Protein
Determination Of Plant Proteins Via The Kjeldahl Method And Amino Acid Analysis: A Comparative Study
The standard method for calculating protein content of plants is flawed and overestimates the protein by 16%-93%
Abstract: The amount of protein in most foods is usually determined by multiplying its Kjeldahl nitrogen content by a factor of 6.25. The reliability of this method in quantitating plant proteins was investigated. Ten lesser known plant leaf samples of nutritional significance among certain populations in Nigeria were used for this study. Protein contents of the plant samples were determined via the kjeldahl method using the conventional nitrogen to protein (N:P) conversion factor 6.25 (i.e. total nitrogen × 6.25) and by summation of amino acid residues (considered more accurate and taken here as the actual protein content). From data of total amino acid and total nitrogen, specific N:P conversion factors were calculated for each sample. The N:P factors ranged from 3.24 to 5.39, with an overall average of 4.64. Protein contents were also calculated using this new factor. Comparison of the calculated protein contents showed that the traditional conversion factor of 6.25 overestimated the actual protein content of the samples. The degree of overestimation ranged from 16%-93%. Protein contents calculated with our adjusted factor (4.64) gave results that are in good agreement with the actual protein content. Our results indicate that calculation of protein content by N × 6.25 is highly unsuitable for plant samples.
According to Malaena Medford, besides the above overestimation of protein in plants:
"And the fact that plant proteins are bound to protease inhibitors--which block protein digestion of plant proteins--it means that not only is detecting protein content wrong, but actual digestion and absorption is so far below what one needs that it can make people ill."
The standard method for calculating protein content of plants is flawed and overestimates the protein by 16%-93%
Abstract: The amount of protein in most foods is usually determined by multiplying its Kjeldahl nitrogen content by a factor of 6.25. The reliability of this method in quantitating plant proteins was investigated. Ten lesser known plant leaf samples of nutritional significance among certain populations in Nigeria were used for this study. Protein contents of the plant samples were determined via the kjeldahl method using the conventional nitrogen to protein (N:P) conversion factor 6.25 (i.e. total nitrogen × 6.25) and by summation of amino acid residues (considered more accurate and taken here as the actual protein content). From data of total amino acid and total nitrogen, specific N:P conversion factors were calculated for each sample. The N:P factors ranged from 3.24 to 5.39, with an overall average of 4.64. Protein contents were also calculated using this new factor. Comparison of the calculated protein contents showed that the traditional conversion factor of 6.25 overestimated the actual protein content of the samples. The degree of overestimation ranged from 16%-93%. Protein contents calculated with our adjusted factor (4.64) gave results that are in good agreement with the actual protein content. Our results indicate that calculation of protein content by N × 6.25 is highly unsuitable for plant samples.
According to Malaena Medford, besides the above overestimation of protein in plants:
"And the fact that plant proteins are bound to protease inhibitors--which block protein digestion of plant proteins--it means that not only is detecting protein content wrong, but actual digestion and absorption is so far below what one needs that it can make people ill."
Does protein harm the kidneys - a blog by Amy Berger of Tuit Nutrition
More Than You Ever Wanted to Know About Protein & Gluconeogenesis - Amy Berger of Tuit Nutrition
Protein Leverage Hypothesis - by Alice Klein
"Over many years, Raubenheimer and his colleagues have studied the eating habits of monkeys, cats, pigs, insects, fish, birds, mice, mink, and even slime mould, in an effort to find universal laws of nutrition that also apply to humans. What these studies have revealed is that animals exhibit a ‘dominant appetite’ for protein. If they are given food that is low in protein but rich in carbohydrates, they will keep eating the carb-heavy food until it has supplied them with enough protein. This increases their overall energy intake, leading to weight gain.
Does this hold true for humans?
Increasing evidence suggests that the answer is yes. Similarly to animals, humans also appear to have a fixed daily protein target that must be reached for optimum functioning. The amount of protein that we require each day is believed to have evolved over the course of human history and is now programmed into us."
