Our gut bacteria live in our gut. OK that's obvious, but if the system is in good working order they are almost all, several trillion of them, in our colon.
Our colon is anaerobic. No oxygen.
In general oxygen is required to accept electrons at the end of the respiratory chain. As mammals we are exquisitely dependent on molecular oxygen for this. Not so the bacteria. Given a few billion years you can learn how to use other susbstances, sulphur being a favourite, to accept the respiratory chain driving electrons. In fact sulphur may have come first. Bacteria were around long before plants poisoned the planet with oxygen. Anyone who has eaten a sulphur and fiber rich meal will be well aware that hydrogen sulphide can be a highly aromatic feature of subsequent flatus. I won't translate that, let's just say roomclearing.
So bacteria are pretty sophisticated at energy extraction. I mentioned extracting sugars from fiber and extracting short chain fatty acids from sugars in my last post. So if there is some sort of electron acceptor around bacteria will extract energy. But some circumstances defeat even these metabolic wizards.
Strict anaerobic conditions impose certain limits.
Getting energy out of glucose without molecular oxygen is easy, just rearrange the molecule to free up the oxygen from those six hydroxyl groups. The end product can be anything from methane through ethanol, hydrogen or acetic acid. They all contain less oxygen than the parent glucose because the parent glucose has provided oxygen to the gut bacteria.
Given long enough bacteria will extract so much oxygen from organic molecules that all that is left is carbon and hydrogen. Bury an intact swamp with some bacteria for long enough and you end up with natural gas and crude oil.
But what I'm really driving at is that not even bacteria can extract energy from pure hydrocarbon molecules without oxygen.
Our colon is anaerobic. Eating a balanced diet feeds our gut bacteria with fiber. In return they grace us with flatulence and suppressed levels of Fiaf. At their behest we store fat under these conditions.
The bacteria never ask for the fat back directly as there is very little even the most enthusiastic bacterium can do with palmitic acid under the strict anaerobic conditions of the colon. Long chain fatty acids, especially the saturated ones, contain enormous amounts of energy per gram but we absolutely must have oxygen to liberate it.
So let's consider a normal fiber consuming rolly-polly human being carrying around 20kg of excess fat, property of their gut bacteria. Each day they consume their routine 1500kcal of food, which has failed to allow weight loss while it has been made up of a balanced fiber rich diet.
Then one day they eat 1500kcal of lard. Please don't try this at home, it's a thought experiment, strictly in your head. Under the anaerobic conditions of the colon there is no way the bacteria there can tap in to any of this energy, assuming some of the fat gets that far. It just might, which could be unpleasant.
So the gut bacteria are swimming in a sea of energy rich lipid, without any oxygen to work with. They cannot extract any of this energy. Energy deprived bacteria are hungry.
The human is not hungry!
What happens to Fiaf when our gut bacteria get hungry? As far as the gut bacteria are concerned this is starvation land and it's time to get Fiaf levels up, mobilise some host fat and get the host metabolism switched to serious fat burning. Weight loss under these circumstances becomes easy.
So with a little information it is quite possible to manipulate our gut bacteria and modify their ability to manipulate us.
High fat diets are a simple energy balance between us and our prey. Once the carbs, especially fiber rich carbs, come in there is a whole new ball game going on which includes our gut bacteria.
There is a paper out there on pubmed which I found and lost and cannot re locate. If our gut bacteria control our weight to their own advantage, wouldn't you expect them to control our food preferences to their own advantage too? They actually do this by altering peptide neurotransmitters in our brain. Anyone with a reference for this? I'd love a copy!
But it's worth noting that humans LOVE sweet things, yet there is absolutely no biological need for any carbohydrate in our diet whatsoever, except avoiding full ketosis might be benefical in terms of energy balance.
Which organisms want us to eat carbohydrate? The ones that want us to be fat! And, no, I'm not talking about the FDA of the USA here, though that organisation does seem to be acting on behalf of our gut bacteria.
You want to control your weight? Control your own energy balance.
To quote the title from one of Barry Groves' books:
Eat fat get thin.