I hope everyone’s water intake has increased since reading my column last month, cautioning against drinking too many sugar-sweetened beverages. I know I was guzzling more water with all this heat we’ve had recently—what a beautiful start to fall!
This month, I’m revisiting protein. I wrote a basic piece on protein back in June, addressing the (likely) need for more protein in our diets, different protein sources and a bit about protein quality.
Quality of protein is what I’m going to address here. I recently read three studies that investigated whether ‘ounce equivalents’ of plant-based sources are metabolically equivalent to animal-based sources. Spoiler alert: they aren’t.
To review, proteins are made up of amino acids, which are the building blocks of our bodies. We can make some of them on our own, but we have to consume the rest, which are called ‘essential’ amino acids (EAAs). Most meat and dairy proteins are what we call ‘complete’ proteins, which means they include all nine EAAs. Very few plant-based proteins are complete proteins, which is why it’s important for vegetarians and vegans to consume combinations of plant-based proteins that are referred to as ‘complementary.’ Examples of complementary proteins include grains and legumes (ex. rice and beans), dairy and grains (ex. yogurt and cereal) and legumes and dairy (ex. beans and cheese). By pairing these items together, you’ll get all your essential amino acids. Also, it’s not critical to eat complementary proteins at each meal; eating them throughout the day is sufficient.
The Dietary Guidelines for Americans (DGA) released ‘ounce equivalents’ to help consumers meet their protein requirements whether they eat a diet that includes meat or not. The DGA has stated that 1 oz meat, 1 cooked egg, ¼ C red kidney beans, 1 T peanut butter, 2 oz tofu and .5 oz mixed nuts are all ‘equivalent’ as protein sources. However, these food items vary significantly in terms of their protein, fat and calorie content. For example, one ounce of beef sirloin contains about 50 calories, 8.5 g protein and 2.75 g fat, while one ounce of mixed nuts contains 85 calories, 2.5 g protein and 7.5 g fat. Most importantly, the beef contains 3.5 g of EAAs, while the nuts contain only .9 g EAAs.
The studies used isotope tracer methodology to analyze the effects of the protein equivalents in the subjects’ bodies after digestion. According to the study titled Metabolic Evaluation of the Dietary Guidelines’ Ounce Equivalents of Protein Food Sources in Young Adults: A Randomized Controlled Trial, “Overall, animal-based protein food sources elicited greater anabolic responses than plant-based protein food sources.”
In layman’s terms, the studies consistently show that the degree to which our bodies simultaneously synthesize protein and prevent protein breakdown is directly related to the EAA content of the food we eat. Because animal protein sources contain more EAAs, they are a more efficient way to consume the protein we need. While it’s the EAAs that matter more than the source (plant-based proteins show the same metabolic effect as animal-based proteins when there are equivalent EAAs), there are other factors to consider when judging two different proteins’ ‘equivalence.’
One concern with relying largely on non-animal protein sources is their calorie content. For example, to get the same essential amino acid content as two eggs, you would have to eat 525 calories of nuts, while the eggs contain only 155 calories. One study revealed that those avoiding animal proteins would need an average of 300 extra calories per day to get the equivalent amount of protein. In light of the obesity epidemic facing our nation, it’s potentially detrimental to equate the two as ‘equivalent.’
Dietary protein is important not only for our muscle mass (both maintenance and strength), but also our nervous system, immune system, and more. These studies are not meant to dissuade anyone from adhering to a vegetarian or vegan diet, but rather to address the misleading nature of establishing protein ‘equivalents’ that are not metabolically equivalent. Vegetarians and vegans can meet their protein needs, but to do so certainly requires above-average nutrition knowledge that informs specific daily food choices, and may also lead to increased calorie intake.
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