Clever marketing often makes us believe that certain foods are healthy when they’re actually nutrient-poor, highly processed, or contain refined ingredients, dubious additives or lots of sugar or salt. Here are some of the biggest culprits.

It’s easy to mistake couscous for a grain when in fact it’s made with durum flour, like white pasta. This makes it a moderately high GI (glycemic index) food. If you enjoy it opt for the wholewheat variety.

Seen as a healthy alternative to ice cream, frozen yogurt has become big business; in the USA alone the industry is worth around $2 billion (£1.59bn). But size is everything – a small cup with fruit is much lower in fat, sugar and calories than a large cup with granola or cereal topping. Don’t rely on probiotic claims either – both manufacturing and stomach acid kills these off, though research is being done into hardier strains.

Dried fruit seems like a beneficial snack but it has its downsides. It’s higher in sugar than fresh fruit and isn’t as filling, and may contain added sweeteners, or allergy-inducing sulfites (which act as preservatives). And don’t even think about banana chips, which have had most of the goodness fried out of them. Snack on frozen fruit or a handful of nuts instead.

An egg white omelet is lower in fat, calories and cholesterol than the full egg version. But taking the yolk out of the equation removes essential B and D vitamins and iron – all of which are beneficial to us.

Energy bars are naturally calorific to provide extra energy – the point being that we're supposed to burn it off. But some provide energy in the form of refined sugars and white flour rather than natural ingredients, making them no better than candy. Choose one that contains only dried fruit, nuts and seeds. Or look for ones with a short ingredient list or where the main ingredient is a wholegrain such as brown rice.

Not all salads are wholesome. While salads that are high in good fats from nuts and avocados are beneficial some fast food chains and supermarkets offer salads that are deceptively calorific or high in bad fats, and some don’t even offer one of your five a day. For example, Pret A Manger’s Chef’s Italian Chicken Salad with dressing has 577 calories and 46.5g fat. Taco Bell’s Fiesta Taco Salad, meanwhile, contains 770 calories and 42g fat – more than a Burger King Whopper.

Once the prime choice over butter, margarine has fallen from favor in recent years because it’s so processed. It’s not even a natural food – it's manmade. Some margarine brands contain trans fats or refined vegetables oils while all contain colorings (to change it from grey to an appetizing yellow). No margarine can beat the natural fat in vitamin-rich butter.

It may be fruit but when fruit juice is processed it destroys benefits such as Vitamin C. Even if you extract the juice at home you’re left with sugary liquid and little else. On the other hand, whole fruit is the whole package: it contains fiber, vitamins and minerals, and is digested more slowly, allowing the body to absorb the natural sugar gradually.

Low fat, or skimmed, milk is now ubiquitous but as we learn more about the benefits of good fat the less desirable low fat products become. Not only does full fat milk fill us up for longer, negating the desire to snack, the fat helps us absorb the vitamins A and D that are in, or added to, milk.

While it contains a good amount of fiber and is perceived as a nutritious breakfast granola can be as sugary as shop-bought cereals. Eat a small amount, supplementing it with nuts and fresh fruit, or sprinkle it on plain Greek yogurt rather than pouring out a big bowlful.

Rice cakes are eaten as a low calorie snack but they’re carb dense, contain very little fiber and nutrition, and only a small amount of protein. Opt for oatcakes instead, which have a lower GI, meaning you avoid blood sugar peaks and troughs.

Be wary when buying commercially produced salad dressings as many are highly processed products that contain GM ingredients, high fructose corn syrup and trans fats. Study the labels or make your own.

Traditionally, legumes are good for us but how they are cooked or processed can have a deleterious effect on their health-giving properties. An example is tinned baked beans – while a good source of fiber and protein they are high in sugars and salt, which unnecessarily bumps up the calories.

According to research by BBC TV's Trust Me I’m a Doctor, Dr Saleyha Ahsan found that although smoothies contain plant compounds that are good for us (and the NHS states that 150ml glass counts as one of our five a day) most smoothies contain more sugar than Coca-Cola. This is backed up by Which research in the UK that compared the nutritional value of 52 smoothies and found that 41 contained more sugar than a 250ml bottle of Coke.

These green versions of our favorite carbs may look healthy but the spinach in them is negligible and added to color the products rather than infuse them with nutrients. While they’re not unhealthy as such they are misleading – add fresh spinach to pasta dishes and sandwiches to reap the benefits of this green vegetable.

Sushi is regarded as a healthy food but not every roll is created equally. The white rice is carb-heavy and mixed with sugary rice vinegar, and there are only small amounts of veggies and seaweed. But it’s California rolls and the ones with fattening mayo that are the ones to resist: the former contains around 250 calories per roll compared to 140 calories for an avocado roll. By all means eat sushi but do so sparingly, and fill up on sides of soups, salads and edamame.

