How to Optimize Protein Digestion
Does animal protein belong in the human diet? Is it truly as bad for our health as many “experts” claim? Read on to learn why science supports the consumption of animal protein as part of a whole-foods diet, and why we should think twice before accepting claims that meat is harmful to our health.
Have you come across headlines claiming that animal products are harmful for our health? It’s a popular—and frequently misrepresented—topic in the media. In this article, nutritionist Lindsay Christensen sets the record straight on animal protein. #nutrition #wellness
We Can Thank Animal Protein for Making Us Human
When considering what constitutes a healthy diet for humans , looking at diet through an evolutionary lens offers profound insight. Our hunter–gatherer ancestors lived lives largely free of the chronic diseases we face today, such as cardiovascular disease and diabetes. Did our ancestors eschew animal protein in the name of health? Not even close! Animal products, including meat, bone marrow, and brains, have been a central part of the diet of Homo sapiens for approximately 2.5 million years, as evidenced by the presence of anthropological artifacts such as stone tools, used to crack open animal bones for marrow and for butchering animal flesh, at sites once occupied by prehistoric humans. ( 1 ) Before the emergence of humans, other hominids, including some members of the Australopithecus genus, also consumed animal protein and fat. Meat-eating thus appears to be a long-standing hominid activity. ( 2 , 3 )
Our ancestors’ appetite for animal protein wasn’t just a matter of taste. Research indicates that the consumption of animal protein and fat, perhaps acquired first through the scavenging of bone marrow from carcasses and eventually through hunting, was “a critical step in all animal and human evolution.” ( 4 ) Proteinaceous (or protein-containing) animal foods provided our ancestors with the bioavailable protein, fat, and micronutrients they needed to grow complex, social brains, such as docosahexaenoic acid, or DHA, and nicotinamide. In fact, the consumption of animal protein appears to have been critical for making us human. ( 4 , 5 ) Some research suggests that, when readily available, early humans consumed 50 to 250 grams of meat per person per day, a quantity high even by modern standards! ( 4 )
While animal protein is inarguably a natural part of the human diet and an important part of the ancestral health approach, it is not the only food humans should be eating. An abundance of anthropological and nutrition science research indicates that the optimal human diet includes both plant and animal foods —not just meat.
Now that we’ve established that meat is a natural part of the human diet, let’s discuss why animal protein has been so maligned in the scientific literature and why we should think twice before trusting the latest studies suggesting that animal protein is “bad” for us.
The Problems with Research on Animal Protein and Health
A Google search on meat consumption and human health may lead you to believe that animal protein is detrimental to your health. Many of the sources you’ll find refer to epidemiological studies on meat consumption and health. While the purported relationship may seem straightforward, the reality is that there are significant problems with the research on animal protein and health. These research problems have led to erroneous conclusions about the impact of animal protein on physical well-being.
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Epidemiological Evidence and the Bradford Hill Criteria
It is difficult to do randomized controlled trials of dietary changes, as people tend to know what they are eating! As a result, we’ve had to rely mainly on epidemiological evidence for assessing the effects of meat consumption on health. However, the problem is that, statistically speaking, we cannot demonstrate causality with epidemiological research. Upon closer observation with a set of criteria called the Bradford Hill criteria, the claims about meat consumption and harmful health effects don’t hold up to scrutiny.
In epidemiology, the Bradford Hill criteria is a framework used to assess evidence of a potential causal relationship between a presumed cause, such as meat consumption, and an observed effect, such as chronic disease. The criteria assess factors including the plausibility of a biochemical pathway linking the exposure to the outcome and the strength of the correlation in statistical terms. The more of these criteria that are met, the more likely it is that a causal relationship exists between the exposure and observed effect. Research has found that the epidemiological studies used to claim the harmful effects of meat on health do not meet the Bradford Hill criteria for inferring causality. In other words, we cannot use these studies to argue that animal protein is bad for our health! ( 6 ) Unfortunately, many figures in the medical community and influencers use these studies to do just that.
The epidemiological studies on meat consumption and human health are also highly susceptible to “confounding,” the process by which one comes to a spurious conclusion about a cause and an observed effect based on the influence of an unaccounted for variable. Most epidemiological studies on meat and health also don’t report the absolute magnitude of the observed health effects, which is typically quite small and nonsignificant.
In many cases, organizations that produce anti-animal protein dietary guidelines have not conducted rigorous systematic reviews of the evidence or accounted for conflicts of interest in the development of those recommendations, raising questions about the trustworthiness of their anti-animal protein dietary advice. ( 7 ) Conversely, a growing body of research indicates that the consumption of animal protein appears to be completely healthy in the context of a whole-foods diet. ( 8 )
Based on these findings, we have a perfect reason to doubt the research claiming meat is harmful to our health.
Nutrition Science Supports the Role of Animal Protein in the Human Diet
While anthropological evidence supports the vital role of animal protein in human evolution, modern-day nutrition science continues to validate its importance for optimal human health. There are four reasons why animal protein is superior to plant protein for promoting human health:
Animal protein is highly bioavailable in the human body.
