Some nutrients are lost (folate, thiamine, vitamin C.) through the processing (including heating/cooking to prolong shelf life) . Nutrients which are unstable, such as folate, thiamine and vitamin C.are lost first, with others disappearing over time.
Effects of processing
There are a number processes used in the manufacture of ultra-processed foods processes, which can affect the nutritional value of foods. These include:
- grinding, milling or sifting of cereals, nuts, seeds and pulses - this can remove some of the most nutritional parts of the raw food such as phytochemicals and other essential nutrients. It also lowers the fibre content of the product undergoing these processes making it more difficult for an average person to meet their recommended daily fibre intake. This process also exposes the final product to air which can result in the oxidisation of the nutrients which are left and also allow microbes to also enter the food causing spoiling and degradation.
- blanching - typically used or tinned and frozen foods to kill any microbes which may result in premature spoiling of the foods. Blanching results in the water soluble nutrients being washed or leached from the food or the heat in itself destroys the nutrients.
- cooking - while this may occur in the home kitchen, typically processed foods are cooked more than one would usually do. This is to ensure that the food is safe to eat as processed foods have a high risk of microbe contamination and also the food is essentially double or triple cooked (blanched, cooked at the food processing plant and then heated/cooked again in the home kitchen). Each heating cycle destroys the nutritional value of the food even more.
- canning/pasteurisation - high prolonged temperature is applied to foods to ensure that they are sterile after the cooking or before/immediately after packaging (e.g. canning process where filled cans are subject to high temperature water bath), This high temperature have a significant impact on the nutritional values of the food. It impacts on heat and water soluble nutrients. One advantage of canned foods is preservatives are not needed as the contents remain sterile until the outer metal can is opened or ruptured. This means that the nutritional value of the can is unlikely to change much over time (unlike fresh foods which nutritional value can deteriorate through prolonged storage.
- freezing - while freezing has the potential to retain and maintain the food when processed, the frozen food is usually subject to bleaching (see above).
- high pressure processing - this is becoming more mainstream for fresh fruit juices and there has been some reports that it is also suitable for fresh milk. It is also used for cooked food processing where an industrial sized pressure cooker may be used to speed the cooking process. While for juices and milk it can reduce nutritional losses which would otherwise occur through heating, often processed foods are also subject to high cooking temperatures which affect the food as outlined above.
- desiccation/dehydrating - this can result in the loss of some unstable nutrients, but may also concentrate other nutrients, sugars and salts. It also can allow one to eat more of the food as more food is needed to feel full compared to the undesiccated product (e.g. dried fruits compared to fresh fruits…one can consume dozens of sultanas but would struggle to eat the same number of grapes).
- food additives - a wide range of food additives are added to processed food for a range of different reasons. Some of these additives may be beneficial (such as replacing nutrients lost through processing or addition of preservatives for food safety), many consumed in excess can be detrimental (such as salts, fats, sugar, artificial flavours and colours etc) and are added to improve the taste of the food or make it more attractive for one to consume…
What can be done?
Unless processed foods are banned, the only thing to do is to ensure that there is education on the disadvantages of consuming processed (inc. ultra-processed foods). Good and accurate labelling also has an important role such as that being championed for Choice for sugar, but there is is also room for warning labels like that used on other countries (Chile is a good example) to warn the consumer on purchase packaged and processed foods which are high in salt/sodium, fats (inc. saturated), sugars and calories.
In the past all government have been reluctant to add warning labels to processed foods, potentially due to lobbying from the (multinational) food manufacturing industry and also because the science has not been fully resolved. As the science has been resolved and there is overwhelming proof of the negative health consequences of highly or ultra-processed foods containing additives, it is long and truly overdue for some more serious action to be taken (such as highly conspicuous warning labels on all products which are unhealthy).
The government has also believed that its role has been in advertising…but its success has been limited otherwise conditions like type 2 diabetes and obesity would have become less prevalent.
While the 5-Star health rating system has its merits and is endorsed by the food manufacturing industry (which they would as it hides or makes it difficult for the average consumer to determine why a product is unhealthy), what is is needed is more confronting change to labelling to ensure the customer fully aware when making purchase choices…