Prospects improve for food energy labelling using SI units

One of our readers wrote to Sainsbury’s to ask that guideline daily amounts (GDAs) of energy shown on packaging should be shown in kilojoules, the SI unit, as well as or instead of kilocalories. He has received a reply that provides cause for optimism.

But why are there are two metric units in common use for food energy labelling? As is often the case, tradition and inertia are partly to blame.  The calorie was the first unit used, over a century ago, to measure the energy we get from food. It is a metric unit, but has several drawbacks as explained at the end of this article. The modern international system of units (SI) uses in its place the joule, and the use of the calorie is declining in many countries around the world.

One of our readers is closely following the switch from calories to joules wherever these units compete for our attention. He wrote recently to Sainsbury’s on the matter of food labelling, and this is their reply:

“Thanks for contacting us regarding the display of Guideline Daily Amounts (GDA) energy values of our mini shredded wholegrain wheat cereal.  We appreciate you taking the time to contact us.

The Food Information Regulation (FIR), which you refer to in your e-mail, has a transition period ending in December 2014 by when pre-packed foods sold in the UK will be required to show the energy content of a food on drink product on the front of the packaging in kilojoules.  I can confirm between 2012 and December 2014 we will be changing all our packaging to incorporate the labelling changes required by the FIR.

GDAs are guidelines for healthy adults and children about the approximate number of calories (kcal), fat, saturated fat, carbohydrate, total sugars, protein, fibre, salt and sodium required for a healthy diet. GDAs were developed by the Institute of Grocery Distribution as voluntary, back-of-pack nutrition labelling guidelines in 1998 and are widely used in the UK in their current format which at present does not include kilojoules. Food Drink Europe (FDE) are currently consulting with the European Commission to establish what format GDA labelling should take under the new FIR legislation.  Once the European Commission has provided guidance on the inclusion of kilojoule information on front-of-pack multiple traffic light labelling and back-of-pack GDA labelling, we will update our labelling accordingly.

Thank you again for contacting us, I hope this answers your query.  If there’s anything else I can help you with, don’t hesitate to contact me.

Kind regards

Jo Macintyre, Customer Manager
Sainsbury’s Supermarkets Ltd, 33 Holborn, London  EC1N 2HT”

Sainsbury’s is a leader in clarity of food labelling and follows the Government’s preferred ‘traffic light’ labelling for GDA information, unlike many of its competitors.

Don’t delay your weekly shop, however. We have been here before:

Technical note

The calorie (cal)

The unit of the energy that is favoured by the UK and US food, fitness and slimming industries is the Calorie. In reality it is 1000 calories, sometimes written as kcal. The calorie approximates to the amount of heat energy required to raise 1 gram of pure liquid water through 1 degree Celsius. However, it suffers from three drawbacks:

  • The amount of heat required to raise 1 g of pure liquid water through 1 °C depends upon the initial temperature of the water. Therefore, in reality the unit is meaningless unless the initial temperature of the water is also stated.
  • Not being part of any integrated system of measurement, the unit has little practical application in wider physical calculation.
  • It is not a recognised by the Units of Measurements Regulations that govern the units to be used in the UK.

The joule (J)

Historically, it was thought that there were several different forms of energy: heat energy (often measured in calories or British Thermal Units), work energy (measured in ergs, kilogram metres or foot pounds) and electrical energy (measured in joules or kilowatt hours). About two centuries ago, scientists realised that all these forms of energy are convertible with varying degrees of difficulty but at fixed rates of exchange. Thus, one calorie is about 4.2 joules.

SI recognises only one unit of energy – the joule. It is used to measure all forms of energy, including the energy content of food. The joule is defined in terms of the units of distance in metres, mass in kilograms and time in seconds. Power in watts is energy in joules divided by time in seconds. So, for example, the energy content of sugar is about 17 MJ/kg and that of petrol (gasoline) about 35 MJ/L; the engine of a Mini Cooper has a maximum output of about 90 kW.

