Protein and Its Discontents
Busting Common Myths
This piece is the second in a series called Polemics on Protein, which addresses several topics surrounding the consumption of protein.
As always, any cited scientific research that is open source will be italicized. Also note my disclaimer about medical advice.
In How Much Protein Do We Actually Need?, we learned that emerging research suggests the following recommended daily allowance (RDA) for protein consumption:
Healthy active adults in energy balance or energy surplus: 1.6 to 2.2g/kg of body weight (0.68 to 1g/lb. of body weight)
Consumption of protein above 2.2g/kg/day may not increase lean mass accretion or strength during energy balance or surplus
Healthy active adults in energy deficit: 2.3 to 3.1g/kg of body weight
Individuals may even gain lean mass with heightened protein consumption during an energy deficit
Older adults who are healthy and active, with an acute or chronic illness, or with a severe/critical illness: 1.2 to 1.5g/kg of body weight
Certain guidelines advocate for greater than 1.5g/kg/day during critical illness
Left unaddressed in this first piece were several important topics, such as the timing of protein consumption, protein requirements over the life-span, the quality of various sources of protein, concerns about overconsumption of protein, and other commonly-held misperceptions about protein.
This follow-up piece will tackle each of these topics.
Too Long; Didn't Read (TL;DR)
One's focus should remain on consuming 1.6 to 2.2 grams of protein/kg of body mass. If feasible, one should aim to space intake throughout the day (i.e., consume reasonably high amounts of protein at each meal). Theoretical work suggests that ideally ~ 30 to 50 grams of protein are consumed every three to five hours with the last high-protein meal consumed one to three hours before bed.
Older adults should take care to mitigate the “anorexia of aging” to still meet the above recommendations for protein consumption. To attenuate the satiety-producing effects of protein intake, supplemental protein shakes based in soy or casein should be consumed immediately prior to pre-planned meals to help meet this goal.
Vegans and vegetarians likely do not need to increase their protein consumption over the recommendations stipulated above to compensate for lower-quality sources of protein in plant-based foods. They also do not need to carefully pair food items in a given meal to ensure they are consuming a “complete protein.” Consuming more plant-based proteins may considerably decrease all-cause mortality compared to animal-based proteins.
Those with preexisting kidney damage should exercise caution with increased protein consumption and plan to work with healthcare professional to determine intake goals. Consuming primarily plant-based proteins is likely to be beneficial for kidney health over those that are animal-based.
Heathy individuals likely do not need to worry about increased protein consumption causing kidney damage or negatively affecting bone health. Nonetheless, emerging research suggests that increased nondairy animal-based protein consumption may carry a higher risk for kidney disease compared to plant-based protein in otherwise healthy patients.
Timing of Protein Consumption
Many devotees of weight-lifting subscribe to the so-called “anabolic window” for peak muscle growth and recovery: at least 30 grams of protein should be consumed within 15 to 60 minutes of completing resistance training.
Contemporary research suggests there is far more nuance to this rule of thumb. A 2013 review found that the interval between a pre-exercise meal and a post-exercise meal should ideally not be longer than 3-4 hours for maximal benefit to muscular growth (hypertrophy). If each of these two meals is especially large, this period may be lengthened to 5-6 hours.
For instance, if breakfast is consumed at 5am, followed by a 60-minute session of resistance training from 5:30-6:30am, the latest one should consume a high-protein meal is about 9am, four hours after the pre-exercise meal.
The same review also found that consuming 0.4-0.5 grams of protein per kilogram of lean body mass in both the pre- and post-workout meals is ideal for optimal muscular hypertrophy. This amount equates to 20-40 grams of protein in each meal for most individuals.
(For those desiring a more precise amount, rough estimates of lean body mass may be calculated based on delineated formulas. Some modern weight scales automatically measure lean body mass.)
A 2018 review delineated two additional recommendations surrounding the timing of protein consumption to maximize muscle protein synthesis (MPS):
Over the course of the waking period (16 hours, assuming 8 hours of sleep), protein consumption should be spaced every 3-5 hours.
To offset declines in MPS that occur while fasting overnight, aim to consume a high-protein meal 1-3 hours prior to sleep.
These suggestions stem from the inherent limitations of MPS. Like all biological reactions, there is a point at which this synthesis plateaus at its “maximum velocity.” Even with more inputs (here, amino acids), the reaction is fully saturated and cannot be further stimulated. One may think of a bus filling up with passengers: eventually all seats and standing room will be taken, and no further individuals can be accommodated.
