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Updated 26 February 2013

Banana myths

Bananas are among my favourite foods, but the type of exaggerated health and nutrition claims currently doing the rounds cannot be taken seriously, writes DietDoc.

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Bananas are among my favourite foods, but the type of exaggerated health and nutrition claims currently doing the rounds cannot be taken seriously, writes DietDoc.

In our part of the Highveld, they say that lightning always strikes twice and this seems to apply to bananas too. During the past week I have not only received an e-mail from a dear friend with the earnest request to comment on its content regarding the superlative nutritive value of bananas, but a Health24 reader reported that she had been told that bananas should not be eaten after 3pm or included in a slimming diet. In fact she said, and I quote: “I was told NOT to eat banana when trying to lose [weight], AND never to eat it after 3pm.  What’s your take on this banana business??” My take on this banana business is that I am amazed by the both the positive and negative hype about this fruit, which happens to be a firm favourite of mine.

Health claims

The e-mail extolling the nutritional superiority of bananas, also made a number of health claims, namely that eating a banana will lower cholesterol, soothe an upset stomach and diarrhoea, and provide immediate relief from hangovers, and premenstrual syndrome. The tryptophan in bananas is also credited with promoting sleep. The e-mail then went on to state that “bananas have positive effects in relation to the following ailments: anaemia, blood pressure, bowel problems, constipation, depression, heart problems, morning sickness, nervous disorders, stress and ulcers.”

Anyone reading the banana e-mail would conclude that bananas are the solution to every ailment and problem know to mankind, and that they are bursting with nutrients.

It is evident that a most efficient advertising campaign is responsible for the positive statements, whereas I suspect that the negative weight-related statements and the ban on eating bananas after a certain time of day, are old wives’ tales.

Humans are omnivores

I am always suspicious when claims are made that one food, in this case the banana, can cure so many different ailments and prevent so many different diseases. 

Each food can make a contribution to our nutritive intake and our health and if we eat a balanced diet that contains a variety of different foods, then as omnivores we humans will stand the best chance of surviving and keeping healthy. In contrast to carnivores that only eat meat and herbivores that only eat plants, omnivores have developed the capacity to eat foods derived from both plants and animals. I have often thought that it was specifically this ability to eat such a wide variety of foods that gave the human species the push towards world dominance. After all, a species that is able to eat practically anything, is more likely to thrive and survive, than a species like the panda, that only eats a specific type of bamboo!

In keeping with the above, the first and most important South African Food-Based Dietary Guideline states “Eat a variety of foods”.

So it stands to reason that a single food, such as the banana, does not hold the key to curing or preventing all the diseases listed above.

The overenthusiastic approach

Ad agencies who promote the sales of foodstuffs often fall into the trap of overenthusiasm and will sing the praises of nutrients found in foods just because those nutrients happen to occur in a given food. The enthusiasts never consider the actual content of the nutrients in the food and if it can have a meaningful impact on our nutritive status or our health, or not.

Let’s look at an example: Bananas contain 0.03 mg of thiamine (vitamin B1) per 100g, which for the purposes of this argument we will regard as a “single serving”. We can, therefore,  argue that thiamine is actually found in bananas, but when we compare this thiamine content with the Nutrient Reference Value* for thiamine currently in use in South Africa, namely 1,2 mg thiamine per day (Gov Gazette, 2010), then eating a 100g banana is only going to supply us with 2,5% of our requirement. Most people will thus agree that bananas are not really a wonderful source of thiamine. Compared to sheep liver which provides 0.35 mg/100g or 29% of the NRV* (Nutrient Reference Value) for thiamine, banana cannot be regarded as a significant source of thiamine and any claims made about this vitamin in bananas are over optimistic.

New labelling regulations

The South African Labelling Regulations published in 2010 (Gov Gazette, 2010), which will come into effect as of 1 March of this year, set out to prevent this kind of over-the-top advertising. The Regulations specify that no nutrient claims are permitted for nutrients where a single serving of a food does not provide more than 5% of the NRVs of those nutrients. In terms of our example, we would, therefore, not be allowed to make a nutrient claim about the thiamine content of banana and also not to list it in the Nutritional Composition Table.

The Regulations go on to specify that if a single serving of a given food provides between 5% and 15% of the NRV of a nutrient, then it may be mentioned or listed in the Nutritional Composition Table, but we still cannot even say that the food is a “source” of the nutrient.

Only when the single serving of the food contains more than 15% of the NRV of a nutrient may we say that it is a “source” of the nutrient. Furthermore, we can only state that a food is “high in” a nutrient if a single serving provides 30% or more of the NRV (Gov Gazette, 2010).

Now let’s see how bananas shape up:

Measured against the strict specifications of the new SA Labelling Regulations, bananas can only be promoted as:

  • A source of potassium because a 100g serving contains 400 mg, which represents 20% of the suggested potassium intake per day
  • High in vitamin B6 or pyridoxine, because a 100g serving contains 0.58 mg  which represents 34.1% of the NRV
    (Mahan et al, 2011; Wolmarans et al, 2010)

None of the other vitamins and minerals are present in sufficient quantities to allow their mention in the Nutritional Composition Table or in any claims about the fruit.

Refuting the negative statements

The negative statements about eating bananas can also be refuted. There is no reason why anyone who is slimming is not allowed to eat bananas. On average, bananas provide 384 kJ per 100g serving (Wolmarans et al, 2010), which represents 6,1% of the daily energy requirement for adult women when trying to lose weight. Banana can thus be used as an excellent snack or as one of your fruit servings in a balanced slimming diet. Firm slightly green bananas have a lower glycaemic index (GI) than soft, ripe ones.

As to not eating bananas after a certain time of day, well there is no logic to this prohibition either. Bananas contain hardly any fat and as a mainly carbohydrate fruit (21.8 g carbs per 100g), can be easily digested and absorbed by the human body.

Bananas are among my favourite foods, but the type of exaggerated health and nutrition claims made in the ‘banana e-mail’ that does the rounds from time to time, as well as the illogical negative statements reported by my reader, cannot be taken seriously.

Let’s just enjoy bananas as a tasty fruit that can provide variety to our diets.

- (Dr IV van Heerden, DietDoc, February 2012)

Any questions? Ask DietDoc

References:

(Government Gazette (2010). Regulations relating to the labelling and advertising of foodstuffs. No. R. 146. Foodstuffs, Cosmetics & Disinfectants Act, 1972 (Act 54 of 1972). 1 March 2010. Government Gazette, No. 32975, Pretoria;Mahan LK et al (2011). Krause’s Food & the Nutrition Care Process. Ed. 13. Elsevier, USA; Wolmarans P et al (2010). Condensed Food Composition Tables for SA. MRC, Parow Valley, Cape Town.) 

*NRVs - have replaced the RDAs as nutrient intake criteria in the new SA Labelling Regulations (Gov Gazette, 2010)  

Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Health24.com. Read more of her articles.

 
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