Tinned food - healthy enough?
The government says food supplies will be secure whether we leave the EU with or without a deal.
But what would happen if you did cut out fresh fruit and veg and ate only tinned goods?
In 2017, BBC Radio Derby's Andy Twigge set himself a challenge of eating only canned food for a week.
"I did it for a laugh really.
"I love tinned potatoes and marrowfat peas, so I wondered what it would be like to live off tinned food for a while. I set myself a week. I thought it should be quite easy."
He almost managed it, but quit on day seven. The thing that broke him? A Sunday roast.
"I stuck at it for six days. I even ate tinned Brussels sprouts!
"I did have a Fray Bentos pie, and that was very nice, but it did all become a bit of a chore. I was physically fine on it though. I didn't waste away or anything." He says he's not sure he would call what he did "nutritional".
Because he was only doing the diet for a short period, Andy didn't check with a dietitian.
But we have, and here's what they think.
To be tinned, foods are sealed and preserved by pressure cooking them at a very high temperature.
Like regular cooking, this destroys some of the nutrients.
Canned foods are often thought to be less nutritious than fresh or frozen foods because of this. But that's not always the case, say diet experts.
Bridget Benelam is a nutrition scientist at the British Nutrition Foundation.
She says: "Generally speaking, there's a wide range of canned foods that you could eat - from fruit, veg, potatoes and pulses to fish and ready-made foods like soup, baked beans or chilli.
"And some of them are nutritionally better than others. Tinned oily fish like salmon, for example, is healthy. And beans and pulses, like chickpeas and lentils, are a good source of protein and fibre while being low in fat.
"Unfortunately, there's not a lot of data about nutrients in canned food versus fresh or frozen."
She said the main nutrients that could be lost or diminished in the canning process were some of the water-soluble vitamins which cannot be stored by the body and are vital for healthy skin, blood vessels and bones, and the nervous system.
Researchers have attempted to measure the loss, comparing fresh, frozen and canned fruit and veg.
Findings suggest that although frozen foods lose fewer nutrients initially when they are packaged, when you get them home and eventually boil them, they can lose a similar amount to the tinned version.
Likewise, although freshly picked, uncooked fruit and veg contain lots of nutrients, these will degrade over time, even when you store them in the fridge.
Bridget says: "With tinned foods, there may be some losses of nutrients like vitamin C and thiamine, which can be lost when cooking, but whether this would have an impact on health would depend on the diet overall.
"Nutritionally, it could be OK, as long as you get a good mix. My main concern would be the tedium. The texture could be quite dull. Food can get a bit mushed and squished when it is canned. You won't be able to have tinned salad, so you'd have to make sure you are getting the right variety of food."
So, when it comes to picking, what are the pitfalls?
What to buy
Dietitian Frankie Phillips, from the British Dietetic Association, agrees that variety is the key.
"You'd be fine over a few days, but a tinned food diet might be quite limiting over a long period of time. You'd need to be quite careful about what cans you choose to eat."
- How to cook with tins from your store cupboard
- How canned food became a million dollar idea
- My Brexit box: The people stockpiling food
- Doomsday Diet: ten foods to live longer
Ingredients such as salt, sugar and fat are sometimes added to processed foods to make their flavour more appealing.
That means you could consume more than the recommended amounts and take on more calories than you need. "This is where you might fall down in terms of nutrition," says Frankie.
Fruit tinned in syrup will contain lots of sugar, for example, and vegetables in brine will be salty.
But all fruit and veg canned in their own juice will count towards your 5-a-day.
Frankie says: "It should be quite easy to get most of your major food groups, such as protein, carbohydrates. Dairy might be a bit harder.
"One of the concerns I would have is around canned meats. They are generally quite salty because of the way they are preserved.
"Nutrition labels on cans will help guide you," says Frankie. The guidelines for adults are:
- Total fat - High: more than 17.5g of fat per 100g, Low: 3g of fat or less per 100g
- Saturated fat - High: more than 5g of saturated fat per 100g, Low: 1.5g of saturated fat or less per 100g
- Sugars - High: more than 22.5g of total sugars per 100g, Low: 5g of total sugars or less per 100g
- Salt - High: more than 1.5g of salt per 100g (or 0.6g sodium), Low: 0.3g of salt or less per 100g (or 0.1g sodium)
There are some other practical considerations too, including food safety.
Is it OK to keep leftovers in my fridge?
Cans are made of steel, with a fine coating of tin or chromium oxide to protect them from rusting. For acidic foods like tomatoes, a thin coating or lacquer is needed on the inside of the can.
When you open a can of food and you're not going to use all the food straightaway, empty the food into a bowl, or another container, and put it in the fridge, food safety experts advise.
It's best not to store food in an opened tin can, or re-use empty cans to cook or store food. This is because when a can has been opened and the food is open to the air, the tin from the can might transfer more quickly to the can's contents.
This advice doesn't apply to foods sold in cans that have resealable lids, such as golden syrup and cocoa, because these types of food don't react with the can.
The US food safety regulator has some more advice:
- Heed the sell-by date - Check your pantry every few weeks and use canned goods you have had on hand for awhile. High-acid canned foods, such as tomatoes, pineapple and pickles, will store well for 12 to 18 months. Low-acid canned foods such as spaghetti, potatoes and beans, will store well for two to five years.
- Beware damaged cans - If a can containing food has a small dent, but is otherwise in good shape, the food is probably safe to eat. A bulging lid, or a dented or leaking can is a sign of spoilage. When you open it, look for other signs, such as spurting liquid, an "off" odour or mould. Don't taste or use these canned foods. Throw them away immediately.
- Is it normal to hear a "hiss" when you open it? - Some cans may hiss because they are vacuum-packed and the noise is a result of air pressure, which is perfectly normal. However, if a can hisses loudly or spurts forcefully when opened, it may be an indication that the food is spoiled and should be discarded.
What about the chemicals?
Some people worry that cans can contain harmful chemicals, including a substance called Bisohenol A (BPA).
BPA is mainly used to make plastics, including containers that come into contact with food, but it's also used to make some protective coatings and linings for food and drinks cans.
The UK's Food Standards Agency has examined BPA, and says that levels of the compound people would typically consume do not represent a risk to consumers.
The European Food Safety Authority has also assessed the evidence and says dietary exposure to BPA is "not a health concern for any age group".
The US National Toxicology Programme has been carrying out a long-term study into BPA, looking at the effects of exposure in rats before and after giving birth to see if there might be any link to diseases such as cancer. A final report is expected in the autumn of 2019.
Other canny facts
The history of canning is said to have begun with Napoleon. It's believed he offered 12,000 French francs to anyone who could find a way to prevent military food supplies from spoiling. Napoleon gave the prize in 1795 to Nicholas Appert, who invented the process of packing meat and poultry in glass bottles, corking them, and submerging them in boiling water.
This military secret soon reached England where, in 1810, Peter Durand patented the use of metal containers for canning.
Today, we still love canned food. According to consumer research group Kantar Worldpanel, people in the UK spent more than half a billion pounds on tinned food during the 12 weeks to 30 December 2018. Unsurprisingly, we tend to buy more canned products over winter than summer.
A study of 2,000 adults carried out for the Metal Packaging Manufacturers Association found the average adult has 16 cans of food in their cupboard and relies on tinned food for at least three meals a week.
Baked beans were named as the most popular canned food to use in everyday cooking, followed by tinned tomatoes, soup, fish such as tuna and salmon and other vegetables such as sweetcorn.