Author: UK Metric Association

Campaigning for a single, rational system of measurement

7 thoughts on “Prospects improve for food energy labelling using SI units”

  1. After some Googling, I think I found the law in question:

    Most of the information on units and guidelines is in the Annexes 13-15. For energy value, it appears to require both the kilocalorie and kilojoule. As in most dual labelling, those used to the kilocalorie will tend to continue using it and ignore the information in kilojoules. There will be little real transition unless there is an announced plan to phase out the kilocalorie. (Still, it is more progress than the US is making).


  2. There is another reason for dropping the calorie apart from those mentioned in the article.

    The SI base units reduce measurement to the minimum number of independant variables required to capture everything, either directly or in combination.
    Using the thermal properties of water would retain an unnecessary variable and duplicate what is already contained in mass length and time.

    Interesting to note as well that thermal and mechanical energy are actually the same thing. Temperature is a measure of the kinetic energy (energy by virtue of motion) of the molecules of a substance due to thermal agitation.

    Getting rid of the calorie though, wont be easy outside of engineering and scientific circles. Unfortunately a lot of people tend to think that we need different units for different applications even when they actually measure the same thing.


  3. This 1971 paper from a nutritional conference may be of interest:

    Quoting one snippet:
    “The Joint FAO/WHO Expert Committee on Nutrition (3) considered the implications of substituting joules for calories in 1966. In view of its importance it was decided to refer this matter to the Committee on Nomenclature of the International Union of Nutritional Sciences (IUNS) and to other appropriate organizations. The conversion from calories to joules was considered by the IUNS Committee at its pre-congress meetings, in Belgrade on 20 to 23 August 1969 and again in Prague on 26 August 1969 (4). It was formally recommended that the change from the calorie to joule should be made, however, such change should be gradual. The conversion factor to be used is debatable; for those engaged in research on energy change involving calorimetry an exact figure of 4.1840 J = 1 calorie is required, whereas for most nutritionists and dietitians a less accurate ratio of 4.19 or even 4.2 kilojoules per kilocalorie will probably suffice.”

    1969? 2012? I believe the “gradual” requirement has been adequately met. Could we now go full bore? The experts in nutrition science have not pushed this agenda item very hard.


  4. Just to repeat something that was mentioned a couple of years ago:-
    The British Science Association doesn’t want to take a position on this matter.
    In a letter dated 17 March 2010 from the BSA’s Chief Executive, Sir Roland Jackson stated “I have to say this is an area in which the British Science Association does not take a position”.
    Way back in 1972 The Royal Society recommended doing away with the Calorie/calorie/kilocalorie; now four decades later the British Science Association doesn’t support this.
    The current President of the BSA is Professor Dame Jocelyn Bell Burnell FRS, FRSE for details see:

    I wonder if she supports this position, and is she happy with the UK’s failure to complete metrication?


  5. I don’t think the Government has published a final report following this consultation, however there are updates:
    1. Posted 9 November 2012
    – there was a letter sent to interested parties on 5 Nov. 2012

    Click to access 2012-11-05-Letter-to-interested-parties-FoP-update.pdf

    2. another update following a meeting held on 14 December 2012
    Published: 21 December, 2012
    it includes slides:
    – a summary of the British Retail Consortium led work on format and presentation

    Click to access BRC.pdf

    – details of the Department of Health/Oxford University modelling work on thresholds

    Click to access DH.pdf

    – research by Sainsbury’s on colour coding of energy

    Click to access Sainsburys.pdf

    And another letter –

    Click to access meeting-on-the-Front-of-Pack-labelling.pdf

    It includes:
    “In the New Year, DH will also be seeking to understand key stakeholders’ final positions on front of pack labelling [… … ] with the aim, if possible, of making a Recommendation in early spring. ”

    Am I correct that all this (above) is to try and get a voluntary code for Front of Pack labelling, and there will be no legislation to ensure the energy unit shown on the FoP will be kJ?


  6. Re: Mary’s comments above; BSA announcement 8 Jan 2013

    Will the new chief executive of the British Science Association Imran Khan have a different view to the departing CE Sir Roland Jackson?

    The BSA President, Professor Dame Jocelyn Bell Burnell said: “I am delighted that Imran Khan has accepted the role of chief executive of the British Science Association. His commitment to science and to dialogue about science is paramount. It is a time of change and I look forward to working with him in his new role” Link for more info:

    What is the BSA and The Royal Society doing to encourage the Government to complete metrication without further delay?


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