The Ultimate Guide To Protein
What The "Textbooks" Say About ProteinApril 17th, 2012
By Brian Rigby, Clinical Nutrition Writer
Protein is one of the most talked about nutrients, partially because it fulfills such an important role in our body. Unfortunately, everybody seems to have their own opinion over how much protein, and what sorts of protein, offer the most benefit.
While a certain amount of debate is inevitable, many of the recommendations can be dangerous, and when scrutinized scientifically, most of them don't hold up. Scientific literature is fairly clear about protein's role in our diet, and while it is always open to new research and discussion, a lot of our knowledge is textbook at this point.
Protein isn't just muscle, it fulfills many roles in every living organism alive, all the way down to bacteria. Understanding this is crucial to understanding why animal products are not the only good sources for protein, and helps to explain how protein is important in our own body as well. Unlike fats and carbohydrates, whose primary purpose is to supply fuel, protein has another, more important role. This role lies at the heart of the discussion, and it begins with amino acids.
What Is Protein?
Protein is more than a nutrient we eat, protein is one of the most essential building blocks of life. Protein forms the majority of our body, and not just the muscles we generally think about--our hair, nails, connective tissue, blood cells, and digestive enzymes are all proteins as well. In fact, there are about 50,000 different kinds of proteins in our body!
Protein is formed of chains of molecules known as amino acids. If you imagine a specific protein as being a word, like "elephant", then the amino acids are the letters forming the word. There are twenty common amino acids in our body, and number of uncommon amino acids as well. Of those twenty, nine are considered essential because our body cannot create them itself--it must find them in food. All of the uncommon amino acids our body is capable of creating itself.
Just like a single letter of the alphabet, individual amino acids on their own have limited use. A couple may be useful individually, such as the letters 'i' and 'a' can be, but for the most part the power of amino acids is expressed when they are organized into a chain, just like words and sentences mean much more than a single letter.
If you imagine proteins as words, then our body is a dictionary with 50,000 words in it. Some of the words are much more frequently used, such as myosin and actin (the proteins our muscles are primarily composed of), but in the end, all the words are composed of the same letters, just in different orders and of different lengths. In order to form new words, we need to supply our body with letters to write them with. This is where dietary protein enters.
How Much Protein Is Necessary?
For the average adult, the recommended intake of protein per day is .85 g/kg bodyweight. This means that for a 160lb human, roughly 60 grams of protein is necessary to maintain our body. However, this number assumes a sedentary lifestyle, which not everybody leads. A better way to measure recommended intake is as percentage of calories consumed, as this will account for differences in activity level.
Most adults should consume 12-15% of their daily calories in the form of protein. If you are an athlete, you will naturally consume more total grams of protein as your daily calorie intake increases. It is not challenging to meet this requirement, even on a vegetarian diet, as most vegetables are considerably higher than 15% protein. Here is a list of various vegetables, grains, and legumes for reference:
Red Bell Pepper: 15%
Brown Rice: 9%
White Potato: 11%
Black Beans: 23%
White Mushrooms: 56%
Pinto Beans: 25%
By comparison, here are some animal products:
Whole Cow's Milk: 21% Grain-Fed Beef Ribeye: 35%
2% Cow's Milk: 26%
Grain-Fed Beef Sirloin: 55%
Chicken Egg: 35%
Chicken Breast, w/ Skin: 61%
Skim Cow's Milk: 39%
Lean Pork Chop: 65%
Animal meat is clearly very high in protein as a percentage of total calories, but so are most of the non-starchy vegetables. Even the grains are close to the percentage of protein required by healthy adults. If you eat a healthy and diverse diet of vegetables, with limited intake of cereal grains, you will certainly get more than enough protein from your diet. In fact, the only foods you can really find which do not give an adequate supply of protein are the processed foods, which tend to be extremely high in carbohydrates and fats while lacking in protein.
