For my first post here, it seems obvious to tackle one of the world's biggest realms of disinformation - dieting. This is an absolute goldmine for the bullshit artists of the globe. Almost everybody in the western world suffers body dysmorphia to some degree, so if you can make up any old nonsense to sell a book or a pill, some sucker will be around to make you rich.
Much of this seems to be based around one essential fallacy - that you are what you eat. Reality is not quite that straightforward - what we put in our mouths are the raw materials of what our body uses, but it does a lot to change them. Your stomach is basically a sack of hydrochloric acid and enzymes - it is extremely good at breaking down what you put into it. Once (and if) it is absorbed into the body, the organs of the body (particularly the wonderful liver) do an excellent job of turning it into whatever the body is in need of at that particular moment.
There is another thing to consider - the dose curve. Biochemistry is counter-intuitive in that it does not follow the simple logic of "more of a good thing is better". Everything has an ideal level. Too much of anything, be it a vitamin, or even just plain water, is bad for you. Also too little of something is also bad for you, even if it is usually thought of as bad for you: the body has a certain minimum expectation of even things we would normally consider poisons, right up to things like gamma radiation (which we naturally encounter every day in our air, water and food). Bottom line - moderation is key, too much is always bad, too little is always bad. This is because the body is good at converting things and dealing with the unwanted, but too much will overrun its natural buffers, and too little gives it nothing to work with. Those are all massive simplifications, but its a start. With all that in mind, let's break down some nonsense.
1. Myth: Fat makes you fat
Nope, not really. Your body will store fat in the body when it has too many calories to use at the present moment. It doesn't really care where those calories come from - it will do an excellent job of turning things into fats, and an equally great job of turning fats into other things as and when they are necessary. Fat does have a larger energy density than most things (i.e. calories per gram) - but most people would eat less by weight in the normal run of things anyway. The recent obesity epidemic in the west has largely been due to switching from the demon fat to eating much more in the way of carbohydrate (not that carbs are evil either, of course). And the feelings of satiety from eating fatty foods (particularly as they are often high in protein) can often make you eat less overall. Ultimately, balance is the key.
2. Myth: Meat, dairy etc. are bad for you
Wow, couldn't be more wrong. If you stand against these things for some moral reason, then fair enough, no metabolic argument is going to sway you. But removing things from your diet is generally a bad idea. Your body needs a wide range of vitamins and minerals (and trying to get them from pills isn't a good idea either - the body often has trouble absorbing vitamins and minerals delivered this way). You should eat as wide a range of foods as possible. Meat and dairy are wonderful suppliers of protein, calcium, vitamin A, etc, etc. A lot of nonsense is talked about lactose intolerance, etc. - in fact, this condition is very rare, you most likely don't have it. Plus, partly due to protein content, they make you feel full, meaning you eat less overall. I'm not suggesting the Atkins diet - that is ruinous due to its own problems in delivering balance. Some people do just fine on a vegan diet, if they are very careful. But others, no matter how well-informed they are and no matter how well they balance their vegan diet, simply cannot survive without animal products. The combination of protein and vitamins makes meat and dairy hugely beneficial to wellbeing, and you'd better have a really good reason to give them up.
(While I'm on the subject of fats, it's also worth mentioning that the magical properties of omega-3 and fish oils are also a lot of nonsense - not that they're bad for you, but some claims about them are, to say the least, overhyped.)
3. Myth: Antioxidants are good for you
This is an easy one to dispel. While it's true that antioxidants are used at a subcellular level to combat oxidative damage, those are the body's own productions. For the reasons given above, there is no reason to imagine even for a second that antioxidants you put in your mouth will either enter or have any effect in the cells. And indeed, no effect is precisely what was found - see the Cochrane review, the gold standard of evidence, which combined the results of 67 studies covering nearly a quarter of a million people (here, summary here). For those unfamiliar with that institution, it is non-profit, and has no particular axe to grind - unlike all those people telling you to buy their books/supplements/training courses.
Of course, eating all those foods isn't a bad idea - most things recommended are fruit and veg, which everbody can benefit from eating. That benefit has nothing to do with antioxidants, though.
4. Myth: detox will clear out all those poisons
Your body is incredibly good at dealing with toxins. Unless you have a serious disorder of, say, the liver or kidneys, your body is doing an amazing job. Nothing you can eat or drink is going to make much difference. When you wake up with a hangover, chances are your body has already cleared a lot of the toxins, and what you are feeling is good old-fashioned self-inflicted damage, not poison. Add to which, no company shilling their "detox" snake oil can even agree on what these toxins are supposed to be, or what detox is. For an excellent takedown of the gibberish spouted by people trying to steal your money, see senseaboutscience's excellent (and free) leaflet.
5. Myth: you can make long-term changes to your blood pH with diet
I don't even know where to begin with what a load of crap this new fad is. Your blood pH stays at an extremely stable level (just to the alkaline side of neutral). Your body is incredibly good at maintaining this level. That is because enzymes are extremely sensitive to pH, and will stop working if it varies very much - at which point you will die quite fast. Varying pH by more than about 0.3 will put you in hospital. The body is not going to let you do that if it can stop you. Consequently all living organisms are almost miraculously good at maintaining their pH levels, thank you very much. Again, unless you have something very wrong with you (such as kidney failure), any pH-related shenanigans are going to be either non-existent or short-lived.
6. Further myths - blood group diets, etc.
And the list goes on. So many fad diets are based around something real but utterly irrelevant to metabolism - blood group is popular right now. Why you would imagine that a mechanism used by the immune system to recognise invaders is relevant to your metabolism, and thence to your diet, is quite beyond me. It doesn't. I could go on forever, but must stop at some point. Other, better people have written exhaustively on just about any fad you could think of - check Bad Science, holfordwatch, senseaboutscience, etc. Just please do at least a little homework before signing up for anything.
The bottom line
There is one diet that works, and is good for you. It is the diet where you vary your food. Eat fruit and vegetables. Eat meat and dairy, unless ethically prevented (that's another argument I may return to later). You could maybe cut down on carbs, but there's no reason to go crazy about it - low blood sugar is bad for you too (it will switch the body to starvation mode, where you will burn fewer calories as well as feeling like crap).
Variation will give you the mix of energy, protein, vitamins and minerals you need. If you really want to lose weight, reduce portion size, but don't just go round cutting certain foods out of your diet - that road leads to imbalance, which is probably the thing making you feel bad. It can certainly work in the short-term for weight loss, just by sheer dint of reducing your choices for eating, but it won't do your metabolism any favours, and chances are your body will crave the things it knows it wants, causing you to cheat sooner or later.
Oh, and who am I to be arguing with all these published authors? Well, I do have a degree in biochemistry from a leading university. That was a few years ago now, and I'm nobody special. But I am still vastly more qualified than every single person in the UK describing themselves as a "nutritionist".