogram of body mass per day (g/kg/day) — sedentary individuals can likely obtain adequate protein near the lower end of this range, while active individuals and those looking to gain muscle should skew their intake toward the higher end.

You don’t need to supplement to achieve your daily protein intake goals — protein can come entirely from whole foods or from a combination of whole foods and protein supplements (e.g., whey protein powder). However, protein powders can be a great and convenient way to get more protein. If you want more information on how to determine your optimal protein intake, check out our optimal protein intake guide or easily calculate your protein needs with our protein intake calculator.

As for protein intake per meal, it seems that 0.4 g/kg/meal is optimal for stimulating muscle protein synthesis (MPS) for most younger adults; a dose of 0.4 to 0.6 g/kg/meal is best for older adults.^[39][40] And no, your body doesn’t “waste” protein if you eat more than 30 grams in one sitting — this is a common myth.

Whey protein concentrate is the least processed form of whey protein and is 35%–80% protein by weight, although most whey protein concentrate powders tend to be standardized at 80% protein by weight.^[54]

Whey protein isolate is defined as being more than 90% protein by weight.

Whey hydrolysate is protein that has been pretreated with enzymes and acid to reduce its peptide size; it’s the fastest absorbed form of whey. Hydrolysis reduces the allergic potential of whey and milk protein by breaking down immunogenic, larger peptides into smaller ones less-apt to be recognized by the immune system. This why hydrolyzed whey is often used in infant formula. Hydrolyzed whey also tends to have increased solubility compared to whey isolate, although it is important to note that whey protein in general (including whey isolate) is quite soluble. Several studies comparing whey hydroylsate to whey isolate and other milk proteins such as casein failed to make a difference in nutritional quality.^[55]

Is one form better than the others? Not necessarily, but this can vary by the individual. Since whey hyrolysates are inherently less immunogenic, they are useful for people who can't tolerate whey concentrate or isolate. As far as efficacy in-general, including their ability to faciliate muscle hypertrophy or recovery, there haven’t been many comparison studies. One trial noted that whey hydrolysate may enhance muscle recovery more than whey isolate.^[56] Whether or not the differences observed in this trial would be experienced outside of a controlled laboratory setting is unclear.

The popular idea of an “anabolic window” — a crucial period of time before/after training during which protein must be ingested to maximize muscular adaptations — has been called into question. Indeed, the largest determinant of gains in muscle strength and hypertrophy seems to be total protein intake throughout the day (and a well-structured resistance training program), rather than nutrient timing per se.^[41]

But protein timing may not be inconsequential; exercise does have a “sensitizing” effect on muscles, and consuming protein in close proximity to a workout can ensure that one maximizes this anabolic sensitivity. Furthermore, exercising on an empty stomach can put the body into a negative protein balance; reupping on protein afterward helps maintain a positive protein balance to promote muscle protein synthesis instead of breakdown, and seems to be better than eating a protein-containing meal before or a few hours after working out.^[42]

Whey protein is highly bioavailable, rich in essential amino acid (including leucine), and quickly digested. Consuming whey causes a larger increase in blood amino acids than does casein or soy protein. And, both at rest and after exercise, whey protein stimulates muscle protein synthesis (MPS) to a greater degree than casein and soy — likely due to the quicker digestion and/or higher leucine content of whey hydrolysate.^[43]

Pregnant and lactating people may need more protein than previously recommended — 1.66 to 1.77 grams of protein per kilogram of body weight per day (g/kg/day) seems to be ideal,^[44][45] with 1.5 g/kg/day being the lower threshold for maintaining a positive nitrogen balance.^[46] Furthermore, some studies have observed that supplementing with protein during pregnancy seems to reduce infant health risks, including low gestational weight, low birth weight, and stillbirth.^[47]

While there haven’t been any studies on whey protein supplementation for pregnant/lactating people per se, there’s some evidence that maternal consumption of dairy protein — and in particular whey protein — may benefit infant weight and body composition.^[48]

However, whey protein (and other protein) powders come with the risk of being possibly contaminated with heavy metals or other pesticides. After all, dietary supplements (including protein powders) aren’t regulated by the Food and Drug Administration (FDA). Some protein powders may also include added sugar and other ingredients that pregnant/lactating people may want to avoid. The best advice: read the labels carefully, and always discuss any supplements with your obstetrician/gynecologist (OB/GYN) or other healthcare professional before implementing any dietary changes.

Aging is associated with anabolic resistance — a muscle’s resistance to growth or stimulation of muscle protein synthesis (MPS) — making it harder to build or maintain muscle mass. In other words, older muscles require a greater dose of protein to stimulate a similar amount of MPS as younger muscles.^[49] For this reason, older adults who want to build or maintain muscle may need more protein (per day and per meal) than the RDA recommends, and whey protein is a great source because of its potent ability to stimulate MPS.

