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from our previous Fitness Friday in conjunction with our friends at examine.com, today we're going to talk about optimal daily protein intake.
Incase you missed it, you can read last week's post here: HOW MUCH PROTEIN DO YOU NEED PER MEAL?
Sarcopenia is defined as an impairment of physical function (walking speed or grip strength) combined with a loss of muscle mass. It is the primary cause of frailty with aging, which itself is associated with a higher risk of having disabilities that affect your ability to perform daily activities of living, having to go to a nursing home, and experiencing fractures, falls, and hospitalizations.
Collectively, the link between sarcopenia, frailty, and associated morbidities may explain why sarcopenia is associated with a greater risk of premature death and reduced quality of life.This isn't a minor issue, either, as more than 40% of men and 55% of women over the age of 50 in the US have sarcopenia.
A low protein intake is associated with frailty and worse physical function than a higher protein intake. Aging results in anabolic resistance, a term used to describe how muscle tissue becomes less responsive to the growth-promoting effects of eating protein. Accordingly, older adults need to consume higher doses of protein in each meal to achieve maximal stimulation of muscle protein synthesis.
Although per-meal requirements for protein are higher in older adults, total daily protein requirements are similar to that of young adults. The RDA for protein for adults aged 50+ years is the same as that for younger adults, 0.8 g/kg. Like with younger adults, however, studies using the IAAO method have suggested that a more appropriate RDA is 1.2 g/kg. Several authorities now recommend older adults to consume 1.2-1.5 g/kg.
Notably, doubling protein intake from 0.8 to 1.6 g/kg has been shown to significantly increase lean body mass in elderly men. Similar observations have been made in elderly women who increase their protein intake from 0.9 to 1.4 g/kg. Even a small increase in protein intake from 1.0 to 1.3 g/kg has minor benefits towards lean mass and overall body composition.
The protein RDA for pregnant women is 1.1 g/kg. This value was estimated by adding three values:
However, as we saw previously with non-pregnant healthy adults, the RDA may not be sufficient, let alone optimal. There's some evidence with the IAAO method that the RDA for pregnant women should be about 1.66 g/kg during early gestation (weeks 11-20) and 1.77 g/kg during late gestation (weeks 32-38). Moreover, a meta-analysis of 16 intervention studies reported that protein supplementation during pregnancy led to reduced risks for the baby:
This effect was more pronounced in undernourished women compared with adequately nourished women. Importantly, these values were determined from sedentary women carrying one child, meaning that pregnant women who engage in regular physical activity and/or are supporting the growth of twins may need even higher amounts.
Also, we aren't medical doctors, and we don't know what you could have going on with your health and pregnancy. Please be sure to consult with your OB-GYN before making any changes.
Pregnant women may require a daily protein intake of 1.7 g/kg (0.77 g/lb) to support both the fetus and themselves. Protein supplementation during pregnancy appears to lower some risks for the baby, especially in undernourished women - including the risk of stillbirth.
Plants contain anti-nutrients that inhibit protein digestion and absorption, such as trypsin inhibitors, phytates, and tannins. While cooking does reduce anti-nutrient concentrations, it doesn't eliminate them completely. Turning a plant into a protein powder can, however, which is why the protein digestibility of plant protein concentrates is greater than their whole-food counterparts and similar to levels seen in animal foods.
The amino acid profile of a protein source matters because all protein, including the protein you eat and the protein in your body, is made from some combination of 20 amino acids. Our bodies can produce 11 of these, making them nonessential amino acids (NEAAs). The other nine can't be produced by the body, making them essential amino acids (EAAs) that we must consume.
Building muscle requires that, cumulatively, muscle protein synthesis (MPS) exceeds muscle protein breakdown (MPB), resulting in a net accumulation of muscle protein. All 20 amino acids are required to build muscle tissue, but the EAAs are primarily responsible for stimulating MPS.
Regardless of whether protein comes from the whole plant or more digestible (bioavailable) plant-based protein powder, plant-based proteins contain less EAAs than animal-based proteins, which further contributes to their lower quality.
In particular, plant-based proteins are lower in the EAA leucine, which is believed to act as a signal to "turn on" MPS and anabolic signaling pathways, although all EAAs are required for the effects to persist.
The lower leucine and EAA content of plant-based proteins helps explain why several studies have reported lower rates of MPS with soy protein powders and beverages compared to whey protein, skim milk, whole milk with cheese, and lean beef.
Differences in MPS appear to translate to differences in lean mass as well, at least when modest supplemental protein doses are used (-20 grams). However, both animal-based and plant-based proteins appear to have similar effects on lean mass when used in higher doses of 33-50 grams per day, suggesting that consuming more protein overall can help offset the lower quality of the plant-based proteins.
Plant-based proteins also contain limiting amino acids, which are EAAs present in such small amounts that they bottleneck protein synthesis. Lysine is the most common limiting amino acid, especially among cereal grains like wheat and rice. Nuts and seeds also tend to have lysine as a limiting amino acid. Beans and legumes, on the other hand, contain sufficient lysine but lack sulfurous amino acids such as methionine and cysteine. Combining different plant-based proteins can help overcome these inherent deficits.
Vegans and other individuals who obtain most of their protein from plants will need to consume more protein than an omnivore to achieve similar muscle growth, because plant-based protein is less bioavailable and of lower quality.
The simplest method to overcome EAA deficits with plant-based proteins is to eat more of it. As mentioned already, a handful of studies have shown that large doses (33-50 grams per day) of rice and soy protein cause similar improvements in body composition as whey protein.
Another way to bolster the EAA profile of plant-based protein powders is to combine several sources with complementary EAA profiles. Historic examples of these complements include beans with corn in the Americas, and rice with soybean in Asia. These grain-legume combos work because legumes supply the lysine missing in grains, and grains supply the methionine and cysteine missing in legumes.
Unfortunately, most plant-based proteins are low in leucine, meaning that combining sources will not have a large benefit unless one of those sources is a freak of plant nature, like corn (whose leucine content rivals that of whey protein). A lower leucine content means that more protein needs to be eaten to maximize MPS.