1960s, the average intake of the adult male population when weight stable was about 3000 kcal/day when the population was engaged in a lot of physical activity. Then over the next 40–50 years, significant industrial developments occurred, limiting the need for physical activity and in effect reducing the energy needs by perhaps 700 kcal/day on average, as shown by the continuous line falling from 3000 kcal/day. This means that intake should have fallen by the same 700 kcal/day. However, in many European countries, intake did not fall sufficiently, so positive energy balance led to weight gain. This weight gain involved an increase in lean as well as fat tissue, so the total maintenance energy needs of the concomitant lean tissue rose, and there was also an increase in the weight‐bearing cost of physical activity. The overall increase in energy maintenance costs amounts to about 239 kcal/day for each10 kg weight gain, as estimated by Hall et al. [57]. However, in the United States, it has been estimated that food intake has risen, which probably applies to many populations in the Middle East, thereby explaining their marked current obesity rates. In European countries and elsewhere, the physiological drive to limit intake at lower expenditure levels was unsuccessful because the food industry developed techniques to enhance food and drink purchases (see below).
Now, as well as the secular decline in physical activity, there is a concomitant reduction in activity as people age. This was shown most vividly in the Baltimore aging studies, where one can recalculate the data on the energy needs of men first when they were 25 years of age and then when the same men were aged 70. If one applies the energetic analyses to the fall in activity and tissue metabolism as the muscle mass slowly declines but adjust the data so that they were the same body weight, then the overall reduction in energy output amounts to a fall of 2100 per day. This means that over the 45 years the falling output is equivalent to an annual average reduction of nearly 50 kcal/day. So in effect the Baltimore men’s food intake needed to fall by nearly 50 kcals each day with further equivalent falls in daily intake each year decade after decade to avoid putting on weight as they age [62]. If extra food is eaten, then weight gain occurs, and the classic analyses suggest that about 20–25% of this is lean tissue which then contributes to increasing the maintenance energy requirement.
Using detailed analyses of lean body mass changes in men and women, James and Reeds showed many years ago that women do not build lean tissue as much as men [63], and so their maintenance energy expenditure does not rise to the same extent as men. Therefore women store more of the excess dietary energy as fat which in part explains why women are likely to gain more weight than men under the same energy imbalance conditions. It is also why women are usually more prone to obesity than men and particularly prone to extreme obesity, i.e. BMIs >40.
This interaction of secular falls in demand for physical activity, together with the natural reduction in physical activity with aging, explains why in the 1970s, obesity was mostly confined to older adults. To prevent obesity, the body’s appetite sensing system would need to progressively reduce our food intake as we grow older, and this has become far more difficult with such limited levels of physical activity.
A revolution in food industrial strategies which increase food intakes
In the mid‐1980s, one of the authors W.P.T. James was invited by the UK government to join an expert panel examining broad aspects of national industrial policy ranging from financial management to manufacturing and the service sector. The author’s remit was to deal with the food, drink, and agricultural industry. Each member led a team with Delphi exercises involving a variety of experts and industrialists and with workshops held in different parts of the country. Given the extraordinary changes in agriculture and food policy that supported self‐sufficiency during the Second World War [64], the author was alarmed to discover the proportion of food, including fruit and vegetables, that were now imported from abroad. Discussions with the Treasury Ministry revealed that they were more concerned about the balance of trade than the availability and access to quality food for the British public. At that time, food product development and marketing were unsophisticated, but suggestions around introducing new health criteria for food composition with the recently proposed WHO criteria based traffic light labeling of healthy food [65] were viewed with horror as this was an industrial enhancement, not a health promotion exercise. However, behavioral research began to develop rapidly in the United States and Europe, leading to a very sophisticated understanding of human behavior and how to manipulate it. Exceptionally detailed analyses of human reactions in shops around time spent examining foods, their position in relation to the height of customers, the value of big rather than small displays, the huge bonus of stacking special price inducements at the end of aisles, and the degree of price manipulations needed to stimulate buying all became carefully defined features for selling more product. Then they discovered the value of stimulating people’s curiosity and providing unexpected stimuli for purchases at all hours of the day and night through the provision of food and drinks in machines or other facilities wherever people might pass or congregate. A multiplicity of flavors in a variety of products encourages greater consumption as using just one flavor leads to what Rolls termed “sensory‐specific satiety.” [66]. Then with the discovery of the range of molecular olfactory receptors for different flavors [67] came the special development of food and drinks with specifically added flavors which were known to have a powerful effect on the brain’s pleasure and addictive centers. Author W.P.T. James had a detailed account from a major industrialist of the finding that specific flavors were favored by women in both the follicular or luteal phases of their menstrual cycle, so these flavors were then used with vodka to produce alcopops, which then in practice transformed the drinking habits of young women in the United Kingdom. This strategy was so successful that alcohol consumption by young women rose alarmingly in the 5 years following the introduction of these new products leading to medical concerns about the impending problem of alcoholism and indeed cirrhosis of the liver in young women – a feature never seen before in the United Kingdom [68]. Neurological MRI testing is now one of the routine assessments of new food products, many of which have added flavorings aimed at stimulating the pleasure centers with huge factories synthesizing the specific sensory enhancing products. Whether their greater use has anything to do with what Brownell now recognizes as food addiction [69] is still unclear. The subtlety of marketing is also illustrated by the use of a picture of a salad in the options of a famous fast‐food chain. This representation of healthy food stimulates young women to not necessarily purchase the salad but to treble their purchases of fried potato chips as the salad image creates a false association with the healthiness of the whole menu and thus provides an excuse to purchase chips. Such sales ensure a good profit margin for the company but have very dubious effects on weight gain and health!
Globalization, modern food supply chains, advanced food processing techniques, and ever more sophisticated and aggressive marketing approaches have created a modern food environment that Swinburn et al. [70] have termed obesogenic (literally designed to induce obesity). The current food supply and consumption patterns are dominated by the wide availability of ultra‐processed food products that are highly palatable, cheap, convenient, long‐lasting, and heavily promoted. A high level of consumption of these products replaces core foods (such as fresh fruits and vegetables, meat, milk, and wholegrain cereals). Modern lifestyles have also led to changes in eating and lifestyle behaviors. We have fewer formal meals, we eat in front of the TV, we take away more food rather than cook it at home, and at home, we rely more on ready‐prepared foods. These behaviors are associated with poorer diet quality. Food is also now cheaper and more widely available than it has been at any point in human history, and the portion size of a single serving has increased dramatically. In addition, we are encouraged by marketing to consume even when we are not hungry. Many of these issues are addressed in later chapters.
So we can conclude that major industrial developments have reduced the need for energy expenditure, but the normal physiological adaptive lowering of food intake to match this new lower requirement is counterbalanced by intense food marketing. Furthermore, the greater weight and energy requirements of the obese frame mean, for example, that in the United States, the food industry is profiting from the extra food purchases required to maintain the population with obesity. This has been estimated to amount to many hundreds of billions of dollars of extra sales each year if one
