Protein Nutrition
When you break it down, people get their energy from three sources:
Carbohydrates (Starches, Sugars, but not all carbohydrates because fibre fits into this category also and your body can't digest that. Which is why your poop has bulk, or else it'd all be like diarrhea.)
Lipids (A fancypants way of saying "Fat". You need Omega-3 and Omega-6 fatty acids [called lineolic and alphalineolic acids] to make HDL ["Good Cholesterol", but actually stands for "High Density Lipoprotein"] to move LDL ["Bad Cholesterol", means Low Density Lipoprotein] to the liver, but this is a whole different story.)
Protein (A string of amino acids thrown together -- it looks like powder; or maybe tuna. Another thing about protein is that your body rips it apart to amino acids and puts it back together to make enzymes. It can make 12 of them as an adult -- you need to acquire 8 of them through diet.
This is what hemoglobin, a protein, is shaped like!
Anyways, in fundamentals of nutrition we're now focusing on proteins. As I said, these are amino acids put together, which make muscle, enzymes, hormones, and transport proteins (like hemoglobin, which carries oxygen around your body -- it's what makes red blood cells red). But also you can break down proteins to make glucose (sugar; easy to obtain energy from), glycogen ("stored energy in muscle"), and triglycerides (the backbone of many fat based structures).
Amino acids come in two variants: L and D. But not really, as they'll almost always occur as "L" in proteins and "D" only shows up in some weird sea life or something. They have both a positive charge and a negative charge at our body's acidity, and are called "Zwitterions", which stands for "Twice Ions" in German. And they can join together if supplied with water, which we have conveniently in our bodies, but it takes enzymes to do so.
Kinda cryptic
Basic amino acids: K, R, H
Acidic: E, D
Neutral amides of acidic: N, Q
Aliphatic; Straight: G,A
Aliphatic; Branched: L, I, V
Aliphatic; Hydroxylated: S, T
Sulfur Containing: C, M
Aromatic: F, Y, W
Imino: P
Essential amino acids0:
FCK MY WIT V (HR in infants)
(Fuck My Wit, V is a silly phrase...)
Phenylalanine, Cysteine, Lysine, Methionine, Tyrosine, Tryptophan, Isolucine, Threonine, Valine.
(Histidine, Arginine in infants)
*Cystine can substitute itself for Methionine, so they kind of count as one.
**Tyrosine can substitute itself for Phenylalanine, so they kind of count as one.
Back from seemingly random letters
So there's a term called "Protein Quality", which describes how good the protein is for you.
1) Does the protein have a good balance of amino acids? Animal proteins tend to have all the essential amino acids we need, but plant protein is usually deficient in one area. For example, grains are low in lysine and legumes are low in amino acids with sulfur (SAAs)
2) Digestibility. If the protein is in a form we can't digest, or we have horrible diarrhea (we learned about diarrhea in principles of disease -- professor's comical anecdotes to follow at the end of this post) then it won't do much good for us.
3) Presence of toxic factors. Animal protein usually has few contaminants with our protein, but plants have lots of various toxins that can damage the protein and make it pretty much useless to us.
4) Species consuming the protein. Humans have different nutritional requirements in terms of protein than rats. (I believe rats require the proteins human infants do at any stage of development -- other than that they're pretty close to adult humans. They also need more methionine for hair production...)
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So the "official method in Canada" for evaluating protein quality is called the "Protein Efficiency Ratio". In this method, for a period of 4 weeks, young rats are fed a diet with all nutrients at adequate levels except for protein which is included at 10% of the diet. (Presumably according to rat weight.)
Because the amount of protein is very little for the rat, if there is anything wrong with the protein source it won't grow as much. So they scale the weight gain to the amount of test protein consumed over the four weeks to make the PER. This is better than chemically testing to see what proteins there are because it mimics digestability -- but worse because the limiting factor could be one of the two proteins normally required only by infants, or methionine, making it a bad representation of an adult's requirements or the whole population respectively.
a little more technical -- eggs are protein god!
A while egg will give a PER of about 2.0. This is important because it gives rise to the "Chemical Score" of a food, or CS. After chemically digesting it and mathematically comparing the results to the composition of a whole egg, the CS is equal to the abundance of the limiting amino acid in a test protein to the abundance of the same amino acid in an egg.
Example: Suppose that rats fed wheat didn't grow optimally because they didn't have enough methionine. 2.5% of wheat protein is methionine, and 4.1% of egg protein is methionine. The CS for wheat is then 2.5%/4.1% * 100, or 37.
