We all think we know the facts: vegetables are best when fresh, you shouldn't eat late at night and white bread's bad for you but are they really true? Here we uncover some of the biggest myths floating around in the food world.

There seems to be a bit of a craze for avoiding gluten right now, but unless you have an actual allergy, think twice before you hold off on that sandwich. “For the majority of people there is no evidence that gluten is bad for you," says Jo Travers, registered dietitian and author of The Low-Fad Diet. In fact gluten-free products may be worse, as they add in products to replicate the texture. “If you don’t need to eat them then I would recommend eating the traditional versions,” she says.

Along similar lines, unless you have lactose intolerance or an allergy to cow’s milk protein, dairy isn’t a demon either. “For most people eating dairy produce, especially low-fat dairy, is very healthy and an easy way to get plenty of calcium and other nutrients,” says Jo.

Bone broth, or stock, isn’t as nutritious as you think. “For a start it is mainly water, and while there are some water soluble vitamins, some protein, some fats and some minerals, you would be far better off eating actual food,” says Jo. You’ll get more protein from eating an egg, so put away the bones.

While it’s true there’s quite a high level of cholesterol in egg yolk, it doesn’t necessarily raise your blood cholesterol levels – your body just produces less to make up for it. Eggs also contain useful nutrients like Vitamin D, protein, Vitamin B12 and riboflavin, so don’t throw them away just yet. That doesn’t mean overdoing it; the American Heart Assocation recommends no more than 300mg of cholesterol a day (a large egg contains around 211mg on average).

Eat spinach and you’ll turn into Popeye, right? Not necessarily. “Although it contains plenty of iron it’s not always easy to access that iron because it contains something called oxalic acid, which makes it difficult to use,” says nutritionist and writer Fiona Hunter. It’s best consumed with other sources like meat, fish, broccoli, potatoes and tomatoes. This isn’t the case for all leafy green vegetables (eg kale), and cooked spinach is better as some of the oxalic acid is released.

Wholemeal bread is healthier, but white still contains some important nutrients such as fiber, calcium and iron, according to Fiona Hunter. “People tend to think of it as just as a carbohydrate but even white bread delivers a good amount of nutrition,” she says. And packaged brown bread isn’t necessarily as good as you think – the brown color can be from coloring agents – so check it actually contains whole grains before you buy (that means it contains all parts of the grain).

There’s a common conception that frozen veg isn’t as good for you as the fresh stuff. But research shows it can actually be the other way round, because nutrients can be lost from the time the product is picked to the time it hits the shelves. “When vegetables are frozen the vitamins are locked in, so they don’t deteriorate in the same way as they do from fresh,” says Fiona. “So frozen peas, spinach and other vegetables can actually contain more Vitamin C than fresh ones”.

In the same vein, canned vegetables can be better than fresh ones too – especially when it comes to tomatoes. That’s because lycopene, shown in some studies to help prevent lung, stomach and prostate cancers, is trapped in the cell walls in fresh tomatoes so it can’t be used as well as in canned, cooked tomatoes. “During the canning process the cell walls are broken down, so the body can access more lycopene,” says Fiona.

Like tomatoes, carrots are actually better when they’re cooked as heating them makes the beta-carotene more accessible.

Health nuts rave about the nutritional benefits of artisanal rock salts like this pink variety from the Himalaya, but don’t go replacing your bog-standard salt just yet. Although it does contain a host of minerals, the measures are apparently too small to make any real difference. “You’d literally have to be eating kilos of the stuff for it to make any proper contribution to your diet, so they’re no healthier than regular salts,” says Fiona. It does look pretty, though.

Think tuna, think brain-building Omega-3, right? Wrong. While fresh tuna is an oily fish containing high levels of Omega-3, a lot of it is removed in the canning process. Levels vary according to how it’s prepared, however. Opt for tuna canned in water rather than oil, or better still go for tinned salmon.

We’ve all heard this one – swallow your gum and it will be with you for the next seven years. Not true, according to Dr Richard Desi, gastroenterologist at the Institute for Digestive Health and Liver Disease at Mercy Hospital in Baltimore. "This is certainly a myth,” he says. “A portion of gum is indigestible, and like any indigestible substance that is consumed, it will simply pass through the gastrointestinal tract and be evacuated." Hoorah.

Caffeine fans may be pleased to hear coffee has a variety of health benefits, provided it’s drunk in moderation (the EFSA recommends up to 400mg of caffeine a day – about four cups). According to Authority Nutrition, one standard cup contains 11% of the recommended daily intake of riboflavin (as well as various B vitamins and antioxidants). Studies have also suggested it can lower the risk of type II diabetes, certain cancers, and neurodegenerative disease such as Alzheimer’s and Parkinson's.

