Eight foods you should never eat again

You may have heard this phrase before, "There are no good or bad foods — there are only bad diets" and on the whole this is true. Chocolate, cake or a few slices of pizza are not necessarily nutritious, but when enjoyed occasionally will not cause any long-lasting ill effect.

But what is important to know is that there are some foods that have the potential to be so bad for us nutritionally that you would argue they are bad foods, and best avoided altogether.

Here are some of them and the scientific reasons why they are best eliminated from your diet completely.

1. Margarine

Spreads are a controversial food topic among nutrition professionals as the recommended switch from butter to margarine originally came from evidence that plant-based oils were better for the heart than animal-based fat. While this is true, nutrition professionals will generally recommend foods that are as natural as possible and when it comes to margarine it is an added fat that we do not "need" in our diet, especially fat that comes from heavily processed, refined vegetable oil. A high intake of processed vegetable oils is linked to increased inflammation long-term, which is extremely damaging to the body's cells over time.

2. Processed meat

It is the high nitrate and salt content of canned and cured meats that has resulted in processed meats being classified as a Group 1 carcinogen (cancer causing), increasing the risk of developing both bowel and stomach cancer.

We should be steering clear of processed meats. Photo / Getty Images

In New Zealand we consume a lot of processed meats via our bacon, snags, salami and beef jerky and a single 50g serve increases the risk for developing bowel cancer.

3. Soft drink

No surprises here. Not only are soft drinks one of the most concentrated sources of added sugars in the diet with a 600ml bottle giving you 13 teaspoons of the white stuff, but they are highly acidic which means a nightmare for dental health. And just in case you thought the diet option was a safe bet, while diet soft drinks contain no sugar, rather a range of sweeteners, there is more evidence building to link the consumption of diet soft drink to increased blood glucose levels, greater appetite and cravings for sweet foods and obesity.

4. Extruded snacks

They're fun but we shouldn't eat Twisties, Cheese Balls and other cheese puffed snacks all that often. Photo / Getty Images

Extruded snacks include the rings, tubes, strings and puffs of processed corn, rice or wheat that are heavily flavoured with cheese or chicken and cooked with processed vegetable oils to give us what we know as Burger Rings, Toobs, Cheezels and Twisties. Not only are these snacks high in fat and specifically saturated fats, it is the combination of processed carbs and fats that makes these foods both appealing but also so bad for us nutritionally. Neurological studies have shown that the more concentrated the mix of carbs and fat within a food, the increased risk of overeating, which may somewhat explain why we can finish an entire packet of high fat snacks without even noticing.

5. Deep-fried food

Spring rolls and hot chips may be appealing party options to enjoy occasionally, but it is important to remember that these are one of the few groups of foods that remain a source of dangerous trans fats in Australians diets. Trans fats aren't just found in deep-fried foods either. Those commercially produced sausage rolls, pies and quiches are also on the list. Trans fats are produced during the manufacturing process used to make baked goods heated at high temperatures commercially and are best avoided completely in the diet as they are highly damaging to the arteries. And more recently we have also identified that when carbohydrate-rich foods like potatoes are fried in extremely high temperatures they produce a nasty molecule called acrylamide — a substance that increases the risk of developing cancer.

6. Diet food

Diet drinks give the illusion we're doing something good for our health, when in reality the opposite is true. Photo / Getty Images

While we do have some naturally sweetened products available in supermarkets, when you take a closer look at the diet soft drinks, jelly, desserts and yoghurts, many still contain the artificial sweeteners 951, 954 and 955. There has been concern over these sweeteners for a number of years about the long-term effects of consuming them. Not only do these intense sweeteners change the way foods taste and as such impact our natural appetite management cues, the regular consumption of sweeteners is linked to an increased risk of developing metabolic syndrome, which increases your risk of diabetes, stroke and heart disease. There is also some evidence to show that they change the natural bacteria found in the gut. And with so many natural sweeteners now available, there is really no need any longer to seek out the artificial versions.

7. White bread

With the average block of plain white bread having a similar glucose response in the blood stream to pure glucose, it is difficult to recommend the white stuff as our daily bread of choice. While some varieties may claim to be just as good as wholemeal or wholegrain breads with extra fibre and nutrients added, it is still not as good nutritionally as wholegrain bread. It is the high blood glucose response observed when we consume processed white bread that is partially responsible for increases in glucose and insulin levels over time, which is turn is linked to an increased risk of developing diabetes.

8. Blended vegetable oils

Now we are not talking about extra virgin olive oil in this case, rather blended oils simply listed as vegetable oil on food labels. Not only do vegetable oils offer little nutritionally compared to extra virgin olive oil or nut oils, but often the primary oil in the blend is palm oil, an oil primarily made up of saturated fat, the type of fat known to increase heart disease risk factors. It is this blend of saturated and omega-6 fats found in processed vegetable oils that is strongly linked to inflammation and cell damage over time. And another reason to avoid vegetable oils is that palm oil plantations cause much environmental damage and impact a number of animal species.