Nitrogen Balance
Proteins contain nitrogen. Our nitrogen balance is how much we take in, minus how much we lose through urine, feces, sweat, skin erosion, etc. As we grow up, our nitrogen balance is positive, and when we get old it becomes negative.
If you're growing and protein quality is marginal, then you will not have as much of a positive nitrogen balance and you will grow slowly. In adults, it will become increasingly negative as you lose "lean mass" -- that is, your proteins are being consumed to fuel your body functions, and you atrophy.
For humans, the Protein required is 0.78g / kg body weight per day, x1.1 for the quality of the protein we eat here (it's pretty good in North America!) So a 70kg person will require about 60g of protein per day. (Sidenote: The nutritional information on the side of cans, when it gives percentile of requirements, is good for 99.5% of people. So it's likely to be more than what you need according to that. Many North Americans consume 100-150g of protein per day, causing increased risk of Cancer, Cardiovascular disease, and it can aggrevate kidney disease.
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Protein Energy Malnutrition (PEM) or Protein Calorie Malnutrition
These are pictures of two children suffering from Protein Energy Malnutrition. The child on the left has "Kwashiorkor", which is caused by a diet very low in protein (~1% to 2%). Your body continues to bring fatty acids to the liver, which cannot make the VLDL proteins to distribute it to the body, so triglycerides build up in the liver. The decreased plasma protein causes your blood to be more watery, so it oozes into your cells, causing edema (cells retaining water and being bloated) in the central area, causing the bloated stomach appearance.
The child on the right is suffering from Marasmus. This is caused by a low intake of a reasonably balanced diet (~8 to 10%). The body will use up absolutely ALL body fat to sustain itself, including fat under the skin (causing the wrinkled appearance). Weight and height will decrease, and the body may shift towards Kwashiorkor in infants as the stress of the disease causes the body to forsake protein from the diet to convert to glucose in the body for energy.
Both of these cause immune depression: Immune functions will be lost, and death will commonly happen due to diarrhea, pneumonia, etc. -- typically faster in the kwasiorkor patient. The mortality time for these diseases is typically 1 to 2 months. There are more chronic cases of PEM that allow survival, but these are the most severe or dangerous.
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Protein, from tuna to small intestinal cells:
1) You eat it. Your mouth mashes it. It's a fairly distributed paste.
2) It hits your stomach. The acid in the stomach changes the shapes of the proteins you eat so they are no longer doing their proper function. Your body releases two precursors to enzymes here: Pepsinogen, and Parapepsinogen 1 and 2.
3) It hits the small intestine. Because your small intestine is no longer acidic, pepsinogen and the parapepsinogens will activate to become pepsin and parapepsin 1 & 2. Because they were saturated with the food in the stomach, they will activate throughout the food and act quickly, turning the protein into small tiny amino acids.
4) Your pancreas releases trypsinogen, chymotripsinogen, proelastase, and procarboxypeptidase A&B into the small intestine. Enterokinase (or "enteropeptidase") will turn trypsinogen into trypsin, which digests proteins. Trypsin will turn Chymotripsogen, proelastase, and procarboxypeptidase A&B into chymotrypsin, elastase, and carboxypeptidase A&B. Your small intestine will also release aminopeptidase on its own. Essentially, a lot of precursors are released here that turn into enzymes to digest protein, and it gets pwned into amino acids.
5) The intestinal cell membrane has a transporter to bring amino acids into it without coercion, as well as transporters that bring it in using a sodium gradient as energy, and it also has a pump that converts ATP (a molecule with high potential energy) to ADP (less energy) to pump sodium out of the cell so it doesn't accumulate.
To sort things out what enzymes do what:
Trypsin attacks basic groups.
Elastase attacks neutral aliphatic.
Pepsin, parapepsins, and chymotrypsin attack large neutrals.
*These three can digest from the middle, and are called endopeptidases
Amino peptidases attack NH2 groups.
Carboxypeptidases attack COOH groups.
*I think these start at the end amino acids of a protein, and are called exopeptidases
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The small intestinal cells all have their veins drain to the "Portal Vein" NOW WE'RE STUDYING WITH PORTALS, and the liver is situated at the end of the portal vein conveniently. Nutrients and toxins get removed from the bloodstream here, which regulates the blood levels of amino acids after a large meal. Any amino acids that the liver misses are degraded: NH3 goes to the urea cycle, carbon skeletons from them go to energy production, lipogenesis, or gluconeogenesis.
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So, er, changing gears entirely: Let's Talk About Cows
As we all know, cows are weird and have four "stomachs". The first is for temporary storage and does some bacterial digestion. The second focuses more on just bacterial digestion.
