There is a lot of information out there on how best to manage your protein intake. You can search and easily find information telling you protein can prevent cancer, help you lose weight, prevent heart disease, and even slow down aging!
Claims without citations make it difficult to know what is true, what has been exaggerated, and what is flat out false.
After some research into the scientific literature, scouring blogs from nutritionists, and combing through reports from health institutions like the Centers for Disease Control (CDC), the National Academy of Medicine, the American Heart Association (AHA), the World Health Organization (WHO), and others, I put together this list of facts about your protein intake.
This list of 51 things to know about your protein intake; broken down into The Basics (1-6), Protein and Your Diet (7-13), The Details (14-28), Facts for Athletes (29-37), and Global Health & Chronic Diseases (38-51).
Your caloric intake is generally broken down at a high level into three categories, or “macronutrients.” These include proteins, carbohydrates, and fats. All three are generally regarded as part of a well-balanced diet.
While the World Health Organization (WHO) suggests protein intake should constitute 10-15% of your caloric intake, the CDC and the Institute of Medicine have established an Acceptable Macronutrient Distribution Ranges of 10-35% for adults aged 19 and older, 10-30% for children aged 4-18, and 5-20% for children under 4. However, some modern diets challenge this (more on this, later).
Another guideline for recommended dietary protein intake is 0.8 grams of protein per kilogram of body weight (0.36 grams per pound).
According to the USDA guidelines, the percentage of calories from your diet derived from protein do not differ between men and women. However, women typically require fewer calories than men. So while the percentage may be the same, the overall quantity of protein consumed will be less for women than it is for men.
As mentioned in fact #1, protein is a term to describe one of the three macronutrients. You may know that fats and carbohydrates are also broad terms that include specific subcategories like omega-3 fatty acids or sugars. Proteins work the same way. Proteins can be broken down into amino acids. We’ll go into more detail on these, later.
According to the CDC, the diet of American men and women averages 16% and 15.5% protein, respectively. This falls in line with the National Academy of Medicine’s recommendations. This also aligns well with NHANES data. Check out our interactive charts to learn more about the average American’s dietary patterns with respect to macronutrients and micronutrients!
The USDA and the Department of Health and Human Services maintains that “strong evidence shows that there is no optimal proportion of macronutrients that can facilitate weight loss or assist with maintaining weight loss.” Diets with different proportions have all demonstrated weight loss and weight gain - the critical component is still total caloric intake. But, protein may still help…
High satiety for certain proteins means you feel fuller after eating them. So while proteins themselves don’t cause weight loss, a diet rich in protein may help you lose weight by helping you feel full, and thus, consume fewer calories.
Those looking to lose weight may experience an unfortunate side effect when they succeed - their muscle mass declines along with the fat! In order to maintain muscle mass during weight loss - particularly important for the elderly to maintain mobility and prevent falls - studies show that maintaining a relatively high protein intake can help.
The standard ketogenic diet recommends that 20% of your caloric intake comes from protein, while the high protein ketogenic diet recommends 35%. The rest? Primarily fats.
A comparison of restricted diets showed vegetarians had less protein intake than omnivores, and vegans even less so. Nevertheless, their protein intake levels were still within a healthy range.
The Blue Zones harbor some of the healthiest and long-lived individuals in the world, so their diets are worth investigating. Their diets vary quite a bit, but they all fall within the recommended range for protein intake of 10-35%. Based off of research from the Blue Zones Solution, the breakdown of the percentage of calories derived from protein is as follows:
Despite eating more protein than the average American, their protein source is largely derived from non-meat products. The breakdown of their caloric intake derived from meat is as follows:
There are 20 standard dietary amino acids. The body degrades and resynthesizes proteins continuously throughout the day. But this process is not perfectly efficient. Some are lost, so they must be replaced. Sometimes termed indispensable amino acids, these 9 amino acids cannot be produced from other molecular precursors in the body. What does that mean? The only way to make sure your body has them is to eat them!
The quality of protein is more important than simply the number of grams of protein in your food. The Food and Agriculture Organization of the UN and the World Health Organization describe how this essentially comes down to the digestibility of the protein (how well your body can actually absorb and use the protein you eat), and the amino acid composition (how complete the protein is to meet your health needs).
The FDA’s labeling protocols stipulate that the protein quantity on nutrition labels take into account both the amino acid profile and its digestibility to give, more or less, a measure of nutritionally available, quality protein.
