As a scientist then, I believe you must talk about science like this: "Some studies suggest", "There's a consensus about", "There are some researches that found out", "It's been proved", etc.

However, you know that's not how most people talk about science. They talk like "I saw a guy on the telly from Oxford saying that this can kill me, I'll stop having this now". That's the exactly attitude I'm against with and that's why food examples explain my point better.

I used points that are easily identifiable like food and the ice age. You know that the new ice age and global cooling were covers of magazines like Time and every grandfather of ours will remember those talks. As a scientist you can say that I can't take Time magazine to back any argument, but by taking it I mean that there were enough scientists and universities back then studying this (and evolving it to the current climate change thing) to the point that the subject become paper's covers and headlines. I'm not a scientists, but I've met scientists and university professors that remember all of this or have read about them. It's well known.

The food stuff, you also know that I don't need to source it, because its another easy to find out about topic. Every doctor in the 90's and before were saying to its patients that they should stop having butter and animal fat. Why? Because they had access to studies that told them so. Because it was indeed a consensus. My grandmother had a diet that banned eggs, animal fat and her doctor wanted her to have only margarine, because studies shown back then that it was the right way to protect her heart.

My mother on the other hand had a different experience. A few years ago her doctor encouraged her to use butter. He said that studies showed that butter is actually better than margarine and that all the fuss against butter, eggs and such was incorrect. She was surprised, she said "it's not what they used to tell on TV, they tell us to have those margarine that are good for the heart because the smart guys say so". More recent studies show that actually butter is better for the heart in reasonable levels. Some doctors now are even saying that we should stop having margarine entirely. The thing is pure gross chemistry stuff.

My father was a doctor and he never believed in such stuff. He kept having bacon, eggs and butter back then in the 80's and 90's even though every paper for doctors had articles saying that he should tell his patients to avoid animal fat or stop it entirely because it surely causes cholesterol according to many studies. He believed that vegetable fat was worse than animal, but he was called a "denier" or maybe an old bag doctor. He was right. Now there's all this "good animal cholesterol" thing.

Why bring sources to back this? Anyone in the 90's and 80's defending butter, milk and eggs was called nutter. In old films, from the sixties, you see kids getting home and going to the fridge to a have a good milk glass. The world got so against it to the point that films started changing milk to juice. Juice is another issue, tho. Doctors encouraged kids to have as much juice as they can, instead of milk. Today, doctors explain that more recent studies show that actually juice has too much sugar, a glass of natural orange juice can have much more sugar than a coke can and sugar is far worse than fat. Those are all doctors that read doctors' papers and studies and it all shows how researches having been changing a lot what we know about food. And this is all well known. This is basic pub chat. You can go to your GP and talk to them about it, if he's old enough in the profession, he knows. Asking me to bring sources to this is not necessary and saying that I'm stupid exactly because I brought the easy examples that everyone knows, is malice. All my examples are common knowledge and easily verifiable examples of how science was wrong and as you say "has to correct itself from time to time".

My apologies for the late reply, I knew this would take some time to think about and write out and life has been busy. 

I agree that laymen talk about scientific research in the way you describe, using single studies and modeling their decisions around what the media portrays the conclusions to be. I think that skepticism of any specific study or what is read in the media is healthy. My concern is that if one takes that too far you start to disbelieve things that become detrimental. The example of climate change is an apt one, while I would not hang my hat on a single study or a story in the media, meta-analyses of studies I find quite trustworthy to get an idea of the consensus of the scientific community and that is overwhelmingly on the side of "it's happening and we're causing it". The line "well at one point you all thought it was going to be global cooling" is often used as a way to dismiss the current understanding even though I don't think there's been any meta analysis done of any time range that indicated that the consensus was global cooling. Hence my concern that you are dismissing the findings of current climate change science based on a perceived consensus from decades ago. 

I disagree with the example about having a consensus that butter was to be avoided. At least, not a consensus among scientists though I would agree there was a consensus among doctors seeing patients. Biological questions like that are incredibly complex and I would be surprised to find a consensus among scientists in that field about any given food to avoid as there are so many variables to account for. You can appeal to common sense but you were not interacting with scientists doing these kind of studies, rather you were interacting with the doctors and media trying to make recommendations based off how they perceived these studies. Similar to your original example of how one should take research and how those not in the field often do, I suspect that the differences in your grandmother, mother, and father's dietary recommendations are due to similar factors. 

