We all want to live long and prosper but, when health advice regularly changes or contradicts, it's hard to know whether you're doing your best. Here, we take a look at some of the current trends and beliefs and how much truth there is to them.

While packaged granola can contain nutritious oats, fruit, nuts and seeds, it also tends to include lots of sugar and not enough fibre. For example, a serving of several popular granola brands contain more sugar than a can of Coke. Try this homemade granola instead – it has no added sugar and is sweetened only with maple syrup.

Foods labelled light means lighter, but not as light as you might think. For food to be labelled light, lite, reduced fat or low-fat in the UK, it needs to be 30% lighter than a similar product, while in the US products with 50% or more calories from fat are required to have a 50% reduction in fat in light versions. This means, if the original item is high in fat, a light version may still contain a lot of fat. The likes of mayo and cheese may still be a high-fat product even when marketed as a low-fat one.

Our low-fat fixation is still going strong but many now argue that what replaced fat in our diet – refined grains, more sugar – hasn't proved more beneficial. The current thinking is that it's actually the type of fat that causes problems (for example, polyunsaturated fats are good and trans fats are bad) but that hasn’t stopped the low-fat food industry which remains awash with products high in refined sugar like low-fat yogurt.

Not all fats were created equal is a conclusion the fat-wary public has come to recently (and even then advice is regularly revised – consider the ongoing dispute surrounding coconut oil). Current guidelines recommend that we get the majority of fat from polyunsaturated sources (oily fish, rapeseed oil, walnuts) or monounsaturated sources (avocados, olive oil, almonds) and be careful of our daily intake of saturated fat (butter, cheese, fatty meats).

Natural, unrefined sugar comes from lactose in dairy and fructose in fruit (this includes agave nectar, honey, maple syrup and stevia) while refined sugar goes through a manufacturing process that strips nutrients. Natural sugars are currently thought to be best but are the lesser of two evils – sugar is sugar and eating natural sugar doesn’t give us free rein on our intake.

Energy balls contain healthy ingredients but can also pack in more calories, some exceeding the calories by weight of a chocolate bar or an ice cream. Though energy balls are often full of natural ingredients such as raisins, dates and hazelnuts, these billed-as-healthy products can still be high in fat and sugar.

This diet replaces acidic foods (processed, dairy, sugar, wheat) with alkaline foods (vegetables, legumes) and proponents claim it both improves health and can cure diseases. Others claim it's harmful and without scientific basis, including Cancer Research UK, who called its anti-cancer claims "biological nonsense".

Clean eating – originally defined as consuming a diet of unrefined, whole and natural foods – could be seen as a reasonable reaction to the processed food industry, yet the health claims and glorification of the movement have now been called into question. Taken to extremes, it is now linked to an eating disorder known as orthorexia, a term coined in the 1990s to describe the obsessive pursuit of a healthy diet.

Juicing can provide a couple of our recommended five a day, but sadly five lots of fruit and veg squeezed into one drink doesn’t mean we hit our daily quota. This is because fibre is lost in the juicing process, and while some claim that not having to digest that fibre makes it easier for us to absorb nutrients, it’s also fibre that slows the release of sugar into our bloodstreams and prevents an insulin spike. Juicing isn’t bad but eating whole produce is better.

The current preoccupation with coconut oil shows no sign of abating and neither does the disagreement between enthusiasts and critics. It has much-lauded health benefits – it can potentially fight dementia, thyroid disorders and aid weight loss – but science currently regards it as a product high in saturated fat (even more so than lard) which can increase cholesterol and the risk of heart disease and strokes.

The word superfood has been bandied about a lot but has no scientific definition in the US or the UK. While many products marketed as superfoods are packed with vitamins and nutrients, take the advice of dietician Alison Hornby who states: "No food, including those labelled as superfoods, can compensate for unhealthy eating."