The same 2018 review stated that the saturation point of MPS occurs at a protein intake of 0.3 grams per kilogram of body mass in younger adults. In practice, this saturation level occurs at an intake of ~30 grams of protein in a serving (Symons et al., 2009).
Conversely, Trommelen et al. 2023 found that ingestion of 100 grams of protein in a single serving had a more prolonged anabolic effect compared to 25 grams. Challenging the above assertion, they conclude, “ … the anabolic response to protein ingestion has no apparent upper limit in magnitude and duration in vivo in humans.”
This finding pairs with other work showing that protein intake above the putative limit of ~0.3 grams of protein per kilogram of body mass may still help to suppress muscle protein breakdown (MPB) (Deutz & Wolfe, 2013).
Taken as a whole, one’s primary objective should still be to meet their overall daily protein consumption goal without too much concern given to the optimal intake at each meal.
Protein Considerations in Older Age
For the purposes of this discussion, “older adults” are individuals aged 65 years and above. Of course, age is just a number, but one’s physiology does change significantly over the lifespan, leading special considerations to be taken into account.
The above recommendation for overall protein intake (1.5-2.2 grams of protein per kilogram of body mass) remains in effect for older populations. Among adults of any age, only those with severe kidney damage (as discussed more comprehensively below) should actively limit their protein consumption.
Consuming an optimal level of protein is especially pertinent in older patients who have an acute or chronic disease, severe malnutrition, or a considerable injury (Bauer et al., 2013). Increased protein can aid in offsetting the pro-inflammatory state found in each of these conditions. Excessive inflammation sets the stage for catabolism, a metabolic state in which tissues are broken down. Over time, runaway catabolism can ravage such tissues as muscle and internal organs.
It should then come as no surprise that increased protein intake can bolster wound and burn healing (Cawood & Stratton, 2011) and improve bone mineral density (Darling et al., 2009), amounting to overall decreases in morbidity and mortality (Naghshi et al., 2020).
Thus, to improve the quality of life (found in such factors as mobility and independence) and avert poor health outcomes in older adults, concerted efforts must be taken to increase protein intake. But sadly it's not that easy.
Many older adults are afflicted by a decreased appetite, the so-called “anorexia of aging," presaging vitamin and mineral deficiencies, loss of muscle mass, and increased risk of mortality (Chapman et al., 2002). (Note that “anorexia” is a broad medical term describing decreased appetite; the eating disorder “anorexia nervosa” is one variant of anorexia. Anorexia might also be induced by certain disease states, such as particular cancers and AIDS.)
The sequela of this anorexic phenomenon among older adults are further heightened by the typical pattern in which Americans, young and old, obtain their protein. At the turn of the 21st century, the average American breakfast contained 15 or fewer grams of protein (USDA, 2002). More than 60% of daily protein intake tends to occur at dinner. With a lower overall appetite, though, some older adults might not even get around to consuming supper.
Increasing protein consumption in older adults is made even more vexing by the satiety-related effects of protein. In essence, eating more protein makes one feel more “full,” which may lead to lower overall caloric consumption. To be sure, increasing protein intake is a powerful mechanism for weight loss (Veldhorst et al., 2008), as will be discussed in a forthcoming piece, but is decidedly unhelpful in this case. On balance, older adults should be consuming more calories, not fewer.
To mitigate the satiety-related effects of proteins, it is likely preferable to increase protein intake through a liquid-based protein supplement (i.e., a "protein shake") compared to a “whole food” source, such as tofu or steak. In practice, it is easier to “drink your calories” than it is to eat them. (I will concede that I was unable to find any pertinent research comparing the relative satiety effects of whole food-based protein to isolate protein-based shakes, so this point is ultimately anecdotal.)
This protein shake should ideally be consumed immediately before a planned meal. A 2011 study showed a significant decrement in caloric consumption in a pre-planned meal when a protein shake was consumed 30 to 45 minutes before that meal. Again, this is the exact outcome we are hoping to avoid in older populations. There was no meaningful caloric reduction, however, when this protein shake was consumed directly before the meal, suggesting a potential attenuation of the shake’s satiety-producing effects.
The content of this protein shake is also important. Some research suggests a pea-protein based shake causes more satiety than one based in whey protein (Diepvens et al., 2008). In turn, other work shows whey protein decreases hunger more than casein or soy (Hall et al., 2003; Veldhorst et al., 2009; Pal et al., 2014). Thus, using casein or soy-based supplemental protein may be optimal to further dampen satiety, although further research is necessary in this area.
A 2016 study of older adults showed that supplemental protein shakes at breakfast and lunch meals correlated to significant increases in lean body mass, which helps to attenuate age-related muscle loss (sarcopenia) and prevent frailty and debility. The concomitant practice of resistance exercise can further increase lean body mass when increasing protein consumption (Nunes et al., 2022).
