The lead article by Behrens et al. (1) provides an important synthesis of obesity science and its links to planetary sustainability. Its central claim—that modern food systems dominated by ultra-processed foods (UPFs) have reshaped human phenotypes at scale—is compelling and increasingly supported by evidence. The authors also rightly emphasize that popular treatment strategies, including bariatric surgery and long-term anti-obesity medications, cannot resolve the crisis given their limited sustainability. While we agree that more durable, prevention-focused solutions are urgently needed, several aspects of the argument would benefit from closer engagement with the complexity of real-world dietary behavior. In particular, we believe that even greater attention to socioeconomic drivers of UPF consumption, the long-term and multidisciplinary nature of lifestyle change, the limitations of plant-based and alternative-protein proposals, and the critical role of mental health would further strengthen policy development in this area.

Behrens et al. discuss UPFs as an important driver of the global obesity epidemic, and they include taxation as one of the recommended policy responses. Their article reports that individuals with a higher UPF intake tend to have a lower consumption of fruits, vegetables, legumes, and seafood. While this pattern may indeed hold true—and we concur that reducing UPF intake is important given its adverse health impacts—it is equally critical to consider who the main consumers of UPFs are.

A systematic review (2) found strong links between higher UPF intake and indicators of social vulnerability, including lower socioeconomic status, lower educational attainment, and younger age.

In many communities—particularly those located in food deserts—UPFs may be the most accessible and affordable sources of energy. As Behrens et al. highlight, efforts to reduce UPF consumption must be accompanied by strategies that increase the availability and affordability of healthy foods, particularly for low-income populations. Implementing UPF taxes without ensuring access to subsidized nutritious alternatives could inadvertently increase the risk of undernutrition or food insecurity among vulnerable groups, whereas nutritious-food subsidies can help offset this risk (3). While we agree that reducing UPF consumption is essential, such measures are most effective when embedded within comprehensive social and public health programs that address the socioeconomic barriers to healthful eating.

Initiatives such as Food is Medicine in the United States—which emphasizes access to, and education about, nutritious foods—illustrate how such complementary strategies can benefit at-risk populations. Emerging technologies, such as continuous glucose monitoring, may further support these efforts by allowing individuals to see the immediate metabolic effects of unhealthy eating and potentially motivating healthier choices (4). Expanding these approaches to incorporate broader lifestyle supports, including mental health services and opportunities for physical activity, could further strengthen obesity-prevention efforts.

Behrens et al. (1) note that overconsumption contributes to both obesity and climate change, placing food intake within broader environmental and health systems. They acknowledge that food systems produce approximately 30% of global greenhouse gas emissions and intersect with land use, livestock production, and energy systems; they also link obesity to socioeconomic conditions, physical activity, and other contextual factors. Building on this systems perspective, we suggest framing overconsumption as one interacting driver—rather than the dominant common denominator—to better reflect the complexity of both crises. This approach highlights that food intake operates alongside, and does not overshadow, parallel influences such as agricultural practices, energy and transportation systems, and structural inequities.

Behrens et al. suggest that “plant-based foods” are a solution to both obesity and climate change. This terminology requires careful qualification. Many plant-based products—such as plant milks, meat analogues, energy bars, and snack foods—are highly processed and can be more energy-dense than many animal-sourced foods. Simple calorie comparisons illustrate this: gram-for-gram, bread offers as much (or more) energy than lean meat, yet meat provides more protein per calorie and greater satiety, which is beneficial for weight control.

Moreover, proposals to substantially or fully remove animal-sourced foods from the diet represent a major cultural and nutritional shift that may carry unintended consequences for public health. Populations are not uniformly ready for major dietary change, and current evidence is insufficient to determine how large-scale reductions in animal-source foods would affect intake of essential nutrients, as plants are limited sources of these nutrients or have lower bioavailability. These uncertainties are particularly relevant for at-risk groups such as children, older adults, pregnant and lactating women, and individuals with chronic disease.