Meat, by and large, has all of the amino acids necessary for dietary health in digestible forms.
This means that although a vegetable might contain a decent amount of protein, your body might not be able to efficiently digest it all, and therefore not use it all. But this is very much vegetable-dependent and nutrient-dependent.
And because plants typically lack appreciably digestible amounts of one or more amino acids, the Institute of Medicine classifies them as incomplete proteins.
Does this mean vegetarians are doomed to a life of poor protein intake? Not at all! Simply because one vegetable might be missing an essential amino acid doesn’t mean they all do. As per NIDDK recommendations, vary your vegetable intake and you can easily obtain all essential amino acids well above the required protein intake recommendations to overcome concerns about digestibility. Not to mention, eggs are an excellent source of quality protein.
If you are looking for vegetables with high quality protein, look to soy and the so-called superfood, quinoa. According to a review in the British Journal of Nutrition, it has been shown “from nitrogen balance studies, the protein quality of isolated soya protein appears to be comparable to that of animal protein sources such as milk and beef in adult humans.”
Approximately 43% of your body’s protein lies within your skeletal muscle. Structural tissue, such as skin and blood each contain approximately 15% of total protein. Metabolically active visceral tissue like the kidneys and the liver contain roughly 10%, and other organs like the brain, the lungs, bone, and others contain the rest.
Our cells are constantly producing and degrading protein. When protein intake fluctuates, the rate of protein turnover fluctuates. For example, if dietary intake of a particular amino acid is low, the rate of production and degradation of that amino acid in your cells slows down, accordingly.
Labile protein, stored in the body ready for use during periods of fasting, is likely below 1% of total body protein. Thus, according to the Institute of Medicine, there is “no evidence for a protein reserve that serves only as a store to meet future needs.”
Whole-body protein synthesis is roughly 17.4 grams per kilogram of body-weight per day for newborns, 6.9 for infants, 3.0 for adults, and 1.9 for the elderly. This, in part, is why maintaining adequate protein intake in the elderly can help reduce loss in muscle mass.
It is quite possible to have a diet too high in protein. Protein poisoning occurs when your diet is often in the range of 90% protein and above for extended periods of time. This was called rabbit starvation among early hunters and trappers, who subsisted largely on lean rabbit meat. Although getting enough calories, they would ultimately fall ill from little to no dietary fat intake. It can be deadly if left unchanged.
Is there a way to test how much protein you’ve been eating? Urinary nitrogen content is a test used to determine recent protein intake. As your body metabolizes amino acids, nitrogen is released as a by product and excreted as waste through the kidneys. Monitoring whether you are in positive or negative nitrogen balance is a clinical method for determining your recent dietary protein intake.
The Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine recommends 1.2 to 2.0 grams of protein per kilogram of body weight per day for athletes, depending on training intensity.
Casein is known as a “slow” protein, while whey protein is known as a “fast” protein. Whey protein typically increases plasma amino acid levels much greater than casein initially, but reduces substantially after around 3 hours. Casein produces a much small initial spike, but produces elevated plasma amino acid levels for around 7 hours. Some have used this to suggest eating protein in the evenings to enhance muscle protein synthesis overnight, but a recent study has shown this may have little to no affect on body composition over other times.
According to a review of ultra-endurance athletes and experiments regarding their dietary intake patterns, “at the present time, evidence would suggest no additional benefit from consuming supplementary amino acids or protein during ultra-endurance running events.”
When protein oxidation exceeds protein synthesis, muscle breakdown occurs. This generally happens after exercise of increasing intensity. Increasing protein intake after exercise has been shown in some studies to increase protein muscle synthesis, and thus, prevent excessive muscle breakdown.
For those who are looking to get into weight lifting or resistance exercises and gain muscle mass and strength quickly, supplementing your protein intake can accelerate your progress. However, this works primarily for some people new to working out, starting from a low level of muscle mass, or coming back to working out after a long hiatus.
Leucine is one particular amino acid associated with triggering protein muscle synthesis. It has been suggested that maximizing protein synthesis after a workout in order to increase muscle mass requires you to meet a threshold of 1.8 grams/day of leucine. More than that, and studies suggest that you can’t squeeze any more benefit out it.
In those that do respond positively to protein supplements for lean muscle synthesis after resistance exercise, it appears the benefits only tend to occur in the beginning phases of training. Chronic training appears to attenuate the response to protein supplementation. Over the long-run, those that supplement with protein don’t appear to have statistically significant differences in strength.