Much demonised but universally craved, salt has been used as a natural flavour enhancer and preservative for millennia but too much of it has been linked to stomach cancer and high blood pressure that, in turn, is linked to cardiovascular disease. However, opinion on how much salt is safe to consume varies.

Unless you’re coeliac (around 1% of the population in the UK and US), gluten-intolerant or allergic to gluten, there’s little scientific proof that avoiding gluten will improve your health. Some swear avoiding it gives them less digestive issues but one theory for this is that ill effects are due to industrialised food manufacturing methods, not gluten.

It’s feasible to lose pounds on a low-carb diet but it’s not for everyone. One suggestion is that, without carbs, the body burns stored fat as fuel instead, resulting in weight loss, though this has been questioned. Low-carb diets are likely to boost metabolism initially and reduce appetite (mainly because of the extra protein being consumed), but side effects can be debilitating as important food sources such as fruit, veg and wholegrains are limited. The long-term effects of following a low-carb diet are still unknown.

Eggs have been criticised over the years because yolks contain cholesterol but the new school of thinking is that it’s fine to include eggs in our daily diet because the harmful effect of the cholesterol in eggs is too small to affect our blood cholesterol. What’s more harmful is how we cook eggs, so go for poaching and boiling over frying and scrambling in saturated fats like butter.

Science has proven so far that eating certain foods won't cure cancer. While a healthy, balanced diet with lots of fresh fruit and veg can certainly reduce the risk of certain cancers, especially those of the lung, mouth and throat. But the disease, which evolves as a result of a number of factors including genetics, stress, environment and lifestyle, cannot be wholly prevented by what we eat.

Yes, it could be, but for all oenophiles out there taking this to extremes, wine could have the opposite effect. Red wine contains several antioxidants, markedly resveratrol and quercetin, that are anti-aging and anti-inflammatory. So far so good. But what is still being debated is whether the benefits from these antioxidants outweigh the negatives from consuming alcohol regularly and if enough antioxidants can be absorbed from drinking.

This advice has been doing the rounds for decades. Yes, it’s very important to our health and wellbeing to stay hydrated, but that the required amount should be eight glasses when people’s needs differ depending on factors such as body shape, environment, and food and drink intake is erroneous. Alcohol and caffeine, though regarded as dehydrating, still contribute to our fluid intake and we get around a fifth of our water from food.

The jury remains well and truly out about organic food. Produce from the well-regulated UK organic market contains fewer pesticides, additives and antibiotics and organic milk can have more omega-3 fatty acids than non-organic. Yet other studies contend there’s only a marginal difference so it’s not worth the extra cost and that organic simply offers a placebo effect on the worried well. However, in the UK, organic sales grew by 7.1% in 2016, while organic food now accounts for $45.2 billion of total food sales in the US.

Plain, probiotic yogurt can be beneficial to some extent but the claim that it contains enough probiotics to make a significant difference is inconclusive. While probiotics (also called friendly bacteria) can play a useful role, and there’s evidence that varying strains can counteract the harmful effects of antibiotics, aid digestion and IBS, you're better off taking a good-quality supplement with live or active cultures.

Read more: Savvy tips to cut your food bill in half

The detox craze is a prime example of the halo effect – when we believe something is better or more virtuous than it probably is. While it makes us feel healthier and lighter, unless the liver, kidneys, skin or lungs aren’t functioning properly, our bodies work effectively at removing toxins. But we will put a strain on those organs if we’re not eating a balanced diet and regularly indulge in smoking, drinking or eating junk food. An unhealthy lifestyle can't be remedied by the odd detox.

Read more: 29 essential things you need to know about reheating food

Most importantly, keep an open mind. Fads, diets and food fashions are constantly modified; scientific research frequently debunks previously held notions; our diets and lifestyles differ; and what works for one person because of their body shape, metabolism, DNA or an underlying condition may not work for another. What most experts agree on is that a healthy, balanced, varied diet with moderate amounts of the bad stuff twinned with regular exercise is our best chance of staying well.

Read more: 38 foods that shouldn't be kept in the fridge