If you're reading this expecting me to either endorse or stand in opposition to high-protein diets, turn back now. In nutrition, it's difficult to make a simplistic recommendation out of the mounds of scientific literature that exists on a topic - I can't imagine the stress that the Food and Nutrition Board of the Institute of Medicine (IOM) is under while making population-level recommendations.
Protein is probably the most well studied of the macronutrients, from a physiological and biochemical perspective - the worldwide obsession with ensuring adequate 'complete' protein intake enveloped a lot nutritional sciences research in the 1900's. From this research, we learned a lot about amino acid metabolism/catabolism and understand the basic needs of most humans. It's known now that it's not necessary to only eat complete proteins, and that eating a combination of plant foods can provide all of the amino acids - hence, vegetarians not completely wasting and dropping dead (Hint: stop asking them where they get their protein - it just makes you sound uneducated).
Lately, there's been a big resurgence in the idea of protein intake, and the amount of protein essential for ideal weight/lean muscle/kidney functioning. Protein is quite satiating, though different proteins vary in their satiety measures (1). Because of this satiation, protein has been studied as a potential anti-obesity/weight management tool - and the results are pretty good (2, 3, 4). I don't think many people are doubting this.
However, saying the phrase 'high protein' is about as vague as saying the phrase 'high carbohydrate'. When we talk about carbs, are we talking about table sugar, white bread, whole grains or beets? When we talk about protein, are we talking about various isolates, legumes, eggs, nuts, muscle meats, organ meats, or dairy? There is quite the clear difference in the nutrient density of these foods and each may have their own benefits. Legumes and nuts are great sources of fiber, phytonutrients, some minerals and a potent source of vitamin E (nuts/seeds). Dairy is obviously a great source of Bvitamins and Calcium, as well as fortified vitA and D. Muscle and organ meats provide not only the densest sources of proteins but also fats, some vitamins (liver=VitaminA) and may contain heme iron, B12 and cholesterol. Eggs might be a good source of omega 3 fatty acids (depending on what they're fed), cholesterol, b-vitamins spectrum, choline, vitA/D, iron and selenium. Protein isolates (think whey/casein/soy/pea/rice - your typical protein powders), which I am generally not the biggest fan of, are a good addition to a vegetable/fruit smoothie in the morning- though, on their own, they are pretty nutrient devoid besides protein and maybe some calcium - whey is touted as being a good source of dietary glutathione; however, it's quite hard to find good scholarly information on the digestion and absorption of glutathione, and how significant dietary intakes play opposed to endogenous synthesis- more of the research has focused on dietary cysteine, the rate limiting component of glutathione, spurring glutathione synthesis.
Clearly, all proteins don't come in the same package, and each package is pretty unique. The issue now is: how much should you be consuming? Currently, there is no upper limit set by the IoM - the DRI is set at .8g/kg of body weight (divide your weight in lbs by 2.2) for adults or 10-35% of your calories. If you consume a 2000kcal/day diet, this means that the upper limit of the recommended range for you is 166.5g of protein - pretty high in my opinion. The evidence of long term consumption of diets higher than this is pretty dim - the concern over high protein diets comes from animal models that clearly show renal hypertrophy and damage (6). However, human data doesn't show this same effect (7). Some people will cite Eskimo/Inuit intake of protein as part of the reason for their low serum calcium levels and higher rates of osteoporosis (8), but these rates are far too confounded by a number of other factors, particularly alcoholism (9), to draw a clear causation between high protein diets and osteoporosis - there is still, however, a concern regarding overconsumption of high protein, and ultimately high phosphorous diets, and long term effects on bone density. It's clear that individuals with kidney problems need protein restricted diets, but to say the reverse, high protein diets cause kidney problems, is unfounded in the scientific literature for humans.
