The problem with health advice is the space is completely polluted with all kinds of grifters relating personal anecdotes as fact, hucksters hawking pills and gym-bunnies yelling about stuff that only affects people like them.  It's all a bit of a mess and there is a lot of mis-information out there.

Some notes ...

* You need extra protein if you're trying to build muscle following exercise
 -- This is true, but you don't need anywhere near what they will tell you and protein bars/shakes/yoghurts/whey powder are likely unnecessary!  In order to maintain muscle mass, nutritionists recommend 0.8g of protein for every kg of weight - so if you weigh 75kg then you should be consuming 60g of protein a day.  In order to make gains you want a tiny bit more than this but not a lot.  Hitting that much protein a day turns out to be pretty easy - there is plenty of protein in grains (such as wheat) and the like, and loads in meat cheese and nuts, and the added protein bars / yoghurts are unnecessary.  *Maybe* if you're vegan you might struggle, but if that's the case, eat more beans of various types.

* X diet is a miracle and you will lead to significant weight-loss
 -- All diets that aim to lose weight are proxies for calorie counting.  I don't care what it is, whether it's slimming world or weight watchers or slim-fast or keto or caveman or whatever the latest fad is right now.  There's no easy way, it is going to take willpower and you will feel hungry occasionally (at least without pharmaceutical help).  That said, I think it is useful to switch diets around as it means that you pay attention to what you eat (and therefore hopefully eat both better and less!).  It's a massive pain in the arse, but I would strongly recommend that you do a full calorie-counting diet for a while (2-4 weeks, example https://docs.google.com/spreadsheets/d/1KSpSIzbg1Zb231qd1DawTsEIcJ98UyeBJCnyU142kJ0/edit?usp=sharing ) so that you inform yourself better on what is good and what isn't (please make sure you have adequate protein intake too and note the exercise calories as negatives!).  The broad recommendation to maintain weight is 2000 kcal for women and 2500 kcal for men - so aim for less than this but bear in mind you'll have to figure out what works for you personally.

* You should eat 5 fruit and veg a day
 -- Fruit and Veg are both great in terms of micronutrients, fibre and also help fill you up (100g of apples is less calories than 100g of beef).  So fruit and veg are *great* but the 5 a day thing is very much governments trying to encourage people to eat more rather than any scientific basis - in other countries it's 3 a day and others 7 - it's much more "what can we get away with recommending" rather than any particular scientific basis.  That said, given that one of the things you're trying to do here is to adequately provide yourself with micronutrients, then as wide a variety as possible is better.  So if you eat your 5 a day but it's always the same fruit and veg every day, then this is not as good as say, eating 3 a day but different ones every day so 21 different fruit and veg a week.

* "Breakfast is the most important meal of the day"
 -- Cereal companies came up with this.  It's largely horse-shit.  Breakfast cereals are not great nutritionally - you know why they all have added vitamins and iron?  Because they were found to be so nutritionally deficient as to not be worth consuming - so they now advertise that they are fortified with vitamins and iron - but that's mainly because they started from such a low bar in the first place!  If you want breakfast and want to be healthy, go for something with high fibre (Bran Flakes, Muesli) rather than very sugary (crunchy nut cornflakes, sugar puffs)

* Nuts are good for you
 -- I mean, it depends on what you're going for, but generally no.  They are high in protein, but they are also extremely high in saturated fat.  Macadamia nuts are basically lumps of saturated fat for example.  Delicious but not healthy!  Some nuts are better than others - e.g. almonds and hazelnuts look decent, and pecans and macadamia look particularly bad!  Read the labels!

* Fat is bad for you
 -- Fat is extremely calorific but as part of a calorie controlled diet, it's perfectly ok to have some and fat is where the flavour is.  Generally, unsaturated fat like olive oil and sunflower oil is fine, saturated fat like butter and most nut oils isn't great as it will raise your cholestorol, and trans fats found in deep-fried food is really bad for you (even worse on the bad cholestorol and linked to various cancers).

