What is an ideal diet anyway?

It’s easy to assume we know what healthy eating looks like. Think, an apple vs a packet of chips. While we’re probably on the right track, when it comes to quantifying and advocating a healthy ‘plate’ (or in what proportions we eat particular types of food each day) for optimal nutritional and health outcomes, it gets trickier. Further complications arise with cultural, ethical and economic considerations of a population determining the types of food people want to eat, what they have reasonable access to. As such, the setting of an ‘ideal’ diet cannot be untangled from values and motivations because it can be a means of putting forward a dietary ‘vision’ for a country or community (Gonzalez Fischer & Garnett, 2016) that may intend to address other objectives such as agricultural and economic policies, physical performance (for sporting or military purposes) or cultural/religious adherence.

My task in this project isn’t to decide what a healthy diet should be—three modules in nutrition haven’t quite qualified me for that—but rather to canvas the current consensus on ideal diets (and yes, I expect there to be more than one) and convert that into a set of parameters that I can use to test whether national food supplies, on average, can deliver that ideal.

Here are some initial musings as I work my way through the literature on healthy diets.

Do we agree on what a healthy diet should look like?

The exact make-up of a diversified, balanced and healthy diet will vary depending on individual characteristics (e.g. age, gender, lifestyle and degree of physical activity), cultural context, locally available foods and dietary customs. However, the basic principles of what constitutes a healthy diet remain the same.

WHO, 2018.
Image credit: Sourced from the Mirror article “Diet dilemmas: Eight ‘healthy’ foods that are secretly bad for you” (28/06/2016)

Our aim in this study is to compare the relative make-up of national diets against an ideal diet (or series of diets) for health. We must then distil what we know about what’s considered a healthy diet from the range of national and other recommended diets into a single metric (or set of metrics) to compare against.

The short answer to the above question is (surprise, surprise): no.

Let’s look at the World Health Organisation’s (WHO) Healthy Diet Factsheet (2018) as a starting point:

A healthy diet for adults includes:

Fruit & vegetables (at least 400g/five portions excl. potatoes, sweet potatoes, cassava and other starchy roots)

Legumes, nuts and whole grains
Less than 10% total energy intake from ‘free sugars’ (around 50g or 12 teaspoons) but ideally less than 5%

Less than 30% of total energy intake from fats – unsaturated preferable to saturated fats.

Less than 5 g of salt (about one tsp) per day.
(WHO, 2018.)

The WHO’s guidelines of course provides further details and includes other recommendations such as dietary diversity (to confer a wide range of nutrients for health). However, even at this point I’m questioning whether you can really say that the principles of a healthy diet ‘remain the same’, outside of the WHO’s perspective anyway.

My reading so far suggests broad agreement with the healthfulness of consuming fruits and vegetables (particularly when they are fresh). But for instance, some would highlight the sugar content of many fruits and its inflammatory effects (e.g. in low glycemic index (GI) diets)(Katz & Meller, 2014). In national food-based dietary guidelines, starchy vegetables are included as staple foods and grains that, for some, should make up the bulk of the daily plate, and others come second to other vegetables and fruit, or they are simply included with vegetables. Dietary recommendations such as that for the Paleolithic diet (Paleo) promote the avoidance of legumes and grains (Katz & Meller, 2014). And while not far off the mark, the Mediterranean diet promotes fat intake of 35-40% of daily calories, though unsaturated fats such as olive oil are emphasised (Katz & Meller, 2014).

One of the simplest expressions of what we ‘should’ eat is the now well-known ‘Eater’s Manifesto’ from Michael Pollan: “Eat food. Not too much. Mostly plants.”

Image credit: lettuce from the cover of Pollan’s book (2008).

By ‘food’ Pollan is referring to whole and minimally-processed foods, rather than refined, energy-dense foods with high calorific and low nutritional value. ‘Not too much’ is pretty self-explanatory but goes towards our problems with obesity as well as the social and environmental consequences of consuming more than we need. And ‘mostly plants’ reflects the principles expressed by the WHO in terms of minimising intake of saturated fats (that principally come from meat and dairy) and emphasis on eating fruits and vegetables, but also whole grains and legumes. Consumption of animal-based foods is also associated with environmental costs such as greenhouse gas emissions, land degradation and deforestation as well as displacement of plant foods for humans with animal feed (Katz & Meller, 2014).

So, while we may not agree on what a healthy diet should look like in detail (i.e. What constitutes food? How much is too much? What plants? And by how much more?), perhaps this is an adequate starting point for agreement. And, for me, a useful framework to think about what an ‘ideal’ might be from afar before I get bogged down in the ways particular dietary recommendations can get us there.

National food-based dietary guidelines (FBDGs)

National food-based dietary guidelines (FBDGs) provide context-specific advice and principles on healthy diets and lifestyles, which are rooted on sound evidence, and respond to a country’s public health and nutrition priorities, food production and consumption patterns, sociocultural influences, food composition data, and accessibility, among other factors.

FAO, 2019.

At a country level, approaches to dietary ideals can be unpacked from looking at national food-based dietary guidelines (FBDGs)—a government’s advice on how people can eat well (Gonzalez Fischer & Garnett, 2016). Over 100 countries have developed FBDGs and handy for me, the FAO has compiled 92 of them.

Top L-R: USDA MyPlate (YEAR), China’s healthy food pagoda (2016), Canada’s EatWell Plate (2015)
Bottom L-R: Japan’s food guide spinning top, a food pyramid, and a food plate.

These dietary recommendations are meant for the public, so they translate nutritional evidence-based knowledge such as recommended daily intakes of specific nutrients and the nutritional composition of foods by grouping foods based on their potential to contribute to particular nutrition outcomes. FBDGs are generally accompanied by a graphic such as the food ‘pyramid’, showing foods that should be consumed most at the base, and least at the top. Other examples of this include China’s ‘healthy food Pagoda’ and Japan’s ‘spinning top’ (an inverse pyramid).

A more recent trend is presenting FBDGs through a healthy food ‘plate’ which shows the recommended proportion of daily food groups to eat in a pie chart to more clearly illustrate what meeting the FBDGs would look like. Examples include the Harvard ‘Healthy Eating Plate’, USDA ‘MyPlate’, the UK ‘Eatwell Guide’ and the EAT-Lancet ‘Planetary Health Plate’ (which includes both nutritional and environmental considerations).

As I embark on my project design and literature review I am weighing up the value of comparing all of these FBDGs to come up with a method to test country-to-country alignment with healthy dietary ideals compared with looking at what measures are already out there and adapting them as a baseline for this comparative analysis.

Next, I’ll explore the field of dietary quality indices (DQIs)—used to test adherence to particular dietary patterns including ones based on FBDGs—to 1) see how others are measuring alignment with ideal diets; and 2) whether these tools are fit for what I want to find out.


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