Nutrition

Question

This piglix contains articles or sub-piglix about Nutrition

Answer 1

Protein (nutrient)

Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue, and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram; in contrast, lipids provide 9 kcal (37 kJ) per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.

Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the synthesis of the essential amino acids that cannot be biosynthesized by the body.

There are nine essential amino acids which humans must obtain from their diet in order to prevent protein-energy malnutrition and resulting death. They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. There are five dispensable amino acids which humans are able to synthesize in the body. These five are alanine, aspartic acid, asparagine, glutamic acid and serine. There are six conditionally essential amino acids whose 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.

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Answer 2

Protein combining

Protein combining (also protein complementing) is a dietary strategy for protein nutrition by using complementary sources to optimize biological value and increase the protein quality. Originally applied to for animal nutrition, since 1971 it has become a chemical critique of food values of vegetarian dishes.

Protein nutrition is complex because any proteinogenic amino acid may be the limiting factor in metabolism. Mixing can optimize for growth, or minimize cost while maintaining adequate growth. Similarly, human nutrition is subject to Liebig's law of the minimum: The lowest level of one of the essential amino acids will be the limiting factor in metabolism.

Plants are thus rated as protein sources by their limiting amino acids.

The first biochemist to enter the field was Karl Heinrich Ritthausen, a student of Justus von Liebig. Thomas Burr Osborne continued what Ritthausen started and published The Vegetable Proteins in 1909. Thus Yale University was the early center of protein nutrition, where William Cumming Rose was a student. Osborne also worked to determine the essentials, and later led the Biochemistry Department at the University of Chicago.

When Ritthausen died in 1912, Osborne praised his efforts in biochemistry:

Osborne then joined forces with Lafayette Mendel at the Connecticut Agricultural Experiment Station to determine the essential amino acids.

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Answer 3

Protein digestibility

Protein digestibility is how well protein is digested. Along with amino acid score, protein digestibility determine the values for PDCAAS and DIAAS.

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Answer 4

Protein Digestibility Corrected Amino Acid Score

Protein digestibility-corrected amino acid score (PDCAAS) is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it. The PDCAAS rating was adopted by the US Food and Drug Administration (FDA) and the Food and Agricultural Organization of the United Nations/World Health Organization (FAO/WHO) in 1993 as "the preferred 'best'" method to determine protein quality.

A PDCAAS value of 1 is the highest, and 0 the lowest. The table shows the ratings of selected foods.

The formula for calculating the PDCAAS percentage is: (mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x fecal true digestibility percentage.

The PDCAAS value is different from measuring the quality of protein from the protein efficiency ratio (PER) and the biological value (BV) methods. The PER was based upon the amino acid requirements of growing rats, which noticeably differ from those of humans. The PDCAAS allows evaluation of food protein quality based on the needs of humans as it measures the quality of a protein based on the amino acid requirements (adjusted for digestibility) of a 2- to 5-year-old child (considered the most nutritionally demanding age group). The BV method uses nitrogen absorption as a basis. However, it does not take into account certain factors influencing the digestion of the protein and is of limited use for application to human protein requirements because what is measured is maximal potential of quality and not a true estimate of quality at requirement level. Nevertheless, BV can be used to assess requirements of protein derived from foods with known quality differences and measure the proportion of absorbed nitrogen which is retained and presumably used for protein synthesis as an accurate indicator for protein measurement.

Using the PDCAAS method, the protein quality rankings are determined by comparing the amino acid profile of the specific food protein against a standard amino acid profile with the highest possible score being a 1.0. This score means, after digestion of the protein, it provides per unit of protein 100% or more of the indispensable amino acids required.

The FDA gave two reasons for adopting the PDCAAS in 1993: 1) PDCAAS is based on human amino acid requirements, which makes it more appropriate for humans than a method based on the amino acid needs of animals. 2) The Food and Agricultural Organization/World Health Organization (FAO/WHO) had previously recommended PDCAAS for regulatory purposes.

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Answer 5

Protein dispersibility index

The Protein Dispersibility Index (PDI) is a means of comparing the solubility of a protein in water, and is widely used in the soybean product industry.

A sample of the soybeans are ground, mixed with a specific quantity of water, and the two are then blended together at a specific rpm for a specific time. The resulting mixture and original bean flour then have their protein content measured using a combustion test, and the PDI is calculated as the percentage of the protein in the mix divided by the percentage in the flour - a PDI of 100 therefore indicates total solubility.

It has been shown that the PDI can be affected, not only by the type of soybean used, but also by manufacturing processes - heat has been shown to lower the PDI.

The PDI required of a soyflour is dependent on the purpose to which the soybeans are to be put. Manufacturers of soymilk and tofu products want a high PDI to ensure the maximum protein content in their products. However, manufacturers of soy-based fish feed require a low PDI to avoid loss of valuable protein into the surrounding water.

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Answer 6

Protein quality

Protein quality is the digestibility and quantity of essential amino acids for providing the proteins in correct ratios for human consumption. There are various methods that rank the quality of different types of protein, some of which are outdated and no longer in use, or not considered as useful as they once were thought to be. The current protein ranking standard in use is the Protein Digestibility Corrected Amino Acid Score (PDCAAS), which was recommended by Food and Agriculture Organization (FAO), and became the industry standard in 1993, and FAO has recently recommended the newer Digestible Indispensable Amino Acid Score (DIAAS) to supersede PDCAAS, due to the limitations of PDCAAS. The dairy industry is in favor of this, because while PDCAAS truncates all protein types that exceed the essential amino acid (EAA) requirements to 1.0, DIAAS allows a higher than 1.0 ranking, and as such, while for example both soy protein isolate and whey isolate are ranked 1.0 according to PDCAAS, in the DIAAS system, whey has a higher score than soy.