Coconut this, coconut that – it might all be another fad. Coconut oil contains 90% saturated fat – more than butter and lard – which raises “bad” (LDL) cholesterol levels that can in turn raise the risk of heart disease, according to Walter C. Willett of the Harvard School of Public Health. Although there may be benefits (it contains antioxidants and can boost “good” cholesterol), not enough research has been done yet, so some experts recommend sticking to vegetable oils like olive and rapeseed.

Among the newer list of potential baddies is orange juice, but 100% juice doesn’t contain any added sugar, just the naturally occurring fructose. It’s also a good source of vitamins, potassium and folic acid. That said, it’s best to combine sugar with fiber, as it slows down digestion and helps to curb off blood sugar spikes. A lot of the fiber is lost in juice, so you are still better off eating the actual fruit.

Uncooked dishes, like these courgette noodles, are one of the latest trends to have hit the health scene, but they might not be quite as good for you as you think. While certain advocates claim the plant enzymes you get from raw food (which are destroyed in cooking above 118°F) are essential for digestion, some nutritionists say this isn’t the case. Our stomach acids are able to break down protein without recourse to plant enzymes, apparently.

First off, good fat is an essential nutrient. Secondly, while saturated and hydrogenated fats can lead to high cholesterol, low-fat ‘health’ foods – like cereal bars and granola – often contain more sugar and salt. And when it comes to what you spread on your bread, butter may be better than margarine, even though it was designed as a healthier option (some contains trans fat, which is bad news). Opt for avocados, nuts, seeds and vegetable oils to get the good fats.

You obviously need a certain amount of protein, but too much can be dangerous as it puts strain on the liver and kidneys. And if you completely replace carbs with protein, there can be several negative effects; including bad breath (because your body will be burning fat instead of carbs to make energy).

On that note, it’s a myth that carbs alone make you fat. According to Jean Harvey-Berino, Department Chair of Nutrition and Food Sciences at the University of Vermont, carbs aren’t inherently fattening. Complex carbohydrates in grains, fruits and vegetables are essential for energy, and it’s simple or refined ones that you should avoid – think white flour and high-sugar foods.

Traditionally it was believed you had to combine legumes like beans with complementary sets of amino acids, such as grains, to get the protein from it. But apparently these two food groups don’t have to be paired together in the same meal. As long as you get some intake throughout the day it still works, according to Winston J. Craig, Professor of Nutrition at Andrews University in Michigan.

According to research, eating loads of fruit and vegetables to boost your Vitamin C doesn’t actually prevent you from catching a cold, unless you’re a skier or taking part in a sub-Arctic army exercise...

Although it is low in calories (and high in fiber) you don’t, as the old wive’s tale goes, burn more than you ingest when you munch on a celery stick. According to estimates by the Mayo Clinic, only 5 to 10% of the calories you burn are through eating/digesting, which means you probably only burn around one calorie when you eat celery.

It’s a classic we grew up believing, but is there any truth in it? A study by the British Cheese Board in 2005 concluded not; they gave 200 participants different types of cheese 30 minutes before bed, and none of them recalled having any nightmares. Interestingly though, those who ate the blue cheese Stilton apparently had the most psychedelic dreams. More research needed, it seems.

Although it’s true that some foods, like blueberries and acai berries, are packed with health-giving nutrients and antioxidants, the jury’s still out on whether ‘superfoods’ really exist. As pointed out in a report by the European Food Information Council, studying their effects in a lab doesn’t necessarily reflect normal human intake, so their effect isn’t quite clear. And cheaper, more basic staples like carrots, apples and onions can be just as good. All three are full of nutrients.

It was a long-held piece of wisdom that eating dinner just before bed was bad, but nutritionists have since changed their tune. Apparently it’s more a case of what and how much you’re eating rather than when. A study by researchers in Israel even found that those who ate their biggest meal at night actually lost more fat than those who did so at breakfast, and had fewer cravings.

Although organic fruit and veg can of course be better because they don't use pesticides, organic doesn't always mean super-healthy. Chocolate is chocolate and cakes are cakes, so beware the marketing.

Not always the case; especially if it’s smothered in sugary dressings, or toppings like bacon and croutons. Opt for olive oil rather than creamy sauces and choose lean meat like grilled chicken over the deep-fried versions.

The idea that microwaving removes nutrients is pure myth, apparently. It’s more about how hot the food gets and how long you cook it for. That means microwaving can actually limit the amount of nutrients lost, because the food is cooked very quickly.

There’s no scientific evidence that going on a fast, such as a juice detox, helps cleanse your body of toxins any better than it would normally, according to Keith-Thomas Ayoob of the Albert Einstein College of Medicine. We’re well-equipped to deal with them already, thanks to our kidneys, liver and spleen.

The notion that intake of aluminium can increase the risk of Alzheimer’s was a fear for decades, but these days the majority of researchers say there isn't a link between the two, and even the Alzheimer’s Society say there is “no convincing evidence” to support the claim.