Kale and blueberries might not be the superfoods we are led to believe

There is much talk of superfoods these days. But what constitutes a superfood? PVFs or Powerhouse Fruits and Vegetables, a more scientific name for these, have been described as “foods most strongly associated with reduced chronic disease risk”.

Instagram is full of images and recipes of so called superfoods. Facebook and Internet are no different. However, there doesn’t seem to be a scientific definition agreed by all on what a superfood really is. Or is there?

What is a nutrient?

Before we take a closer look at the concept of so called superfoods, we must understand that there is a concept at the basis of all healthy diets and nutritional science. This is based on the knowledge that there are nutrients that we all need for basic survival and overall health. But what is a nutrient?

Nutrients are substances we need for energy, as building blocks and as controls of all body processes, including growth. You might be more familiar with the six major classes of nutrients which have been classified on the basis of their biochemical properties. These are carbohydrates, proteins, lipids, water, vitamins and minerals. Sometimes an additional nutrient class is added to the above list, fibre, although technically speaking it consists largely of non-digestible carbohydrates.

Essential and non-essential nutrients

There is another categorization of nutrients, perhaps less commonly discussed and known. These are what are called essential and non-essential nutrients. The difference between these is not that we need some and can live without the others, rather that some nutrients can be synthesized by our bodies (non-essential nutrients) whilst others cannot be synthesized (essential nutrients) and therefore we must consume foods full of these essential nutrients to obtain sufficient enough quantities for our bodies to function normally.

Examples of non-essential nutrients are carbohydrates (with the exception of fibre), 9 non essential amino acids such as arginine. These are still obtained from food and are equally important for overall health, but the body can make them from other foods.

In contrast, essential nutrients cannot be made (or synthesized) by our bodies and must be part of our diet. Water is one such nutrient, vitamins and minerals such as iron and vitamin D, omega 3 fatty acids are other examples of essential nutrients we must get from food sources.

The Food and Agriculture Organisation (FAO), which is part of the United Nations (UN), has identified 17 nutrients as being of “public health importance”. These are potassium, fibre, protein, calcium, iron, vitamins B1, B2, B3, B6, B9 and B12, zinc, Vitamins A, C, D, E and K.


What are Powerhouse fruits and vegetables or PVFs?

Let’s move onto a 2004 study by Dr Jennifer Dinoia, PhD published on the webpage of the Centre of Disease Control. The report outlines some research done on what it terms PVFs, Powerhouse Fruits and Vegetables, a more scientific term than “superfood”. The definition of PVFs is those “foods most strongly associated with reduced chronic disease risk”.


In the study, which is based on a 2,000 kcal per day diet, the classification of PVFs is rests on the following criteria: the foods must provide at least 10% of the daily value per 100gm of 17 nutrients. The choice of these 17 nutrients is by no means random. Indeed, they are the same nutrients listed by the FAO (as seen above).

The 17 essential nutrients for overall health

1.       Potassium - Potassium is a mineral and an electrolyte which helps all muscles work, including the muscles that control heartbeat and breathing.

2.       Fibre - Dietary fibre is important for our digestive health and regular bowel movements. It can also help us feel fuller for longer, may improve cholesterol and blood sugar levels and can aid in the prevention of diabetes, heart disease and bowel cancer.

3.       Protein - Our bodies uses protein to build and repair tissues, make enzymes, hormones, and other chemicals. It is an important building block of bones, muscles, cartilage, skin, and blood. Studies have shown that we need increased amounts of protein as we age.

4.       Calcium - Calcium is needed to not just to maintain strong bones and teeth, but also to carry out many important functions in our bodies, to allow muscles to move and nerves to carry messages between the brain and other organs.

5.       Iron -  This a mineral which the body needs for growth and development. Iron is needed for the production of haemoglobin, a protein in red blood cells that carries oxygen from the lungs throughout the body, as well as myoglobin, a protein that provides oxygen to muscles. Iron is also the building block for some hormones..

6.       Thiamin (Vitamin B 1) -  Also known as thiamine, it enables the body to use carbohydrates as energy. It is essential for glucose metabolism, and it plays a key role in nerve, muscle, and heart function. Vitamin B1 is a water-soluble vitamin, as are all vitamins of the B complex.

7.       Riboflavin (Vitamin B2) - Riboflavin is a vitamin that is needed for growth and overall good health. It helps the body break down carbohydrates, proteins and fats to produce energy, and it allows oxygen to be used by the body.

8.       Niacin (Vitamin B3) - Niacin is a vitamin which is made and used by our bodies to turn food into energy. It also aids to keep the nervous system, digestive system and skin healthy.

