But.

"To say all processed food is bad is a mistake," said Dariush Mozaffarian, the dean of Tufts University's Friedman School of Nutrition Science and Policy, at the Aspen Ideas Festival this week.

"I think it's interesting, even the question 'fresh versus processed' ... as though they were opposites.

"You can have something that's fresh and processed and something that's fresh and not processed."

The scale of what Mozaffarian is referring to can be simple or complex.

At the confusing end of the scale, in America, legally "fresh" foods include those that have approved waxes or coatings added, post-harvest pesticides applied, are mildly washed in chlorine or acid or treated with a capped level of ionising radiation.

Everything else, like bread you bake at home or the greens you steam are "processed".

"Cooking is processing at the end of the day, so to call all processed foods bad is just silly," explains dietitian Dr Joanna McMillan.

In this sense, "processed" foods can be better for us.

"Some processing makes nutrients or phytochemicals more available to us – lycopene in tomatoes is a classic example," McMillan says. "You get far more lycopene from tomato paste than raw tomatoes."

Freezing, another form of processing, is often another example.

"Freezing is an excellent way of preserving food without the need to add chemical preservatives," McMillan explains.

"Freezing also preserves the nutrients. Veggies and fruit are frozen on the day they are picked. Compare that the produce that is picked, transported to the supermarket, sat on shelf and then sat in our kitchen for however long before eating."

She adds: "Vitamin C declines rapidly after picking and so levels tend to be much higher in frozen produce. It's not the only nutrient this applies to. It's only the texture that is affected by the freezing and thawing process – nutritionally these foods are just as good for us."

There is of course a vast difference between your frozen peas or home-cooked bread and your can of Coke or frozen McCains meal.

"I've been purposefully using the term highly processed in an albeit clumsy attempt at differentiating what we mean," McMillan says.

We are eating "huge amounts" of highly processed foods.

Every day, the average Australian eats about three kilograms of food and drink. More than one-third of daily energy is coming from foods high in saturated fat and sugar such as cake, biscuits, alcohol, soft drink and chips.

This is the "processed" that makes a real difference to our weight and health. If we're quibbling over "fresh" or "processed" in terms of frozen or canned, then it's more of a moot point.

Canned foods can be higher in salt, but much of this can be rinsed away, McMillan says.

"Canned legumes are much more likely to be eaten than those bought dried (soaking overnight and then boiling for hours just won't happen in most homes!)," she points out. "In fact with the right canned produce and packet dried produce in your pantry, along with some frozen vegies you can produce several pretty healthy meals without any 'fresh' ingredients."

This bit of perspective is important, said Mozaffarian at the end of his talk.

"I'm a cardiologist," he said, "and I had a patient come in once asking about salmon. He said, 'I heard there's PCBs in salmon. Should I be eating wild salmon or farmed salmon?' I said, 'Stop smoking.'"