Animal proteins are nutrient-dense.
Animal proteins contain higher levels of essential amino acid content than plant proteins.
Animal proteins contain higher amounts of sulfur-containing amino acids that are crucial for many aspects of physiological function.
Please note that this article does not discuss the implications of eating animal protein from an ecological perspective. This is another whole topic too nuanced for me to discuss here. However, I will say that regeneratively raised meat, from animals allowed to graze on pasture, is the clear winner, over mass-scale production of plant proteins, for supporting environmental health, as indicated by a growing number of studies. ( 9 , 10 )
For more information on this topic, I’ll refer you to Chris’s podcast with Will Harris of White Oak Pastures , as well as Diana Rodgers’ blog post, “ Meat is Magnificent: Water, Carbon, Methane & Nutrition .” Be sure to check out her Instagram feed and the many other articles on meat and the environment on her website.
The Quality of Animal Protein Beats Plant Proteins
The digestible indispensable amino acid score (DIAAS) is a scientifically validated system used to rate the amino acid profile and bioavailability of dietary proteins. ( 11 ) On the DIAAS scale, animal proteins consistently rank higher than plant proteins in terms of their amino acid profiles and bioavailability. On the DIAAS scale, higher numbers represent robust amino acid scores and high bioavailability, while low scores represent the opposite. For example, the DIAAS score for eggs is 1.13, beef is 1.10, and peanut butter is a mere 0.46. ( 12 )
Essential amino acids are amino acids that cannot be synthesized by the body and must be consumed in the diet. While specific plant proteins do contain the full spectrum of essential amino acids, it is the levels of these amino acids that matter. Essential amino acids limit the rate at which protein synthesis can proceed in the body. The lower amount of essential amino acids in plant proteins, including leucine, lysine, and methionine, can thus limit protein synthesis. ( 13 ) Animal proteins, on the other hand, are rich in essential amino acids and have been shown repeatedly to optimize protein synthesis, unlike plant proteins.
Finally, plant proteins contain chemical compounds that reduce the digestibility and bioavailability of protein, including phytic acid and protease inhibitors, once again making animal protein the superior choice in terms of protein quality. ( 14 )
Animal Proteins Are Nutrient-Dense
Animal protein is one of the most nutrient-dense foods available. ( 15 ) Proteinaceous animal foods offer a spectrum of micronutrients, including the following.
Vitamin B12 is critical for red blood cell formation, cardiovascular health, and neurological health and is found almost exclusively in animal proteins, except purple laver (a type of seaweed) and wild mushrooms. ( 16 ) B12 deficiency is prevalent worldwide, especially in populations with low consumption of animal foods, such as vegetarians and vegans . ( 17 ) Chris has previously written at length about the importance of B12 for our health and the risks of deficiency .
Vitamin B6 is a cofactor for enzymes involved in neurotransmitter synthesis, cardiovascular function, and detoxification. Fish, beef liver , and other organ meats are the richest dietary sources of B6. Significantly smaller amounts can be found in potatoes, bananas, and other vegetables. ( 18 )
Heme iron is the form of dietary iron found exclusively in meat, poultry, seafood, and fish. It is a component of myoglobin, an iron- and oxygen-binding protein located in muscle tissue sarcoplasm, or the cytoplasm of striated muscle cells, where it is used in cellular respiration to produce energy. Upon consumption, heme iron is readily absorbed and available for use in the body. Non-heme iron, on the other hand, is found in grains, beans, vegetables, nuts, and seeds and is much less bioavailable to the human body.
Bioavailable iron is crucial for red blood cell formation, neurological function, and many other physiological processes. Iron deficiency is prevalent in vegetarians and vegans, since these diets supply no meat and, thus, no heme iron. ( 19 , 20 )
Zinc is critical for cell growth and division, wound healing, immune function, and neurological health. Foods of animal origin, such as oysters, red meat, beef liver, and poultry, are the most bioavailable sources of zinc in the human diet. ( 21 ) Diets devoid of meat are linked to low zinc status. ( 22 )
Beta-alanine is a non-essential amino acid and precursor to carnosine, a dipeptide molecule required for optimal muscle and brain function. ( 23 , 24 ) Beta-alanine is found in meat, poultry, and fish. Vegetarians and vegans have 50 percent less carnosine in their muscles compared to omnivores, which may have repercussions for strength, fitness, and healthy aging . ( 25 , 26 , 27 )
Taurine is an amino acid derivative found in shellfish and dark meat poultry. It is important for cardiovascular and skeletal muscle function and stabilizes cell membranes. ( 28 ) Vegans have been shown to consume almost no taurine in their diets. ( 29 , 30 )
Animal Protein and Health
Research demonstrates that animal protein plays diverse roles in supporting optimal human growth, development, and long-term health.
