Protein. People seem to talk a lot about protein, don’t they? You are probably familiar with protein, in a general sense, but do you really know what protein is? Where is it found? Why do we need it? And how much of it do we really need? Read on and find out...
What is protein?
Protein is one of the three macronutrients, along with fat and carbohydrate, that provides the body with energy. Protein provides 4 calories per gram, but it is so much more than a fuel source.
Protein is often called the building block of life, as every single cell in the body contains protein. Proteins form muscles, organs and blood cells. Proteins build the enzymes which promote chemical reactions in our body. Proteins build our immune system. Proteins digest our food. Proteins facilitate communication within the body. Proteins are essential to life and are involved with the majority of the body’s processes, in one way or another.
All proteins can be broken down into smaller units called amino acids. These amino acids are what link together, in various combinations, to make different proteins. There are 20 unique amino acids that are utilized by humans, 11 of which can be made by our body and 9 of which cannot. Those 9 amino acids that cannot be made endogenously (i.e. by the body) are considered essential. These essential amino acids must be obtained through diet.
Sources of Dietary Protein
There are two major categories of dietary protein, one being from animal sources and the other from plants. Animal proteins, such as those found in meat, fish, eggs and dairy are considered the most complete sources of proteins. Complete proteins are those that contain significant amounts of all 9 essential amino acids needed for human growth and maintenance. Complete proteins are considered to have a greater biological value, as the body is able to use these more completely.
Plant proteins, such as those found in nuts, grains, seeds and legumes, are viewed as incomplete or of lower biological value as they do not contain all the essential aminos acids needed for protein metabolism within the body. And this makes sense because humans are not plants and as such we need different amino acids to build the proteins we use.
For those following a strict vegan diet (i.e. those consuming no animal products), a little effort must be taken to ensure all essential amino acids are obtained. The good news is that plant proteins are not completely devoid of essential amino acids, they just may be low or lacking in specific ones. The even better news is that different plant proteins have different amino acid profiles. While some are low in certain essential amino acids, others are not. Eating a variety of plant-based proteins throughout the day, such as nuts, seeds, legumes and whole grains, along with a balance of fruits and veggies is usually enough to provide the body with a complete amino acid pool from which it can use to make proteins.
There was once a notion that plant proteins needed to be eaten in certain combinations at the same time, in order to ensure the body gets all the amino acids it needs but this has been debunked. We now know that as long as the body receives the amino acids it needs within a short period of time (say...in a 24 hour period) that the body can synthesize its proteins. It looks as though our body is able to bank amino acids, at least for a little bit, and draw upon what it needs to continue building proteins as required.
Essentially, protein requirements are based on the amount of amino acids needed to replace the body’s daily protein losses (a normal process) and for general body maintenance, growth and repair within the body. Sometimes the body can reuse amino acids already in its system for protein metabolism, while other times it needs new ones added into the rotation (from our diet).
The current protein recommendation, for healthy adults, is 0.8 grams per kilogram of body weight per day(or g/kg/d). There is some evidence, however, that the current recommendations are too low for the healthy adult population. Based on revised methods of tracking amino acid use and excretion, some believe that protein requirements should be closer to 0.9-1.0 g/kg/d. For now, though, the recommendations remain at 0.8 g/kg/d.
Individual protein requirements are calculated based on weight, usually expressed in kilos. If your brain only works in pounds, grab a calculator and divide your weight in pounds by 2.2 to get kilos.
Now, to get your recommended daily protein needs, multiply your weight in kilos by 0.8 (or whatever factor most applies to you). For example, a 64 kg (140 lb) women would need about 50 grams of protein and a 80 kg (175 lb) man would need 64 grams of protein a day based on the current recommendations of 0.8 grams of protein per kilo.
Remember that any number we calculate for protein requirements is a rough estimate. Everyone varies on the spectrum of protein needs and no single calculation can be exactly right. People are too complicated to be reduced to a simple static number. You need not worry too much if you are eating a little more or less than what you calculated. It is simply a ballpark number for you to get an idea of what is appropriate for you to be consuming. Some days you’ll need more, some days less. Let’s not get too hung up on the numbers, as it takes the fun out of eating.