9.       Folate (Vitamin B9)- Our bodies needs folate to make DNA and other genetic material. We also needs folate for our cells to divide. Folic acid is a form of folate, found in fortified foods and many dietary supplements.

10.   Zinc - Zinc is an essential mineral which aids growth, DNA synthesis and immune function among others.

11.   Vitamin A - This is a fat-soluble vitamin that is important for normal vision, the immune system, and reproduction. Vitamin A also helps the heart, lungs, kidneys, and other organs function properly.

12.   Vitamin B6 (Pyridoxine) – This vitamin plays a key role in metabolism, brain function and healthy hair and skin.  It helps create red blood cells and neurotransmitters. It is an essential nutrient which our bodies cannot synthesize.

13.   Vitamin B12 - Vitamin B12 helps keep the body's nerve and blood cells healthy and to make DNA, the genetic material in all cells. Vitamin B12 also helps prevent megaloblastic anaemia a which makes people tired and weak.

14.   Vitamin C - Also known as ascorbic acid, is a water-soluble nutrient which acts as an antioxidant, helping to protect cells from the damage caused by free radicals, and to build immunity.

15.   Vitamin D - Vitamin D is a nutrient found in some foods, needed for health and to maintain strong bones, teeth and healthy muscles. It does so by helping the body absorb calcium from food and supplements.   Vitamin D helps regulate the amount of calcium and phosphate in the body. Lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.

16.   Vitamin E – This fat-soluble nutrient acts as an antioxidant, helping to protect cells from the damage caused by free radicals.

17.   Vitamin K - Vitamin K is important for blood clotting and to maintain healthy bones as well as other functions.


As a rule of thumb, the 17 nutrients can be found in foods which are:

·       Leafy greens (chard, beet greens, spinach, chicory, leaf lettuce)

·       Orange/Yellow in colour (carrot, tomato, winter squash, sweet potato)

·       Citrus (lemon, orange, lime, grapefruit)

·       Cruciferous (watercress, Chinese cabbage, collard greens, kale and arugula)


The foods that did not meet the PFVs criteria

Based on the above criteria, of the 47 foods studied only 41 classified as PFVs and were more nutrient dense than non PVFs. The definition of nutrient dense being:

“Food that is high in nutrients but relatively low in calories. Nutrient-dense foods contain vitamins, minerals, complex carbohydrates, lean protein, and healthy fats. Examples of nutrient-dense foods include fruits and vegetables, whole grains, low-fat or fat-free milk products, seafood, lean meats, eggs, peas, beans, and nuts.”(source cancer.gov)

The foods which did not meet the PVF criteria were:

a.       Raspberries

b.       Tangerines

c.       Cranberries

d.       Garlic

e.       Onions

f.        Blueberries


Surprised? You might well be. How many times have we seen blueberries touted as superfoods? According to this study they are not as super as we are led to believe.


The full list of Powerhouse Fruits and Vegetables (PVFs)

So which fruits and vegetables made the list? And what was at the top?  The full list below.

1.       Watercress

2.       Chinese cabbage

3.       Chard

4.       Beet greens

5.       Spinach

6.       Chicory

7.       Leaf lettuce

8.       Parsley

9.       Romaine lettuce

10.   Collard greens

11.   Turnip greens

12.   Mustard greens

13.   Endives

14.   Chives

15.   Kale

16.   Dandelion greens

17.   Red pepper

18.   Arugula

19.   Broccoli

20.   Pumpkin

21.   Brussels sprouts

22.   Scallions

23.   Kohlrabi

24.   Cauliflower

25.   Cabbage

26.   Carrot

27.   Tomato

28.   Lemon

29.   Iceberg lettuce

30.   Strawberry

31.   Radish

32.   Winter squash (all varieties)

33.   Orange

34.   Lime

35.   Grapefruit (pink and red)

36.   Rutabaga

37.   Turnip

38.   Blackberry

39.   Leek

40.   Sweet potato

41.   Grapefruit (white)

Hands up who would have guessed that something as insignificant looking as watercress would be top of the list? (I won’t hide from you that as soon as I read this study I rushed out to buy some …). Kale is only 15th on the list. Much further down than the good old romaine lettuce we all used to consume before the days of Instagram. Who needs to spend lots of money on kale when lettuce, spinach and parsley will deliver? Notice also that not all grapefruits are the same? Blackberries made the cut, but blueberries didn’t….

I can also happily report that I’ve covered a number of these PVFs in previous blog articles (dandelion, kohlrabi, pumpkin, cauliflower, winter squash….), and that apart from watercress they’re all part of my regular diet. What about yours?

Stop instagramming, and put your health (and your wallet’s)back at the top, where it should be!

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