Essential nutrients - what do we need to eat?

[steve_bank]

According to an infomercial you need to eat worms from a special place in Australia if you ant to be healthy.

 

[Jokodo]

According to an infomercial you need to eat worms from a special place in Australia if you ant to be healthy.

Surely one of the best sources of vitamin g (for gullible).

 

[Jokodo]

For human nutrition, there are six types of essential nutrients. Some are needed in much greater quantity than some others: macronutrients vs. micronutrients.

Water - H2O - every organism needs it to metabolize, and thus to grow and reproduce

Sure, but does every organism need to ingest it? Water is produced as a waste product during the aerobic metabolism of carbs and fat, an organism that's better at retaining it could make do with that, at least hypothetically, no? Are there any examples of organisms that do?

Carbohydrates - sugars and sugar-like stuff, combinations of C6H12O6 units:

I've read conflicting claims on whether carbs are truly essential. They are our default source of calories, but we are well capable of extracting calories from fat, proteins, even organic acid and alcohol (indeed the caloric content of alcohol per 100g is significantly higher than carbs and close to fat, and acetic acid's isn't much below carbs).

 

[bilby]

Water is produced as a waste product during the aerobic metabolism of carbs and fat, an organism that's better at retaining it could make do with that, at least hypothetically, no? Are there any examples of organisms that do?

There are many alleged examples, though "obtains all required water from its food" isn't exactly "obtains all required water as a metabolic byproduct of its food", and I am not aware of any demonstration of the latter.

For example, Merriam's kangaroo rat (Dipodomys merriami) can survive without drinking water, but sources differ in their explanation of how they achieve this. One hypothesis is that carbohydrate metabolisation provides sufficient water; But other sources suggest that their habit of storing seeds in their humid burrows causes the seed to absorb moisture which the animals then consume.

Koalas similarly can survive without drinking water, but the Eucalyptus leaves that they eat do contain some water; Whether they could survive on completely dry Eucalyptus is not, as far as I am aware, known.

I would be surprised if some simpler organisms weren't able to obtain all of their water by metabolising anhydrous compounds; Perhaps the extremophile bacteria would include some examples, but I don't know of any off the top of my head.

 

[Elixir]

According to an infomercial you need to eat worms from a special place in Australia if you ant to be healthy.

According to another, fruits&vegetables in pill form is all you need.

 

[Elixir]

the caloric content of alcohol per 100g is significantly higher than carbs

Hmm. Ethanol (CH 3CH 2OH) is a pure hydrocarbon... is that different from a carbohydrate, functionally/metabolically speaking?

 

[Loren Pechtel]

Too much or too little sodium is not good.

Too much or too little ANYTHING is not good.

Too little of some things is tolerable, as long as you can synthesise or substitute that thing. But as a general rule, bigger or smaller amounts than is typical, in the wide range of human long-term diets, is going to be uncomfortable, if not fatal.

Humans are fragile creatures, like all organisms that evolved in an environment where complex nutrients were readily available.

If I can out-compete my contemporaries, by dropping ascorbate synthesis in favour of obtaining it from my diet, then that's obviously the winning evolutionary strategy - right up until my environment changes to an eighteenth century transoceanic sailing ship, which has no citrus fruits or sauerkraut on board.

I doubt it's so much that it's an evolutionary advantage, but that it came along with something beneficial. The energy cost of being able to synthesize it simply isn't that great.

It doesn't need to even come along with anything beneficial. If you are a frugivore, losing the ability to synthesise vitamin c is a perfectly neutral mutation. A frugivore will starve to death long before suffering a lack of vitamin c if they can't find enough fruit to cover their vitamin needs. Obviously different fruit have different vitamin content, say 30mg per 100g or thereabouts for apples, depending on breed and location and climate etc, up to 1250mg/100g, which is the figure most widely quoted for rose hips (yes, that's more than 1% by mass). But even with a relatively low vitamin c fruit, by the time you've ingested enough fruit sugar to cover your calory needs - let alone enough protein - vitamin c isn't something you need to worry about.