In adults older than 60, whey protein supplementation (often when combined with resistance training) increases physical function, improves lean mass/skeletal muscle mass and upper-body strength in those with sarcopenia/frailty,^[50][51] and is effective for increasing total protein intake and MPS.^[52] Whey protein and resistance training also help postmenopausal women build more upper body strength and lower-body lean mass.^[53]

Bone health

The acid-ash hypothesis states the following: The metabolism of certain foods — namely protein and grains — increases acid production in the body, as evidenced by an increase in urinary acidity.^[7] To counteract this increase in acidity, bone is broken down to release calcium bicarbonate (a base) corresponding with an increase in urinary calcium excretion, which is thought to reflect negative body calcium balance or bone loss. Therefore, a high-protein or acid-producing diet accelerates bone loss and increases the risk of osteoporosis.

However, changes in urine pH don’t necessarily reflect changes in blood pH, which is maintained within a narrow range primarily by the renal and pulmonary systems in healthy people.^[8] Additionally, variations in diet have virtually no effect on blood pH, as any nutritional influence that slightly disrupts acid-base balance is immediately corrected by biochemical buffering systems that do not involve bone.^[8]

While an increase in urinary acidity has been correlated with an increase in urinary calcium excretion, dietary changes that increase urinary acidity do not lower body calcium balance.^[9] Relatedly, a higher-protein diet does not negatively affect dietary calcium retention because although it increases urinary calcium excretion, it increases intestinal calcium absorption by a similar magnitude.^[10][11]

Ultimately, the available evidence does not support the acid-ash hypothesis,^[12] and in accordance, higher-protein diets do not have a negative effect on bone health.

Meta-analyses of prospective cohort studies have reported that a higher-protein diet was either not associated with the risk of hip fracture,^[13] or, compared to the group with the lowest protein intake, there was an 11%–16% lower risk of hip fracture in the group with the highest protein intake.^[14][15][16]

With respect to bone mineral density (BMD), a meta-analysis of randomized controlled trials 12–24 months long reported that a higher-protein diet had a protective effect on lumbar spine BMD.^[17] A higher-protein diet also tended to have a protective effect on total hip BMD, although this finding was not statistically significant. The data from prospective cohort studies is mixed on whether higher-protein diets have a protective effect on BMD (some studies suggest a benefit with more protein, while others have reported no impact), but there is a lack of evidence indicating that higher-protein diets are associated with lower BMD.^[15][17]

Concerning protein intakes significantly greater than the Recommended Dietary Allowance (RDA), there are a couple of long-term prospective cohort studies in older adults that shed light on the topic. In one four-year study that included older men and women (average age of 75), the quartile with the highest protein intake (1.24–2.78 grams of protein per kg of body weight per day) showed the least BMD loss at the femur and lumbar spine.^[18] Compared to the quartile with the highest protein intake, the quartiles with the lowest (0.21–0.71 g/kg/day) and second-lowest (0.72–0.96 g/kg/day) protein intakes experienced a significant reduction in femoral neck BMD.

In a separate five-year cohort study that only included older women (average age of 75), a higher protein intake was associated with greater whole-body bone mineral content, and the tertile with the highest protein intake (about 1.6 g/kg/d) had significantly higher whole-body and appendicular bone mineral content than the tertiles with lower intakes.^[19]

Kidney health

The idea that a high-protein diet puts undue stress on the kidneys stems from early research in rodents and dogs that reported increased urea excretion, renal blood flow, glomerular filtration rate (GFR; a marker of kidney function), and kidney size in animals fed a high-protein diet.^[20] From this data, it was determined that a high-protein diet increases the workload of the kidneys, and thus may damage the kidneys over time and increase the risk of chronic kidney disease (CKD).

A 2018 meta-analysis of randomized controlled trials that compared the effects of a high-protein diet (1.8 grams of protein per kilogram of body weight per day, on average) to a low-protein diet (0.93 g/kg/d) in healthy adults reported that higher protein intakes may slightly increase GFR.^[21] Other data indicates that a high-protein diet does not adversely affect blood markers of kidney function or blood pressure.^[22][23]

Given these findings, a high-protein diet does not appear to pose a serious threat to kidney health. In further support of this conclusion, the issue at hand can be viewed through a different lens altogether; that is, is an increase in GFR a risk factor for CKD in healthy people? Such a relationship has yet to be clearly established.^[21]

In fact, an increase in GFR in response to an increase in solute load (e.g., nitrogen from protein) is a normal adaptive mechanism.^[24] For example, GFR can increase by as much as 65% during pregnancy^[25] but does not increase the risk of CKD.^[26] Also, surgical removal of a kidney is not associated with a deterioration in kidney function in the long term (> 20 years), despite the increase in workload.^[27][28][29]

While a low-protein diet is recommended for people with CKD to help prevent disease progression,^[30] this does not mean that a high-protein diet is harmful in all cases. The available evidence suggests that, in healthy people, a high-protein diet does not adversely affect kidney function or increase the risk of CKD.