Could someone tell me how antibiotics promotes weight gain in livestock? Is the use of antibiotics only a necessity because so many animals are kept in close quarters? What about antibiotics causing weight gain in humans?

The immune system is reactive and takes both energy and nutrients. Antibiotics reduce this expenditure which adds up over time.

Consider how many of these steps involve cell growth and or tissue damage that needs to be repaired: https://www.youtube.com/watch?v=zQGOcOUBi6s

TLDR; Low dose antibiotics don't eliminate infections, but by reducing their growth the immune system puts far less effort into defense.

Wouldn't low dose antibiotics be more likely to create antibiotic resistant bacteria than high dose?

Precisely. Constant exposure to less-than-therapeutic doses of antibiotics is a huge source of resistance. The bacteria in an animal with low doses or antibiotics are not exposed to enough of the drug to outright kill them, but the bacteria start to develop defenses. Bacteria can evolve extremely rapidly -- they don't even need to reproduce, as bacteria can exchange DNA horizontally[1].

Also, this is why if your doctor prescribes a course of antibiotics you should always complete the entire course, even if you feel fine. Stopping the antibiotics early can select for resistant strains.

1. http://learn.genetics.utah.edu/content/microbiome/resistance...

>Stopping the antibiotics early can select for resistant strains.

Some people are claiming this is not supported by evidence: http://www.bmj.com/content/358/bmj.j3418.full

Previous HN discussion: https://news.ycombinator.com/item?id=15311274

Depends on what you do with the 'saved' medication.

If you get 5 day subscription stop on day 3, then take the rest next week that's bad.

Ah, that's relatively recent in the literature, and I found a reference to it at the NIH[1] as well.

I'm glad for all the research into causes of antibiotic resistance, and if medicine comes up with a better way to treat infections and minimize resistance, I'm all for it.

1. https://www.ncbi.nlm.nih.gov/pubmedhealth/behindtheheadlines...

I was extremely fascinated by bacterial resistance growth mechanisms (DNA exchange). It was the first time I realized how immensely complicated the biosystem is at lower level. The 2nd time I had this feeling was when introduced to space of possible protein structures & the futility of prediction strategies. Suddenly the “known universe” and things like “number of known stars” started looking “reasonably sized” or even small.

Fascinating stuff. People can read more about it here: https://en.m.wikipedia.org/wiki/Protein_structure_prediction

> The 2nd time I had this feeling was when introduced to space of possible protein structures & the futility of prediction strategies. Suddenly the “known universe” and things like “number of known stars” started looking “reasonably sized” or even small.

This is a common experience in combinatorics ( https://en.wikipedia.org/wiki/Combinatorics ).

Similar things happen when beginner programmers (like me!) try to solve chess by recursing/looping through possible moves (there are about 10^123 separate paths, if duplicate configurations are merged together), or brute-force a cryptographic hash/key (2^k possibilities for keys of length k; keys of length 2048 and above are common).

The "standard big number" that gets thrown around when pop-sci articles talk about this stuff is the number of atoms in the observable universe, which is estimated at around 10^80. It irks me that this is used so much for comparison, since combinations of things are so overwhelmingly larger than collections of things that it feels like a category error to compare them.

After all, "the number of atoms in the observable universe" isn't a particularly intuitive quantity; unlike, say, "football field" as a unit of length or "bag of sugar" as a unit of mass/weight (UK media loves to use the latter; since a bag of sugar is 1kg, it shows off both their laziness and lack of faith in their audience...).

Also, picking "the number of atoms in the universe" is really trying hard; yet these combinatorial numbers (protein foldings, chess positions, etc.) are actually small, everyday examples! People have no problems (either conceptually or practically) with playing board games, choosing passwords, etc. despite these large numbers lurking in there.

The "atoms in the universe" number would be a hopeless comparison if we really tried to make a big combinatorial number. For example, "the number of binary sequences that can be represented by all the world's computer storage"; a quick Google search estimates the world's data storage as 295 exabytes, so that makes this number around 256^(295 * 10^18)

> It irks me that this is used so much for comparison, since combinations of things are so overwhelmingly larger than collections of things that it feels like a category error to compare them.

I think this is the core of the issue. "Atoms in the universe" is only such a relatively 'small' number if you assume that the way they're arranged is unimportant.

one thing, if you were talking keys of length 2048, your talking RSA, and to break it you are applying GNFS, not trying all the numbers up to 2^2048.

