A healthy diet has numerous benefits. But what does a healthy diet consist of? And how do we, researchers, measure diet quality?
What’s considered a healthy diet in one country or culture, may not be regarded as such in another. For instance, low-fat and unsweetened dairy products are regarded as healthy in my country, the Netherlands, but not in many Asian countries where a vast proportion of the population is lactose intolerant. Differences in regional availability of foods further determine dietary habits across, and even within, countries. Fish, for example, is often at the core of a healthy diet in countries surrounded by water such as Japan (48.6 kg/year per person), but not in landlocked countries such as Hungary (5.1 kg/year per person) .
Here I will describe six common ways in which researchers may assess diet quality in Western populations.
1. Fruit and Vegetable Consumption
Probably the quickest way to obtain an estimate of an individual’s diet quality is by assessing fruit and vegetable consumption of the individual. Generally speaking, fruits and vegetables are high in healthy nutrients such as vitamins and fibers. Moreover, fruits and vegetables often replace unhealthier options such as energy-dense snacks. Finally, while fruit and vegetable consumption is only one aspect of diet quality, it has been shown to correlate with overall diet quality. Thus, fruit and vegetable consumption can be seen as a fast but crude way to assess diet quality.
2. Total Energy Intake
One could consider calculating total energy intake as an indicator of diet quality. Generally speaking, unhealthy foods are more energy-dense than healthy foods. Therefore, high-calorie diets likely contain more unhealthy foods. Of course, this is not necessarily the case; some foods, for instance avocado, are both energy-dense and nutrient-rich. Moreover, low energy intake may result in nutritional deficits. Therefore, total energy intake is not generally used as an indicator of diet quality.
3. Mediterranean Diet Score
The Mediterranean Diet Score (MDS) measures compliance to a Mediterranean-type diet, consisting of legumes, fruits, vegetables, unrefined cereals, olive oil and fish. Points are subtracted for dairy and meat . The Mediterranean diet was inspired by the eating habits of Greece and Italy, where people seem to live longer and have lower risk of heart disease compared to other Western regions.
4. Western-Type Diet Score
A Western-style diet is a modern dietary pattern, that is sometimes referred to as the Standard American Diet. A Western diet consists of red and processed meats, pre-packaged foods, fried foods, whole-fat dairy products, refined grains, potatoes and sugar-sweetened beverages, among others . Contrary to most diet quality scores, a higher Western diet score indicates a less healthy diet.
5. Healthy Eating Index
The Healthy Eating Index (HEI) measures how well an individual adheres to the key recommendations of the 2015 Dietary Guidelines for Americans. These guidelines are often used by US-based nutrition and health professionals, to help people to consume a healthful and nutritionally adequate diet. A total score is calculated based on nine advised food groups/components (including fruits and vegetables, whole grains, plant proteins), and four components that should be moderated (including salt and saturated fat) .
6. Dietary Approaches to Stop Hypertension
The dietary approaches to stop hypertension (DASH) dietary pattern emphasizes fruits, vegetables, low-fat dairy, whole grains, nuts and legumes, and limits saturated fat, cholesterol, red and processed meats, added sugars, and sugar-sweetened beverages. It was originally developed in the US to treat hypertension without medication . Several medical associations and institutions have since incorporated the diet in their clinical guidelines .
 Ritchie & Roser (2019). Meat and Seafood Production & Consumption. Published online at OurWorldInData.org. Retrieved from: https://ourworldindata.org/meat-and-seafood-production-consumption on 28 August 2019
 Dinu, Pagliai, Casini & Sofi (2018). Mediterranean diet and multiple health outcomes: an umbrella review of observational studies and randomised trials. European Journal of Clinical Nutrition, 72(1), 30-43. doi: 10.1038/ejcn.2017.58
 Cordain, Eaton, Sebastian, Mann, Lindeberg, Watkins et al. (2005). Origins and evolution of the Western diet: health implications for the 21st century. American Journal of Clinical Nutrition, 81(2), 341-354. doi: 10.1093/ajcn.81.2.341
 US Department of Agriculture, Food and Nutrition Service. Retrieved from https://www.fns.usda.gov/resource/healthy-eating-index-hei on 28 August 2019
 Sacks, Svetkey, Vollmer, Appel, Bray, Harsha et al. (2001). Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. The New England Journal of Medicine, 344(1), 3-10. doi: 10.1056/NEJM200101043440101
 Chiavaroli, Viguiliouk, Nishi, Mejia, Rahelic, Kahleova et al. (2019). DASH Dietary pattern and cardiometabolic outcomes: an umbrella review of systematic reviews and meta-analyses. Nutrients, 11(2), 338. doi: 10.3390/nu11020338
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