Diet is one of the ‘big three’ modifiable health behaviours (together with sleep and physical activity) (Wickham et al., 2020). The World Health Organization (WHO, 2020) defines a healthy diet as achieving energy balance, limiting energy intake from total fats, free sugars and salt and increasing consumption of fruits and vegetables, legumes, whole grains and nuts. Regular consumption of a wide variety of foods from key food groups in the right proportions and consuming the right amount of food and drink are conducive to achieving, improving, enhancing and maintaining a healthy body weight (National Health Service (NHS), 2022) and health by reduction of the risk of chronic illness (WHO, 2020).

I have met few adults who are happy with their own bodies, at least in Western societies. But even in non-Western societies, many people are unhappy with their bodies. The exact nature of this unhappiness varies, but what overwhelmingly dominates is the thought, whether objectively true or not, that they carry too much weight, and following that, the thought that they really should lose weight. I have met very few people who actively want to put on weight, and they have almost all been of athletic disposition, and the weight gain sought is usually (but not always) in terms of muscle. Some people are entirely ‘fat-phobic’ and not persuaded that some types of body fat might actually be good, healthy even. Many people don’t know that there are different types of fat deposit, and that some deposits of fatness carry limited or no negative health consequences – around the buttocks, hips and thighs, for example. Body fatness is a ‘hot potato’ issue for many people; I like hot potatoes.

The basic principle of nutrition is the provision of adequate nutrients for populations or groups within populations. Adequate nutrition requires that all nutrients are consumed in adequate amounts and in the correct proportions. Energy is one of the most important things we obtain from food. In the body, energy consumed is used to support metabolic processes. Energy expenditure is made up of three components: basal metabolic rate, thermic effect of food and physical activity. Within the diet, the role of carbohydrates is to be a source of fuel, but overall carbohydrates are also part of energy stores, structural components of cell walls, part of nucleic acids (RNA and DNA) and part of many proteins and lipids. Protein is the most abundant nitrogen-containing compound in the diet. It is a major functional and structural component of all body cells. Fats, also known as lipids, are composed of a carbon skeleton with hydrogen and oxygen substitutions. Understanding the pathway for each nutrient allows for the development of dietary reference values, which aim for optimal levels of a nutrient for each population group. The types of foods eaten in different countries are influenced by factors such as ethnicity, culture, dietary habits, food preferences, intake patterns and food availability, and so the classification and types of foods contained in the major ‘food groups’ can vary somewhat from country to country.

But the idea that ‘metabolism’ is just concerned with how fast, or slowly, we might burn off excess energy is a very restricted one. A commentator announced recently on the radio that ‘the economy has slowed by 30%’ (as a result of the coronavirus pandemic). I suppose this refers to the Gross Domestic Product, GDP. But I don’t know what things contribute to this, or how they interact and how each is regulated. My wife and I try to buy produce from local shops, thinking we are doing some good for ‘the local economy’. I guess the overall economy is made up of many ‘local economies’, together with other things like, for instance, manufacturing and garbage disposal. If that is so, then there are many parallels with metabolism. I am guessing that my understanding of economics is very similar to most people’s understanding of metabolism. Yes, there are ways of capturing an ‘overall’ figure for a person’s metabolism, but that in turn is made up a myriad of smaller components. And we can’t understand the ‘overall’ picture, let alone how it might change, without having some knowledge of these components that contribute to it.

This chapter explains what avoidant/restrictive food intake disorder (ARFID) is and provides diverse and relatable case examples of each of the three prototypical ARFID presentations, including sensory sensitivity, fear of aversive consequences, and lack of interest in eating or food.

This chapter will help readers determine whether they might have ARFID and whether they might therefore benefit from the program outlined in this book. The chapter walks through the diagnostic criteria for ARFID and introduces a self-test called the nine-Item ARFID screen that the reader can take to determine which ARFID presentation is most relevant to them.