Avoiding ultra-processed foods makes it easier to control body weight

Obesity has become in recent years, one of the leading causes of mortality and morbidity, accounting for more than 4 million deaths each year worldwide. Fundamentally, weight gain is the result of an imbalance caused by calorie intake that exceeds the body’s energy needs. Research over the past several years has shown that this imbalance is driven more by excessive food consumption than by insufficient physical activity, particularly when calories come from industrially ultra-processed foods; in Canada, these account for 43.4% of daily caloric intake among adults. A very large number of epidemiological studies have indeed observed an association between consumption of these products and the incidence of obesity—an effect attributed to several characteristics intrinsic to these foods, such as their very high energy density (foods rich in fat and sugar), their particular orosensory properties (soft texture, lack of fiber) that promote calorie overconsumption, as well as their content of various additives (emulsifiers in particular) that disrupt metabolism.

Several official dietary guidelines, such as the British Eat Well Guide (EWG) and the 2025 U.S. Dietary Guidelines for Americans Committee (DGAC), nevertheless consider the evidence insufficient to recommend reducing ultra-processed foods in current guidelines. Instead, a standard approach to body weight control and general health maintenance continues to be promoted—namely, consuming five daily servings of fruits and vegetables, obtaining most calories from carbohydrates, limiting fat, sugar, and salt intake, and consuming a variety of foods—without taking into account whether these foods are minimally or highly industrially processed (it should be noted that the Canadian food guide recommends limiting consumption of these foods).

According to a recent British study, it is high time to update these recommendations, because even when people adhere closely to the main principles of these dietary guidelines, the presence of ultra-processed foods undermines body weight control.

First, this study clearly shows that when individuals have poor eating habits and adopt the government-promoted recommendations for healthy eating outlined in the Eat Well Guide, they generally lose weight. But the real strength of this study lies in demonstrating that not all calories are equal: following these recommendations without reducing the proportion of ultra-processed foods (UPF) constitutes a major obstacle to weight loss. The trial indicates that UPF are the Achilles’ heel of official recommendations—without reducing them, weight loss remains limited. In the study, those who ate meals based on fresh foods or minimally processed foods (MPF) lost twice as much weight as consumers of ultra-processed foods (-2% vs. -1%), while following the same nutritional recommendations. What had been lacking, until now, was this kind of strong evidence—data from perfectly controlled randomized clinical trials comparing UPF and MPF in the context of adherence to dietary guidelines. This study highlights that following a so-called healthy diet loses part of its effectiveness when UPF are maintained, whereas a diet based solely on MPF fully maximizes the benefits. We have also previously reported that UPF have harmful effects on health, both mental and cardiovascular, and promote weight gain by encouraging excessive food consumption—around 500 calories per day.

Let us take a closer look at the study: the researchers sought to determine whether the obesogenic effect of UPF could interfere with the weight loss normally observed when adhering to a healthy diet. To do so, they measured weight loss induced by two types of diets: one composed primarily of minimally processed foods (MPF), and, conversely, one in which ultra-processed foods (UPF) made up the majority of calories (see Table 1).

Table 1. Average nutrient composition of the provided MPF and UPF diets and Eatwell Guide recommendations. Abbreviations: MPF: minimally processed food; UPF: ultra-processed food.

The impact of these two types of diets was compared at the same time and in the same subjects in a crossover design. That is, for 8 weeks, volunteers followed the recommendations of the Eat Well Guide (EWG), which include ultra-processed foods (UPFs) in the diet, with no other changes to their lifestyle habits. Then, after a 4-week washout period without any guide or constraints, the same volunteers were required to follow the EWG recommendations again, but this time eliminating UPFs and thus incorporating minimally processed foods (MPFs). Half of the subjects started in the UPF group and the other half in the MPF group, assigned randomly and in a blinded manner, before switching groups for the second phase of the study.

Essential criteria: none of the individuals who had voluntarily enrolled in the study understood the primary objective of the study, namely the difference in their body weight between the beginning and the end of the study. Furthermore, all study participants received an excess amount of food, prepared appropriately according to the group to which they were assigned, without knowing whether the menus included UPFs or only MPFs; therefore, they could eat as much food as they wished. They were not allowed to add any foods— even tea and coffee were provided. Therefore, there was no possible bias.

The results are unequivocal (see Figure 1 for a summary). In Great Britain, more than 60% of the adult population is overweight, and more than 60% of dietary calories come from UPFs. The study population (90% women, mean age 42.6 ± 1.6 years) was representative, with a body mass index (BMI) of 32.7 ± 0.5 kg/m², a mean body weight of 89.4 ± 1.7 kg, and a consumption of 67.3 ± 1.1% of kcal/day from UPFs, all without adherence to the Eat Well Guide except for red meat intake. Once enrolled in the study, adherence to the Eat Well Guide led to weight loss in both groups (Figure A) over 8 weeks. However, in the MPF group, there was a 2.06% reduction in body weight (~1.8 kg), whereas in the UPF group this reduction was smaller (p = 0.012) and limited to 1.05% (~0.9 kg).

The benefit of eliminating UPFs in favour of MPFs therefore amounts to nearly an extra kilogram of weight loss over 8 weeks (Figure 1B). Other consequences should also be noted: only the MPF diet reduced blood pressure, as well as fat mass, including visceral fat mass (p = 0.008), whose harmful effects on health were recently reported. Logically, this loss of fat mass was associated with a reduction in prediabetes markers. Moreover, weight loss implies a reduction in caloric intake: although study participants ate ad libitum and were unaware of which diet they were following, they consumed 327 ± 110 fewer kcal per day on the MPF diet than on the UPF diet (p = 0.005). As mentioned in the introduction, this difference is explained by the greater palatability created by UPFs—that is, these processed products promote an instinctive desire for foods that satisfy a natural inclination.

The difference observed in only 8 weeks is striking and unequivocal, considering the constraints imposed by the study design, since participants not only followed the government dietary guidelines, but also ate without restriction and in a blinded manner the foods corresponding to the assigned dietary pattern. This had been suspected, but this study has the merit of eliminating any ambiguity regarding the harmful impact of industrial ultra-processed foods on our cardiometabolic health and, in the long term, on our healthy life expectancy.

During the writing of this text, a study by researchers at the Montreal Heart Institute showed that the ingestion of a single ultra-processed meal (compared with a minimally processed meal) had direct consequences on cardiac muscle perfusion and cognitive performance. The subjects were young (31 ± 11 years) and healthy, yet hemodynamic and cerebral regulation were temporarily disrupted. These data illustrate the extent to which such a diet represents a stressor, and that when this type of diet becomes chronic, the accumulation of stress it generates is harmful to our cardiovascular system, among others. All of these data therefore confirm the harmful effects of ultra-processed foods, and there is no doubt that attempting to eliminate them from our diet can only be beneficial.