Inflammation is the reason why. The grain-fed, hormone laden chicken is high in omega-6 fatty acids. Too much omega-6 in one's diet produces excess swelling in the body. You also have beer, which is a high-glycemic food. It also is toxic to the liver and kidney, which filter waste in the body. It is also possible that Scenario B can still produce acne as well. What makes something healthy is individualistic. I recommend you read The Metabolic Typing Diet By William L.Wolcott.

In my (humble, of course) opinion, confirmation bias, and the 'appeal to nature' logical fallacy play into this a lot.

Also, (and I get that you were purposefully using quick examples, so I'm not criticising) we have no context for Paul and Peter's experiences. Does Peter EVER get acne? Maybe he is just not genetically prone to it? Maybe he could have eaten Paul's meal every day for his whole life and remained clear?

But taking Paul's case: maybe a few days before the scenario Paul read something online where someone said that eating healthy would cure acne. Paul thinks 'hey, that seems to be good common sense stuff, eating healthy would cause my skin to be healthy', so Paul starts to think this could well be true. So when he gets his little breakout Paul tries to work out what has caused it, and now he thinks 'oh it MUST have been that meal'. So to him that is evidence backing up his new belief. The next week Paul eats some cheese. He gets a breakout. It MUST  have been the cheese. Belief further confirmed. Next week Paul doesn't eat anything unhealthy. He gets a breakout. By now he strongly believes that unhealthy foods cause acne. 'Hmm, it MUST be my body DETOXING from all the unhealthy food I've eaten before.' Next week Paul goes to a party and eats some unhealthy food. He doesn't break out. 'Well, that was a lucky escape!! It must have been all that healthy food protecting me'. Next week Paul eats healthy, and he breaks out. 'It MUST be a delayed reaction to the unhealthy food from last week'.

If you carry this on and make a timeline or something, then you can see that Paul gets a breakout approx every 1-2 weeks. Paul has always had break outs every 1-2 weeks. But now because he formed this belief, he will fit all the the information he sees into this model / belief system. Nothing has really changed.

So in relation to your question at the start - it could be that there is no quick reaction at all - we are just primed to believe that there will be, and ignore any contradictory information?

Now, I'm not saying that I don't believe diet can ever affect acne - I'm sure it can, especially in more mild / moderate cases. Probably one day those scientists will work out which gene makes us prone to acne, and which gut bacteria can cause it to worsen etc etc, and maybe we can have special individual diets designed for us based on our exact body - that would be awesome. For now though, there has not yet been a thorough, well deigned study that makes conclusive links between diet and acne, so all the rules that people come up with are basically guess work

I was thinking of the appeal to nature fallacy based on what you indicated were 'healthy' and 'unhealthy' meals, but I don't think you were really looking to discuss that aspect? Anyway, it's an interesting subject if anyone wants to look it up

1 hour ago, WittySock said:

 

Thanks for the great analysis. If anything, you must have noticed that I'm 'Paul'. Constantly seeking some form of confirmation bias to justify breakouts or periods that are calm. In fact, this new diet thing I'm trying is driving me crazy. I have been eating all sorts of crap all my life and still had relatively clear skin, save the occasional breakout and blemish. So in my recent desperation, I thought food definitely has something to do with acne (I'm sure it does for some people here) but what I'm trying to say is, if it really does, I reckon it's more of an allergy rather than a my-human-body-triggers-acne-from-this-food-that's-otherwise-perfectly-edible. I'm so dying to go back to my normal diet that includes fried food, milk (never broken me out but I have been abstaining for irrational reasons these few months) and other glorious foods. Yes, glorious. Sigh.

So yeah, I think you're right. What really defines 'healthy' and unhealthy'? Crude oil and sewage would be straight out unhealthy. But why would fried chicken be unhealthy (vis- -vis acne, not health in general)?
 

It's definitely difficult, because it does seem that a change to diet works for some people. However it also seems clear that it doesn't work for everyone. So it's totally understandable when people want a change in diet to work for them, because if you can identify a dietary cause then it is very easy to understand and very easy to control by yourself.

I guess I basically have 2 concerns with this 'method':
1. people may be spending years with bad skin convinced that they can find 'that food', when maybe they could have got a prescription topical or pill in month 2 that might have worked - I'm always surprised at people being unwilling to try medicines, when they have a medical condition.

2. if someone is spending months and years searching for 'that food' then all food starts to be treated with suspicion. People start seeing food as the enemy. People start being scared of everything they eat or drink. This can really easily lead to an eating disorder (or at least 'disordered eating'). And this can happen when people were eating perfectly healthy diets to begin with

So essentially I worry about people ending up doing more harm than good to their health by going overboard with this, and with no guarantee at all that they will ever even get what they want. And they will probably blame themselves, because it worked for other people so why not them. And.. ugh...it just makes me sad...

57 minutes ago, WittySock said:

It's definitely difficult, because it does seem that a change to diet works for some people. However it also seems clear that it doesn't work for everyone. So it's totally understandable when people want a change in diet to work for them, because if you can identify a dietary cause then it is very easy to understand and very easy to control by yourself.

I guess I basically have 2 concerns with this 'method':
1. people may be spending years with bad skin convinced that they can find 'that food', when maybe they could have got a prescription topical or pill in month 2 that might have worked - I'm always surprised at people being unwilling to try medicines, when they have a medical condition.
Exactly! Exactly! Exactly!

2. if someone is spending months and years searching for 'that food' then all food starts to be treated with suspicion. People start seeing food as the enemy. People start being scared of everything they eat or drink. This can really easily lead to an eating disorder (or at least 'disordered eating'). And this can happen when people were eating perfectly healthy diets to begin with
Exactly! Exactly! Exactly!