Skeletal muscle mass is intrinsically tied to our longevity and vitality as we age, and having a higher ratio of muscle or lean body mass to fat mass is associated with healthy aging. ( 31 ) The consumption of animal protein may support a healthier body composition in aging adults, according to a study that found: ( 32 )
“… increasing the ratio of animal-based protein relative to plant-based protein in the diet may help to mitigate age-related losses of muscle mass and strength.”
A higher lean mass/fat mass ratio is also associated with reduced risks of heart disease, diabetes, and cognitive dysfunction. ( 33 , 34 , 35 ) By supporting muscle protein synthesis, the consumption of animal protein as part of a whole-foods diet may thus aid heart health, brain health, and blood sugar control.
Blood Sugar Control and Satiety
Dietary protein reduces the glycemic response after meal consumption and regulates food intake by inducing satiety. ( 36 ) The digestibility and amino acid composition of dietary proteins influence their effects on satiation. ( 37 ) Because animal proteins have a higher digestibility rate and better amino acid profiles, they may be more efficient than plant proteins for regulating blood sugar and satiety. For example, a high intake of dairy proteins and eggs, one of the least expensive forms of protein, is related to improved blood sugar regulation and a reduced risk of type 2 diabetes . ( 38 , 39 )
Pregnancy, Infancy, and Childhood
Animal protein intake is associated with improved outcomes in pregnancy and infancy. Supplementation with animal protein in pregnant mothers, preterm infants, and full-term infants reduces the odds of stunting and enhances growth. ( 40 ) Children fed higher amounts of animal protein in infancy and early childhood demonstrate improved growth and better cognitive function both immediately in childhood and throughout the lifespan. ( 41 , 42 , 43 )
Protein quality is crucial for elderly adults because protein is needed to support their muscle health, maintain energy balance, and prevent sarcopenia, or the destruction of muscle tissue related to aging. Research indicates that in the elderly, sufficient meat intake can prevent or improve malnutrition and sarcopenia, thus improving quality of life. ( 44 ) The PROT-AGE study, a study designed to review protein needs in aging, recommends that elderly people focus on obtaining high-quality dietary proteins, which, by definition, means animal protein. ( 45 )
Athletes have higher protein needs than the average individual. The American College of Sports Medicine and Academy of Nutrition and Dietetics recommends that athletes consume 1.2 to 2.0 grams of protein per kilogram of body weight to support the growth and maintenance of their muscle. ( 46 , 47 ) Research indicates that plant proteins have less of an anabolic effect than animal proteins due to their lower digestibility, lower essential amino acid content, and deficiency in other amino acids such as lysine. ( 48 ) These findings suggest that animal protein is an optimal protein source for athletes.
Your Body Is Wired to Seek out the Protein It Needs
Research suggests that we don’t need to overthink our level of protein consumption; our bodies appear to be “wired” to seek out the protein they need. This idea is summed up in the protein leverage hypothesis, which posits that humans will continue to eat food until their protein needs are met. ( 49 ) If protein-rich foods are insufficient in the diet, people may thus keep eating carbohydrate- or fat-rich foods until they finally achieve the amino acid levels they need. This theory may explain the insatiable hunger of many vegetarians and vegans!
Note that ultra-processed foods, which comprise nearly 60 percent of energy intake in the United States, may partially drive energy overconsumption via the protein leverage hypothesis. Maintaining a sufficient intake of high-quality animal proteins while simultaneously decreasing ultra-processed food consumption may thus be a potent strategy for reducing extraneous energy intake in the United States. ( 50 )
How to Customize Your Animal Protein Intake
The amount of animal protein a body needs to function optimally may differ significantly from one person to the next. Protein needs hinge on several factors, including:
Pre-existing health conditions
Gut health and digestive capacity
Your health goals
While eating protein to satiation is a simple way to gauge your protein needs, you can find strategies for more precisely customizing your protein intake in Chris’s article “ How to Calculate Macronutrient Ratios that Work for You .”
How to Optimize Protein Digestion
To optimize your body’s utilization of the animal protein you eat, you need to take steps to ensure optimal protein digestion:
Protein digestion begins in the mouth with the mechanical process of chewing. Make sure to chew your food thoroughly before swallowing.
The stomach is the next location of protein digestion, where hydrochloric acid (HCl) denatures dietary proteins. You can support your stomach acid production with a betaine HCl supplement or by taking a shot of apple cider vinegar before meals.
Taking time to relax for five to 10 minutes before a meal (i.e., stop answering texts, phone calls, and emails) can help your parasympathetic nervous system kick in, which regulates HCl production and digestive enzyme release in the stomach and intestine. ( 51 )
Finally, supporting a healthy gut microenvironment by addressing microbial imbalances can also support protein digestion.
Animal protein has been much maligned, and its health effects misconstrued in the media. Animal protein played a critical role in human evolution, and it supports health throughout the lifespan from infancy to old age. It supplies nutrients our bodies need to thrive, and it is delicious to boot! Rest assured that the scientific research supports animal protein as part of a healthy, whole-foods diet.
Additional Resources on Animal Protein and Health:
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