News release

From:

What is driving the obesity pandemic? Ultraprocessed foods, our bodies being fooled by them, and it’s easier to gain weight than lose it

New research presented at this year’s International Congress on Obesity (ICO2026) hosted by the World Obesity Federation (WOF) in Mexico City, Mexico (15-17 July) asks what is driving the obesity pandemic – and suggests several things have combined to make it so – the structure and nature of the ultraprocessed foods (UPF) industry; the fact that UPFs fool our bodies by allowing us to eat them quickly before we know we are full (by being energy dense/packed with calories, consumed rapidly and hyper-palatability or ‘tastiness’ leading to passive/unintentional overconsumption); and the simple reality that it is easier to gain weight than lose it.

The so-called “Synergistic Systems Theory’ is being proposed by obesity expert Professor Boyd Swinburn, University of Auckland, New Zealand, who says that the drivers of the obesity pandemic are caused by two intersecting complex, adaptive systems which are both working perfectly as designed – the UPF system and the physiological energy balance (EB) system.

He uses modelling and empirical data from multiple weight change studies to analyse five different energy balance ‘modes’ and how weight changes over time in each. They are weight maintenance, passive calorie loss, weight loss diet, overfeeding, and obesogenic environment exposure. He then used systems modelling to join these two complex adaptive systems together creating three sets of characteristics (UPF, UPFxEB, EB).

His analysis says the UPF system, and its four ‘subsystems’ of product development, marketing, food supply chain, and political economy operate within a standard capitalist, profit-seeking feedback loop, and contain 22 positive feedback loops meaning the UPF system always exists with strong potential to grow. This potential is realised through the increasing displacement of the ‘real food’ (non-UPF) systems. All actors (including consumers, retailers, suppliers, politicians, manufacturers) experience benefits and detriments from the UPF system thus becoming ‘semi-willing captives’ within the system and making it difficult to change.

The EB system has a ‘Tonic‘ subsystem to ensure energy intake meets the needs of the body’s lean mass (this means the body operates at near energy balance levels to ensure there is enough energy intake to meet the body’s energy needs which mainly come from the lean mass). However, an ‘approximation’ step (where the body tries to match food intake to energy intake) can be ‘fooled’ by a diet high in UPF which are energy dense, hyper-palatable (very tasty), and rapidly eaten. Over time, this leads to ‘passive overconsumption’ and slow weight gain.

A ‘Dynamic subsystem’ becomes activated when there are large changes in energy balance to try to minimise the impact of that energy imbalance on changes in lean mass. This subsystem uses two active feedback loops - the ‘Metabolic Dial’ turns the body’s metabolic rate up or down and the ‘Appetite Dial’ stimulates or dampens the drive to eat. The response to weight loss (Metabolic Dial down, Appetite Dial up) is far more vigorous than the response to weight gain, presumably because weight loss is perceived by the body as a far greater threat to the organism. This asymmetric activation of the Dynamic subsystem creates a ‘ratchet effect’ (easy to gain, hard to lose) which contributes to the increases in weight over time.

Professor Swinburn concludes: “All these systems – that is ultraprocessed foods, the energy balance system, and how the two combine - are theoretically needed to drive the obesity pandemic. If it was easy for us to change or escape from ultraprocessed foods – if they didn’t trick our bodies and make us slowly gain weight - and if losing weight was as easy as gaining weight, we would not have an obesity pandemic. While it is obvious to the world we have an obesity pandemic, and this must clearly include overconsumption of food – the relationships behind it are complex and this theory presents sound reasons as to why the pandemic is evolving and we appear powerless to stop it.

“We need to take action at multiple levels to tackle the rising prevalence of obesity in all countries. This means implementing several powerful policies to reduce ultraprocessed food consumption, such as sugary drinks taxes, front-of-pack warning labels, and bans on marketing to children. On the energy balance side, the GLP-1 drugs assist weight loss by reducing the impact of the Appetite Dial. So when these drugs and their derivatives become more widely available, I think we will see significant impacts on the population prevalence of obesity. ”