Neutral mutations however can spread and reach fixation by pure chance, as per genetic drift. So in a frugivorous population, losing this ability isn't going to do anything, and the mutants can easily (especially in a small population) come to dominate and eventually the wild type become extinct by pure chance - millions of years before their descendents switch to an insect or grain based diet where this becomes an issue.

If there's no advantage why would it spread through the population?

It would be possible for it to spread because it happened in the same critter that also gained a beneficial change but that's quite a coincidence.

 

[lpetrich]

CH3CH2OH isn't a pure hydrocarbon. Its overall formula is C2H6O -- one oxygen.

 

[Jokodo]

Too much or too little sodium is not good.

Too much or too little ANYTHING is not good.

Too little of some things is tolerable, as long as you can synthesise or substitute that thing. But as a general rule, bigger or smaller amounts than is typical, in the wide range of human long-term diets, is going to be uncomfortable, if not fatal.

Humans are fragile creatures, like all organisms that evolved in an environment where complex nutrients were readily available.

If I can out-compete my contemporaries, by dropping ascorbate synthesis in favour of obtaining it from my diet, then that's obviously the winning evolutionary strategy - right up until my environment changes to an eighteenth century transoceanic sailing ship, which has no citrus fruits or sauerkraut on board.

I doubt it's so much that it's an evolutionary advantage, but that it came along with something beneficial. The energy cost of being able to synthesize it simply isn't that great.

It doesn't need to even come along with anything beneficial. If you are a frugivore, losing the ability to synthesise vitamin c is a perfectly neutral mutation. A frugivore will starve to death long before suffering a lack of vitamin c if they can't find enough fruit to cover their vitamin needs. Obviously different fruit have different vitamin content, say 30mg per 100g or thereabouts for apples, depending on breed and location and climate etc, up to 1250mg/100g, which is the figure most widely quoted for rose hips (yes, that's more than 1% by mass). But even with a relatively low vitamin c fruit, by the time you've ingested enough fruit sugar to cover your calory needs - let alone enough protein - vitamin c isn't something you need to worry about.

Neutral mutations however can spread and reach fixation by pure chance, as per genetic drift. So in a frugivorous population, losing this ability isn't going to do anything, and the mutants can easily (especially in a small population) come to dominate and eventually the wild type become extinct by pure chance - millions of years before their descendents switch to an insect or grain based diet where this becomes an issue.

If there's no advantage why would it spread through the population?

Because some individuals live and others die, and the one that live usually are rarely prefectly representative of the overall population. Mathematically, it's a random walk in a finite space with absorbant walls: if you start with 0 and randomly add or subtract 1 until you reach +/-100 (eg if you you'd coins for a dollar per round), chances are you won't be playing very long before you either gained or lost a hundred. A new neutral Mutation is like that game, only it starts with -99: most of the time, it hits the left wall, ie -100 or going extinct again, pretty fast - but some new mutations survive by pure chance and eventually hit the right wall, that is reach fixation. Gamblers have been known to come home with 1000s of dollars after going to the casino with tens, and their situation is more like that of a moderately negative mutation, statistically.

The real question is: "why not?" Without a Good reason against, it will happen some of the time just because it can, and this may just be one of those times.

 

[Elixir]

CH3CH2OH isn't a pure hydrocarbon. Its overall formula is C2H6O -- one oxygen.

I think it needs that O to stay together, but I may be (probably am) wrong.
Anyhow, is it metabolically a lot different from cane sugar?

 

[bilby]

According to an infomercial you need to eat worms from a special place in Australia if you ant to be healthy.

Or should that be 'you need to eat ants from a special place in Austria if you worm to be healthy'?

 

[bilby]

CH3CH2OH isn't a pure hydrocarbon. Its overall formula is C2H6O -- one oxygen.

I think it needs that O to stay together, but I may be (probably am) wrong.
Anyhow, is it metabolically a lot different from cane sugar?

One could class ethanol as a carbohydrate, as it's basically ethylene plus water; But it's not metabolised in the same way as carbohydrates are.

Ethanol is converted to acetaldehyde (by the removal of the hydrogen atom from the OH group), via the action of the rather boringly named enzyme 'alcohol dehydrogenase'

The acetaldehyde is then converted into a form (Acetyl Co-enzyme A) that can be fed into the Krebs Cycle and used to provide metabolic energy. This step is accomplished by removal of a further hydrogen atom, by an enzyme called (you guessed it) 'acetaldehyde dehydrogenase'.

