Ultra-processed foods cause weight gain: not just about calories

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We know we should limit junk food such as chips, store-bought pizzas, and sugary drinks. These “ultra-processed” foods, as nutritionists call them, are high in sugar and fat.

Many believe these are the reasons they cause weight gain. However, a new study by the U.S. National Institute of Health (NIH) shows there’s more to it than just calories.

Previous research has linked junk foods to weight gain, but this is the first randomized controlled trial (RCT), the most trusted type of study, to explore this connection.

Details of the Study

In the NIH’s RCT, 20 adults around the age of 30 were randomly assigned to two diets.

One diet consisted of ultra-processed foods, and the other was a “control” diet of unprocessed foods. Participants ate three meals a day and snacks and could eat as much as they wanted.

After two weeks, the participants switched diets for another two weeks. This crossover study design increases the reliability of the results since each person experiences both diets.

Findings of the Study

The study found that participants consumed, on average, 500 more calories per day when on the ultra-processed diet compared to the unprocessed food diet.

Consequently, they gained nearly a kilogram of weight when eating the ultra-processed foods.

Interestingly, despite consuming 500 more calories from ultra-processed foods, participants reported no significant difference in palatability between the two diets. They were also unaware of having a bigger appetite for ultra-processed foods.

Though snacking on ultra-processed foods is often linked to overeating, most of the extra calories in this study were consumed during breakfast and lunch, not as snacks.

The study provided a possible explanation for the overconsumption of ultra-processed foods: participants ate these foods faster, resulting in more calories per minute.

This fast consumption can lead to overeating before the body’s fullness signals kick in.

The Importance of Dietary Fiber

Unprocessed foods are often high in dietary fiber, which can help induce feelings of fullness. Ultra-processed foods, on the other hand, tend to be low in fiber due to the manufacturing process.

The NIH researchers tried to balance this by adding fiber supplements to the ultra-processed diet. However, fiber supplements aren’t the same as natural fiber found in unprocessed foods.

Natural fiber slows down calorie consumption because it’s part of the food’s structure.

The Takeaway

This study and others suggest that keeping food structure, like in unprocessed foods, can help regulate calorie intake. This encourages slower eating, which gives the body’s fullness signals time to kick in.

However, finding time for slow meals of unprocessed food can be a challenge. In some cultures, like in France, seated mealtimes and a leisurely pace of eating are encouraged.

This approach could potentially offset the weight gain associated with quick meals of ultra-processed foods.

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