Protein Requirements: Animal Proteins vs Plant-Based Proteins

by Brooklin White MS, RDN, LDNNutrition
nuts, lentils, and tofu on a gray surface

Most American adults are eating about 100 grams of protein per day, which is nearly twice the recommended amount (1). Many individuals are avoiding carbohydrates from all sources (including vegetables and fruits) and are increasing protein intake instead. According to the 2018 Food and Health Survey, Americans considered proteins as a healthier option than fruits and vegetables when it comes to overall health. This survey also showed that most Americans are getting less fruits and vegetables but more protein (38% of diet) than is recommended by the USDA MyPlate (2). For comparison, Okinawan communities in one of the world’s longevity hotspots, estimate 9-10% of their calories from protein yet are living longer and healthier lives (3)(4).

This is reflective of how confusing nutrition information can be. Various news channels and media outlets have been selling us the idea that meat is an ideal source of protein and that the more protein we eat, the healthier our bodies will become. This information is flawed and unfortunately not backed by scientific evidence.

Protein Requirements

  • According to the Academy of Nutrition and Dietetics and the American Medical Association, adults ages 22-64 should consume 0.8 grams of protein per kg of body weight (you weigh 150 lbs. / 68 kg, that would equate to roughly 54-55 grams of protein per day)(5).
  • Protein requirements do increase slightly for those over the age of 65 since muscle mass is harder to build and maintain. For individuals ages 65+, protein intake should be around 0.9-1.2 g per kg of body weight per day (6).
  • Serious athletes also have higher protein (and nutrient) requirements than sedentary people. The Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine recommend 1.2-2.0 grams of protein per kilogram of body weight (5)(7). These requirements are of course dependent on exercise intensity and duration – It is best to work with a registered dietitian to establish individual protein needs.

Excess Protein Consumption

Amino acids are the building blocks of proteins and are thus a requirement for human health. The body requires a total of 20 different amino acids to function properly and nine of these, which are considered essential amino acids, must be obtained through the diet as our bodies are unable to create them. Essential amino acids are required for staving off malnutrition, promoting growth and development, adequate energy, immune function, tissue repair and additional metabolic functions. Excess protein, including those from essential amino acids however, promotes metabolic changes that can lead to certain disease states. Research suggests that our intestines cannot absorb more than 30 grams of protein at one time and thus increased amounts of protein can exhaust our vital organs (8). For example, low carbohydrate and high protein diets have been associated with bone demineralization and kidney stones (9).

Proteins cannot be stored in the body like carbohydrates can (glucose is stored as glycogen). Instead, the amino group of amino acid molecules are deaminated (broken down) in the liver and excreted from the body as urea. What is left of these amino acids is something called alpha keto-acids which are ultimately turned into triglycerides and stored as fat. These alpha-keto acids can be converted into glucose and used for immediate fuel if in a fasting state or if consuming high amounts of protein, but this is not the body’s preferred source of energy (glucose is) (10). Excess protein intake increases the time your body spends converting protein into glucose for energy, rather than utilizing fat as a fuel source. This ultimately makes it harder to enter a state of ketosis, which has been shown to be beneficial for brain health (11).

Plant-Based Protein

It’s crucial to recognize that plant foods contain all of the essential amino acids required for adequate health and cellular functioning. The distribution of these essential amino acids however, varies across different plant foods. What has once been considered an ‘incomplete’ protein might be better described as a ‘less concentrated’ protein, which means it contains lower levels of specific essential amino acids (12). Beans, for example, are low in the amino acid methionine but high in lysine, while nuts are low in lysine but high in methionine. This is why it is crucial to eat a variety of plant based foods. Eating a variety of plant-based foods such as green leafy vegetables, beans, nuts, olive oil, lentils, and chia seeds ensures individuals are receiving sufficient quantities of the nine essential amino acids.Fortunately, most plant foods are highly complementary, making a well-rounded plant-based meal not only sufficient in essential amino acids, but also rich in vitamins, minerals, phytonutrients and flavor. Despite what the rumors say, vegetarian and vegan diets will provide most adults with an ample supply of protein and essential amino acids - pregnant women and older adults are an exception as they may benefit from selective animal-based proteins such as fish (13)(14). It is important to work with a registered dietitian nutritionist to formulate individual needs.

Meat-Based Protein

The biggest perceived benefit of consuming meat and animal-based products as a source of protein is that they are high in protein and considered a complete protein. Although this makes obtaining essential amino acids easier, it does not necessarily promote health. Excess protein can lead to increased levels of circulating IGF-1 levels, which tells our cells to be in a constant growth mode, leaving little time for repair and regeneration. Eating meat as a main source of protein has additional health implications. Meat, especially red meat, is high in saturated fats and low in fiber, which has been shown to increase metabolic diseases (15). When we focus on meat rather than vegetables for protein sources, we tend to miss out on the vitamins, minerals and fiber that our bodies need to thrive. Iceberg lettuce, which is one of the least nutrient dense vegetables for example, still has nearly 3x the antioxidant content of chicken (16).

One exception is for adults ages 65 and older. This population may benefit from incorporating more fish, eggs and other animal products into their diet in small amounts to prevent muscle loss.

What’s the Takeaway?

Results from the National Health and Nutrition Examination survey indicated that 97% of men and women ages 19 to 50 received adequate protein, including those who are vegan and vegetarian (17)(18). The 3% who are not getting adequate protein seem to be those on extreme low calorie diets. Communities around the world have been thriving on vegetarian diets for thousands of years – it is only recently that our society has convinced its people that eating meat is required for muscle synthesis and optimal health. Most people don’t realize that the animals we eat are typically herbivores and are thus meeting their energy needs through plant-based foods such as grass or grain. Cutting out “the middleman” so to speak, allows us to focus on consuming our nutrients from their source rather than obtaining them from the animal who once ate them. If consuming animal products in moderation however, it is important to purchase organic and grass-fed products. Animals who have been raised on a grass-based diet consume the antioxidants and phytonutrients contained in these plants and thus provide considerably more vitamins and minerals such as beta-carotene and vitamin E than grain-fed (corn and soy) animals (19).

When looking at the bigger picture, it’s crucial to look at the diet as a whole rather than its individual components. Yes, protein is a vital macronutrient, but it shouldn’t be idealized from the other remarkable qualities in whole foods such as phytonutrients, antioxidants, fiber, vitamins and minerals – all of which are found in the highest amounts in plant-based foods. Studies have shown that when we substitute animal protein with plant proteins, all-cause mortality falls significantly (20)(21)(15).Rather than focusing on a single type and amount of protein, it is best to consider the quality of the whole foods you are consuming and incorporate a variety of plant-foods with minimal animal products.

“Remember, any diet that relies on beans instead of meat is going to be healthier than any diet that relies on meat instead of beans” – Dr. David Katz


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