A recent consultation by the UK Department of Health about food labelling has drawn attention to two long-standing issues, both relating to food energy and the calorie.
In May 2012, the Department of Health (DoH) launched a UK wide consultation about front of pack (FoP) food labelling. The consultation is now closed, but details may be found on the DoH web site, FoP consultation.
UK health ministers want to see all food manufacturers and retailers using the same system to show – on the front of packs – how much fat, salt, sugar, and how many calories (the ministers’ words, not mine) is in the products. Readers will be familiar with both the ‘traffic light’ system used by, for example, Sainsbury’s, Waitrose and the Co-op, and with the rather more obscure GDA system used by other supermarkets and certain brands such as Kellogg’s.
UKMA responded to the consultation, supporting consistency of FoP labelling as valuable aid for consumers wishing to compare food products at the supermarket, nationally, across the EU and internationally. However, we suggested that two other issues relating to food labelling deserve attention:
1. The use of the word ‘calorie’ to mean food energy. After all, we don’t say we are going to the DIY superstore to buy square metres when we mean flooring, or to the street market to buy kilos when we mean potatoes.
2. The continuing use of calories, kilocalories (kcals) or Calories to measure food energy, in preference to the SI unit, the joule.
The unsatisfactory nature of the calorie to measure food energy has been recognised for some time. The calorie was developed by the British Association for the Advancement of Science and introduced in 1873 as part of the centimetre-gram-second (cgs) system of measurements. However, it was soon realised that these units were too small for most practical purposes. One of the specific problems with the original calorie was its inconsistency across a range of temperatures – a calorie at a low temperature was larger than a calorie at a higher temperature.
When further development of the cgs system of units was considered in 1889 (yes 1889!), the calorie was replaced by the joule as the single unit of energy for all activities. Unfortunately, the calorie had by then become well established in the fields of diet and nutrition.
Hitherto, UKMA has taken the view that the use of the calorie should be avoided, and that internationally agreed standards and best practice should be used whenever possible. However, at this stage in the UK’s prolonged metric transition there may be something to be said for seeing the calorie as a friend not an enemy:
• It is certainly metric, if not SI.
• It has no Imperial rival – no one would dream of measuring food energy in foot-pounds or in British thermal units.
• It is still widely used around the world, particularly in countries which formerly used the cgs system and in the USA, but also in some newly metricated countries too.
One the other hand, the joule has been successfully adopted for measuring food energy to the exclusion of the calorie in, for example, Australia and New Zealand, and the continuing use of the calorie by the British public while scientists use the SI alternative is likely to add to the divide between the two.
Clearly issues relating to the calorie are unlikely to be resolved any time soon. UKMA’s measurement units style guide suggests ways of dealing with them in the mean time.
Metric Views 
You may find the linked paper (free pdf) on the history of the calorie to be of interest.
Click to access 2957.full.pdf
Per the paper:
*The use of the term calorie is documented at least back to Clement in 1824. It may have originated with him or been used earlier. He used it in the sense of a kg-calorie (1 kg water, heated 1 °C). This is long before the battlelines of cgs and mks were so firmly drawn, and muddled use of gram-calories and kilogram-calories persisted through most of the 1800’s.
*Joule first published his work on the mechanical equivalent of heat in 1845 and published improved values over the next 30+ years. However, he used foot pounds of energy, degrees Fahrenheit, and perhaps pounds of water. He did not use the term calorie until a publication in 1878.
*The joule was initially defined as an electrical unit (1 V x 1 A x 1 s) in 1888. Incidently the joule is an mks unit, the erg is the corresponding cgs unit of energy, 1 J = 10^7 ergs. A definition as 1 N x 1 m was not established until 1918, and served to unify mechanical and electrical work and energy.
*In 1939, Keesom recommended that all other heat units be defined relative to the joule and not to the heating of water. The CGPM recommended discarding the calorie in 1948.
I would note that the varibility of the calorie is a problem in some fields of engineering. Yet the variability in various values of the calorie fall within about plus or minus 0.1% of the IT value. In the case of food, combustion values are measured, but the reported values are adjusted for an estimated metabolic cost of metabolizing the food. This adds an element of uncertainty to all food caloric values that most likely exceeds the variability of the calorie.
It would be better if we all switched to kilojoules for measuring food energy, but I don’t see it happening in the US for a very long time. I would also say that almost any other aspect of metrication seems to warrant a higher priority than “killing the calorie” at least for nutrition science. It is a more important issue in fields of engineering that involve heat engines and efficiency calculations.
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1. Healthier lifestyles
It is possible to find articles about adopting healthier lifestyles that don’t mention calories. For example the British Nutrition Foundation’s web page on
Behaviour change in relation to healthier lifestyles
see: http://nutrition.org.uk/nutritionscience/behaviour/behaviour-10-key-facts .
It refers to energy dense foods.
And on another web page
http://nutrition.org.uk/nutritionscience/behaviour/behaviour-discussion
during the discussion the word calories isn’t used even once.
2. The Dept of Health’s website has plenty of references to ‘calories’, however for anyone interested in the nutrient values of eggs, there’s an analytical report which gives metabolisable energy values. See:
Click to access Nutrient-analysis-of-eggs-Analytical-Report.pdf
The metabolisable energy values were calculated using energy conversion factors from protein, fat and carbohydrate. Values are given in kcal and kJ.
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In its response to the FoP labelling consultation, UKMA did not take a view on the issue of ‘traffic lights’ v. GDAs. However, readers may be interested to hear that Which?, which has been campaigning for ‘traffic light’ labels for years, now reports that Tesco, Aldi and Lidl have agreed to implement them on their own own-brand foods.
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The issue of labelling calories and Joules is being discussed on Which? in a new thread.
http://conversation.which.co.uk/consumer-rights/energy-food-labels-do-we-need-calories-and-kilojoules/
While both are metric, only Joules are SI.
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I am afraid that the Which? article is actually destructive, anti-scientific and not in the best interests of consumers, for whom some knowledge of nutrition science would be far more beneficial in the long run than sticking with obsolete “calories”. The writer obviously intended the reader to conclude that kJ are confusing and should be removed. Once again, the Consumers’ Association is on the wrong side of the argument and is betraying its mission. Fortunately, the law does not allow this.
What is particularly infuriating (though this is not Which?’s fault) is that the pack label gives “sugar, fat, sodium” etc followed by the quantity correctly indicated in grams, but it then gives “calories” and a number – as though calories were some sort of substance. I wonder how many people realise that what is being measured is energy.
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@Erithacus
Yes, pretty much my thoughts on the article, which is why I posted the link here.
The government consultation on nutrition towards the end of last year was, to my untrained mind, pretty close to a farce.
I get the underlying impression that, for anything the government gets involved with, a great deal of care is taken not to recognise the real benefits of, firstly metrication in any form, and secondly to the obvious benefits of the SI system, both of which the government supports in the global sense.
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The Which? article has a poll at the bottom. So far, kcal is winning over kJ. Maybe the readers of this forum can open the article and then select their choice for kJ at the bottom to increase that share of the poll results? 🙂
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