"Over many years, Raubenheimer and his colleagues have studied the eating habits of monkeys, cats, pigs, insects, fish, birds, mice, mink, and even slime mould, in an effort to find universal laws of nutrition that also apply to humans. What these studies have revealed is that animals exhibit a ‘dominant appetite’ for protein. If they are given food that is low in protein but rich in carbohydrates, they will keep eating the carb-heavy food until it has supplied them with enough protein. This increases their overall energy intake, leading to weight gain.
Does this hold true for humans?
Increasing evidence suggests that the answer is yes. Similarly to animals, humans also appear to have a fixed daily protein target that must be reached for optimum functioning. The amount of protein that we require each day is believed to have evolved over the course of human history and is now programmed into us."
Protein leverage and energy intake
A. K. Gosby A. D. Conigrave D. Raubenheimer S. J. Simpson
First published: 28 October 2013
https://doi.org/10.1111/obr.12131
"Increased energy intakes are contributing to overweight and obesity. Growing evidence supports the role of protein appetite in driving excess intake when dietary protein is diluted (the protein leverage hypothesis). Understanding the interactions between dietary macronutrient balance and nutrient‐specific appetite systems will be required for designing dietary interventions that work with, rather than against, basic regulatory physiology. Data were collected from 38 published experimental trials measuring ad libitum intake in subjects confined to menus differing in macronutrient composition. Collectively, these trials encompassed considerable variation in percent protein (spanning 8–54% of total energy), carbohydrate (1.6–72%) and fat (11–66%). The data provide an opportunity to describe the individual and interactive effects of dietary protein, carbohydrate and fat on the control of total energy intake. Percent dietary protein was negatively associated with total energy intake (F = 6.9, P < 0.0001) irrespective of whether carbohydrate (F = 0, P = 0.7) or fat (F = 0, P = 0.5) were the diluents of protein. The analysis strongly supports a role for protein leverage in lean, overweight and obese humans. A better appreciation of the targets and regulatory priorities for protein, carbohydrate and fat intake will inform the design of effective and health‐promoting weight loss diets, food labelling policies, food production systems and regulatory frameworks."
A. K. Gosby A. D. Conigrave D. Raubenheimer S. J. Simpson
First published: 28 October 2013
https://doi.org/10.1111/obr.12131
"Increased energy intakes are contributing to overweight and obesity. Growing evidence supports the role of protein appetite in driving excess intake when dietary protein is diluted (the protein leverage hypothesis). Understanding the interactions between dietary macronutrient balance and nutrient‐specific appetite systems will be required for designing dietary interventions that work with, rather than against, basic regulatory physiology. Data were collected from 38 published experimental trials measuring ad libitum intake in subjects confined to menus differing in macronutrient composition. Collectively, these trials encompassed considerable variation in percent protein (spanning 8–54% of total energy), carbohydrate (1.6–72%) and fat (11–66%). The data provide an opportunity to describe the individual and interactive effects of dietary protein, carbohydrate and fat on the control of total energy intake. Percent dietary protein was negatively associated with total energy intake (F = 6.9, P < 0.0001) irrespective of whether carbohydrate (F = 0, P = 0.7) or fat (F = 0, P = 0.5) were the diluents of protein. The analysis strongly supports a role for protein leverage in lean, overweight and obese humans. A better appreciation of the targets and regulatory priorities for protein, carbohydrate and fat intake will inform the design of effective and health‐promoting weight loss diets, food labelling policies, food production systems and regulatory frameworks."
Essential amino acid
An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized de novo (from scratch) by the organism, and thus must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H).
Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. These six are arginine, cysteine, glycine, glutamine, proline, and tyrosine (i.e., R C G Q P Y). Five amino acids are dispensable in humans, meaning they can be synthesized in sufficient quantities in the body. These five are alanine, aspartic acid, asparagine, glutamic acid and serine (i.e., A D N E S)
An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized de novo (from scratch) by the organism, and thus must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H).
Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. These six are arginine, cysteine, glycine, glutamine, proline, and tyrosine (i.e., R C G Q P Y). Five amino acids are dispensable in humans, meaning they can be synthesized in sufficient quantities in the body. These five are alanine, aspartic acid, asparagine, glutamic acid and serine (i.e., A D N E S)
There is no evidence that protein damages the kidneys. Furthermore, high-protein diets appear to have no harmful effects on other valued health markers.
Dr. Benjamin Bikman - 'Insulin vs. Glucagon: The relevance of dietary protein'
Low Carb Breck - 2018
Low Carb Breck - 2018
why do my blood sugars rise after a high protein meal? - Article by Marty Kendall in Optimising Nutrition
There is a lot of controversy and confusion over gluconeogenesis and the impact of protein on blood sugar and ketosis.
There is a lot of controversy and confusion over gluconeogenesis and the impact of protein on blood sugar and ketosis.
Worrying about getting too little or too much protein is largely irrelevant. We will get enough protein when we eat a nutritious diet. Left to its own devices, our appetite typically does a good job of seeking out adequate protein to suit our current needs.
Meanwhile actively aiming to minimise protein will make it harder to maintain lean muscle mass which is critical to glucose disposal and insulin sensitivity.
A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations - 2005
Conclusions: An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.
Conclusions: An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.
Studies
- The relationship between gluconeogenic substrate supply and glucose production in humans. PMID: 2407133 Published 1990
“Our data so far indicate that under almost any physiological situation, an increase in gluconeogenic precursor supply alone will not drive glucose production to a higher level, suggesting that factors directly regulating the activity of the rate-limiting enzyme(s) of glucose production normally are the sole determinants of the rate of production; hence, there will be no increase in glucose production if the increase in gluconeogenic precursor supply occurred in the absence of stimulation of the gluconeogenic system.”
(This paper suggests that gluconeogenesis is driven by the hormones that regulate glucose production and not by the amount of substrate. It is possible that Protein consumption affects the rate-limiting enzymes.) - Regulation of hepatic glucose production and the role of gluconeogenesis in humans: is the rate of gluconeogenesis constant? PMID: 18561209 Published 2008
“… the rate of gluconeogenesis remains remarkably stable in widely varying metabolic conditions in people without diabetes.”
(This paper suggests that unless you have diabetes that gluconeogenesis is remarkably stable. This is what you would expect. Why would your body build glucose unless it is short of glucose? So, what happens to people with diabetes.) - Hormonal regulation of hepatic glucose production in health and disease. PMID: 21723500 Published 2011
Link to full study see also below for a link to the PDF
HGP (Hepatic glucose production) is exquisitely sensitive to glucagon and insulin. Glucagon sets the basal tone, but insulin trumps glucagon at any concentration–just as it does in vitro.
“In type 2 diabetes, HGP is higher in the post-absorptive state, and fails to be properly suppressed by insulin, resulting primarily from excessive gluconeogenesis, rather than glycogenolysis”
(This provides an interesting insight. In T2D where the pancreas has started to fail, we have a decrease in the production of insulin. Insulin is the master hormone in terms of stopping gluconeogenesis. It would seem that gluconeogenesis only goes up when you have T2D and are producing insufficient insulin.
With the probable exception of T2 diabetics gluconeogenesis will also increase on a ketogenic diet. This is simply a result of the reduction of dietary glucose. The body increases the rate of gluconeogenesis to ensure that there are adequate basal levels of glucose. The level will depend on the amount of CHO in the diet. There is more than enough substrate from the glycerol backbone of triglycerides and protein turnover waste to fuel this increase. T2 diabetics are typically already making more glucose than they need, so can’t and won’t see this increase.)