Although the current protein recommendations are set at a level that is believed to be sufficient for 97.5% of the healthy population, there are some medical conditions which require altered levels of protein intake such as kidney and liver disease, cancer or other hypermetabolic conditions. If you have a chronic or acute illness, there may be a need to deviate from general nutritional guidelines, whether it be related to protein or other nutrients. Remember, what is healthy for one person may not be healthy for another. It's a good thing there are Registered Dietitians around to help you sort out what’s best for you.
Just as illness can affect an individual’s protein requirements, we are now learning that old age can also influence protein needs. As we age, our body utilizes and metabolizes proteins differently. Recent research indicates that adults 65 years and older may need more daily protein, 1.0-1.2 g/kg/day to be exact. In the European-based PROT-AGE study, it was found that a higher intake of protein in seniors was associated with less lean muscle and bone loss, higher bone density, and greater muscle strength. A higher protein level, as suggested by this study, is not expected to cause harm in healthy, non-kidney impair seniors. As of yet, however, our current protein guidelines lump seniors in with adults and it may take some time and more evidence for them to be officially revised.
Athletes, as well, require higher amounts of protein compared to that of non-athletic adults. When muscles are used more, such as with endurance or strength training, the body requires a greater amino acid pool to function and grow. However, when these athletes stop or taper their training, their protein intake must, too, be lowered accordingly.
Another group of people that may benefit from a slightly higher protein intake are overweight individuals wishing to shed excess pounds. Protein has an ability to satiate, or induce a feeling of fullness, more so than the other macronutrients of carbohydrate and fat. This satiation factor is one reason that many suggest boosting protein intake to promote weight loss. A few studies have also found that overweight individuals consuming a high protein diet were able to retain more lean body mass while losing weight. In other words, they were able to lose fat mass but keep more of their their lean, metabolically active muscle compared to those on a normal protein diet. As there is some evidence that higher protein diets can be helpful with weight management, it may be tempting to load your plate with excessive amounts of protein. Please refrain from doing this as there is research that finds that modest increases (rather than excessive) are actually more beneficial in promoting weight loss.
Remember, these protein guidelines are not one-size fits all. If you have an acute or chronic illness, are a senior, an athlete or desire weight loss, it is best to consult with Registered Dietitian (RD) to see if you require individualized protein recommendations and eating plan.
Now that you have calculated your estimated protein requirements, what does it mean when translated into real life? It’s great and all to have a cute little number of protein grams calculated but how can you ensure you are meeting these needs? What do your X grams of protein look like on your plate?
If life were simple, which it isn’t, you could easily grab your kitchen scale and weigh out the protein amount you’ve calculated for yourself. Unfortunately, our protein-rich foods aren’t 100% protein (or amino acids). A 90g chicken breast does not have 90 grams of protein. Food doesn’t just consist of one macronutrient. Rather, foods contain various percentages of protein, carbohydrate, fat and micronutrients.
For protein rich foods, us dietitians have a way to roughly estimate the protein content:
Chicken breast (average sized/3 oz or 90g) = 21 grams
Meat - beef, pork, etc. (“palm”-sized, 3 oz or 90g) = 21 grams
Filet of fish (3 oz or 90 g) = 21 grams
Sliced meat (1 oz or 30 g portion) = 7 grams
Ground meat or fish (¼ cup) = 7 grams
Egg = 6-7 grams
Lentils, cooked (¾ cup serving) = 14 grams
Legumes, cooked (¾ cup serving) = 11 grams
Soybeans, cooked (¾ cup serving) = 21 grams
Tofu (¾ cup serving) = 15 grams
Peanut butter (2 tablespoon serving) = 7 grams
Nuts (¼ cup serving) = 7 grams
Milk or yogurt (1 cup serving) = 8 grams
Cheese (¼ cup serving) = 8 grams
So, our theoretical women of 64 kg (140 lbs) needs about 50 grams of protein per day. This can be easily obtained by the following:
Breakfast: Glass of milk, toast with peanut butter (15 grams protein)
Lunch: Salad with a serving of chickpeas (11 grams protein)
Snack: Serving of unsalted almonds (7 grams protein)
Dinner: Chicken breast (21 grams protein)
*please note: only protein foods listed...these are not complete meals
This sample meal plan provides about 54 grams of protein. Of course, the other foods she will eat during the day to complete this meal plan (fruits, veggies, grains) will also have small amounts of protein, too. This fictional women will be getting slightly more protein than her calculated needs but it’s nothing that any well trained nutrition professional would be concerned with.
