​Diets are increasingly important in a world of economic growth and rising incomes. And two concerns, in particular, are emerging: the effect of diet on health; and the demands made by changing diets on agriculture. The impact is most marked in the developing world, where we now see both the fastest acceleration in over-consumption and the greatest continuing toll of under-consumption.

The over-consumption of food, coupled with lives that are increasingly sedentary, is producing large numbers of people who are overweight and obese – primarily in high-income countries, but also in emerging middle-income countries. Indeed, the world has seen an explosion in overweight and obesity in the past 30 years. Globally the percentage of adults who were overweight or obese grew from 23% in 1980 to 34% in 2008, with the vast majority of this increase seen in the developing world. Here, the numbers of people affected more than tripled from around 250 million people in 1980 to 904 million in 2008. By contrast, the number of people who were overweight or obese in high-income countries increased 1.7 times over the same period (Stevens et al, 2012).

The evidence is well-established: obesity, together with excessive consumption of fat and salt, is linked to the rising global incidence of non-communicable diseases including some cancers, diabetes, heart disease and strokes. What has changed is that the majority of people who are overweight or obese today can be found in the developing, rather than the developed, world.

At the same time, under-consumption of dietary energy, protein and micronutrients is still a problem for hundreds of millions of people. Again, most of them are in the developing world, where the greatest concern is the inadequate nutrition for infants that impairs their mental and physical development and puts them at a life-long disadvantage. Progress on reducing the incidence of stunting amongst children has been slow:  it is still thought that up to one-third of infants in the developing world are stunted. Increasingly, however, the wider concern is less about macro-nutrition and more about micro-nutrition: the lack of key minerals and vitamins – particularly iron, iodine, vitamin A and zinc – that affects an estimated two billion or more people.

Diets also matter for future demand for food. It should be easier to feed the expected global population of 8 billion in 2030, and 9 billion in 2050, if diets are moderate rather than high in livestock consumption. Any additional production of meat and dairy will probably have to come, in large part, from feed grains, with less energy consumed from grain and more from meat and milk. High demands for feed grains in the future will put pressure on land, water and fertiliser supplies, drive up costs of agricultural production, and make it more difficult for those on low incomes to afford an adequate diet.

Given this scenario, this report addresses three sets of questions.

1. How far do diets vary between countries? What is known about the reasons for the marked differences seen in diets? How far can the differences be attributed to income?
   
2. Are there examples of public policies that have had a real impact on choice of diet, and if so, which polices have been most effective and under what conditions?
   
3. How big will the gap be between the food available and the food that is needed in the future, if diets shift to match those recommended by nutritionists, rather than converging to resemble the diets seen in North America or Western Europe? And what are the implications for the prices of staple foods?
   

These have been addressed by reviewing the existing literature and by analysing data and statistics on food consumption worldwide, by major region, and for five middle-income countries selected to show how diets have changed over the past 50 years as a result of economic growth and urbanisation. 

Sharada Keats and Steve Wiggins