Welcome back to the final post in my discussion of the macronutrients!
Protein, like the other macronutrients, IS a fuel source. Just like carbs, one gram of protein provides 4 calories (recall that one gram of fat yields 9 calories). But, protein is an essential macronutrient, primarily because of it’s amino acid content.
Comparatively speaking, proteins are much more complex and variable in their structure compared to fats or carbs. Most proteins are comprised of tens to thousands of amino acids, so there are multiple combinations. There are 20 amino acids that make up proteins, nine of which are “essential,” meaning that they must be consumed from the diet. The other eleven amino acids are considered “nonessential,” meaning that the body is able to create them. It’s worth noting that some of these nonessential amino acids are “conditionally” essential, because in order for the human body to create them, there are other conditions that must be met (e.g. adequate B vitamins).
The essential amino acids are:
The non-essential amino acids are:
- Aspartic acid
- Glutamic acid
A “complete” protein contains all 9 essential amino acids. Animal proteins, quinoa and soy are all considered sources of complete proteins. This is relevant for vegetarians and vegans, because they must often combine foods to get all nine essential amino acids into their diets.
Let’s look at protein digestion a bit. As with all digestion, food is mechanically broken down in the mouth. However, there is no chemical digestion of proteins in the mouth. Food then enters the stomach, where protein digestion is initiated. The parietal cells of the stomach produce hydrochloric acid, which does two things: first, it denatures proteins (in other words, it changes the shape of the protein so that it has more surface area for enzymes to act on it) and second, it activates pepsinogen into pepsin. Pepsin is an enzyme that cleaves proteins into smaller portions, including polypeptides and some free amino acids. So, if you’re someone that takes antacids all the time, it’s actually going to impair your body’s ability to break down proteins! As an aside, if you do experience recurrent heartburn, it is likely that your body isn’t producing enough hydrochloric acid. Yep, you read that right. Our lower esophageal sphincter is stimulated to close with increasing levels of hydrochloric acid. So, too little hydrochloric acid and that sphincter may not close and you can experience acid reflux. For this same reason, I dissuade people from drinking more than 6-8 oz of water in the 30 minutes leading up to, during, and 30 minutes following a meal. Drinking too much water can dilute the effect of your hydrochloric acid and can therefore affect your body’s ability to break down protein.
Protein digestion continues once the food enters the small intestine, where the vast majority of protein digestion and absorption occurs. The hormones secretin and cholecystokinin are released, which essentially tells the pancreas to secrete bicarbonate-rich juices to neutralize the hydrochloric acid from the stomach and triggers the gallbladder to release bile into the small intestine. From here, pancreatic enzymes and brush border enzymes work together to activate one another in a complex feedback loop to ensure that polypeptides are broken down into amino acids, which are then absorbed into the blood and transported to the liver and body tissues. The liver can store amino acids and can distribute them to cells when needed to synthesize the proteins necessary for body function. This means that you do NOT need to get all essential amino acids every single day.
So how do you know if you’re not breaking down protein? Here are the key signs:
- Indigestion and acid reflux
- Slowed stomach emptying and “heaviness” after a meal
- Bad breath and foul – smelling gas
- When protein isn’t digested properly, it putrefies, making gas VERY stinky!
Let’s talk about the function of protein. The body is made of proteins, all of which are continually being broken down and synthesized. When proteins break down, amino acids are freed to join the dietary amino acid storage pool. Believe it or not, 60-70% of all amino acids available in the body are actually recycled from old tissue proteins. Cells will use amino acids to make all of our tissues (e.g. muscle, tendons, bones, blood, organs, hair, skin, nails), hormones, enzymes, hormones and DNA. Proteins also play a key role in maintaining our blood volume, immune function, blood clotting and pH regulation.
So here’s the deal – we want to be sure that protein synthesis happens at a rate greater than the rate of protein breakdown. That makes sense, right? This process is called “protein turnover,” and is often limited by the following essential amino acids: lysine, methionine, threonine, and tryptophan. So, if you’re recovering from an injury or illness, or if you’re in a period of growth (e.g. adolescence, or if you’re simply trying to increase muscle mass), you will have an increased demand for protein.
