It's become the most vilified food of modern times: red meat, particularly the type you buy in a packet. 

According to the World Health Organisation, processed red meat like bacon, ham and sausages definitely causes cancer due to toxic additives in the products.

British shoppers have got the memo. We're eating 6,000 fewer tons of processed pig products this summer than we were at the beginning of the year. 

The concerns surround preservatives called nitrites, which give cured meat its characteristic pink colour and are commonly found in ham, sausages and bacon, along with other deli meats.  

Nitrites are known to react with compounds in meat to form chemicals called nitrosamines in the stomach, which have been linked to digestive cancers. 

A major 2019 study found that the risk of deadly bowel cancer rises by 20 per cent with every rasher of bacon – or slice of ham – eaten daily.

But I will put my reputation as a diet expert on the line to say, with confidence, that not all processed red meat is bad for you.

In fact, I believe one of the biggest nutritional travesties of the last decade is the vilification of what was once a much-loved British lunchbox staple: the ham sandwich.

First, the surprising benefits. Most packaged ham is in fact a great source of protein-heavy energy that's low in calories.    

Two average-sized slices deliver around 8g of protein for less than 50 calories, and less than 0.5g of saturated fat – drastically lower than an equivalent serving of cheddar cheese at 8.5g. There's twice as much protein as you'll find in cheese, in fact, and slightly more than in one egg.

It also provides a boost of vitamin B12 and thiamin – both of which are essential for helping convert food into energy. 

If you add a couple of slices of wholemeal bread into the mix, you're looking at an extra 7g of vital fibre – a quarter of your recommended daily intake of the nutrient proven to prevent bowel cancer.

Crucially, the nitrites in ham don't carry the same risk as they do in bacon.

The preservatives – which are almost exclusively added to processed meats and a handful of continental cheeses – can be harmful because they trigger a chain reaction that leads to cancer-causing chemicals.

The heat involved in frying, as well as the acidity in the gut, provokes a chemical reaction between nitrites and compounds in meat protein called amines. The result is carcinogenic nitrosamines.

Interestingly nitrites – and similar compounds called nitrates – also naturally occur in green, leafy vegetables like watercress and rocket, where they've been found to lower blood pressure.

Importantly, the amount of harmful nitrosamines produced depends enormously on how the meat you're eating is prepared and cooked.

High heat is where much of the danger lies. Pan-frying bacon until it turns crisp can in fact encourage nitrosamines to form right there in the pan. 

At the same time, the browning and charring produced by frying, grilling or barbecuing any meat creates other potentially cancer-causing chemicals called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), adding another layer of risk.

By comparison, boiled or steam-cooked ham is prepared at relatively gentle temperatures of around 70-80°C before being eaten cold. Because it never experiences the intense heat of a frying pan or barbecue, it contains far fewer pre-formed nitrosamines than crispy bacon.

The raw ingredient matters, too. Pork naturally contains less haem iron – the red pigment that gives meat its colour – than beef. 

Haem can fuel the chemical reactions that create nitrosamines during curing and cooking, which means ham may have a lower nitrosamine‑forming potential than cured beef products like pastrami or salt beef.

The cancer-causing reaction is also hampered by the recent addition of ascorbate – a form of vitamin C – to brines used to flavour both ham and bacon. 

Vitamin C helps intercept nitrites before they can react with compounds in meat and stomach acid to form nitrosamines.

This is all thanks to modern food safety regulations, which have also enforced much lower nitrite limits since the 1970s and 80s.

So a ham sandwich eaten with a glass of orange juice, some crunchy red pepper or a crisp side salad may produce fewer nitrosamines in the stomach than the very same sandwich eaten on its own.

There are two small drawbacks to a ham sandwich, the first being the salt content. A two-slice serving will set you back around 10 per cent of your daily limit. 

However, this is still roughly half as much as you'll get in two rashers of bacon and no different to the amount in supermarket to-go sandwiches that don't contain any red meat (like M&S' chicken salad option). 

The other detail to note is the addition of phosphates in some products, which are used to retain moisture. 

Additive versions of the mineral – as opposed to the type that naturally occurs in food –  are absorbed rapidly by the body. For people with kidney disease – and potentially for healthy individuals over many years – consistently high intakes have been linked to poorer bone and cardiovascular health.

However, phosphate-free varieties are widely available and don't necessarily cost any more. And if you're a regular Diet Coke drinker, it's likely you're consuming far higher quantities of phosphate as the drink is teeming with phosphoric acid. 

If you're still concerned about nitrites, opt for a parma ham or Serrano variety, which are made without the compounds. Supermarkets now stock nitrite-free versions of most deli hams. 

I wouldn't eat a ham sandwich every day, but that is true for all foods; studies show the healthiest diets are the most varied. 

But I would happily eat ham a couple of times a week – even one containing standard nitrites and phosphates. 

On wholemeal bread with a generous handful of salad, it’s a lunch choice I’d make without a second thought.