Fortified breakfast cereals can be a useful source of fibre, vitamins and minerals – but some are considered ultra-processed food.

We're often told that breakfast is the most important meal of the day. Get this decision right and your nutritious morning meal can help keep you energised and focused for whatever challenges come your way. Yet the choice of what to eat for breakfast – or what to give your children if you have them – can feel overwhelming at times.

If, like 53% of the US population you decide to go the breakfast cereal route every week, then you can take your pick. There's porridge oats, granola, muesli, bran flakes, corn flakes, and puffed rice – the options are endless, with each colourful box promising to deliver a healthy, nutritious meal. Yet, although breakfast cereals have traditionally been seen this way, some scientists warn that these are ultra-processed snacks – and they are not actually good for us at all.

So, what is the truth, and what kind of cereals – if any – should we be eating?

First off, some facts. Cereals are grasses from the Poaceae family, cultivated for their edible seeds, or grains. Cereal crops include wheat, rice, oats, barley and corn. Each cereal grain has three main edible components. There's the outer layer of bran, which is rich in fibre, B vitamins and trace minerals. Then there's the endosperm, which is packed with starch and proteins to support the developing plant embryo. Finally, the germ contains the embryo, and is rich in oils, vitamins and minerals.

One of the first people to come up with the idea of turning grains into breakfast cereals was John Harvey Kellogg, an American physician. At the time he was a superintendent of the Battle Creek Sanatarium – a kind of hybrid between a hospital and a health resort. To improve the patients' diet, Kellogg developed, patented and introduced a variety of new foods, including Granola and Corn Flakes. However, these have now become so ubiquitous that there are dozens of generic versions on the market.

Today the production of breakfast cereals is an industrial affair. After the grains are harvested, breakfast cereals will undergo various processing steps before being packaged and sent to supermarket aisles. Some cereals – such as bran flakes – are made from the entire, or whole grain, while in others, such as some corn flakes, the grain is crushed between large metal rollers to remove the outer layer of bran. Some cereals then undergo further processing where the grain is milled into flour.

The resulting product is then mixed with flavourings, salt, sweeteners and other ingredients such as vitamins and minerals. They are then cooked and shaped into flakes, loops or other forms. Finally, the cereal is baked or toasted to give it a crisp texture.

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Because cereals are fortified with minerals and vitamins, they have long been seen as an effective way of ensuring that people get the nutrients they need. This is especially true for individuals with restricted diets who may struggle to get the vitamins they require from food.........

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