For the vast majority of adults, getting adequate protein is simply not something to worry about. Most will get more than the recommended minimum of 12-15%, unless their diet is unusually high in processed foods or grains. Even vegetarian diets easily attain adequate protein and even high protein intake! Just to make this point more clear, here are a couple examples:
If a sedentary 130 lb. woman eats her daily recommended intake of calories (around 1400) in the form of a vegetarian meal, including various vegetables, beans, and grains, then she would consume a minimum of 9% and a maximum of 56% of those calories in the form of protein, depending on how much rice she eats versus mushrooms. Beans and grains are more calorically dense than vegetables, so we'll assumed that more of the protein will come from these calories. A safe estimate of total protein percentage of the foods put together is 15-20%, to account for both the high-protein vegetables and beans and the low-protein grains.
15-20% of 1400 (her total caloric intake) is 210-280 calories in the form of protein. Protein contains 4 calories per gram, so 210-280 calories works out to 52.5g to 70g of protein. At the low end, this is more than enough protein for a sedentary person of her weight, about 50g (130lbs = 59kg, 59 * 0.85 g/kg = 50.15g protein). At the high end, she has consumed about 20 grams of protein more than necessary!
What if she were athletic? You may have heard athletes need more protein than average, to account for gains in strength and endurance. The recommended amounts listed usually fall between 1.2 g/kg and 1.8 g/kg. It is true that athletes need more protein, but consider the next example, using the same woman but with a different lifestyle.
If the same 130 lb woman was very active, and needed to consume 2200 calories per day to account for the extra activity, her protein requirements would change, but her diet does not need to. If she ate the same overall food, for the same 15-20% of calories from protein, she would consume between 330 and 440 calories in the form of protein, which works out to be between 82.5g and 110g of protein per day. At 130 lbs., this would account for between 1.4 and 1.86 g/kg bodyweight. Thus, as she got more active and consumed more food, her protein intake increased and naturally fell between the recommended guidelines for athletes. It takes no special effort to achieve higher protein requirements if you already eat a healthy diet!
Animal vs. Vegetarian Protein Sources
One concept always brought up when debating animal versus plant protein is the completeness of the protein. Animal proteins offer a complete array of the amino acids our body needs, and has always been set as the golden standard of protein completeness. Vegetable proteins, on the other hand, are derided as being "incomplete", or lacking in certain essential amino acids. This is true, but in a limited sense.
In reality, the only commonly lacking amino acid in plant-based protein sources is lysine, and plant-based proteins are only lower in it, not completely devoid of it. The amount of lysine considered necessary is a highly debated topic. Low estimates put it at 12 mg/kg, or 870 mg a day for a 160lb. adult, whereas high "safe level" estimates place it at 60 mg/kg, or 4350 mg a day. The estimated amount of lysine the average American consumes in a day is 7600 mg, which is 175% more than the amount even the highest recommendations place.
Different vegetables have different amounts of lysine, with some being close to or even above what animal products contain as a percentage of total protein. A few examples of high-lysine vegetables are all the legumes, spinach, quinoa and amaranth, pistachios, pumpkin seeds, apples, potatoes, and pineapples. Many more are close enough as to be considered good sources. As long as your diet consists of a variety of plant-based foods, it is unlikely you will consume too little lysine, or any other essential amino acid.
It is also not necessary to combine proteins in one meal, as was once taught. As long as your diet is diverse throughout the week, your body will be able to use the amino acids as they come.
Can You Eat Too Much Protein?
It may seem very exact to attempt to consume 12-15% of all calories in the form of protein each day, and frustrating to try to keep track. The good news is that 12-15% is the amount required for simple maintenance, meaning that you can view it as a sort of minimum. Eating more than this amount is not likely to cause any problems as long as the protein is eaten in conjunction with other healthy foods.
