Obesity has slowed in high-income countries since the 1990s, and in Spain it has stabilised

Is the study of good quality?

Yes, this is a methodologically robust, high-quality study based on a very large sample comprising approximately 232 million participants from different countries and age groups. The research analyses temporal trends in age-standardised obesity prevalence in both adult and paediatric populations, allowing for robust international comparisons.

In addition, the study not only evaluates obesity prevalence itself, but also the rate at which this prevalence is changing, providing valuable insight into the epidemiological dynamics of obesity across different regions of the world. The breadth of the dataset and the use of statistical modelling further strengthen the validity of the findings.”

Are there any limitations that should be taken into account?

“In addition to the limitations acknowledged by the authors, one of the study’s main limitations is the use of body mass index (BMI) as the diagnostic criterion for obesity. Although BMI is the most widely used tool and is recommended by the WHO because of its simplicity, reproducibility and standardisation, it has important limitations in terms of clinical validity, as it does not distinguish between fat mass and muscle mass, nor does it take fat distribution into account.

Related to this, there are ethnic differences in the relationship between BMI and cardiometabolic risk. For example, in Asian populations, obesity-related risk may arise at BMI values below 30 kg/m², meaning that the use of a single universal cut-off point could underestimate the true prevalence of obesity in certain population groups.”

What are the implications of the study, and how does it fit with the existing evidence?

“Analysing obesity trends is of enormous importance for public health, given that obesity remains one of the leading global health challenges. The study’s findings reveal considerable heterogeneity between countries, age groups and sexes, reinforcing the need to design preventive strategies tailored to specific populations.

The study is consistent with previous evidence indicating that obesity is the epidemic of the 21st century. However, these data also suggest that sustained public health policies over time can be effective in reducing, and even reversing, obesity trends. Nevertheless, these improvements are mainly observed in wealthier, more economically developed countries. Likewise, within individual countries, despite the overall reductions observed, more disadvantaged groups continue to be disproportionately affected and should therefore be prioritised in prevention and health-promotion policies.”

In Spain, not only has the rise in obesity slowed, but it has even shown a slight reversal, making it one of the few countries where this has occurred. What might explain this?

“Although the prevalence of overweight and obesity in Spain remains high, the study’s findings suggest a slight reversal in obesity trends in recent years, which may be explained by several factors.

On the one hand, Spain has a universal healthcare system and a public health infrastructure that facilitate the implementation of preventive strategies and campaigns promoting healthy lifestyles. On the other hand, certain sociocultural factors — such as partial adherence to the Mediterranean diet, greater consumption of fresh foods, and lifestyle habits characteristic of Mediterranean countries — may also help to curb the rise in obesity.”

Is the study of good quality?

“This is an extremely robust study analysing more than 4,000 population-based studies using measured — rather than self-reported — height and weight data from over 230 million people across 200 countries between 1980 and 2024. Its main strength is that it does not simply examine ‘how much obesity there is’, but also the speed at which obesity rates are increasing, stabilising or declining.”

Are there any limitations that should be taken into account?

“The main limitation is that, as this is a global analysis, some countries have less available data and the estimates therefore rely on statistical modelling. In addition, the study describes trends, but it cannot establish with certainty which policies, social changes or cultural factors may explain the stabilisation or decline in obesity.”

What are the implications of the study, and how does it fit with the existing evidence?

“In my view, the most important message is that obesity is not progressing uniformly across the world: in many high-income countries it appears to have slowed or stabilised, whereas in low- and middle-income countries it continues to accelerate. This fits with the concept of an ‘obesity transition’: obesity initially rises with the modernisation of food systems and lifestyles, and may later stabilise if social norms, diet, education, public policies or access to healthier environments improve.”

What is happening in Spain, and what might explain it?

“Spain is among the few countries where, in adults, the trend has not only levelled off but may even be showing a slight reversal, in both women and men. This is likely not due to a single factor, but rather to a combination of influences, including partial preservation of the Mediterranean diet, greater nutritional awareness, more physically active lifestyles, healthier living patterns, increased health awareness, and possible generational changes. Nevertheless, the study itself makes clear that, with the available data, direct causality cannot be established.”