The second step generally takes rather longer than the first, and it's the build-up of highly toxic acetaldehyde in the body that causes many of the symptoms of a hangover*; In some populations, the levels of acetaldehyde dehydrogenase are so low that the toxic effects are rapid and severe, and this is the condition known as alcohol intolerance, that is common in Southeast Asian populations.






* The other major contributor to a hangover is dehydration, but it's the acetaldehyde that explains why drinking water is only partly effective in making you feel less dreadful. Drinking water also helps to clear some of the acetaldehyde via direct excretion through the kidneys, taking some of the load off the acetaldehyde dehydrogenase processes in the liver.

 

[Jokodo]

Too much or too little sodium is not good.

Too much or too little ANYTHING is not good.

Too little of some things is tolerable, as long as you can synthesise or substitute that thing. But as a general rule, bigger or smaller amounts than is typical, in the wide range of human long-term diets, is going to be uncomfortable, if not fatal.

Humans are fragile creatures, like all organisms that evolved in an environment where complex nutrients were readily available.

If I can out-compete my contemporaries, by dropping ascorbate synthesis in favour of obtaining it from my diet, then that's obviously the winning evolutionary strategy - right up until my environment changes to an eighteenth century transoceanic sailing ship, which has no citrus fruits or sauerkraut on board.

I doubt it's so much that it's an evolutionary advantage, but that it came along with something beneficial. The energy cost of being able to synthesize it simply isn't that great.

It doesn't need to even come along with anything beneficial. If you are a frugivore, losing the ability to synthesise vitamin c is a perfectly neutral mutation. A frugivore will starve to death long before suffering a lack of vitamin c if they can't find enough fruit to cover their vitamin needs. Obviously different fruit have different vitamin content, say 30mg per 100g or thereabouts for apples, depending on breed and location and climate etc, up to 1250mg/100g, which is the figure most widely quoted for rose hips (yes, that's more than 1% by mass). But even with a relatively low vitamin c fruit, by the time you've ingested enough fruit sugar to cover your calory needs - let alone enough protein - vitamin c isn't something you need to worry about.

Neutral mutations however can spread and reach fixation by pure chance, as per genetic drift. So in a frugivorous population, losing this ability isn't going to do anything, and the mutants can easily (especially in a small population) come to dominate and eventually the wild type become extinct by pure chance - millions of years before their descendents switch to an insect or grain based diet where this becomes an issue.

If there's no advantage why would it spread through the population?

In other words, that's just what genes do when survival is not fully deterministic. A carrier of a neutral mutation may have a predicted average of 2.0 offspring of which an average of 1.0 carry his variant, but the actual values will rarely be exactly that. If you initialise a population with 2000 different variants, and create each new generation by randomly picking an individual of the previous one as the progenitor for each of 2000 new individuals, one of the variants eventually comes to dominate, typically sooner than you may think, and each one has an equal chance to do so.

If instead of 2000 different variants we have 1 mutant and 1999 wild type variants, nothing has changed for that one guy, it still has a 1/2000 chance of eventually dominating the population through genetic drift alone.

 

[Jokodo]

It would be possible for it to spread because it happened in the same critter that also gained a beneficial change but that's quite a coincidence.

I don't think that would be possible. The way geneticists usually determine that a gene has been subject to (recent) selection is by finding that the surrounding regions are relatively uniform, showing less variation than the genome in average. But they are not absolutely uniform because recombination, including at the sub chromosome level, is real. A particular neutral variant of the surrounding DNA is piggybacked for a few generations, but eventually the chromosomes splits and merges with its other copy right there, and then an other variant gets piggybacked with the selected gene, and so forth

So your scenario is neither necessary nor sufficient. Unselected genes and traits spread and become universal all the fucking time without parasitising selected traits. Molecular clocks wouldn't work otherwise. Indeed, many (most?) geneticists would argue that, for any given genetic difference between two populations, drift should be the default assumption until selection has been demonstrated.