That being said, there are some issues which are continually brought up in relation to high-protein diets, especially diets high in animal-based proteins. It's very important to note that in all cases, protein is described as a "correlative" figure, not a causative figure. For those of you looking to answer the question, "does meat cause cancer" this means that what we know from these studies is that diets high in protein tend to coincide with certain problems, not that diets high in protein cause them.
Also keep in mind that while it is difficult to accidentally consume too much protein from a healthy diet, purposefully consuming massive amounts of protein by reducing carbohydrate intake is linked to more serious conditions. This is especially true since consuming protein at the expense of carbohydrates often leads to a dramatic increase in the amount of fat consumed as well, and high-fat diets are linked with numerous health issues.
Animal Protein and Osteoporosis
At least one study has linked higher animal protein intake with loss of bone density, but it is important to note the reasons why animal protein is associated with greater risk and plant-based protein is not. When we digest protein, the sulfur-containing amino acids in that protein are converted by our body into sulfuric acid, which acidify our blood. To buffer the effects of the acidic blood, our body has a number of defenses, one of which is to use calcium to counteract the acid. If our body requires more calcium than is available in our blood, it draws extra calcium from our bones. Thus, a diet chronically high in animal-based proteins is often associated with increased loss of bone-density, the result of our bones losing calcium to buffer the acidic blood.
This is not the case with plant-based proteins because most fruits and vegetables contain alkaline compounds as well, which effectively buffer the increased acidity caused by protein. With extra buffering capability built-in, no calcium is needed to buffer the acid, and our bones remain intact. Unfortunately, most Americans eat more animal protein at the expense of vegetables, which is a dangerous combination capable of leading to osteopenia and osteoporosis.
Animal protein does not need to cause loss of bone density, just make sure that every meal which contains animal protein also contains a healthy load of vegetables as well. By providing your body with a buffer to the acidifying effects of protein, you ensure your bones will never suffer as a result.
Animal Protein and Cancer
Like osteoporosis, animal protein has been linked numerous times to cancer, especially red meats like beef and lamb. The mechanisms for why this may be are not fully clear, but the links are strongest when the following factors are all found together: high animal protein intake, higher fat intake, and low fiber intake. When lower-fat meats like fish or chicken are consumed, they were inversely related to cancer risk. Similarly, in diets high in fiber, cancer risk was lower as well.
Whether it is animal protein itself which causes cancer is uncertain, and a much stronger link can be made between diets low in fruits and vegetables and cancer. In many of the studies on animal protein and cancer risk, the common denominator is a diet lower in plant-based foods. As total calories consumed from animal products goes up, total calories consumed from plant products goes down. Most fruits and vegetables have numerous phytochemicals which offer anti-inflammatory and anti-cancer effects, and without these nutrients our body does a much poorer job of fending off chronic diseases like cancer. If you always ensure your vegetable intake is high, the risks associated with animal protein are low.
Related PEERtrainer Article: How To Reduce Inflammation
Protein For Energy
While the most important role protein seems to play in the body is maintenance, it is by no means its only role. Certain amino acids can also be converted into glucose, the sugar fuel for our body and more particularly for our brain. When we exercise or fast, our body runs low on a substance called glycogen, which is a starch-like molecule our liver stores to provide short-term glucose and buffer the effects of hunger and lowering blood sugar. Whereas our muscles and certain other organs can run off fat if they need to, our brain can only use glucose, so it's important for a glucose buffering system to be built into our body. This is where gluconeogenesis comes in.
When glycogen has been exhausted and glucose runs low, the body turns up gluconeogenesis, which takes certain amino acids and turns them into glucose. At the same time, the muscles begin to utilize fat more readily for energy, helping to conserve the glucose being created from protein for the brain. Some scientific reviews assign gluconeogenesis as being the primary role for dietary amino acids (proteins), not maintenance of muscle. At the very least, protein seems to serve a vital purpose as a glucose reserve for the brain and other organs.
