‘Eat like animals: what nature teaches us about the science of healthy eating’. David Raubenheimer and Stephen Simpson

Abstract

With all the burgeoning new methods, not to mention an ever-increasing number of conceptual frameworks, it often feels as if modern science is fulfilling the fear of Konrad Lorenz—that ‘scientists are people who know more and more about less and less, until they know everything about nothing’. As a field, nutrition often seems prone to this scenario, with studies of meals disregarded in favour of foods, disregarded in favour of nutrients, disregarded in favour of cellular signalling, finally disregarded in the last few years in favour of the microbiota. Meanwhile, with all this stellar technological progress, ever more people worldwide are becoming overweight and obese, raising the risk of many diseases. In this volume, David Raubenheimer and Stephen Simpson from the University of Sydney take a very different approach to the field of nutrition, going back to the fundamental question of ‘why’ we eat. Their overarching idea is that nutritionists have, for the entire 20th century, approached human appetite in the wrong way; and that this explains why public health efforts to prevent obesity have been spectacularly unsuccessful. The result is a brilliant discourse on a topic of huge importance. The concept of appetite seems so simple. We need food to supply nutrients for the body, and the most important nutrient is energy, the fuel for all our physiological activities. We think of food as simply the petrol of the body. We therefore have regulatory mechanisms that tell us when the body’s fuel stores are low; this makes us hungry and providing we are able to, we eat more food until we feel satisfied. According to clinical thresholds, people with obesity have eaten too much and must be given advice on how to balance their energy intake and output by exercising more and eating less. Of course, we need other nutrients besides energy, so we need dietary diversity and fresh foods. But if we follow that path, our appetite will work fine, and we will maintain a stable body weight, right? This broad conceptual framework I just described has dominated nutritional science throughout the decades during which the global obesity crisis has surged, yet only a relatively small number of nutritionists have been willing to admit that their discipline’s entire approach to appetite might be inadequate. The argument at the heart of this book is that humans are not actually seeking energy to satiate their appetite, rather they have different appetites for certain nutrients, and energy might not be the primary one. This concept initially emerged from studies not of humans, but of insects. Human nutrition is often labelled a ‘soft’ science, as it makes less use of the experimental approach than is the case in many other disciplines, instead relying extensively on observational epidemiology, with all the limitations that this entails. Working on insects allowed Simpson and Raubenheimer to do so something completely different from conventional epidemiology: early in the 1990s, they methodically allocated 200 locusts to one of 25 different diets, each varying in the balance of protein to carbohydrate, and carefully monitored what they ate and their body composition on reaching adulthood. The results were striking: locusts with a highcarbohydrate low-protein diet overate and became fat, whereas those on the low-carbohydrate highprotein diet were so lean that their survival to adulthood was threatened. Both of these phenotypes were clearly incompatible with evolutionary fitness, whereas locusts that had consumed an intermediate balance of carbohydrate and protein exhibited neither penalty, and were well set to survive and reproduce.