Given these considerations, the issue is not the inclusion of animal-based foods per se but their overconsumption, which drives intensive production systems that degrade the environment and alter meat quality; indeed, evidence shows that grain-fed, industrially produced beef is typically higher in fat and has a less favorable lipid profile than leaner, grass-fed alternatives (5). Additionally, to avoid conflating food source with processing level, it is important to distinguish minimally processed plant foods from ultra-processed plant-based products and to clarify which are expected to reduce obesity risk. Strengthening evidence on their effects on energy intake, satiety, nutritional adequacy, and long-term weight outcomes is increasingly important amid the rapid global growth of the plant-based processed food market.

The lead article also recommends microbial proteins, cultured (cell-based) meats, algae, and insect-derived proteins as co-solutions to obesity and the climate crisis. These innovations may reduce environmental pressures, but many commercial products are ultra-processed under NOVA (6) or similar schemes, and evidence for sustained, population-level obesity benefits remains limited.

Short-term trials show that mycoproteins can increase satiety and, at higher doses, reduce subsequent energy intake (7), but these effects are acute and not yet linked to long-term weight outcomes. For cultured meat, proposed health claims remain largely theoretical; reviews cite potential benefits but emphasize the absence of long-term human outcome data (8). Given these uncertainties, scaling novel proteins as obesity-prevention tools should be accompanied by independent, long-duration trials comparing minimally processed versus ultra-processed versions; tracking energy intake, metabolic outcomes, and body weight; and assessing real-world food substitution. Until stronger evidence exists, it is prudent to emphasize minimally processed options and avoid assuming that climate benefits automatically translate into obesity benefits.

Although Behrens et al. (1) acknowledge the roles of psychological, neuroendocrine, and mental health factors in shaping eating behavior, it remains essential to emphasize the strength of these influences and ensure they are fully integrated into proposed solutions. A substantial body of evidence links depression, anxiety, and chronic stress to reduced physical activity and poorer diet quality; individuals experiencing these conditions are more likely to be sedentary and to consume energy-dense, nutrient-poor foods (9). Physiologically, stress-induced elevations in cortisol can increase appetite, drive cravings for high-calorie foods, and promote visceral fat deposition (10). These neuroendocrine, emotional, and behavioral pathways can significantly elevate obesity risk, independent of broader dietary trends. Taken together, these findings underscore that obesity-prevention efforts must address not only food systems and nutrient composition but also mental health, stress management, and broader lifestyle supports as essential components of comprehensive strategies.

The lead article’s suggestion that obesity requires a strategy similar to the COVID-19 response is a useful prompt for considering coordinated societal action. While Behrens et al. acknowledge that obesity demands more sustained systemic change than COVID-19, the analogy still risks being overextended. Acute infectious threats rely on short-term, transmission-focused tools—testing, isolation, antivirals, and vaccines—whereas obesity arises from long-term interactions among biological, behavioral, economic, and environmental factors. Clarifying which elements of the COVID-19 response are actually transferable, such as coordinated governance, surveillance infrastructure, cross-sector mobilization, and effective public communication, would strengthen the analogy and help avoid implying that obesity can be addressed with acute-response tools.

The lead article by Behrens et al. makes an important contribution by bringing obesity science into conversation with climate and sustainability. Yet its impact would be strengthened by more precise causal claims, clearer distinctions between food processing and food source, and conclusions grounded in robust cross-national evidence. As discussed, obesity is driven not simply by the presence of UPFs but by the socioeconomic inequities that shape reliance on them, particularly in many low- and middle-income countries, where limited affordability and availability of healthier foods, inadequate nutrition labelling, pervasive nutrition misinformation, and the rapid displacement of traditional diets by UPFs intensify dependence on cheap, energy-dense products. Likewise, proposals for rapid transitions to plant-based or alternative-protein diets must consider cultural feasibility, nutrient adequacy, financial costs, and the needs of vulnerable populations—recognizing that it is the overconsumption of both UPFs and animal-sourced foods, rather than their existence in the diet, that most clearly contributes to both obesity and environmental pressures.

Because population-level dietary change is inherently gradual, effective action must pair urgency with realistic timelines and sustained, multidisciplinary support. The rising burden of mental-health challenges further underscores the need to embed psychological well-being into obesity-prevention policies.

Taken together, a more nuanced, evidence-aligned approach will better equip policymakers, clinicians, and researchers to navigate rapidly evolving, increasingly obesogenic food environments and to design interventions that are both sustainable and responsive to diverse population needs.