Though lower in fat than an equal portion of potato chips, vegetable chips contain a similar quantity of calories and then there’s the salt to consider plus sneakily-added sugars and sulfites. Eaten in moderation (a handful) they’re OK but for a healthier option make them in the oven with a good quality oil and less salt.

Oils such as corn, soybean, sunflower and safflower are seen as healthy because they come under the vegetable oil umbrella. However, not only are these oils undermined by an intensive manufacturing process they release toxic chemicals when we cook with them, according to research. Cooking these oils releases aldehydes, chemicals that have been linked to heart disease and dementia. Cook with coconut, rapeseed or olive oil and even butter instead.

They’re filled with vegetables so they must be healthy, right? Not necessarily – many versions contain fillers and additives to lengthen shelf life. An article on Onegreenplanet.org suggests avoiding store-bought burgers that contain the following ingredients, all of which are bad for us when eaten regularly: refined oils such as canola and corn; highly processed textured vegetable protein (TVP); caramel coloring, which is linked to cancer; and hydrolyzed protein (MSG). Make your own instead.

Just because diet soda is free from calories doesn’t make it good for us. People are becoming increasingly aware that diet drinks are chemical cocktails. Nutritionally barren, they’re full of artificial sweeteners that trigger insulin and send our bodies into fat-storing mode leading to an increased risk of diabetes and, conversely, weight gain. Drink sparkling water instead or look for drinks containing natural sweeteners such as Stevia.

Light dressings don’t fare much better. Not only do store-bought versions have a higher sugar content, researchers at Iowa State University in the US found that when we eat low-fat dressings with vegetables or salad we don’t absorb the vegetables’ nutrients as well as when we eat them with fat.

The vast range of gluten-free products on the market has been a godsend to many people who can’t eat gluten. Unfortunately, the junk food products are still junk food – some contain controversial ingredients such as BHA and BHT or use alternative flours that aren’t a healthy replacement for wheat. Tapioca starch is one example – it’s nutrient-poor with a high GI. Look for products with the fewest ingredients and ones containing coconut, chickpea or sprouted flour.

According to WebMD, analysis undertaken in 2010 by WellGen Inc. in New Jersey, USA, found that the polyphenol content in bottled tea beverages is “extremely low”. Polyphenols are the antioxidants found in tea that have an anti-inflammatory effect on the body and help to fight off diseases such as cancer. Bottled teas also tend to contain significant amounts of sugar or high fructose corn syrup. Better to brew your own at home and let it cool.

Like gluten-free products just because organic food is appealingly labeled it doesn’t make it an elixir of health. If it’s processed it will have gone through the same manufacturing processes as non-organic food. While organic ingredients are superior it’s still better to avoid or minimize your consumption of processed food, especially junk foods, as they’re high in sugar, fat and salt.

Fat is becoming our friend (if eaten in moderation) while sugar is the new enemy. This is evident in reduced fat products – in this case peanut butter. An article on Eatingwell.com explains that the fat is replaced by “corn syrup solids, sugar and molasses, plus starchy fillers” pushing up this natural product’s sugar content from around 1g to 4g, and carbs from 6g to 15g. There’s also twice as much salt and less peanuts. So it’s a no-brainer to simply eat less of the original.

Rice milk is used by people with a lactose intolerance or a casein, nut or soy allergy and has developed a reputation as a non-dairy health food. But as it’s the fluid from rice it’s high in carbs (up to four times more than regular milk) and low in calcium and protein. If it’s all you can drink check the label for additives and choose unsweetened brands.

However convenient flavored instant oatmeal is it's best avoided. There’s way more added sugar and salt than is necessary – even in the organic options – and artificial flavors and colors. Measure out plain old oatmeal and add a little honey or apple puree for a more nutritious breakfast.

This convenient treat came under fire when Wayne Watson from Colorado developed ‘popcorn lung’ from inhaling diacetyl, a substance that’s harmless until it’s heated, when it becomes toxic. Although most manufacturers removed diacetyl, there are other chemicals “termed likely carcinogens" by the US Environmental Protection Agency present in popcorn bags that bind to popcorn when heated. The safest bet? Avoid chemicals, trans fats and additives by making your own on the stove.

Fat-free and low-fat foods are not health foods. More often than not the fat is replaced by sugar, bulking agents and additives which are as bad for us, if not worse, than eating fat. What’s more, research indicates that it’s not fat making us fat, but our body’s reaction to excess sugar. Eat smaller amounts of higher fat foods you love, such as yogurt or cheese, rather than low-fat food that’s been tinkered with.

If you’re aiming to lose weight the word ‘diet’ in a product can be very tempting. But a diet ready meal isn’t fresh food, it’s processed, and it contains added salt, sugar, additives, colorings and flavorings you won’t find in homemade meals. For a nutritionally superior meal make it yourself.