2^2048 is so astronomically large a number it has no universe sized meaning, its likely way way more than any discrete chunking you can do of stuff in the whole universe.

Something like 2^128 or 2^256 are more common 'brute' force type numbers, which would correspond to trying every key in a symmetric cipher like AES or a public key signature in ECDSA

2^256 is similarly quite large, but we can practically estimate this to be about the number of atoms in tens of thousands of galaxies.

Yes. The long term consequences don't factor in though because the immediate gains in production and profits are too attractive.

Whether or not people understand, believe the concerns are overblown or believe that we'll always be one step ahead, or will only stop when things get really bad, amounts to the same thing; misuse of anti-biotics.

It's a very human behavior to prefer a pound of cure to an ounce of prevention. It's magnified when you won't be responsible for the cure or the cost of it yourself. It's a weight that will be borne by all of society.

That is precisely the concern.

In cattle, certain antibiotics shift the composition of the bacteria in their digestive system and help them better deal with corn heavy feed (both extracting more energy from the feed and also mitigating illnesses due to the feed mix).

http://edis.ifas.ufl.edu/an285

There is also other growth promotion due to antibiotics.

In addition to the mechanisms described by others, it seems that antibiotics alter the microbiome in a manner that affects nutrient metabolism.

source: https://www.nature.com/articles/nature11400

abstract: Antibiotics administered in low doses have been widely used as growth promoters in the agricultural industry since the 1950s, yet the mechanisms for this effect are unclear. Because antimicrobial agents of different classes and varying activity are effective across several vertebrate species, we proposed that such subtherapeutic administration alters the population structure of the gut microbiome as well as its metabolic capabilities. We generated a model of adiposity by giving subtherapeutic antibiotic therapy to young mice and evaluated changes in the composition and capabilities of the gut microbiome. Administration of subtherapeutic antibiotic therapy increased adiposity in young mice and increased hormone levels related to metabolism. We observed substantial taxonomic changes in the microbiome, changes in copies of key genes involved in the metabolism of carbohydrates to short-chain fatty acids, increases in colonic short-chain fatty acid levels, and alterations in the regulation of hepatic metabolism of lipids and cholesterol. In this model, we demonstrate the alteration of early-life murine metabolic homeostasis through antibiotic manipulation.

The observable is that many antibiotics increase "feed efficiency". It's an aggregate measure, so perhaps it just reflects lower incidence of subclinical infection. And it permits high-density management, which increases the risk of infectious diseases.

No one knows, but it had an effect for every antibiotic tested in this study http://time.com/4082242/antibiotics-obesity/

Also Makes me wonder, Do children having trouble gaining weight ever get prescribed antibiotics?

Good explanation of the history, but I'm a little confused as to what the gained weight is (muscle or fat) - having obese animals probably isn't desirable when they are for food

It's actually very desirable. Fat is an important component in a lot of things we eat. For one thing, we need fat. For another thing, it's delicious. All of the things you really love to eat have a lot of fat in them.

There's a big reason that people breed animals to be obese. I grew up on a sheep and chicken farm. And to be honest, a lot of people would not eat those animals. They are lean, and gamey. Not like anything you would buy in any store.

Personally, I love it, and it makes me sad that I can't buy anything like it in NYC. Not even stuff that claims to be cage-free or organic or whatever. You just can't get that stuff here.

But it has a lot less fat than what you buy in the store. Fat is basically flavor for chefs. Whether it's butter or animal fat or vegetable oil, fat is where it's at.

The more obese an animal is, the better it's going to taste when you cut it up and cook it. That's just an unfortunate truth. When there's a market for something, people find a way to produce it.

The market is for massive amounts of white meats with a lot of fat you can render. That's what people buy, so that's what people sell.

>I grew up on a sheep and chicken farm. And to be honest, a lot of people would not eat those animals. They are lean, and gamey. Not like anything you would buy in any store

Funny you mention this, as recently I accidentally bought an older chicken at the store (a younger one half the size was the same price).

It probably would've worked for coq au vin, but roasting it was a bit of a mistake - meat was quite tough, although I turned it into an okay salad

That was much more informative than I expected. Thanks!

Were? Did this change?