In this article, we examine whether ultra-processed foods actually contribute to obesity, based on the latest data.

We have examined ultra-processed foods in the past. Industrial food production ("ultra-processing", in other words) alters the natural structure of food, introduces modified ingredients and additives, raising concerns that it may create products harmful to health, regardless of their nutritional profile.

However, ultra-processed foods are often characterized by a soft texture, high caloric density, high levels of saturated fat and salt, as well as low levels of dietary fiber and protein—properties that affect health regardless of the degree of food processing.

In the end, are the negative effects of ultra-processed foods due to the ultra-processing itself, or are they a consequence of their nutritional properties?

Two studies involving ad libitum feeding in the United States and Japan, in which overweight or individuals with obesity participated, reported that diets rich in ultra-processed foods contributed to an increase in energy intake (by 500 to 800 kcal/day) and led to weight gain compared to diets that did not include ultra-processed foods.

In the third and the longest-term ad-libitum food intake trial, individuals with overweight or obesity in the United Kingdom consumed either a diet rich in ultra-processed foods or a diet without them. Unlike the other two trials, the diet rich in ultra-processed foods reduced energy intake and promoted moderate weight loss (0.9 kg), although the diet free of ultra-processed foods remained the most beneficial approach, resulting in even greater reductions in energy intake and body weight (1.8 kg).

The texture of the ultra-processed foods in the first two tests was softer than that of the comparison diets, something that affects the rate of consumption and calorie intake regardless of the degree of food processing.

In addition to texture, differences in the caloric density of foods can also lead to proportional changes in energy intake and body weight.

It is worth noting that in all three of the aforementioned tests, the caloric density of the entire food item (foods and beverages) or its solid component (foods only) was 0.33 to 1.0 kcal/g higher in the ultra-processed food groups compared to the reference groups.

These differences in caloric density can reasonably explain all the observed differences in energy intake and body weight between diets rich in ultra-processed foods and those without, regardless of the degree of food processing.

Another, fourth, randomized controlled trial compared the effects of diets rich in ultra-processed foods and diets without them, both with the same caloric content.

In that study, whether energy intake met or exceeded the daily requirements for weight maintenance, diets rich in ultra-processed foods caused weight gain after 3 weeks, even though they did not statistically significantly increase energy intake, which contrasts with the direct correlation between increased energy intake due to ultra-processed foods and weight gain observed in the first two trials we examined.

Although it is easy to assume that food processing may lead to some metabolic effect, this difference in weight between the groups can very easily be explained by differences in dietary fiber intake (4 times higher in those who consumed a diet low in ultra-processed foods), which leads to reduced intake of metabolizable energy and sodium intake (1.5 times higher in those who consumed a diet rich in ultra-processed foods), which leads to water retention.

In fact, in a fifth randomized controlled trial in which diets high in ultra-processed foods and diets low in such foods were matched for dietary fiber and sodium content, the total caloric intake from food required to maintain a stable weight over a 2-week period was identical.

With regard to cardiometabolic risk markers, although diets rich in ultra-processed foods increased total blood cholesterol levels in the first three trials we mentioned, this effect was most likely due to the 30 to 110% higher saturated fat content, as this was not observed in the fourth trial, when the diets had similar saturated fat content.

Other risk factors, such as fasting blood glucose, insulin, and triglyceride levels, insulin resistance, glucose tolerance, and blood pressure, were not significantly or consistently affected by diets high in ultra-processed foods in these randomized trials.

Overall, therefore, the available randomized controlled trials provide weak support for a specific effect of ultra-on the regulation of body weight and cardiometabolic function that is independent of established dietary determinants.

-Suprastratum: The authority on health, fitness and nutrition

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