Since the 1970s there has been an alarming global increase in levels of body fat, to the point where over 60% of adults in The United Kingdom and United States are overweight or obese. This obesity pandemic, along with its associated risks of heart disease, diabetes, stroke, liver disease and cancer represents the great public health crisis of our age. Despite improvements in healthcare provision and control of contagious disease, life expectancy in the UK and USA is decreasing, an effect of which obesity is a primary driver. How have diseases that were until recently virtually unheard of become the norm in our societies? What is driving the global obesity epidemic, why are we so susceptible to gaining fat, so resistant to losing it and what can be done to reverse this process? These are big questions, but ones that Dr. Stephan Guyenet sets out to answer in ‘The Hungry Brain: Outsmarting the instincts that make us overeat’.
Stephan is doctor of neurobiology who has authored many highly-cited papers the field of obesity research. However, he is also a popular blogger and speaker in the field of nutrition and health. As such, The Hungry Brain tackles obesity from a neuropsychopharmacological perspective, but does so in a way that will catch and hold the interest of non-scientists. The logical, convincing and accessible case that The Hungry Brain makes for a neurobiological model of obesity is evidence of Stephan’s practiced hand as a public communicator. I believe dissemination of information like this will prove instrumental in addressing not only the stigma associated with obesity, but also in generating awareness of what needs to be done to tackle it.
Stephan begins by demonstrating that increases in adiposity over the last forty years are driven by a shift towards positive energy balance. We are consuming more calories on a daily basis and expending less energy, causing an inexorable increase in fat accumulation. This is not attributable to a shift in our genes or biology, but an ever more obesogenic food environment that is at odds with our evolutionary history. He argues that the constant availability of cheap, highly calorie-dense, convenient, marketed and palatable food powerfully motivates us to over-consume by hijacking an adaptive homeostatic reward system that evolved in a world where food scarcity was the norm.
In making this case, The Hungry Brain covers a diverse array of key neural mechanisms, from actor-critic models of striatal action selection, to the mesocorticolimbic dopamine system in Pavlovian reward learning, the hormonal ‘lipostat’ and role of leptin and neuropeptides in regulating hunger and preventing fat loss. These are integrated into economic models of optimal foraging strategy. We were hard-wired to be motivated to opportunistically consume high-fat, high-carbohydrate, high-calorie food by the calorie-sparse environment in which these systems evolved. In a modern industrial environment where we are surrounded by food cues and cheap, high calorie foods are available for virtually no effort, it is clear why these systems promote overeating. Finally, The Hungry Brain covers two more critical factors in overeating; sleep and stress. The disturbance of our circadian rhythms by electric light and exposure to chronic low-grade stress undermines our satiety mechanisms, increasing food intake – particularly of highly rewarding ‘comfort food’. These factors complete a ‘perfect storm’ that promotes overeating obesity in the modern industrial environment.
While this may be familiar territory for active researchers or clinicians, these are not topics one normally expects to encounter in a book aimed at a lay audience. The Hungry Brain excels in bringing key strands of research together in a clear manner that is accessible to the lay reader, without sensationalising, dumbing-down or shying away from empirical evidence. This is impressive in a field where such practices are bread-and-butter in ‘public communication’ of research findings in the popular media.
Clearly, there are too many complexities and nuances in the research to fully explore in a single book. Certainly, there are contributions of genetics and epigenetics, specific individual sensitivity to overeating certain food, factors that confer resistance to weight gain and roles of microbiota in these processes. However, these represent the current frontier of obesity research, where there are no clear answers. What I find most reassuring is that where there unknowns, these are openly acknowledged in The Hungry Brain. This is a welcome antidote to the constant churn of dogmatic voices that attempt to reduce obesity down to a single nutritional supervillain; be it fat, carbohydrate, salt or meat.
At the individual level, the clear conclusion from The Hungry Brain is that there is no single ‘correct’ diet for everyone. Rather, people must prioritise sleep, manage stress, understand their individual ‘trigger’ foods and cues and eat high-satiety food to maintain a healthy weight in an obesogenic environment. Stephan offers practical advice as to how to implement these measures; from removing hyper-palatable food from one’s environment, to eating primarily home-prepared, minimally processed meals with high satiety value, to managing sleep, light exposure and stress. While this is by no means ‘sexy’ advice, these are actionable steps that should be widely encouraged to reduce our susceptibility to overweight/obesity.
Stephan suggests that tackling obesity at a population level will require large-scale changes in the food industry. In the same way we are now effectively controlling the advertising powers of Big Tobacco, we must curtail the ability of ‘Big Food’ to market high-calorie, high-palatability convenience food to an increasingly overweight population. I am not sure how simple this will be, given the financial and political heft these industries possess and their vested interest in promoting consumption. However, given our current trajectory, there may soon come a point where the social and economic burden of global obesity outweighs the profit motivation of Big Food and forces governmental intervention. We are beginning to see this already with the implementation of sugar taxes.
The Hungry Brain is an excellent, timely and very important book, which I wholeheartedly recommend to any reader and I hope it gains the wide readership that it deserves. I believe it provides a platform for a rational, large-scale discussion about overeating, obesity and the food industry.