No, we don't eat enough protein

ageing amino acids bones health longevity musculoskeletal nutrient nutrition protein Jun 17, 2023

So I didn’t watch it, but there was a news article that said New Zealander’s get enough protein in their diet, but it’s just that we don’t get enough earlier in the day.
I agree that the way we eat protein is skewed. That more people need to focus on higher protein for breakfast. However, the idea that we get enough protein is fake news. This isn’t just my opinion which based on clinical experience, speaking to experts, reading the research for over two decades now – it is the opinion of all the protein metabolism experts (Don Layman, Luc Van Loon, Stu Phillips, Layne Norton, Bill Campbell) and other notable health and research authorities.
There are a couple of reasons I think that people say, ‘we eat enough protein’. The major one is that protein intakes are often compared against the recommended dietary intake value (RDI). These are recognised as being woefully low for anything other than survival. It’s set at 0.8kg/kg body weight. There is a difference between what we need to survive and what we need to thrive. And those recommendations were derived using short term nitrogen balance studies.
Nitrogen balance is a measure of nitrogen input minus nitrogen output. Nitrogen is a fundamental component of amino acids, which make up proteins. Hence, it is often used as a proxy to estimate the amount of protein in a person's diet or the protein requirement of the body.
However, the use of nitrogen balance for assessing protein intake has its limitations. Here are some of the key issues (and some papers around it herehere and here, as examples):
1. Accuracy of measurement. The accuracy of nitrogen balance studies depends heavily on precise measurements of all nitrogen inputs and outputs. This is quite challenging as it requires complete collection of all food consumed and all bodily waste excreted (urine, feces, sweat, etc.). Any errors in these measurements can result in inaccurate estimates of nitrogen balance. Endogenous losses are also not well accounted for.
2. Individual Variation. Individual metabolic variations can impact nitrogen balance. Factors like age, sex, physical activity level, overall health status, and the presence of certain conditions like illness or stress can affect nitrogen metabolism and, therefore, nitrogen balance. Studies used to inform the recommendations completed on healthy adults.
3. Bioavailability of Nitrogen: Not all the nitrogen consumed in the diet is available for absorption and utilization by the body. The bioavailability of nitrogen can vary depending on the source of the protein (animal vs. plant-based), the individual's gut health, and other dietary factors. This can skew the nitrogen balance.
Overall, while nitrogen balance is a useful tool for estimating protein requirements, these potential limitations mean that it might not provide a complete or accurate picture of an individual's protein needs. Other methods of measuring protein needs, such as the indicator amino acid oxidation (IAAO) method, might provide more accurate results in certain cases. However, each method has its own pros and cons, and the best approach often depends on the specific situation. Last on this, the short-term experimental diets of low protein intake downregulates the body’s processes that are not related to survival, therefore falsely reduces the amount of nitrogen that appears critical for ‘balance.’
And, what does enough even mean? When looking at studies to support muscle hypertrophy, amounts of 1.6g/kg body weight are recommended, with no further requirements to max out muscle protein synthesis. This is, however, just one role of protein in the body. Protein does many things. It regulates water balance, it helps with blood sugar regulations, it forms the basis of enzymes to act as messengers, it acts as a storage protein to deliver nutrients like iron, it does so many things. Yet people go back to muscle protein synthesis and that if you have enough to support that, then that’s all you need. And, in a meal, you need around 30g of actual protein to maximise that response (older adults need more - ~40g, kids need less, around 10-15g). The thing that stimulates that process is an amino acid called leucine and aiming for around 3-4g of leucine in a meal is recommended. However, we have a requirement for 8 other amino acids we can’t make ourselves and must get from food. These include lysine (around 3g in a meal, as suggested by Don Layman, with 15mg/kg body weight across a day) and methionine (a gram in a meal). Eating high quality sources (animal protein) will get you these. Eating plant protein requires a bit more nuance as those amino acids aren’t as bioavailable in a plant protein source (which is why plant sources are ‘incomplete’ sources of protein).
So, while this recommendation of ~30g in a meal is more than the RDI of 0.8g for most people, it still likely isn’t enough to get people to the 1.6g/kg to help build muscle (which hopefully is a goal of everyone reading, as muscle is most important as an organ of longevity). If we then consider that we are an aging population or that many people are improving body composition by dieting (calorie deficit) it’s recognised that we need more than that - 2.2g/kg body weight. These are not factored in if looking solely at the RDI for our protein requirements.
If you’re someone who is a hungry person (I would fall into this category – definitely a volume eater), you should focus on more protein also - if you just stuck to the guidelines, you may get around 12% protein. Maybe a little more, and that is like the protein sweet spot for making you feel even more hungry. Analysis of protein content in diets from our friend Marty Kendall over at Optimising Nutrition has found that people generally overeat calories when their diets are around this level of protein - which is pretty much describing the standard western diet. He’s found the amount of protein you eat correlates with how much you eat overall - an extension on the protein leverage theory. The modern diet is a protein-diluted diet.
My final point around why we can’t say NZers eat enough protein is because: We don’t know what NZers eat, actually, It’s been 2008/09 was the last nutrition survey. Since then, there has been gradual shift in the nutrition environment to more fast food, more convenience food, more focus on ‘plant-based’ and more messages against the protein sources that actually deliver micronutrients that we are low in too. It wouldn't be a stretch to think our diets had become even more protein-dilute.
New Zealanders eat enough protein if we compare these old intake values to the out-of-date RDI. That’s the only conclusion I can draw when I hear someone say we eat enough protein.

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