Further steps can also be taken to address age-related decreases in appetite, such as taking medications that mimic hunger-inducing hormones. These measures are outside the scope of this piece.
As a final aside, to further support the structure of muscle and optimize their growth, older adults should also aim to supplement vitamin D3 at about 800 IU (international units) per day (Landi et al., 2016).
Comparing Animal- and Plant-Based Proteins
The start of 2023 marked twelve years that I have been vegan. I will not burden readers with the numerous reasons I have sustained this lifestyle. Relevant here, though, is a comparison between animal- and plant-based sources of protein.
Of the twenty naturally occurring amino acids, nine are considered “essential” or “indispensable” (usually abbreviated to “IAAs”) and cannot be made independently by our bodies. As such, these special amino acids must be consumed from dietary sources, and they are not easily won. Proteins, either from animal or plant sources, are often folded in tight conformations or otherwise trapped in cellular structures, impeding swift break-down by our digestive system.
Despite all the broadsides cast against “processed” foods, this refinement actually improves the digestibility of proteins. A standard American diet has an average protein digestibility around 90 per cent, signifying that only a small portion of consumed protein is left un-digested and un-absorbed. Diets in developing countries, meanwhile, have a protein digestibility as low as 54 per cent (Joye, 2019).
Indeed, a protein’s “quality” can be assessed based on the ability of our bodies to adequately digest them. A protein’s content of IAAs is another important component of its quality. These two factors are combined into the digestible indispensable amino acid score (DIAAS), a metric produced by the United Nations (Food and Agriculture Organization, 2011).
DIAAS values are normalized to a “reference protein” that contains the minimum daily requirement of all nine IAAs. This reference protein has a DIAAS of 100. A score higher than 100 signals a food item has quantities of some or all IAAs above the minimum recommended amount. A score lower than 100 means that the food is deficient in one or more IAAs.
The following table lists DIAAS values for common animal- and plant-based protein sources. One quickly notes that nearly all plant-based sources fall below 100. It’s not easy being green.
Although we have seen that the FDA recommendation for protein intake of 0.8 grams per kilogram of body mass is inadequate (see How Much Protein Do We Really Need?), it is worth noting that this guideline assumes that at least fifty per cent of protein sources are animal-based, which are almost always “high quality.”
Accordingly, a 2019 study does suggest that vegetarians should increase their daily protein consumption by 10 to 22 grams to compensate for lower quality sources of protein.
This research, however, failed to account for the fruits and vegetables regularly consumed in larger amounts by vegetarians, which provide an additional source of protein (Genoni et al., 2020).
Further criticism of the DIAAS includes a poor representation of legumes, nuts, and seeds, which constitute a significant source of protein for vegans and vegetarians. The calculation of DIAAS also only utilizes raw food items, whereas fermenting and cooking grain proteins can bring their digestibility close to that of meat (Nkhata et al., 2018).
Taken together, protein quality is an important dietary consideration and one that does divide animal- and plant-based foods. At the same time, it is unlikely that vegans and vegetarians need to meaningfully alter their protein consumption goals to compensate for "lower quality" proteins in grains, legumes, and vegetables.
Of note, a higher consumption of plant-based protein is associated with diminished environmental impact compared to animal-based protein (Ferrari et al., 2022). In addition, increased intake of plant-based protein has consistently been shown to decrease mortality from cardiovascular disease, cancer, and all-causes (a catch-all for other disease states that lead to death). See Song et al., 2016; Budhathoki et al., 2019; Huang et al., 2020.
Consuming a "Complete" Protein
When plant-based sources of protein are considered, there is sometimes concern given to whether they are “complete” and contain all nine essential amino acids. Vegetarians are frequently advised to combine foods that are lacking in a particular essential amino acid with others that are high in that amino acid to ensure the meal contains a “complete protein.” Perhaps the most classic example is beans and rice, which together provide all nine IAAs.
While this recommendation may appear intuitive, research tells us otherwise. Provided that a variety of foods are consumed throughout the day, there is no reason that a single meal must contain a “complete protein." Thus, one may enjoy rice for lunch followed by beans for dinner and still obtain all nine essential amino acids (Beck, 2012).
A Quick Note about Leucine
Among the nine essential amino acids, there are three demarcated as BCAAs, or branched-chain amino acids, referring to their molecular structure. This trio includes leucine, isoleucine, and valine.
