What if the forces heating the planet are also shaping what ends up on our plates and our bodies? A new review argues that rising obesity and global warming stem from the same food system incentives.
Cheap calories, long shelf life, and aggressive marketing have reshaped diets worldwide, driving weight gain while increasing pressure on the climate.
Researchers at the University of Bristol project that by 2035, half of the global population could be overweight or obese.
Study lead author Jeff M. P. Holly says the shift reflects decades of consumption-driven food production, rather than a collapse of individual willpower.
When food nudges overeating
Daily eating patterns are shaped less by willpower than by the food environment – the mix of prices, products, and promotions people face.
Researchers often point to ultra-processed foods (UPFs), industrial formulations with additives and little whole food, as a central driver.
Aggressive marketing, oversized portions, and built-in convenience raise energy density, packing more calories into each bite and making overeating feel routine rather than exceptional.
Controlled feeding trials show how powerfully that environment can shape intake. Even when meals appear nutritionally similar on paper, UPF-heavy diets push people to eat more.
In one tightly controlled inpatient study, adults consumed about 500 extra calories per day on an UPF diet. Soft, easy-to-eat foods require less chewing, delay fullness signals, and allow excess calories to slip in before the body registers a stop signal.
Biology favors weight gain
Weight gain follows when excess energy is stored as adipose tissue, body fat that expands when intake remains high.
Appetite signals do not just track calories, and satiety, the feeling of lasting meal fullness, weakens when meals are mostly refined.
Low fiber, rapid digestion, and constant cues can tip hormones and brain reward circuits toward increased eating and gradual weight gain.
The climate cost of processed food
Food production adds heat to the planet by releasing greenhouse gases such as carbon dioxide, methane, and nitrous oxide, while also driving deforestation and water stress.
Altogether, food systems account for roughly a quarter to a third of global emissions. The Intergovernmental Panel on Climate Change links much of that warming to livestock methane, fertilizer use, and land clearing, pressures that increasingly threaten food security.
Animal agriculture carries an especially large footprint. Ruminants like cattle and sheep release methane as they digest grass, and global analyses show that beef requires far more land and generates far more emissions than plant-based foods such as beans or peas.
As demand for beef rises, forests and grasslands are often cleared or converted, rapidly releasing stored carbon and amplifying climate impacts.
Diet choices fuel warming
Current dietary patterns could keep global warming climbing even if energy systems decarbonize rapidly. One modeling study found that food-related emissions alone could block efforts to limit warming to 3.6°F (2°C).
“We can’t solve the climate crisis without transforming what we eat and how we produce it,” said study co-author Paul Behrens, a professor at Oxford University.
Those same dietary patterns also shape how people experience a hotter world. As global temperatures rise and heat extremes intensify, diet-driven weight gain intersects with heat stress.
A 2024 global estimate places heat-related deaths at roughly 546,000 per year between 2012 and 2021.
During heat waves, people who are overweight can struggle to cool down because additional body mass retains heat and places extra strain on the heart.
Health fixes need systems
Recognizing obesity as a disease shifts blame away from individuals, but environmental pressure remains.
New weight-loss medicines can help many people, but they cannot make a neighborhood stop selling cheap UPF-heavy snacks.
Even bariatric surgery, stomach-altering operations that change digestion and hormones, cannot repair a harmful food environment on its own.
Cheap processed food drives harm
Pricing makes unhealthy products cheap in low-income neighborhoods because companies ignore costs that fall on society later.
Economists call those ignored costs externalities, damages paid by everyone through illness and climate harm.
Taxes on sugary drinks and the most energy-dense UPFs can fund subsidies that make whole foods easier to afford.
Labels can change behavior
Marketing budgets reach children constantly, and the loudest messages often promote the least healthy foods.
Public health agencies push front-of-pack labeling, simple warnings placed on the front of packages, to change buying habits quickly.
When governments limit junk-food marketing in schools and online, companies lose a key tool for recruiting young customers early.
Healthy meals start young
Lunchrooms are one place where children meet food policy daily, so school meals can protect health and support local farmers.
Healthy school meals can center vegetables, beans, and whole grains, and districts can buy locally to cut transport emissions.
When children eat fiber-rich food at school, taste preferences can change, and families can feel greater demand for real ingredients.
Smarter rules for packaged foods
Not every ultra-processed food (UPF) affects health or the climate in the same way, a distinction that matters for regulation.
The review separates processed meat and low-fiber, energy-dense UPFs from plant-rich packaged foods that provide more fiber and generally carry lower emissions.
Clearer classification could allow regulators to target the most harmful products without penalizing healthier packaged foods that many people depend on for time and affordability.
The authors argue that individual willpower alone will not reverse current dietary trends. Instead, coordinated policy is needed to shift defaults across food systems.
The stakes are already high: obesity drains more than two percent of global economic output today, and projections suggest those costs could exceed $4 trillion by 2035.
The study is published in the journal Frontiers in Science.
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