Protein can be used for more than just tissue generation and can be used for energy. Amino acids can be converted to fat or glucose when blood sugar levels are too low via a process called gluconeogenesis, which occurs in the liver. Note: this where the keto diet can fail! People often keep their carbs very low, and when they have adequate protein stores, amino acids will be converted into glucose and they will not get into ketosis!
The Recommended Dietary Allowance (RDA) for protein is 0.8g of protein per kg of body weight per day, with higher intake for infants, children, pregnant women and breastfeeding women. This value is truly a minimum value, and in my professional opinion, is often too low for athletes. It’s important to note that these recommendations assume that protein sources are complete!
There are undoubtedly some health risks associated with too little protein intake, including poor growth, poor repair of damaged tissues, poor hair/skin/nail quality, hormone imbalances, impaired immune function, digestive enzyme insufficiency and loss of lean muscle tissue.
On the other hand, there can be some risk of eating too much protein. High protein diets have some notoriety for being taxing on the kidneys, and here’s why. When amino acids are used for anything other than protein synthesis (e.g. gluconeogenesis), the nitrogen group is removed by the liver, which is then converted to ammonia, which must be converted to urea by the kidneys for excretion. Now, research has actually shown that this isn’t a problem if you have healthy kidney function. But, this is yet another reason to ensure that you’re getting adequate carbohydrates and fats, as these will provide an energy substrate so that your body can preserve protein, rather than convert it to glucose. There are also some claims that excess protein consumption can lead to osteoporosis and cancer. But in the absence of kidney disease, and when you’re consuming high-quality protein sources, you don’t have much to worry about!
Which leads me to my next point…
Let’s chat a little bit about protein sources. I’d like to start by saying that I am in full support of a vegetarian or vegan lifestyle. In fact, I was vegetarian for years. However, I personally have found benefit by incorporating meat into my diet. Here’s the thing – if you’re vegetarian or vegan, it is absolutely necessary that you vary your protein sources to make sure that you’re getting all nine essential amino acids, particularly if you’re engaging in high-intensity exercise. So, for example, combining legumes and grains can help to ensure that you meet these needs. Furthermore, you need to be mindful about the quality of your grains and legumes. So often, these products have been processed and may be stripped of nutrients. While soy is a complete protein, be wary – 94% of soy grown in the US is GMO! Furthermore, vegetarians are more likely to be deficient in some key nutrients: heme iron (which is only found in meat), zinc (which is more readily absorbed from animal foods), and calcium (which is found in highest amounts in dairy and fish with bones). All three of these nutrients are bound to phytic acid in plants, which affects their ability to be absorbed. If you’re using a protein supplement, it’s also worth noting that the fiber content of plant protein can actually inhibit the digestibility of plant proteins!
What I will say is this – don’t be swayed by some of the media (documentaries, books) out there. Be sure to question their agendas and see who funded them. Here is a link to my response to a documentary promoting plant-based eating, if you’re interested: https://www.youtube.com/watch?v=i5E-gHD8g-E
If you are eating animal products, remember than organic and pasture-raised animals generally have higher vitamin and mineral content, and contribute to less toxic load for the liver (keep in mind that you are consuming every hormone and pesticide that your food was exposed to, and the liver must detoxify and eliminate these). Additionally, pasture-raised animal foods have higher levels of Omega-3 fatty acids, higher vitamin D and more conjugated linolenic acid.
Protein supplements are widely used, and I could use an entire blog post just to discuss them. But, I will leave it to this – read your ingredients. Protein supplements can have some use when your diet is lacking, but they’re often full of junk that you’re better off without!
Bottom line, be sure you’re getting adequate protein, particularly if you’re an athlete or if you’re healing. Protein is also considered a “thermic” food, which means that it burns more calories to digest proteins than it does carbs or fats, so eating adequate protein can promote fat loss. I want to reiterate that the RDA recommendations for protein intake truly are a minimum, so don’t hesitate to eat up to 2g protein per kg of body weight if you don’t have kidney issues. But, be sure that you’re also incorporating plenty of healthy carbs and fats so that you’re able to utilize those for energy and can reserve your amino acids for protein synthesis. And as always, I want to emphasize that it’s more important to look at the quality of our food and avoid foods exposed to hormones, herbicides, pesticides and processing!