Leucine has been elucidated as the single most important amino acid to stimulate muscle protein synthesis. A daily dose of 2 to 2.5 grams at minimum (Crozier et al., 2005), but ideally 3 to 4 grams of leucine (Stark et al., 2012), will aid in promoting optimal muscle growth. This amount need not be consumed at a single sitting, but should be accumulated throughout the day.
Consuming a sufficient amount of protein from a variety of sources (both those animal- and plant-based) will allow one to obtain optimal leucine.
When protein powder alone is examined:
One serving of whey protein powder contains 2.5 grams of leucine (25 gram scoop serving)
One serving of pea protein powder contains 2 grams of leucine (33 gram scoop serving)
One serving of soy protein powder contains 2 grams of leucine (30 gram scoop serving)
Along with others food sources consumed to meet one's overall protein goal, it should be relatively facile to obtain optimal levels of leucine.
Can Protein Be Too Much of a Good Thing?
There are two chief concerns often associated with increased protein consumption: kidney damage and diminished bone health.
After initial processing in the small intestine, dietary protein is broken down into its building blocks (amino acids) by the liver. These amino acids are primarily used for making structural proteins, enzymes, and hormones. Any excess amino acids are utilized for energy throughout the body, creating nitrogen waste products in the process. This nitrogen-based refuse is then converted into urea, which is dumped into the blood for later processing by the kidneys into urine (Dudeja et al., 2021).
Increased production of urea may theoretically overwhelm the kidneys, leading to damage, but research has not borne out this supposed outcome in otherwise healthy populations (Martin et al., 2005; Layman et al., 2015). Nonetheless, it is principally important to note that several studies suggest there is an increased risk of chronic kidney disease (CKD) and end-stage renal disease (ESRD) among populations consuming high amounts of red or otherwise processed meat. A 2020 review showed a 31 to 62 per cent decreased risk of CKD by substituting just one daily serving of red meat for a plant-based protein.
At this juncture, there is a lack of clarity for why increased animal-based protein consumption may heighten the risk of CKD. Higher meat consumption is known to increase the incidence of high blood pressure and weight gain, which can independently damage the kidneys, as well as cause imbalances in the gut microbiome, leading to a “pro-inflammatory profile” that can bring about further renal injury.
A strictly plant-based diet is also fairly neutral on average (neither overtly acidic or basic), which may increase the growth of healthy bacteria in the gut microbiome. These native bacteria within the gut increase the breakdown of nitrogen-based waste products in the blood. A higher dietary acid consumption (as can occur with intake of animal-based foods), meanwhile, has no such favorable impact on the growth of healthy bacteria, forgoing this renal protective effect.
As an aside, among individuals with pre-existing CKD, increased meat consumption was also shown to cause more significant declines in kidney function compared to plant-based sources (Knight et al., 2003) and heightened mortality (Chen et al., 2016). An increased proportion of plant-based sources of protein, meanwhile, has been shown to decrease mortality among patients on dialysis (Liu et al., 2020).
Most health organizations recommend protein consumption be limited to 0.6-0.8 grams per kilogram of body weight in patients with CKD, independent of the source of protein (Narasahki et al., 2021). In the future, this guideline might conceivably be modified to advise against non-dairy animal-based protein consumption, given the increasing weight of the evidence. Indeed, work by Kalantar-Zadeh et al., 2020 argues that plant-based sources should account for more than 50 per cent of this protein consumption goal in light of the associations between meat consumption and kidney dysfunction.
In addition to nitrogen waste products, amino acid metabolism also releases acidic by-products, which can lower the blood’s pH. A sustained decrease in blood pH may cause calcium to leach from bones, potentially damaging their structure, leading to osteoporosis and fractures over time. Numerous studies in both young and old adults, however, find either no association between increased protein consumption and bone health or a beneficial increase in bone mineral density (Darling et al., 2009; Layman et al., 2015).
Summary
While research does not always provide exacting clarity, there are several impactful insights from recent studies in protein.
To review, one’s principal focus should remain on consuming enough protein to meet the updated daily requirements (1.5-2.2 grams of protein per kilogram of body mass), but some attention should be placed on spacing out protein intake throughout the day. Older adults may benefit from consuming supplemental protein shakes in order to meet these requirements: likely a soy or casein isolated-based protein powder consumed directly before a planned meal.
There is no need for vegetarians to increase their protein intake any higher than the stipulated daily requirement. Additionally, there is likely to be little risk to kidney or bone health with higher protein intake in individual without preexisting damage. Again, those who already have kidney dysfunction should exercise caution.
In an upcoming piece in the Polemics on Protein series, we’ll examine further benefits of higher protein intake, namely its ability to aid in weight loss.