When the body begins gluconeogenesis, one source for extra amino acids is skeletal muscle. Contrary to many fears, drawing amino acids from muscle does not cause muscular atrophy in the short-term, though prolonged periods of intense exercise (such as working out for weeks in a row without rest) and starvation do eventually lead to atrophied muscles. Amino acids taken during gluconeogenesis are replenished once protein is consumed once more, leading to no net loss of muscle.
Increasing dietary protein will increase the rate of gluconeogenesis and ensure there is no net loss, though it is not fully understood as to whether this is because the dietary protein instantly replenishes the muscles post-workout or because the amino acids are converted to glucose first, reducing the need to take protein from the muscles. Either way, eating a higher protein diet (28% protein) increases the rate of gluconeogenesis by about 40%, creating a very effective buffer for low blood sugar and increasing total energy available, which is especially useful for endurance activities.
Protein For Weight Loss
Eating a high protein diet has also been linked with an increased ability to lose weight, using gluconeogenesis as the intermediary. It is crucial to note here that the high-protein diet referred to by the studies and this article is NOT an extremely high protein, high fat diet such as the Atkins diet, where fat can make up as many as 60% of the calories.
High-protein diets, as referred to by studies, usually means a diet composed of 25-30% protein, 40-45% carbohydrate, and 28-30% fat. This is still a very high protein diet, but it incorporates healthy amounts of carbohydrates and fats as well. Additionally, many studies note that protein should NEVER come at the expense of fruits and vegetables, all of which contain vastly more phytonutrients and micronutrients than most high-protein foods, including vegetarian ones (beans can't replace greens!).
One of the key functions protein has on our appetite is to increase satiety, which means more protein makes you feel fuller, longer. More interesting, though, is the fact that when our body converts protein into glucose, it loses 33% of the energy available, meaning that for every 1 gram of protein converted, only .66 grams of glucose is made available. Protein and carbohydrates both have the same amount of energy per gram: 4 calories. When protein is converted via gluconeogenesis, the potential four calories of energy is reduced to only 2.66 calories. When a high protein diet is consumed, more energy must be taken from protein to account for the loss of energy from dietary fats and carbohydrates.
The end result is that when equivalent amounts of food are eaten from a high-protein and a low-protein diet, the high-protein diet fills you up more and creates less, but longer lasting and less likely to be stored energy. Fewer calories are available to turn into fat, and the increased protein supports lean muscle building as well, which when combined with exercise leads to increased muscle, which will further boost the resting metabolic rate of the body as a whole.
For the results to be most effective, protein is high, but carbohydrates must be high as well. Ingesting incredibly high amounts of protein in an attempt to force the body to supply all of its energy from gluconeogenesis, in the absence of carbohydrates, does not seem to work as one would expect. Rather, when glycogen is low (as a result of low carbohydrate consumption), the amount of protein and amino acids consumed does not appear to reduce muscle degradation for gluconeogenic amino acids. In other words, consuming a high protein and low carbohydrate diet leads to an eternal state of slow muscle degradation, the same as working out for weeks on end. While it is possible that the muscles will be ultimately be resupplied with amino acids and suffer no net loss, it is healthiest for weight loss and strength gain to supply the body with adequate carbohydrate fuel, and to use amino acids as a backup buffer, not the primary fuel.
Related PEERtrainer Article: How To Burn Fat: The Science Of How This Really Happens
The Best Sources For Protein
If you already eat a healthy diet, with a diversity of fruits, vegetables, beans, and healthy meats, chances are you already are consuming the perfect amount of protein. To achieve the weight loss results related to high-protein diets, however, a little more effort may need to be made in order to boost your intake from 15% to 25%. The following foods and tips are all great ways to increase protein consumption and overall health. Don't forget, protein should never come at the expense of vegetables and fruits!
1. Don't skip the salad! A healthy salad may not sound like a good way to increase protein intake, but all the components of a large salad added together will supply more than you may think, while keeping calories low and filling you up. One large salad, including a small amount of nuts and seeds, will supply 10-12 grams of protein in less than 200 calories. The more lettuce, spinach, and mushrooms you add, the greater the protein gain will be!
