Malnutrition comes in many forms. Hunger, stunting, and wasting can have severe consequences that are all too visible. A related form of malnutrition - deficiencies in essential vitamins and minerals - often goes unnoticed yet can wreak havoc on the immune system, hinder growth and development and, in extreme cases, lead to death. This “hidden hunger” is the result of poor diets lacking in essential micronutrients.
There are many reasons for inadequate diets in low- and middle-income countries, including insufficient availability, accessibility, affordability, desirability, convenience, and knowledge of nutritious foods. Due to the many barriers to adequate diets, various efforts are needed to fully address hidden hunger and related malnutrition in low- and middle-income countries. These include fortification of staple foods, in which synthetic nutrients are added to regularly consumed foods that are otherwise nutrient poor, and biofortification, in which crops are bred to enhance their nutritional value. Micronutrient supplementation is also an important strategy in many contexts.
Improving diet quality also includes increasing intakes of inherently micronutrient-dense foods which, in addition to containing high amounts of bioavailable essential micronutrients, contain thousands of synergistic compounds bound together in a complex food matrix, which may have important health effects. Importantly, different foods have different micronutrient densities. Thus, prioritising efforts to increase consumption of foods with the highest micronutrient density can help improve micronutrient adequacy most effectively. Some of the most common micronutrient deficiencies that are of greatest public health concern in low- and middle-income countries include iron, zinc, folate, calcium, vitamin A, and vitamin B12 deficiency. Identifying the top food sources of these micronutrients could help aid policies and programmes aimed at improving micronutrient adequacy and reducing malnutrition.
A recent global analysis published in Frontiers in Nutrition sought to answer this question. The authors combined food composition data from different world regions to estimate the micronutrient densities, including bioavailability, of a broad set of foods. The study developed an overall score to rate foods in terms of their density in commonly lacking micronutrients. The top sources of these priority micronutrients are organs (liver, spleen, kidney, heart), small fish, dark green leafy vegetables, shellfish (clams, mussels, oysters, shrimp, crab), ruminant meat (goat, beef, mutton, lamb), eggs, milk, and canned fish with bones (Figure1). Other good sources include cheese, pork, yogurt, fresh fish, pulses (beans, peas, lentils), teff (a traditional grain from Ethiopia), and canned fish without bones.
The general finding that animal-source foods, which are often consumed infrequently and in small quantities in low- and middle-income countries, and dark green leafy vegetables are top sources of commonly lacking micronutrients is not surprising. However, what may be surprising is that certain healthy foods, including most fruits and vegetables, nuts and seeds, whole grains, and chicken, are not particularly dense in bioavailable micronutrients commonly lacking in low- and middle-income countries. These foods certainly provide important nutritional benefits beyond these specific micronutrients, for example, by protecting against non-communicable disease risk. Nevertheless, the implication for many low- and middle-income countries where dietary diversity is low is that nutrition programmes and policies may benefit from specifically targeting the most micronutrient-dense foods - organs, small fish, dark green leafy vegetables, shellfish, ruminant meat, eggs, milk, and canned fish with bones.
However, micronutrient density is just one of many important considerations. For programmes to effectively improve diets, they must be grounded in the constraints of supply and demand, including understanding which foods can be sustainably produced and feasibly made affordable and desirable for consumers. A guiding principle should be to let local contexts determine which micronutrient-dense foods to promote through interventions or policies. From an environmental perspective, there may be challenges to sustainably producing increased quantities of certain micronutrient-dense foods, which must be considered. However, there is great potential to improve the sustainability of their production through regenerative and circular practices suitable to local ecosystems. Where feasible to produce, farmed seaweeds and bivalves (clams, mussels, oysters), and small capture fish tend to have relatively low environmental impacts and are highly micronutrient dense. But parallel efforts would be needed to ensure they can be made affordable, desirable, and convenient for consumers.
The reality is that many micronutrient-dense foods, especially animal-source foods, are unaffordable for people in poverty. But those in poverty are the ones who could benefit the most from increased consumption. Efforts are thus urgently needed to increase incomes and improve affordability through increased productivity, reduce trade and transportation costs, and social protection programmes including cash transfers and subsidies for micronutrient-dense foods. Every one of us deserves to have access to a healthy diet and realise our full potential. We must work together to help ensure that becomes a reality for all people worldwide.