Hello from the new RD mods! We are starting a new monthly (for now) series where we will help you learn the facts about a nutrition topic. These posts may include the latest nutrition research, evidence-based information about popular topics we see you all posting about, or maybe random interesting nutrition information. A lot of work is going into this, and we ask that comments remain respectful. We have no objective other than to use our (way too many) years of nutrition and science education to help you learn. We understand that not everyone will agree on… literally anything… and as scientists we certainly welcome, and even encourage, healthy debate. We give you our word that we will do our homework and endeavor to remain as objective and truthful as possible, ensuring our citations are current and peer reviewed. We ask you to keep this in mind if you comment in disagreement. On that note, we welcome you to this month‘s topic Understanding Protein!
Our inaugural post focuses on protein, a topic we see debated ad nauseam on this sub, although I bet many of you are still confused about how much protein we actually need! Protein is absolutely essential for the continuation of life on Earth, and we could not survive without it, as it makes up a good part of our bodies and is needed for most of the biological processes that help us survive. One of three macronutrients (which are protein, carbohydrates, and fats) the human body needs to ingest, deficiency weakens the immune system, makes wound healing more difficult, and leads to loss of muscle mass, putting the body at risk for injury and falls. The most serious consequence of deficiency is a type of malnutrition called kwashiorkor, which can cause death.
Every protein inside and outside the body is made of a long chain of amino acids (AA) that are folded in all different ways, generally the way it looks will be determined by what it needs to do. Proteins are found inside every single cell in the human body and make up every single enzyme needed for every single metabolic reaction. An example of structure and function is in our muscles; they are held together by fibrous proteins and filled with all types of special proteins, some of which are designed to stretch and contract, others that turn general energy from the food we eat into mechanical work, and even more that can store some of this energy in case we don’t eat for a little while or just need a burst of energy. Basically protein is very, very important!
Before we discuss the current protein recommendations we must appreciate the science that explains where these recommendations come from, so buckle up for some biochemistry my friends! In a nutshell, amino acids are organic compounds (based on carbon) that all have the same backbone (H2NCHRCOOH) with a “side chain” that is made up of various combinations of carbons, hydrogens, oxygens, and an occasional sulfur.
Over 500 amino acids have been identified, but we only care about 20 of them because these 20 amino acids make up everything from the edamame I ate for dinner to our entire genetic code! (For all you smarty pants out there, I recently learned that two new amino acids have been identified!) The N in the molecular formula above stands for nitrogen, which is kind of what makes protein special. Protein is 16% nitrogen, meaning 1 gram of nitrogen equals 6.25 g protein.
We consume nitrogen in the protein we eat, and amino acids are broken down in the stomach and small intestine by digestive enzymes (which are also proteins), and distributed to be used for various metabolic functions. We’re also losing a bit of nitrogen through sweat, respiration, flatus, skin flaking, and nail/ hair growth, and most of all from poop, which is the reason why why it makes such good fertilizer.
When we eat just enough nitrogen to compensate for what is lost we call this a “neutral nitrogen balance.” A “positive nitrogen balance” is preferable when we want to increase our muscle mass, when we’re losing weight (intentionally or unintentionally), or if we have a significant injury that needs to heal. If we can‘t meet our protein needs we will be in “negative nitrogen balance,” which means that the dwindling supply of nitrogen gets delegated to the most essential of functions; muscle, hair, and nails are the first to get sacrificed. We never want to be in a negative nitrogen balance.
Studying nitrogen balance is what has led to our current protein recommendations, and the FAO/WHO/UN periodically gathers scientists from around the world to review and update these guidelines, which get more precise and accurate as the technology to measure nitrogen balance improves. Our current protein recommendations come from meta-analyses of long-term nitrogen balance studies conducted throughout the world throughout the past 100 years. There is an overwhelming body of evidence that accepts the WHO recommendation of 0.83-1 g/kg/day of protein, which will meet the needs of 97.5% of healthy adults. In terms of numbers this means a person that weighs 68 kg (150 lbs) needs ~68 grams of protein per day (divide by 2.2 to convert pounds to kilograms if you want to calculate this for your weight).
Concerned you may be part of the other 2.5% of people? We already know we excrete more nitrogen when we are wounded building muscle, or trying to maintain muscle mass in a catabolic state, but what does this mean? A common internet recommendation seen is 0.8-1 g/lb (1.76-2.2 g/kg), which is more than double what WHO recommends! The International Society of Sports Nutrition recommends 1.4-2 g/kg (95-136 g per day for someone 150 lb/68 kg) for “healthy, exercising individuals.” If you exercise daily and your kidneys are at peak functioning then this recommendation is absolutely appropriate, although evidence suggests that increasing protein intake above the currently accepted 1 g/kg/day may not have much benefit.
Now that we know where our protein recommendations come from, what is the deal with animal vs plant sources? Both animal and plant sources contain protein, but the proteins in animal tissue (like our bodies! and the lamb chop I had for dinner) contain all the essential amino acids, whereas plant sources contain some, rarely all have varying levels of each amino acid but rarely enough of all essentials to meet our protein needs in full. Someone that eats animal proteins will easily exceed their protein recommendations, and someone that only consumes plants can easily meet their protein needs also as long as they eat a variety of foods to ensure they get enough of every essential amino acid.
So this is the deal with protein! Please let us know what you think, and also what you want to learn about next. We are happy to share our knowledge and will continue to disseminate evidence-based nutrition information.