2. Eat at least one cup of beans per day. Beans have enormous amounts of protein for a plant-based food. Even better, beans (including peas and lentils) are extremely high in lysine, the one amino acid most likely to be missing from a vegetarian diet. Beans are also very high in fiber and slow-digesting carbohydrates, helping you stay full for longer.
3. If you eat meat, make sure you find grass-fed or pastured meat. Meat is a great concentrated source of protein, but if you eat grain-fed meats, theyâ€™re also a great source of concentrated fat. Even worse, grain-fed meat is higher in bad fats like omega-6s and saturated fat, and the fat is predominantly intramuscular, meaning it's integrated into the muscle of the meat and you can't cut it off. Remember the grain-fed ribeye steak from the lists above? 35% protein means the cut is also 65% fat. Compare that to a grass-fed ribeye steak which has 57% protein and 43% fat.
Grass-fed meat is also higher in omega-3 fatty acids, which can be hard to get enough of in the diet. Furthermore, the concentration of two specific fats, called "conjugated linoleic acid" (CLA) and "trans vaccenic acid" (TVA) are much higher in grass-fed animal products. Studies have shown that CLA and TVA, which is converted in our body into CLA, increase the rate of fat metabolism in our body, allowing us to burn more fat as energy and store less.
Overall, eating grass-fed meats is a good way to increase protein intake while still limiting fat intake, and may carry additional health benefits with it as well. A great bonus is the richer flavor pastured meats of all types have, which make their grain-fed counterparts taste downright bland!
4. Plant-based protein shakes that are designed for weight loss (as opposed to body-building) can be healthy and useful if you are looking to lose weight.
What Are The Best Protein Bars and Protein Shakes?
Protein shakes, in particular, can be a great source of pure, isolated protein, but you need to be careful of the ingredients. Protein shakes tend to be a huge repository for artificial ingredients, low-quality fillers, and generally unnecessary compounds. A high-quality protein shake, on the other hand, will have a very short ingredient list, often just three to four ingredients or even less!
There are many types of protein isolates, including whey, casein, soy, pea, rice, and even more. While all of them can be, for certain people, a perfectly fine choice (when found in a high-quality isolate), certain protein sources are less likely to cause issues in people who may be sensitive or allergic to certain proteins. Pea and rice protein, in particular, are only very rarely allergenic, making them ideal sources for protein isolates. In addition, they are vegan-friendly, making them an option for any lifestyle.
Related PEERtrainer Article:Guide To Protein Shakes
Protein bars tend to contain many artificial ingredients and fillers, usually in an attempt to make the bar palatable. To disguise the taste of so much protein, generally a lot of fat and sugar is added as well. The end result is an extremely high calorie bar which offers high protein, but also a load of fats and rapidly digested carbs as well. They offer little potential to truly satisfy hunger, leading to extra caloric consumption soon after. It's better to wait for a meal, or if you've just exercised and want some fast protein, to take a shake with you. You can always find high-quality isolated protein in powder and shake form; it's much harder to do so with protein bars.
Good Protein Snacks
The best options available for protein snacks are nut and fruit bars. These are not the traditional ultra-high protein bars found in gyms, but they do have significant amounts of protein, usually 5-7 grams. More importantly, they are composed of high-quality ingredients which offer nutritional benefit beyond the protein, and which have a much better chance of satiating for more than a half an hour. Another option, if you eat meat, is to have high-quality jerky. Try to find pastured jerky, as this will have the healthiest profile. An increasingly common and popular jerky is salmon, which also offers some omega-3 fatty acids with it.