So you might be thinking that i'm endorsing high protein diets at this point. But I don't particularly see it that way. Most high protein diets rest largely on animal and dairy proteins, and dairy isolates. I'm writing this just coming off proteins week in the course that I TA for and it's amazing to see the individuals who describe themselves as adhering to a high protein diet (though they still fall in that 10-35% calorie range) but fall short on fiber and so many micronutrients. Looking at high protein diets from the perspective of weight and kidneys is ignoring every other body system. It's one thing to have a diet rich in legumes/nuts/seeds/eggs/dairy/meats as well as fruits and veggies that provides enough protein to exceed the 35% range; it's another thing to consume a couple cups of vegetables, some whole grains, and overwhelming meat, dairy and protein shakes. Sure, you can argue that meat, dairy and whey protein have some nutrition, but they aren't getting you a significant source of fiber, antioxidants like Vitamins C and E, or any phytochemicals. Vitamin E is particularly difficult to get if you're consuming mostly animal products to achieve a high protein diet. It sounds so basic but balance is the key here - if you happen to have a higher protein diet, while getting adequate amounts of all the other nutrients, I wouldn't be overly concerned. But if your idea of a high protein diet is 3 protein shakes a day, meat at every meal and popping a multivitamin, I'm less convinced that's ideal in the long term.
We, very clearly, evolved to be able to utilize and eat more direct sources of proteins, particularly animal proteins via our skilled hunting abilities, but also through the utilization of plant storage units like legumes and nuts. If you'd enjoy more of a discussion on comparative macronutrient digestion, check out this older post.But how this recent intake is reflected in our genome is barely understood, compared to carbohydrates and lipids- there's the obvious amino acid catabolism defects (inborn errors of metabolism), and there are some characterized variants, like that of the serotonergic receptor 2A, that appear to affect preference for higher protein diets (10). More research on variants in amino acid digestion, metabolism, and excretion need to be characterized/understood.
For now, sticking within the 10-35% range that IoM presents seems feasible, more than adequate, and based in good science. Choosing a wide range of foods to achieve not only this protein level but also all of the other essential nutrients seems best.
1.http://www.nutritionj.com/content/10/1/139
2. http://ajcn.nutrition.org/content/82/1/1.full
3. http://www.ncbi.nlm.nih.gov/pubmed/18296329
4. http://advances.nutrition.org/content/4/4/418.abstract
5. http://www.iom.edu/Reports/2002/Dietary-Reference-Intakes-for-Energy-Carbohydrate-Fiber-Fat-Fatty-Acids-Cholesterol-Protein-and-Amino-Acids.aspx
6. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253035/
7. http://www.nutritionandmetabolism.com/content/2/1/25
8.http://www.ncbi.nlm.nih.gov/pubmed/6624550
9. http://www.ncbi.nlm.nih.gov/pubmed/23326764
10. Kohlmeier, M. 2013. Nutrigenetics: Applying the Science of Personal Nutrition
Protein is probably the most well studied of the macronutrients, from a physiological and biochemical perspective - the worldwide obsession with ensuring adequate 'complete' protein intake enveloped a lot nutritional sciences research in the 1900's. From this research, we learned a lot about amino acid metabolism/catabolism and understand the basic needs of most humans. It's known now that it's not necessary to only eat complete proteins, and that eating a combination of plant foods can provide all of the amino acids - hence, vegetarians not completely wasting and dropping dead (Hint: stop asking them where they get their protein - it just makes you sound uneducated).
Lately, there's been a big resurgence in the idea of protein intake, and the amount of protein essential for ideal weight/lean muscle/kidney functioning. Protein is quite satiating, though different proteins vary in their satiety measures (1). Because of this satiation, protein has been studied as a potential anti-obesity/weight management tool - and the results are pretty good (2, 3, 4). I don't think many people are doubting this.However, saying the phrase 'high protein' is about as vague as saying the phrase 'high carbohydrate'. When we talk about carbs, are we talking about table sugar, white bread, whole grains or beets? When we talk about protein, are we talking about various isolates, legumes, eggs, nuts, muscle meats, organ meats, or dairy? There is quite the clear difference in the nutrient density of these foods and each may have their own benefits. Legumes and nuts are great sources of fiber, phytonutrients, some minerals and a potent source of vitamin E (nuts/seeds). Dairy is obviously a great source of Bvitamins and Calcium, as well as fortified vitA and D. Muscle and organ meats provide not only the densest sources of proteins but also fats, some vitamins (liver=VitaminA) and may contain heme iron, B12 and cholesterol. Eggs might be a good source of omega 3 fatty acids (depending on what they're fed), cholesterol, b-vitamins spectrum, choline, vitA/D, iron and selenium. Protein isolates (think whey/casein/soy/pea/rice - your typical protein powders), which I am generally not the biggest fan of, are a good addition to a vegetable/fruit smoothie in the morning- though, on their own, they are pretty nutrient devoid besides protein and maybe some calcium - whey is touted as being a good source of dietary glutathione; however, it's quite hard to find good scholarly information on the digestion and absorption of glutathione, and how significant dietary intakes play opposed to endogenous synthesis- more of the research has focused on dietary cysteine, the rate limiting component of glutathione, spurring glutathione synthesis.