What happens if you have too little?
Protein deficiency most certainly does not happen overnight. And it won’t happen if you have been eating generally well but not managed to meet your daily protein requirements for a few days. The body can compensate for short periods without sufficient protein intake. It’s really chronic protein undernutrition that is the problem.
For the most part, those in the developed world are able to meet and, usually, exceed their daily protein requirements.True protein deficiency is rarely seen in healthy adults. In the developed world, protein deficiency is more commonly seen in individuals with certain severe illnesses which drive up the body’s metabolic needs, in poverty, alcoholism, eating disorders, poorly planned vegan diets, the elderly and in inappropriately fed infants.
Protein deficiency can also occur when overall energy (or calorie) intake is low. When the body does not receive enough energy to fuel itself, it will start to break down protein (both from the diet and the body) for energy. So even with sufficient protein intake, if calories are lacking, the body can start to develop protein deficiency.
Signs and symptoms of protein deficiency include, but are not limited to, muscle wasting, edema (water retention), poor wound healing, impaired immune system, weakness, fatigue, thinning hair and flaky skin.
What happens if you have too much?
We know that eating too little protein can be quite detrimental in the long term but what about eating above and beyond the recommended protein requirements? Can eating too much protein be bad for your health?
There has been a long standing belief that a high protein diet is bad for the kidneys. Recent research, however, finds that a high protein diet does not negatively affect kidney function in people with healthy kidneys. On the other hand, those with pre-existing kidney disease or at risk for kidney disease (like those with diabetes), should probably steer clear of excessive dietary protein as it is associated with a more rapid decline of renal function in these populations. Also those prone to kidney stones should also abide by the more modest protein intake (of 0.8 g/kg/d) as a high protein diet has been shown to promote stone development.
Osteoporosis and bone loss has also been a concern with high protein diets. A high protein intake, particularly that of animal protein, has been associated with an increase in urinary calcium excretion. Fortunately, this increased calcium loss has not been shown to negatively affect bone density or bone loss. In some cases, a protein-rich diet has been shown reduce fracture risk and promote a greater bone density. It should be noted that although high protein diets don’t seem to bad for your bones like we once believed, it is still recommended that adequate dietary calcium is obtained in conjunction with a higher protein intake to keep bones as healthy as possible.
A high intake of protein, particularly that of red and processed meats, has been implicated in the development of colorectal cancer. In a 2011 literature review, it was found that for every 100g (or 3 oz) of red or processed meats consumed, there was a 14% increased risk of colorectal cancer development. There is some evidence that shows that people who consume the highest amounts of red and processed meats also are those who also eat less fruits, vegetables and fiber-rich foods, all factors associated with increased colorectal cancer development. Still, it is wise to be conscience of your intake of red and processed meats. Considering the current evidence, it is best to limit intake of red and processed meats to no more than a few times per week.
Cardiovascular disease has also been a concern associated with diets rich in animal protein. There seems, however, to be a bit of conflicting information whether or not high protein diets are indeed a factor in the development of heart disease. Several studies show an association between high protein intake and cardiovascular disease, while others do not. Some studies even show a cardiovascular benefit to consuming a high protein diet.
In this dietitian's opinion, if a healthy individual is to consume a high protein diet the most sensible approach would be to choose a variety of proteins, placing a lot of emphasis on fish, plant-based proteins and lean, unprocessed meats. Higher protein diets can be done in a healthy way if the protein amount isn’t too extreme, and includes lots of fruits and vegetables, calcium-rich foods and fiber.
As you can see, protein is an extremely important component of our diet. Protein, and amino acids, are the building blocks of life. Whether you choose to get your protein from plant or animal sources, or both, ensuring you get adequate dietary protein is absolutely essential to living a healthy and energetic life.
Want to learn more nutrition basics? Check out Nutrition 101: Carbohydrates!