The main limitations of PDCAAS is that it doesn't take into account anti-nutrient factors like phytic acid and trypsin inhibitors, which limit the absorption of protein among other nutrients. For this reason, DIAAS is promoted as the superior method and preferable over the PDCAAS. Other older methods like BV, PER, NPU and nitrogen balance may not reveal much about the amino acid profile and digestibility of the protein source in question, but can still be considered useful in that they determine other aspects of protein quality not taken into account by PDCAAS and DIAAS.

Below follows a table that compares various proteins based on their rankings. Some of these results may differ and vary significantly depending on if it is soybeans or soy protein isolate, and so on. For example, while soybeans have a PDCAAS score of 0.91, many soy protein isolates (though not all) typically get a PDCAAS score of 1.0, and as such, is a complete protein. Likewise, the amino acid profile may differ from crop to crop depending on the soil, and between different breeds of soy. Generally speaking, however, soybeans rarely outperform whey protein isolate in PDCAAS rankings.

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Answer 7

Proteinogenic amino acid

Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation. The word "proteinogenic" means "protein creating". Throughout known life, there are 22 genetically encoded (proteinogenic) amino acids, 20 in the standard genetic code and an additional 2 that can be incorporated by special translation mechanisms.

In contrast, non-proteinogenic amino acids are amino acids that are either not incorporated into proteins (like GABA, L-DOPA, or triiodothyronine), misincorporated in place of a genetically encoded amino acid, or not produced directly and in isolation by standard cellular machinery (like hydroxyproline). The latter often results from post-translational modification of proteins. Some non-proteinogenic amino acids are incorporated into nonribosomal peptides which are synthesized by non-ribosomal peptide synthetases.

Both eukaryotes and prokaryotes can incorporate selenocysteine into their proteins via a nucleotide sequence known as a SECIS element, which directs the cell to translate a nearby UGA codon as selenocysteine (UGA is normally a stop codon). In some methanogenic prokaryotes, the UAG codon (normally a stop codon) can also be translated to pyrrolysine.

In eukaryotes, there are only 21 proteinogenic amino acids, the 20 of the standard genetic code, plus selenocysteine. Humans can synthesize 12 of these from each other or from other molecules of intermediary metabolism. The other nine must be consumed (usually as their protein derivatives), and so they are called essential amino acids. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine (i.e. H, I, L, K, M, F, T, W, V).

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Answer 8

Proximate

Proximates are used in the analysis of biological materials as a decomposition of a human-consumable good into its major constituents. They are a good approximation of the contents of packaged comestible goods and serve as a cheap and easy verification of nutritional panels i.e. testing can be used to verify lots, but can not be used to validate a food processor or food processing facility: a nutritional assay must be conducted on the product to qualify said producers. Nutritional panels in the United States are regulated by the FDA and must undergo rigorous testing to ensure the exact and precise content of nutrients in order to prevent a food processor from making unfounded claims to the public.

From an industry standard proximates include five constituents:

Analytically, four of the five constituents are obtained via chemical reactions and experiments. The fifth constituent, carbohydrates, is a calculation based on the determination of the four others. Proximates should nearly always add up to 100%, any deviation from 100% displays the resolution of the chemical test i.e. small variations in the way each test is performed chemist to chemist will accumulate or overlap the composition make-up.

There are additional ingredients that may fall under the category of one of the five constituents. Carbohydrates for example include but are not limited to:

Whereas Ash includes but is not limited to:

Although proximates do not give the entire nutritional assay, they are an inexpensive way to track deviations from the quality of foods.

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Answer 9

Refeeding syndrome

Refeeding syndrome is a syndrome consisting of metabolic disturbances that occur as a result of reinstitution of nutrition to patients who are starved, severely malnourished or metabolically stressed due to severe illness.

Any individual who has had negligible nutrient intake for consecutive days and/or is metabolically stressed from a critical illness or major surgery is at risk of refeeding syndrome. Refeeding syndrome usually occurs within four days of starting to re-feed. Patients can develop fluid and electrolyte disorders, especially hypophosphatemia, along with neurologic, pulmonary, cardiac, neuromuscular, and hematologic complications.

During fasting the body switches its main fuel source from carbohydrates to fatty acids or amino acids as the main energy source. The spleen decreases its rate of red blood cell breakdown thus conserving red blood cells. Many intracellular minerals become severely depleted during this period, although serum levels remain normal. Importantly, insulin secretion is suppressed in this fasted state and glucagon secretion is increased.

During refeeding, insulin secretion resumes in response to increased blood sugar; resulting in increased glycogen, fat and protein synthesis. This process requires phosphates, magnesium and potassium which are already depleted and the stores rapidly become used up. Formation of phosphorylated carbohydrate compounds in the liver and skeletal muscle depletes intracellular ATP and 2,3-diphosphoglycerate in red blood cells, leading to cellular dysfunction and inadequate oxygen delivery to the body's organs. Refeeding increases the basal metabolic rate. Intracellular movement of electrolytes occurs along with a fall in the serum electrolytes, including phosphorus and magnesium. Levels of serum glucose may rise and the B₁ vitamin thiamine may fall. Cardiac arrhythmias are the most common cause of death from refeeding syndrome, with other significant risks including confusion, coma and convulsions and cardiac failure.

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Answer 10

Resting energy expenditure

Resting energy expenditure, abbreviated as REE, is the amount of energy, usually expressed in kcal (food calories), required for a 24-hour period by the body during resting conditions. It is closely related to, but not identical to, basal metabolic rate.

Resting energy expenditure can be measured using indirect calorimetry. While different collection methods exist, more recent advancements include a mobile indirect calorimeter (Breezing® Metabolism Tracker) that have made REE measurements possible under free-living conditions.

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