Defining dietary diversity

5 November, 2015

Sometimes scientific research is used in a way that seems to deliberately obscure the truth of things.

This may not come as a surprise to some of our readers. But a recent study on dietary diversity caught my eye as a good example of this.

A diverse diet means that we eat a greater variety of different foods. In this spirit, and in practice, it would seem obvious that this means a greater variety of healthy and seasonal foods rather than just a greater variety of junk foods.

And yet this latter practice is pretty much what US researchers recently defined as ‘dietary diversity’ – leading them to the conclusion that a diverse diet is bad for your health.

Nothing in moderation?

The multi-ethnic study using data from 6,814 Americans measured diet diversity by looking the number of different foods eaten in a week as well as the distribution of calories across different foods consumed.

It found that, by this measurement, those with diverse diets actually had worse diet quality because they were eating more unhealthy, high calorie foods, such as processed meats, desserts and soda.

Perhaps not surprisingly those who had the greatest ‘variety’ in their diets experienced considerably more weight gain around the waist – a risk factor for diabetes – than those who ate a lower variety of foods.

The researchers also looked at diet quality and found that when quality was the main consideration there was no increase in health risk and that higher diet quality was associated with about a 25% lower risk of developing type-2 diabetes. Well duh.

Nevertheless, their conclusion was that the mantra “everything in moderation” was bad dietary advice and that people eating a lower diversity of foods generally had healthier diets.

Measuring nutrition not calories

According to the FAO “Dietary diversity is a qualitative measure of food consumption that reflects household access to a variety of foods, and is also a proxy for nutrient adequacy of the diet of individuals.”

In other words, in determining diversity we need to look at more than just how many different types of donuts you ate yesterday. Questionnaires to determine dietary diversity usually focus on fresh foods: meats, fruits, vegetables, cereals as well as oils and fats etc.

Consider the source

Measuring diversity, in addition, may be an entirely different task in rural Africa than it is in countries which have embraced the Western pattern way of eating. In these countries, the lesser variety of junk foods you eat, the healthier you probably are.

To measure dietary diversity in Western Pattern eaters it may be better to classify all processed foods which are nutritionally high in fat, salt and sugar as a single category quite separate from fresh, unprocessed or minimally processed foods.

Only then can we get a real picture of diversity that reflects both variety of foods and nutrients necessary to maintain health.

We need healthy diversity

Human beings evolved to eat a wide variety of foods. In contrast to this widely reported study, other studies have shown that consuming a variety of healthy foods improves a range of health outcomes and assures that we get a regular supply of adequate nutrients.

A more diverse diet has been shown to protect from premature death from all causes including type-2 diabetes, heart disease, and cancers including colorectal (bowel) cancer, gastric cancer, oesophageal cancer, laryngeal cancer and oral and pharyngeal cancer.

Eating a variety of nutrient-rich, low-energy foods, like vegetables and fruit, also helps with weight control.

Serving the corporate agenda

Given this we have to ask: who does the conclusion that we should eat a less diverse diet serve?

Commenting on a recent UN FAO report, which confirms that global diets are becoming more and more similar, relying on a small variety of cereals and grains, lead author Colin Khoury said “These foods are critical for combating world hunger, but relying on a global diet of such limited diversity obligates us to bolster the nutritional quality of the major crops, as consumption of other nutritious grains and vegetables declines.”

‘Bolstering’ crops relies on fertilisers, which can over time destroy soil health and with it the nutritional quality of our foods. Most recently it has come to mean genetic modification, which in spite of its big promises has failed to deliver more nutritious food. In other words, research like this leaves our fate in the hands of chemical companies. And when we get sick, pharmaceutical companies.

Studies like this are the reason why most average people don’t trust the dietary advice of so-called experts. Long may this scepticism continue.

Pat Thomas, Editor