* You should walk 10000 steps a day
 -- Whilst almost all exercise is good, the 10000 steps is completely unscientific and arbitrary - along the lines of "what can we get away with recommending" rather than having a scientific basis.  Exercise is very good for you not just physically but mentally too.  So definitely do some.  And do something that you enjoy or can tolerate because then you'll keep it up.  But walking 20000 steps isn't twice as good as 10000.  Variety here is key - so if you do a bit of swimming, or yoga, or weightlifting, or callisthenics or football rather than focusing on a single thing, this is going to be much better for you than just doing more walking.  I think there's something to be said for doing exercise in a non-controlled environment too - so running outside is better for you than on a treadmill because outside you'll be subtly training other muscles because of uneven terrain, obstacles and the like (downside: higher injury likelyhood)

* X is the best form of exercise
 -- There is no one good form of exercise.  Swimming is non-load bearing which means it's very difficult to injure yourself, but is very upper-body focused.  Running is extremely intense but it's awfully easy to injure yourself and does little for the upper body.  Yoga is great for the joints but doesn't get the heart rate up enough.  (I think rowing might be close to the ideal personally but it's awful hard).  It's best to do a variety of different exercise.

* A glass of wine is good for your health
 -- Absolute garbage.  Shouldn't stop you though, just because it's bad for you physically, it can be great mentally!

* Exercise will make you lose weight
 -- Without careful dieting, exercise can often make you gain weight, as muscle is denser than bone.  You should *absolutely* be doing exercise when trying to lose weight but your primary goal wth exercise should be to feel good/maintain muscle rather than lose weight.  You kind of need to do exercise whilst trying to lose weight because otherwise you will just lose muscle and bone rather than fat, which is absolutely not what you want.  See the calorie controlled diet thing above - make sure you are getting enough protein and are doing a reasonable amount of exercise (including some resistance training) - that should mean you lose *fat* not muscle/bone.   Having said all that, it is deeply depressing how few calories exercise actually uses -- want to make up for an extra bag of crisps that you ate?  Yeah, that'll be 20 minutes running, half an hour of swimming, or an hour's walk.  So you should absolutely exercise when losing weight to try to maintain muscle and bone BUT don't rely on it to actually help you lose weight much - what you eat is generally more important (unless you're like a polar explorer or something).

* You should take supplement X
 -- Probably not.  If it's recommended by your doctor then definitely, otherwise probably not.  Largely down to de-regulation in the US, the supplements industry is a seething mass of scammers, mis-information and poorly regulated products.  It's better in the EU (where you likely can't sell much apart from vitamin supplements anyway).  Maybe if you're Irish take some Vitamin D due to the lack of sunshine, or in India an iodine supplement, but if you have a reasonable diet then supplements should be unnecessary.  If your diet is particularly low in fruit and veg, maybe a vitamin supplement can help.

* Should I pay attention to dieticians or nutritionists?
 -- nutritionists.  You need precisely zero qualifications to call yourself a dietician, so ignoring any and all dietician advice is probably safest.  nutritionists are typically doctors with a speciality, or related to sports where it is very important to know your stuff rather than a shady quack whose job it is to hawk you pills.  So listen to a nutritionist's advice, not dieticians.

* Should I worry about ultra-processed foods ?
 -- Probably yes.  The EU has far better regulation of the additives that can be put in food than the US, so in the EU most food additives are broadly safe - the same cannot be said for the US which is much more lightly regulated.  Some examples of ultra-processed foods:  Most shop-bought bread, ready-meals, yoghurt, ice-cream, cured meats, some cheeses.  That said, the majority of ultra-processed food is FINE.  Don't listen to the idiots who think sultanas are ultra-processed (they're grapes treated with grape acid.  Big deal).  We all have busy lives so a bit of ultra-processed I think is ok, just don't try to completely live off a diet of chicken nuggets, white bread and ice-cream and you'll be ok.