Sugars and diet quality

This content has been reviewed by Dr Kelly C Cara, graduate of Tufts University, and Associate Professor Dr Mei Chung, Tufts University, USA.

Sugars and diet quality

When we make steps to improve our diets, it is tempting to focus on an individual food, food group, ingredient or nutrient. However, it is improving the overall diet that is important. The overall quality of the diet provides a much better indicator of health than individual foods or ingredients (1). Assessment of diet quality aligns with the current consensus that the totality of the diet has a greater effect on health outcomes than individual dietary components including nutrients, ingredients and foods (2).

What is diet quality?

Diet quality is a term used by nutrition professionals to assess the overall healthfulness of a dietary pattern based on its parts (1). Diet quality considers the bigger picture and the complete pattern of the diet.

How is diet quality measured?

The concept of diet quality indicates whether the whole diet provides the right balance of energy and nutrients needed for health. Diet quality is measured by scoring food patterns of individuals or populations by how closely they align with national dietary guidelines or dietary patterns associated with risk of chronic disease (3,4). Some indices also assess how diverse the variety of healthy choices is within core food groups. There are many different diet quality indices which are used to score the quality of a diet. There isn’t a universally accepted diet quality index, as the majority are based on national dietary guidelines and recommendations specific to the country or region in which they were developed (3), or they were developed in relation to a single health outcome (e.g., type 2 diabetes, obesity) (5).

Diet quality indices

Commonly used indices include the:

Healthy Eating Index (HEI),
Alternative Healthy Eating Index (AHEI),
Healthy Diet Indicator (HDI),
Healthy Food Index (HFI),
Recommended Food Score (RFS),
Dietary Approaches to Stop Hypertension (DASH),
Diet Quality Index (DQI),
Diet Quality Score (DQS),
Mediterranean Diet Score (MDS) (4,5).

The food groups which are often assessed within a diet quality index include fruits and vegetables, cereals and grains, eggs, meat and dairy products, fish and seafood, nuts and seeds, and sometimes other components like olive oil or sugars-sweetened beverages. Nutrients which often feature include total fat, saturated fat, alcohol, sodium (salt), dietary fibre, protein, and complex carbohydrates (4). Dietary index scores reflect diet quality that ranges from low to high. Some food groups and nutrients increase a diet quality score, whilst others decrease it, depending on dietary recommendations and the thresholds set.

How does diet quality affect health?

Healthy dietary patterns throughout the lifespan can help reduce risk of diet-related diseases, and a high diet quality is a unifying component of dietary recommendations around the world. Lower diet quality has been associated with higher risk of dying and higher risk of dying from specific diseases, such as heart disease and stroke (1,4,5).

Global diet quality

At a global level, in 2021, it was estimated that 38% of the world’s population had poor diet quality (6). In this study, poor diet quality was defined by low intake of fruits, vegetables, whole grains, seafood, nuts and seeds, fibre, legumes, polyunsaturated fatty acids, and milk. This was coupled with the overconsumption of sodium (salt), trans fats, sugars-sweetened beverages, and processed meats (6). The latest Global Dietary Database data, based on dietary surveys, indicates that the global AHEI diet quality score was 40.3 [a score which ranges from 0 (least healthy) to 100 (most healthy)]. Only ten countries, representing <1% of the world’s population, had AHEI scores ≥50 (2). In addition, it has been reported that the vast majority of people in most countries, including in high-income countries, are not consuming diets that adhere to dietary guidelines (7).

How do sugars affect diet quality?

Because our diets contain a mix of foods, research examining the impact of sugars intake on diet quality is challenging, as both nutrient-rich (e.g., fruits and vegetables) and nutrient-poor foods (e.g., sugars-sweetened beverages and sweets) are sources of sugars in the diet (8). A recent systematic review, conducted by researchers at Tufts University in the USA, found that the evidence looking at the effect of sugars intake on diet quality is currently limited resulting in very low confidence in any conclusions that can be made (8). Whilst several studies captured in the review showed that higher intake of added sugars was associated with lower diet quality (based on index scores), two studies found no associations between added sugars intake and diet quality, and one study showed improved diet quality. This review identified the need for further higher-quality research to understand the possible effect of sugars intake on diet quality more deeply. It is also unknown what effect different sources of sugars (e.g., sugars from beverages, processed foods, or fruits) may have on diet quality (8).

Dietary sugars intake is just one part of the overall dietary and lifestyle pattern, and it is difficult to determine which individual elements are of most relevance and importance for health. Focusing on an individual nutrient, rather than overall dietary patterns and behaviours, is likely to have a more limited effect on population health. However, it is recommended that dietary intakes of free/added sugars are within the limits specified in national dietary guidelines and are enjoyed as part of a healthy, balanced diet.

References

Petersen KS, Kris-Etherton PM. Diet Quality Assessment and the Relationship between Diet Quality and Cardiovascular Disease Risk. Nutrients. 2021 Nov 28;13(12):4305.
Miller V, Webb P, Cudhea F, Shi P, Zhang J, Reedy J, et al. Global dietary quality in 185 countries from 1990 to 2018 show wide differences by nation, age, education, and urbanicity. Nat Food. 2022 Sep;3(9):694–702.
Fransen HP, Ocké MC. Indices of diet quality. Current Opinion in Clinical Nutrition & Metabolic Care. 2008 Sep;11(5):559.
Wirt A, Collins CE. Diet quality – what is it and does it matter? Public Health Nutrition. 2009 Dec;12(12):2473–92.
Miller V, Webb P, Micha R, Mozaffarian D. Defining diet quality: a synthesis of dietary quality metrics and their validity for the double burden of malnutrition. The Lancet Planetary Health. 2020 Aug 1;4(8):e352–70.
Brauer M, Roth GA, Aravkin AY, Zheng P, Abate KH, Abate YH, et al. Global burden and strength of evidence for 88 risk factors in 204 countries and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021. The Lancet. 2024 May 18;403(10440):2162–203.
Global Diet Quality Project. Measuring what the world eats: Insights from a new approach. Geneva: Global Alliance for Improved Nutrition (GAIN); Boston, MA: Harvard T.H. Chan School of Public Health, Department of Global Health and Population.; 2022. https://doi.org/10.36072/dqq2022
Cara KC, Fan Z, Chiu YH, Jiang X, Alhmly HF, Chung M. Associations between Intake of Dietary Sugars and Diet Quality: A Systematic Review of Recent Literature. Nutrients. 2024 May 21;16(11):1549.