Do Public Health Professionals Need To Brush Up Their Knowledge of Basic Science?

sharma-obesity-caloric-balance1In a thoughtful paper published in BMC Medicine, Katherine Hafekost and colleagues from the University of Western Australia propose that the main reason why we have yet to see effective public health intervention to sustainably reduce obesity is because the champions of these policies largely ignore the basic scientific facts of human physiology.

Based on their systematic analysis of 27 article published in 2011 proposing public health interventions for obesity, the researchers found that all of these were based on a rather simplistic notion of energy balance. Despite acknowledging the complexity of obesity, the underlying philosophy of these public health approaches was essentially built around the idea that reducing caloric intake (diet) and increasing caloric expenditure (exercise) would result in long-term sustainable negative energy balance and thus result in a lower body weight.

As the authors note,

“Almost all the identified interventions focused on reducing energy intake, increasing physical activity, and reducing sedentary behaviors underpinned by an energy-balance model assuming independence between energy intake and expenditure, with little consideration of homeostatic feedback mechanisms.”

“Research from the fields of biochemistry and human physiology, which provides a more detailed model of energy balance, offers some insight into why many weight-loss interventions have little long-term success and poor program adherence….Although in the short term, food intake and energy expenditure are often influenced by situational factors, over longer time periods numerous neural and hormonal mechanisms operateto regulate body weight. Restrictions in caloric intake and/or increases in physical activity are likely to be matched by behavioral, metabolic, neuroendocrine, and autonomic changes that will limit long-term success.”

Given that body weight is tightly regulated and that our bodies will always “defend” against body weight loss, the best that public health measures can hope to achieve is to prevent further weight gain – they do not and cannot offer sustainable weight-loss.

“The failure of research in the field of public health to incorporate the concept of homeostatic feedback mechanisms into interventions is reflected in the current dietary guidelines, public health policy, and population-wide interventions aimed at targeting overweight and obesity.”

Although public health messages to eat healthier diets and reduce sedentariness no doubt have important cardiovascular and other benefits, when explicitly promoting reduced energy consumption and increased expenditure as the appropriate means by which to achieve weight loss, such measures pose ethical challenges.

“Despite the extensive literature on their long-term ineffectiveness, interventions based on this simplistic understanding of energy balance continue to be advocated under the assumption that previous interventions have not been pursued sufficiently vigorously or that participants have failed to follow the prescriptions of the intervention.”

“Continuing to promote a model that is unlikely to be successful in the longer term, and may result in individuals becoming discouraged, is both unproductive and wasteful of resources that could be better spent on investigating more plausible alternatives to improving weight control.”

I would add that the “energy-centric” model of obesity reduction not only fails to acknowledge the powerful homeostatic defences agains sustained weight loss but also generally fails to address the powerful psycho-biological drivers of weight gain.

Unfortunately, despite first eloquently arguing against overly simplistic “energy-balance” models of obesity interventions, the authors astonishingly still suggest that,

“The focus of future public health research should be on the development of large scale, long-term prospective studies that test dietary and exercise protocols that have been shown to be beneficial to weight loss and maintenance.”

I disagree! Enough effort and money has been spent on this.

I would much rather support their other recommendation, namely,

“..ensuring that funding or grant panels considering proposals for future intervention research include members trained in human biochemistry and physiology as well as public health advocates. This may assist in the development and implementation of appropriate research designs and methods that are underpinned by a complex model of energy balance.”

I also concur with the authors that, while,

“Currently, most research seems to address the question of what factors lead people to eat too much and exercise too little.”,

“Developing and testing interventions that are based on biologically plausible mechanisms [would be] an important step forward in developing effective interventions to combat obesity and its associated metabolic diseases.”

Edmonton, AB

Hat tip to Cindy for pointing me to this paper.
Hafekost K, Lawrence D, Mitrou F, O’Sullivan TA, & Zubrick SR (2013). Tackling overweight and obesity: does the public health message match the science? BMC medicine, 11 PMID: 23414295