Worldwide, consumption of healthy foods such as fruit and vegetables has improved during the past two decades, but has been outpaced by the increased intake of unhealthy foods including processed meat and sweetened drinks in most world regions, according to the first study to assess diet quality in 187 countries covering almost 4.5 billion adults, published in The Lancet Global Health journal.

Improvements in diet quality between 1990 and 2010 have been greatest in high-income nations, with modest reductions in the consumption of unhealthy foods and increased intake of healthy products. However, people living in many of the wealthiest regions (eg, the USA and Canada, Western Europe, Australia and New Zealand) still have among the poorest quality diets in the world, because they have some of the highest consumption of unhealthy food worldwide.

In contrast, some countries in sub-Saharan Africa and some countries in Asia (eg, China and India) have seen no improvement in their diet quality over the past 20 years.

The authors warn that the study presents a worrying picture of increases in unhealthy eating habits outpacing increases in healthy eating patterns across most world regions, and say that concerted action is needed to reverse this trend.

Led by Dr Fumiaki Imamura from the Medical Research Council Epidemiology Unit at the University of Cambridge in the UK, a team of international researchers analysed data on the consumption of 17 key food items and nutrients related to obesity and major non-communicable diseases (eg, cardiovascular disease, diabetes, and diet-related cancers) in countries around the world, and changes in diets between 1990 and 2010.

This analysis was performed by the Global Burden of Diseases Nutrition and Chronic Diseases Expert Group (NutriCoDE), chaired by Dr Dariush Mozaffarian, senior author on the paper and dean of the Friedman School of Nutrition Science and Policy at Tufts University. NutriCoDE is an ongoing project assessing dietary information from more than 300 dietary surveys across the world and UN Food and Agriculture food-balance sheets, covering almost 90% of the global adult population.

The international team examined three different diet patterns: a favourable one based on 10 healthy food items (fruit, vegetables, beans and legumes, nuts and seeds, whole grains, milk, total polyunsaturated fatty acids, fish, omega-3s, and dietary fibre); an unfavourable one defined by seven unhealthy items (unprocessed meats, processed meats, sugar-sweetened drinks, saturated fat, trans fat, dietary cholesterol, and sodium); and an overall diet pattern based on all 17 food groups.

The researchers calculated a diet score for each pattern and assessed differences by country, age, sex, and national income, with a higher score indicating a healthier diet (range 0-100).

The findings reveal that diet patterns vary widely by national income, with high-income countries generally having better diets based on healthy foods (average score difference +2.5 points), but substantially poorer diets due to a higher intake of unhealthy foods compared with low-income countries (average score difference -33.0 points). On average, older people and women seem to consume better diets.

The highest scores for healthy foods were noted in several low-income countries (eg, Chad and Mali) and Mediterranean nations (eg, Turkey and Greece), possibly reflecting favourable aspects of the Mediterranean diet. In contrast, low scores for healthy foods were shown for some central European countries and republics of the former Soviet Union (eg, Uzbekistan, Turkmenistan, and Kyrgyzstan).

Of particular interest was that the large national differences in diet quality were not seen, or were far less apparent, when overall diet quality (including both healthy and unhealthy foods) was examined as previous studies have done.

"By 2020, projections indicate that non-communicable diseases will account for 75% of all deaths. Improving diet has a crucial role to play in reducing this burden," says Dr Imamura. "Our findings have implications for governments and international bodies worldwide.

The distinct dietary trends based on healthy and unhealthy foods, we highlight, indicate the need to understand different, multiple causes of these trends, such as agricultural, food industry, and health policy. Policy actions in multiple domains are essential to help people achieve optimal diets to control the obesity epidemic and reduce non-communicable diseases in all regions of the world."

According to Dr Mozaffarian, "There is a particularly urgent need to focus on improving diet quality among poorer populations. If we do nothing, undernutrition will be rapidly eclipsed by obesity and non-communicable diseases, as is already being seen in India, China, and other middle-income countries."

Writing in a linked Comment, Carlo La Vecchia from the University of Milan in Italy and Lluis Serra-Majem from the University of Las Palmas de Gran Canaria in Spain say, "The key focus of the paper remains the need to understand the agricultural, trade, and food industry, and health policy determinants to improve dietary patterns and nutrition in various areas, taking into account the traditional characteristics of diets worldwide… Information about the environmental effect of dietary patterns will be needed in the future [particularly from low and middle income countries], because food not only drives human health, but also the health of the planet."