It's common to hear the advice to "eat less processed food." But what exactly is processed food? What exactly is minimally processed food or ultra-processed food? And what effect does processed food have on our health?
What is the difference between processed and ultra-processed foods?
Unprocessed or minimally processed foods are whole foods that retain their vitamins and nutrients. The food is in its original (or nearly so) state. To make them suitable for storage and safe to consume, these foods can be minimally altered by removing inedible parts, drying, crushing, roasting, boiling, freezing, or pasteurisation. Carrots, apples, raw chicken, melon, and raw, unsalted nuts are examples of unprocessed or minimally processed foods.
A food is altered from its natural state during processing. Processed foods are created by adding salt, oil, sugar, or other ingredients. Canned fish and vegetables, fruits in syrup, and freshly baked breads are some examples. The majority of processed foods contain only two or three ingredients.
Some foods are ultra-processed or highly processed. They most likely contain a lot of extra ingredients like sugar, salt, fat, and artificial colours or preservatives. Food extracts, such as fats, starches, added sugars, and hydrogenated fats, are used to make ultra-processed foods. They may also include additives such as artificial colours and flavours, as well as stabilisers. Frozen meals, soft drinks, hot dogs and cold cuts, fast food, packaged cookies, cakes, and salty snacks are examples of these foods.
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According to a study published in The BMJ, ultra-processed foods are the main source of calories consumed in the United States (nearly 58 percent) and contribute nearly 90 percent of the energy we get from added sugars.
What effect do processed foods have on our health?
A recent study published in the journal Cell Metabolism compared the effects of an ultra-processed diet on calorie intake and weight gain to the effects of an unprocessed diet. The study included 20 healthy, overweight adults who were hospitalised. For 14 days, each study participant followed an ultra-processed diet and an unprocessed diet. During each diet phase, the study subjects were given three daily meals and told to eat as much or as little as they wanted. Each meal was given up to 60 minutes, with snacks (either ultra-processed or unprocessed, depending on the study phase) available throughout the day.
Total calories, fat, carbohydrate, protein, fibre, sugars, and sodium were all matched across diets. The source of calories made a significant difference: in the ultra-processed diet phase, 83.5 percent of calories came from ultra-processed foods; in the unprocessed diet phase, 83.3 percent of calories came from unprocessed foods.
The researchers discovered that the ultra-processed diet consumed approximately 500 more calories per day than the unprocessed diet. The ultra-processed diet period was distinguished by an increase in carbohydrate and fat intake, but not protein. Participants gained two pounds on average during the ultra-processed diet phase, while losing two pounds during the unprocessed diet phase. Limiting ultra-processed foods, the authors concluded, could be an effective strategy for preventing and treating obesity.
There were several limitations to the study. For starters, this was a very small study with only 20 participants. Another finding was that individual responses to the two diets varied significantly. Eleven people gained a lot of weight on the ultra-processed diet, up to 13 pounds in 14 days, while a few people gained nothing. It's also unclear how generalizable the findings are to a larger population because the study excluded participants with chronic diseases like heart disease or diabetes. Furthermore, the study was conducted in a clinical research setting, which may have influenced their eating habits (the study subjects may have been more isolated and bored than in their natural environments).
Another study, published in The BMJ, looked at the dietary records of over 100,000 French adults over a five-year period. They discovered that those who ate more ultra-processed foods were more likely to develop cardiovascular disease, coronary heart disease, and cerebrovascular disease. Even after the researchers adjusted for the nutritional quality of the diet, these findings remained statistically significant (considering factors such as the amount saturated fat, sodium, sugar, and dietary fibre in the diets). Despite the fact that large observational studies cannot prove cause and effect, the research does suggest a link between ultra-processed diets and heart disease.