Well, the cow ends up consuming, via "traditional digestion", about 60% bacterial and 40% food proteins. The bacterial proteins have high digestability and good amino acid balance in comparison to the feed proteins. In bacteria breaking down amino acids they had in excess, they made ammonia, which they can use to make new amino acids -- however, this is volatile and diffuses out of the rumen to the blood, where the liver turns it to urea (what makes your peeeeee yellow) and shoves it back into the rumen (the 1st "stomach"), and the saliva (which eventually goes to the rumen). The urea is then broken down again in the rumen to make ammonia once more.
When protein turns over in other tissues, like muscle, and the nitrogen is converted to urea, this too may end up in the rumen to support the bacteria, so that's really functional! And, because the bacteria make amino acids, they can get protein from non-nitrogen sources like molasses!
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More About Proteins
Like most things in... living things... there are tags thrown on molecules to mark them for the body. Sorta like how DNA can be methylated, or cell exteriors get tagged with antigens... anyways, proteins have the dame idea.
1) Phosphorylation - This is key for regulating enzymes! KEY! I forget specific enzymes, but IT'S FRIGGIN KEY!
If you take the OH on amino acids S, T, or Y, you can attach a phosphate group to the alcohol group to turn it into a phosphate group.
2) Hydroxylation - This provides a site for cross-linking in collagen and elastin.
Proline, in the presence of Vitamin C, gains an alcohol group.
Similarly, lysine gains an alcohol group in the presence of copper.
3) Gamma Carboxylation - Provides a site for calcium binding
Glutamate in the presence of Vitamin K gets two (carboxyl? COO-) ends.
4) Iodination of thyroid hormones - regulation of metabolic rate
5) ADP-Ribosylation Reactions - Require niacin and are important in DNA repair and the regulation of protein function.
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So, about those anecdotes about Diarrhea:
There was a place he was working at who had a colleague who wanted to go to Thailand to engage in the... services of professionals of some reknown. But one thing he was worried about was getting gonorrhea while he was there. He heard about the existence of penicillin variants, so he wanted an antibiotic other than penicillin to take while he was there.
Telling one of his medical colleagues, the doctor said "No, you really shouldn't do that. Trust me." But there was no dissuading this guy, he said he wanted to go to Thailand and he saved for it, and he was going. So the doctor gave him some capsule antibiotics and told him to take them before he got there.
Now, other certain people whom he worked with had heard of his plan, and felt that it wasn't the right thing to do. So they opened the capsules containing the antibiotic, and emptied out the contents to replace them with epson salts. For those of you who don't know what epson salts do: While in your intestinal tract they draw out water from the surrounding cells, which causes everything to become runny. Very runny.
Poor sucker must've had a shitty time. XD
When he got back, his friends asked him what happened. He told them about his rampant diarrhea, and how even though he took more and more pills as it got worse, it wouldn't stop, and he couldn't do anything all weekend. =)
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There are three groups of reactions involved in interorgan transport of nitrogen:
1) Transamination: You swap the amino groups between "alpha-keto" acids, which places nitrogen on the correct amino acids for interorgan metabolism.
Basically, the normal amino acid becomes an amino acid with a keto group, the R group, and the carboxyl group attached to the carbone.
2) Glutamate Dehydrogenase: This enzyme releases free ammonium from glutamate to use for glutamine synthesis or urea syntheis.
Glutamate is three carbons: At each end is a COOH (so, er, 5 carb0ns?). At one end is an NH2. This turns the NH2 into a double-bonded O, or vice versa -- but removing the NH2 group requires turning NAD+ into NADH. Oh, we love you redox, we love you.
3) Glutamine Synthase / Glutaminase: This enzyme is necessary to metabolize or catabolize a major nitrogen transporter.
Similar to glutamate dehydrogenase, except instead of removing the NH2 group it adds another NH2 at the other end of the glutamate to make glutamine. The reverse of this is done by glutaminasae, which is used in the liver for urea synthesis or in the kidney during fasting for acid excretion.
...I need to switch subjects. >_<
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There are three people in a room debating about what the fastest thing in the universe is. One person suggests sound, because as soon as he shouts you can hear it right away. His friend remains unconvinced, and says that light is faster because as soon as he flicks a switch, the room BAM! is lit, without any warning.
The final guy says that diarrhea is the fastest thing in the world. The two look at him and say "How is that, hmm?"
"Well, when I have it I poop my pants before I can even shout or flick a light switch!"