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Education And Debate

The runaway weight gain train: too many accelerators, not enough brakes

BMJ 2004; 329 doi: (Published 23 September 2004) Cite this as: BMJ 2004;329:736
  1. Boyd Swinburn, professor of population health (,
  2. Garry Egger, adjunct professor2
  1. 1 School of Exercise and Nutrition Sciences, Deakin University, 221 Burwood Highway, Melbourne, Victoria 3125, Australia
  2. 2 Southern Cross University, Military Road, East Lismore, New South Wales 2480, Australia
  1. Correspondence to: B Swinburn

    Obesity seems to be perpetuated by a series of vicious cycles, which, in combination with increasingly obesogenic environments, accelerate weight gain and represent a major challenge for weight management


    The chronic positive energy balance that leads to obesity is apparently relatively small.1 It is therefore paradoxical that obesity is so persistent and difficult to treat, because, in Western countries at least, the basic causes of obesity are readily apparent to everyone (eating too much and exercising too little). Obesity is associated with a substantial loss of quality of life and with social stigmatisation; awareness of the health consequences of obesity has never been greater. Even the body's physiological systems try to prevent weight gain by minimising the impact of energy imbalance on weight change.2

    To help explain this apparent paradox, we propose that numerous vicious cycles are acting as “accelerators” that maintain and even increase overweight. We liken the situation to a “runaway weight gain train” (figure), which already has high momentum from the downhill slope of obesogenic (obesity promoting) environments but is getting faster as the vicious cycles start acting as accelerators. The brakes, which, on the face of it, should be strong enough to slow down the train, turn out to be weak by comparison.

    The runaway weight gain train

    The downhill slope of obesogenic environments

    The obesogenic environments of the modern world have been well described.3 4 They make the unhealthy choices the easy, default choices, resulting in a high intake of energy dense foods and beverages and in reduced physical activity. Examples include the heavy promotion of fast food outlets, energy dense snacks, and high sugar drinks to children; the low cost and large serving sizes of such foods; and the transport systems and urban design that inhibit active transport and active recreation.

    In our runaway train model (figure …

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