All that said, my field does not involve anything as macro as the climate or dietary effects on human health so this is speaking solely within my understanding of how research is done and published in my field. It's possible that those fields are more apt to make more direct and concrete conclusions (with less "outs" if a particular hypothesis ends up incorrect) based on their findings which lead media to make more sensationalist headlines, but regardless I think the doctors acted reasonably because all they can do is base their recommendations off their understanding of recent findings. 

Overall, I cannot accept "common sense" understanding to tell me what the consensus of the scientific community is or was and I hope that you are not dismissing current consensus based on how you perceive it to have changed in the past. Science could always be wrong about something, but the methods for research and publication are rigorous enough that I think it's best to trust the scientific consensus unless you know of particular issues with the studies that make up that consensus. This is why I dislike the sentiment you put forth in the original post, because it can easily lead to viewpoints that are completely against everything we've come to understand about reality like Anti-vaxxer, anti-GMO, anti-human caused climate change, and even things as ridiculous as globe denial. 

When you say that science could always be wrong about something, you're agreeing with me, that was my whole point, even though we can discuss if my examples were the right ones or not.

Now, You say that there were no scientific consensus about butter and eggs even though doctors were giving recommendations based on recent findings.

Two questions:

* Where does those recent findings come from?

* If even the US federal dietary guidelines have been changing its recommendation on eggs (from "limit and avoid consumption" to "ok, dietary cholesterol is not bad"), how can we say that we didn't have a scientific consensus about it?

If advices like those we get from doctors and government aren't a sort of scientific consensus, what's science then? Again, I'm not a scientist and the terms that I use here don't have philosophical and scientific meaning, but you have to agree that I'm not quoting Oprah Winfrey. You can call your GP now and he'll say to you that there were and there are guidelines on foods like eggs and butter and that it's has been changed from sort of bad to good. You can also call your children school and they'll tell you that the amount of eggs and cholesterol they serve to children come from guidelines.

That's why I haven't quoted any source, because this talk on eggs, butter and cholesterol is so consensual everywhere that there's no need to quote, really, and I feel like those who ask me to quote it are just trying to defeat me on the discussion on absurd technicalities.

Now, if you say that my GP, my children school chef, the gov guidelines, the overall media advice on animal fat doesn't come at all from some sort of scientific consensus. Well, then, we should trust no one.

Yes, but my statement about science would be "it could be wrong, but unless you have proof of such it's best to assume it as correct and act accordingly." If we find out later we were wrong at least we were wrong based on the best available evidence. 

So, if I were trying to find the "scientific consensus" on something I'm going to go to meta studies of a number of independent studies as I alluded to previously. For example: https://www.bmj.com/content/346/bmj.e8539.long

Above is a meta study from The BMJ (a journal with an impact factor of 23 so I can be confident that it is a quality journal not just some online-only toss whatever you want in it journal) on egg consumption compared to the risk of coronary heart disease which found no correlation when combining results for 17 independent studies. I would then go through and look at several such meta studies to get an idea of what a field's consensus is. Where meta analyses are not available I would instead go to literature reviews and go through several of those to get an idea of what those in the field have concluded. 

I don't mean to disparage your GP, other doctors, media, and whatnot, but in the end these people are not scientists in those fields and thus can be thought of as laymen, and I would never trust the consensus among laymen to tell me the "scientific consensus" on any particular topic of scientific study. Science is complicated and difficult, and without years of study in the field it's easy to find a single report and make broad conclusions based off of it. When it comes to simple systems like those I work on (studies of purified proteins in solution so you can start to draw direct conclusions) maybe a single report can reach a particular conclusion, but when trying to draw conclusions on complex systems such as human health things are far too complex to make conclusions in the same way. 

So, are you saying that gov and doctors advice on food doesn't come from science?

Do you know where those advice come from?

Government advice on food is based on what legislators decide which may or may not come from science but certainly does not require that it comes from the scientific consensus. I hope the advice from doctors comes from science, but again it does not have to be from a scientific consensus which is what we were discussing. I'm sure they got their ideas from scientific studies, but what they decide does not become the scientific consensus because they say so. It may be that their decisions do match the scientific consensus but to my understanding it is not required when government officials or GPs make their recommendations that they match with scientific consensus. If you want to know what the consensus is you have to go to the primary source (those in the field), and should not infer it from secondary sources.  

Well, now I'm learning new stuff.

Next discussion regarding doctors among friends at the pub, I may want to say that not always doctors are right and sometimes they even don't care to follow science. Then I'll be called medicine denier and I'll be asked to provide sources :(