Some studies, as well as anecdotal evidence, suggests that a “metabolic window”exists after your workout, often around a few hours long, that is ideal for maximizing protein muscle synthesis and where you should optimize your protein intake. However, some studies don’t find any evidence for such an optimized window, and a review of protein intake on protein muscle synthesis suggests there is no evidence for an appreciable effect on timing.
There is significant variability between individuals’ responses to protein and amino acid supplementation with respect to muscle protein synthesis after exercise. Surprisingly, around one third of the population may be in this group that experiences little to no benefit from supplemental protein.
Don’t go overboard with meat consumption. The American Heart Association says that “the main problem is that often the extra protein is coming from meats high in saturated fats, which can add to elevated cholesterol levels of the LDL — or “bad” — cholesterol.” So you may be getting all of your protein, but some bad stuff may be going along for the ride.
The WHO’s International Agency for Research on Cancer (IARC), evaluated over 800 studies to determine that processed meat is a Group 1 carcinogen (same as tobacco or asbestos) for developing colorectal cancer. Harvard’s School of Public Health also indicates the literature suggests links between red meat and diabetes. According to the American Institute for Cancer Research, you should eliminate processed meats from your diet, and reduced red meat intake to 18 ounces per week.
The American Heart Association reviewed the scientific literature, including original research and meta-analyses, to conclude that “in the majority of 22 randomized trials, isolated soy protein with isoflavones, as compared with milk or other proteins, decreased LDL cholesterol concentrations; the average effect was 3%.” But isn’t soy protein bad for women’s health? Well, the science is not as clear as news headlines would lead you to believe. Harvard’s School of Public Health has given an overview of the inconclusive state of the science. Ultimately, some studies indicate soy protein may increase breast tumor growth, while others show a protective effect against breast cancer. More research is sure to come.
Low maternal protein intake during pregnancy has been associated with low birth weight and length. An increase in daily protein intake for pregnant women by 1 gram/day in the first trimester, 8 grams/day in the second trimester, and 26 grams/day in the third trimester is recommended. However, excessive dietary protein intake may also impair fetal growth.
The first 1000 days are critical to a child’s development. During breastfeeding, maternal protein intake should increase by 21 grams/day during the first trimester and 14 grams/day thereafter while breast milk remains a substantial proportion of the infant’s diet.
Stunting is a key indicator and consequence of malnutrition and affects roughly one quarter of children globally. Protein intake appears to be associated with childhood stunting, as evidenced by low concentrations of essential amino acids in circulation.
Kwashiorkor a malnutrition disorder that occurs from a lack of protein and affects growth is prevalent in developing nations. Protein-energy malnutrition results in roughly 6 million childhood deaths per year, globally.
Along with other changes to nutritional demands incurred during cancer treatment, the American Cancer Society states that “people with cancer often need more protein than usual. After surgery, chemotherapy, or radiation therapy, extra protein is usually needed to heal tissues and help fight infection.”
The National Institute of Diabetes and Digestive and Kidney Diseases says that “when your body uses protein, it produces waste. This waste is removed by the kidneys. Too much protein can make the kidneys work harder, so people with chronic kidney disease (CKD) may need to eat less protein.”
A lack of protein does not likely lead to osteoporosis. In fact, protein may contribute to around 1-2% of bone mineral density and helps maintain muscle mass that can help prevent bone fractures.
Animal sources of protein increase excretion of oxalate. When combine with calcium, this can help form kidney stones. The NIDDK suggests limiting animal protein if your risk of kidney stone formation is relevant.
High protein intake does not appear to cause a decline in renal function in normal, healthy adults. However, in individual with slightly declining renal function, high protein intake, particularly from animal sources, has been shown to potentially accelerate the decline in renal function.
The scientific literature regarding protein intake and cancer risk are somewhat contradictory and inconclusive. It’s too early to definitively decide whether low or high protein intake is associated with any change in cancer risk.
Brain function and development is impaired in newborns and adults during long-term protein deficiency, and negative effects on globular and tubular function in kidneys is known to develop.
I hope you’ve enjoyed this list. With so much misinformation out there on proper dietary protein intake, this list will be an updated and ongoing list of useful and pertinent information on the current scientific consensus.
For those managing their diets and performance, keep tracking your protein intake. And if you’re looking for an easy way to do it, try us at Intake!
Please consult your doctor before making any changes to your diet - this information is not intended to be medical advice.
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