Putting It All Together
Protein is more than just a simple nutrient; it is a vastly complex conglomerate of smaller amino acids which act like words, sentences, and even paragraphs of information! The largest protein in our body, titin, is almost 27,000 amino acids long! This is like a 27,000 letter long word. By contrast, this article contains only about 24,500 letters. Protein serves many specialized functions in our body beyond our muscles--different proteins help digest food, carry oxygen to our tissue, and fight off pathogens.
Eating the right amount of protein is important to maintain all of these systems, and without adequate protein intake all of them will begin to suffer. Thankfully, eating enough protein is not hard to do. As long as your diet is healthy and diverse, and not loaded with processed foods, more than likely you are already getting enough protein to maintain health.
Even if you are an athlete, protein requirements as a percentage of daily calories do not change. For most healthy adults, including athletes, 12-15% of total calories should come from protein. As your caloric intake increases, so does your protein as well. No special effort is required to achieve maximal effect from protein as an athlete.
Just as important as getting enough protein is getting the right amount of all the amino acids. Nine of them are essential--our body cannot produce them itself. Another six are conditionally essential because our body may not be able to produce enough of them under certain conditions, such as illness. The most limiting amino acid in any vegetarian or vegan diet is almost certainly going to be lysine. Getting enough lysine is not hard for anyone who incorporates animal products into their diet, as they are very rich in lysine. If you do not incorporate any animal products into your diet, make sure you consume enough beans and other high-lysine foods.
While protein itself does not seem to have a causative factor in the role of certain diseases, there is a high amount of correlation between diets high in animal protein and osteoporosis and cancer. These correlations are strongest when animal protein replaces vegetables and other plant-based foods. If you eat animal products, make sure you always eat vegetables with your meals as well, to offset the acidifying effects of protein and to add the numerous anti-cancer nutrients inherent in vegetables.
Increasing the amount of protein in your diet from 12-15% to 25-30% can be a great way to promote lean muscle and help burn more fat. These high-protein diets are also high in carbohydrates, as they are necessary to fully promote the thermogenic effects of protein. In a high-protein diet, more energy is spent trying to turn protein into glucose and satiety is dramatically increased, leading to a lessened likelihood to overeat.
It's not challenging to meet the basic protein requirements, but if you do wish to up your protein to 25-30% a little more effort is required, especially if you wish to keep your total fat intake down as well. Eat a lot of high-protein veggies and beans and switch to pastured meats, which are significantly lower in fat in most cases. Incorporate high-quality protein shakes into your routine--only one a day may be necessary to get that extra bit of protein!
No matter how you get your protein, make sure it is never a replacement for your vegetables. Protein is just one nutrient out of many, and it cannot do everything. No matter what your goals are, whether they are to lose weight or gain strength, all of the micronutrients and phytonutrients in vegetables and fruits play an exceedingly important role in optimal health. When your body is healthiest, it loses weight and gains strength that much easier.
Protein can help, but don't assign it more importance than it deserves. It is one nutrient in a continuum of nutrients, all of which are important and all of which should be taken into consideration.
Related: How Protein Shakes Are Used In The PEERtrainer Cleanse
References and Resources
Plant proteins in relation to human protein and amino acid nutrition
The nutritional value of plant-based diets in relation to human amino acid and protein requirements
Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults
Dietary protein requirements of younger and older adults
Protein requirements and supplementation in strength sports
Lysine requirement of adult males is not affected by decreasing dietary protein
Effect of Dietary Protein on Bone Loss in Elderly Men and Women: The Framingham Osteoporosis Study
A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women
Protein intake and athletic performance.
Role of fat, animal protein, and dietary fiber in breast cancer etiology: a case-control study.
Meta-analysis of animal fat or animal protein intake and colorectal cancer
Pancreatic cancer, animal protein and dietary fat in a population-based study, San Francisco Bay Area, California
Intake of Fat, Meat, and Fiber in Relation to Risk of Colon Cancer in Men
Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet
A Review of Issues of Dietary Protein Intake in Humans
Protein intake and energy balance.
Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse
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