- The effects of carbohydrate variation in isocaloric diets on glycogenolysis and gluconeogenesis in healthy men. PMID: 10843182 Published in 2000
“Gluconeogenesis was about 14% higher after the very low carbohydrate diet.”
(This study was probably not long enough to see the full increase of gluconeogenesis on a ketogenic diet, and it will of course vary by individual and glucose consumption and T2D status. However, it does show the expected increase when there are insufficient carbohydrates in the diet. ) - Dietary proteins contribute little to glucose production, even under optimal gluconeogenic conditions in healthy humans. PMID: 23274906 Published in 2013
“We can thus suppose that the participation of dietary proteins will be negligible in the presence of carbohydrates in the meal. We provided the first direct evidence that under optimal gluconeogenic conditions and in a realistic nutritional situation, dietary proteins only make a relatively modest contribution to the maintenance of blood glucose levels.”
(This study is amazing in terms of how they tracked the amino acids. So even in a condition where gluconeogenesis was required dietary protein didn’t contribute that much, and dietary protein wasn’t a factor when there was a CHO source.
In my view, these studies supported by anecdotal evidence from researchers such as Professor Benjamin Bikman and protein research specialist Professor Stuart Phillips provide a reasonable conclusion that excess protein doesn’t get converted to glucose, certainly not in most cases. There may be outlying scenarios, but I don’t think it is something that the general public need worry about.)
| hormonal-regulation-of-hepatic-glucose-production-in-health-and-disease.pdf |
Amino acids derived from ingested protein are potential substrates for gluconeogenesis. However, several laboratories have reported that protein ingestion does not result in an increase in the circulating glucose concentration in people with or without type 2 diabetes. The reason for this has remained unclear. In people without diabetes it seems to be due to less glucose being produced and entering the circulation than the calculated theoretical amount. Therefore, we were interested in determining whether this also was the case in people with type 2 diabetes. Ten male subjects with untreated type 2 diabetes were given, in random sequence, 50 g protein in the form of very lean beef or only water at 0800 h and studied over the subsequent 8 h.
Protein ingestion resulted in an increase in circulating insulin, C-peptide, glucagon, α amino and urea nitrogen, and triglycerides; a decrease in nonesterified fatty acids; and a modest increase in respiratory quotient.
The total amount of protein deaminated and the amino groups incorporated into urea was calculated to be ∼20–23 g. The net amount of glucose estimated to be produced, based on the quantity of amino acids deaminated, was ∼11–13 g. However, the amount of glucose appearing in the circulation was only ∼2 g. The peripheral plasma glucose concentration decreased by ∼1 mM after ingestion of either protein or water, confirming that ingested protein does not result in a net increase in glucose concentration, and results in only a modest increase in the rate of glucose disappearance.
How carnivorous are we? The implication for protein consumption
Miki Ben-Dor
Summary by Jennifer Lechner
Miki Ben-Dor
Summary by Jennifer Lechner
- The average size of mammals fell dramatically between the Pleistocene (about 2 million years ago) and the current era. The author argues that this happened due to hunting by humans.
- The diversity of those large mammalian species has been drastically reduced, leaving current hunter-gatherers in a much different environment than what once existed.
- The larger the animals, the more likely they were to go extinct during this period.
- Studying weaning patterns, carnivores, omnivores, and herbivores have their own distinct timetables. Humans land squarely in the carnivore category.
- Carnivores' fat cells are small and numerous. Omnivores have fewer, larger fat cells. "Humans were found to be at the top of the carnivorous pattern."
- The stomach acidity of an omnivore averages 2.9, a carnivore 2.2, and a scavenger 1.3. Human stomach acidity is 1.5.
- Other primates have much larger guts than we do, especially regarding the large intestine, which digests fiber. They all have longer large intestines than small intestines. So do pigs, famous omnivores.
- We are also adapted for endurance running, throwing, and going long periods without eating, all of which point toward life as a hunter of large game.
