We know that we should eat less junk food, such as chips, industrially made pizzas and sugary drinks, due to their high calorie content.
These "ultra-processed" foods, as they are now called by nutritionists, are high in sugar and fat, but is it the only reason they gain weight? An important new study conducted by the National Institute of Health of the United States (NIH) shows that there is much more work here than just calories.
Studies have already found an association between junk foods and weight gain, but this link has never been studied in a randomized controlled trial (RCT), the gold standard of clinical trials.
In the NIH's RNH, 20 adults around 30 were randomly assigned to an ultra-processed food diet or a "control" diet of unprocessed foods, both consumed as three meals and snacks during the day . how they wished.
After two weeks in a diet, they moved on for another two weeks. This type of crossover study improves the reliability of the results since each person takes part in both arms of the study. The study found that, on average, participants ate 500 calories more a day when they ate the ultra-processed diet than when they ate the unprocessed food. And on the ultra-processed diet, they gained weight – almost a kilogram.
Although we know that ultra-processed foods can be quite compelling, the participants reported finding the two equally tasty diets, without the awareness of having a greater appetite for ultra-processed foods than for unprocessed foods, despite consuming more of 500 calories a day.
The unconscious over-consumption of ultra-processed foods is often attributed to snacks. But in this study, most of the excess calories were consumed during breakfast and lunch, not as snacks.
Eat slowly, not fast food
A crucial clue as to why ultra-processed foods caused greater calorie consumption could be that participants ate ultra-processed meals faster and thus consumed more calories per minute. This can cause excessive intake of calories before the body's signals of satiety or fullness have time to start.
An important satiety factor in unprocessed foods is dietary fiber. Most ultra-processed foods contain little fiber (most or all of it is lost during production) and are therefore easier to eat quickly.
Anticipating this, the NIH researchers equalized the fiber content of their two diets by adding a fiber supplement to the ultra-processed diet in beverages. But fiber supplements are not the same thing as fibers in unprocessed foods.
Fiber in unprocessed food is an integral part of the food structure – or food matrix, as it is called. And an intact food matrix slows the rate at which we consume calories. For example, it takes much longer to chew an entire orange with its matrix of intact food rather than gulp down the equivalent calories like orange juice.
An interesting message that emerges from this and other studies seems to be that to regulate calorie intake, we must maintain the structure of food, like the natural food matrix of unprocessed foods. This forces us to eat more slowly, letting the satiety mechanisms of the body activate before we have eaten too much. This mechanism does not work with ultra-processed foods because the food matrix is lost during production.
Finding time for a meal of slowly processed unprocessed foods can be a real challenge for many. But the importance of sitting meals is a vigorously defended approach in some countries, such as France, where a succession of small dishes guarantees a more pleasant and pleasant way of eating. And it could also be an important weight gain antidote caused by grabbing a quick meal of ultra-processed foods.
Richard Hoffman, professor of nutritional biochemistry, University of Hertfordshire
This article is republished by The Conversation under a Creative Commons license. Read the original article.
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