Evan Stevens

The CDC recently released an article detailing how we should start emphasizing the consumption of nutrient-dense foods in our diets over the foods we typically consume in a western diet. This article comes on the heels of the updated statistics that roughly 70% Fruits & veggiesof Americans are overweight or obese. This weight epidemic contributes to a rise in chronic diseases, such as type II diabetes, arthritis, cancer, coronary pulmonary diseases, Alzheimer’s, and even depression.

Nutrient Density is described in a number of different ways depending on geographical location, but the enduring theme is that it is a way to profile the nutrient quantity of a food- that is, a food that gives you the most amount of nutrient at the lowest caloric price. Nutrient dense foods are the mirror to energy-dense foods, which you might know as “empty calorie” foods. Namely, foods that contain high-processed sugars and fats and little else.

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The CDC approached this problem by comparing fruits and vegetables that have previously demonstrated benefits at reducing chronic disease, referred to as Powerhouse Fruits and Vegetables (PFVs). These PFVs include green leafy, yellow/orange, citrus, and cruciferous fruits and vegetables. The ability of these vegetables to reduce chronic disease is usually attributed to the phytochemicals and micronutrients contained within them.

Working Towards a Fruits & Veggies Classification System

Currently, there are no means to qualify PFVs based on the intake of these phytochemicals and nutrients, and that is where the CDC’s article steps in. The article is an attempt to lay the groundwork for a classification system for PFVs. Specifically, this system aims to be based on 17 nutrients of public health importance:

  • potassium
  • fiber
  • protein
  • calcium
  • iron,
  • thiamin
  • riboflavin
  • niacin
  • folate
  • zinc
  • vitamins A, B6, B12, C, D, E, and K

A tentative list of PFVs was developed based on previously published literature, consumer guidelines, as well as selected berries that are recognized by consumers as aiding in the reduction of certain diseases.

The researchers ended up comparing a number of fruits and vegetables to four food items that have been described as low nutrient dense – apples, corn, bananas, and potatoes. This comparison was done by measuring the amounts of the 17 nutrients and calories in 100g of these foods. The actual density of these foods was calculated by dividing the percent daily values (DVs) (based on a 2000 kilocalorie diet) per 100g of food and then weighted based on average bioavailability of the nutrients previously described in the literature.

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The researchers do concede that while some foods may be high in a certain nutrient, they are lacking in others, and capped the daily values at 100 thinking that not any single nutrient would contribute too much to an overall score. Foods were labeled as being classified as PFVs if the end score was greater than or equal to 10 as foods having 10% or more of a particular nutrient are described as being a “good source.”

The PFVs Study

47 foods were studied, and 41 foods were classified as PFVs (raspberry, tangerine, cranberry, garlic, onion, and blueberry were discounted as non-PFVs). The robustness of the classification system was determined by comparing the foods that were classified as PFVs to foods that are listed as protecting against heart disease and cancer; fiber, folate, zinc, and vitamins B6, B12, C, D, and E. The study found that there was a moderate correlation between PFVs and the comparative list.

This study is a good start and is well-needed; people truly need to know that they need to eat nutrient dense foods and this not only suggests which foods people should eat but why as well. The fact that the study describes how food should be desired based on the energy and nutrient value is a huge step in the right direction in helping consumers make proper food selection.

Fruits & veggies

Limitations of the Study

However, if we are to look at the study under a critical eye, there are several issues that have been glossed over. The diet described as being a 2000 kcal diet is extreme. This is becoming more of an arbitrary number than a guideline as our understanding of age, activity, and metabolism broadens. This also doesn’t take into account that the average American is obese and overweight and that the average caloric consumption is often 50% greater than 2000 kcal per day. This also creates a problem for percent DVs as they too are based on a 2000 kcal diet. If a person is large or active or are suffering from certain illnesses, these percent DVs might have little or no meaning to them.

Understandably, basing a diet on a 3000 kcal diet would be extreme, but if the rest of the study is going to take into account averages, then I think to put it in context, the dietary values should be stressed as averages as well. While this is minor, basing averages off of an unrealistic diet can skew results. Another issue is the problem with nutrient density. Nutrient density isn’t something that is static and will always be the same between two of the same vegetable. Seasonal variation, growing conditions, soil conditions, cultivar genetics, and so on means that a lot of the nutrient density qualifications without the accurate measurements of the growing conditions and circumstances creates hugely mixed and sometimes even meaningless results. 

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Further Critique

The authors do mention that discounting other micronutrients may indeed discount several nutrient-dense foods; this cannot be stressed enough if it is to be used to guide and educate the public. By not including phytochemicals such as carotenoids and flavonols, which have demonstrated benefits to disease prevention, the final results and labeling of PFVs could be wildly different from reality. Blueberries, for example, were discounted from this study’s definition of PFVs even though they are considered, not only in popular media but in scientific literature too, as being one of the healthiest foods available. They are loaded with anthocyanins, polyphenols, and other phytochemicals which are currently being researched to the benefit of health.

As well, limiting the nutrient profile to 17 (and then to 8 for comparison) nutrients will discount certain foods from either being higher on the list or appearing on the list. Some foods are excellent sources of important and essential micronutrients, such as manganese (hugely important in the formation of antioxidant networks), may be cut entirely from the list, potentially leading people to think these foods as poor or unhealthy choices.

Comparing bioavailability also presents an area of difficulty because there is so much difference in bioavailability between fruits and vegetables, as well as in individuals. Spinach may be high in iron, but its bioavailability is so low because it is non-heme iron (not from a hemoglobin source) and we are very inefficient at processing it. However, some individuals are efficient at processing it, be it because they have the right genes or right gut bacteria. This means that for them, the bioavailability is much higher.

Takeaways

As stated, this study is a good starting point; there are currently no other papers that have tried to create a schematic of how to designate PFVs or not. It is a needed study especially in a population where food choices and poor lifestyle are creating one of the unhealthiest populations in the world. The reliance on averages and previously published data creates accuracy issues in the results and makes it difficult to put results into the context of a current population. With the growing shift towards personalized nutrition, more needs to be done to account for individual variability as well as how the foods are grown and sourced. While this is an important study, it may be too little, too late.

Had this study been published 10 or 15 years ago, before diet-related illness was really becoming an epidemic and a learning environment could be cultivated for population health, the results may be more impactful. But now, with so much individuality between people’s metabolism and health needs, as well as our growing understanding of nutrient density, bioavailability, and biologically active chemicals within the plants that benefit health, the study is not nearly as impactful.

Defining and promoting (creating an environment that fosters learning about your food choices) the consumption of PFVs is still a worthy goal and still warrants development, but it needs to be acted upon swiftly, focusing on the accuracy of the variables and the inclusion of more nutrients that contribute to health. This study was a good first step, but there is still a long road ahead.

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