Clearly, all proteins don't come in the same package, and each package is pretty unique. The issue now is: how much should you be consuming? Currently, there is no upper limit set by the IoM - the DRI is set at .8g/kg of body weight (divide your weight in lbs by 2.2) for adults or 10-35% of your calories. If you consume a 2000kcal/day diet, this means that the upper limit of the recommended range for you is 166.5g of protein - pretty high in my opinion. The evidence of long term consumption of diets higher than this is pretty dim - the concern over high protein diets comes from animal models that clearly show renal hypertrophy and damage (6). However, human data doesn't show this same effect (7). Some people will cite Eskimo/Inuit intake of protein as part of the reason for their low serum calcium levels and higher rates of osteoporosis (8), but these rates are far too confounded by a number of other factors, particularly alcoholism (9), to draw a clear causation between high protein diets and osteoporosis - there is still, however, a concern regarding overconsumption of high protein, and ultimately high phosphorous diets, and long term effects on bone density. It's clear that individuals with kidney problems need protein restricted diets, but to say the reverse, high protein diets cause kidney problems, is unfounded in the scientific literature for humans.
So you might be thinking that i'm endorsing high protein diets at this point. But I don't particularly see it that way. Most high protein diets rest largely on animal and dairy proteins, and dairy isolates. I'm writing this just coming off proteins week in the course that I TA for and it's amazing to see the individuals who describe themselves as adhering to a high protein diet (though they still fall in that 10-35% calorie range) but fall short on fiber and so many micronutrients. Looking at high protein diets from the perspective of weight and kidneys is ignoring every other body system. It's one thing to have a diet rich in legumes/nuts/seeds/eggs/dairy/meats as well as fruits and veggies that provides enough protein to exceed the 35% range; it's another thing to consume a couple cups of vegetables, some whole grains, and overwhelming meat, dairy and protein shakes. Sure, you can argue that meat, dairy and whey protein have some nutrition, but they aren't getting you a significant source of fiber, antioxidants like Vitamins C and E, or any phytochemicals. Vitamin E is particularly difficult to get if you're consuming mostly animal products to achieve a high protein diet. It sounds so basic but balance is the key here - if you happen to have a higher protein diet, while getting adequate amounts of all the other nutrients, I wouldn't be overly concerned. But if your idea of a high protein diet is 3 protein shakes a day, meat at every meal and popping a multivitamin, I'm less convinced that's ideal in the long term. We, very clearly, evolved to be able to utilize and eat more direct sources of proteins, particularly animal proteins via our skilled hunting abilities, but also through the utilization of plant storage units like legumes and nuts. If you'd enjoy more of a discussion on comparative macronutrient digestion, check out this older post.But how this recent intake is reflected in our genome is barely understood, compared to carbohydrates and lipids- there's the obvious amino acid catabolism defects (inborn errors of metabolism), and there are some characterized variants, like that of the serotonergic receptor 2A, that appear to affect preference for higher protein diets (10). More research on variants in amino acid digestion, metabolism, and excretion need to be characterized/understood.
For now, sticking within the 10-35% range that IoM presents seems feasible, more than adequate, and based in good science. Choosing a wide range of foods to achieve not only this protein level but also all of the other essential nutrients seems best.
1.http://www.nutritionj.com/content/10/1/139
2. http://ajcn.nutrition.org/content/82/1/1.full
3. http://www.ncbi.nlm.nih.gov/pubmed/18296329
4. http://advances.nutrition.org/content/4/4/418.abstract
5. http://www.iom.edu/Reports/2002/Dietary-Reference-Intakes-for-Energy-Carbohydrate-Fiber-Fat-Fatty-Acids-Cholesterol-Protein-and-Amino-Acids.aspx
6. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253035/
7. http://www.nutritionandmetabolism.com/content/2/1/25
8.http://www.ncbi.nlm.nih.gov/pubmed/6624550
9. http://www.ncbi.nlm.nih.gov/pubmed/23326764
10. Kohlmeier, M. 2013. Nutrigenetics: Applying the Science of Personal Nutrition
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