Joules on the menu, please

The very worthy proposal of the Food Standards Agency (FSA) that menus should state energy values is undermined by its failure to use proper measurement units.  UKMA has responded by advocating joules rather than so-called “calories” (whatever they may be).

Consultation closes today on the FSA’s proposal that restaurants (including fast food bars) should state the energy value of the food on their menus.  The purpose of this proposal would be to enable customers to relate their energy intake to their daily energy requirement – an important factor in leading a healthy lifestyle.  (In principle, if your energy intake exceeds your energy use you will gain weight – and vice versa.)

The catering industry has been wary of this proposal (not least because many fast food outlets rely on people eating unhealthily!) and the FSA’s proposal is for a voluntary rather than a statutory scheme.  It would be difficult if not impossible to enforce against the thousands of individual fish and chip shops and Chinese or Indian takeaways, so it is mainly targeted at the chains of fast food restaurants that populate every High Street, shopping mall, and motorway service station.

In its submission to the FSA, UKMA has not commented in detail on the (obviously laudable) principle of including energy values on menus, but has recommended that any scheme that is agreed with the industry should use proper measurement units that are compatible with those used in nutritional science.  In particular it has advocated the use of the joule (J) as the primary (or preferably the only) measurement unit rather than the obsolete and unsatisfactory “calorie” – or “kilocalorie” – or “Calorie”.

Unfortunately, the FSA consultation paper set a very poor example by equating the physical concept of “energy” with the misused word “calorie” – for example, writing “calorie intake” rather than “energy intake”.   This is in direct contradiction to the recommendation of the Royal Society – as long ago as 1972 – that “calories” should be discontinued – including in the media.

We give below an extract from UKMA’s submission (text in blue):

“The use of the kilojoule (kJ) vs. the use of the calorie (cal), Calorie (Cal), and kilocalorie (kcal)

We applaud the principle of giving consumers the ability to make purchasing decisions based on the energy content in food. However the consultation document’s proposed continued use of obsolete measurement units presents several issues:

The “calorie” is often confused with, or used in equivalence to, the “kilocalorie”.

A convention is sometimes applied which attempts to avoid the inevitable misunderstanding that this causes. This involves the use of a capital letter ‘C’ when “calories” are to read as “kilocalories”, such that:

1000 calories = 1 kilocalorie = 1 Calorie

Indeed, the consultation document itself is a good illustration of this issue as it uses the word “calorie” erroneously in several instances where the word “kilocalorie” or “Calorie” is intended. e.g. Annex H, 7.3 (text in green):

“Note: “kcal” is used in these statements but “calories” should be substituted if        “calories” are declared as the energy information at point of choice.”

The consultation document acknowledges that …

“36. To aid consumer understanding and contribute to consistency of labelling only one        form of expression (either kcal or calories) should be used in an outlet. “

However, this stipulation will not prevent inconsistency of labelling across different establishments.

In their 1972 report on nutritional sciences, the Royal Society identified the problem of the continued use of calories to describe energy content of food. Its conclusions remain valid nearly 40 years later (text in dark red):

“We are very much aware of the problems that arise because as a result of 30 years of education the public has an awareness of the term ‘calorie’. We cannot see any easy solution to the problem of substituting the concept that man has a requirement for the energy-yielding constituents derived from food, and this is measured in joules, …”

“We recommend that editors of journals should not allow the use of the word ‘calorie’ and list below some obvious alternatives :

calorie intake                                  energy intake

calorie requirement                         energy requirement …”

The Units Of Measurements Regulations, which implements Directive 80/181/EEC, requires that energy should be measured using the SI derived unit, the joule. The fact that the calorie is not an SI unit, and is not listed in the Directive, means that calories can only be authorised for use as supplementary indications, and should not appear more prominently than the primary measurement, in joules (J) or kilojoules (kJ).

Many packaged foods are already labelled in kilojoules (kJ).

Progressive countries such as Australia, have already adopted the kilojoule as the primary unit of energy to indicate energy content of food.


A single unit, the joule, used for all purposes regarding energy (not just food), will both benefit the consumer, and increase the general public’s understanding of the concept of energy in general.

It is for these reasons that we strongly recommend that the opportunity that this consultation presents should be taken to begin the phasing out of the obsolete unit “calorie” in favour of the “joule” (which incidentally is named after the British scientist, James Prescott Joule).




Report of the Subcommittee on Metrication of the British National Committee for Nutritional Science

Proc Nutr Soc. 1972 Sep;31(2):239-47.

[UKMA submission ends]

Further comment

Some have argued that the general public is familiar with “calories”, and to replace them with joules would be confusing and would reduce the effectiveness of the proposal to include energy values on menus.  This is to patronise the general public and underestimate their intelligence.  It is not difficult, for example,  to remember that the average daily energy requirement of an adult male is approximately 10 megajoules (10 MJ) and hence to relate that to a meal of, say, 4 MJ, or a bottle of wine at 2 MJ.  Moreover, to continue the dumbing down of energy information by using non-scientific units helps to maintain the gulf between the educated scientific community and people who have to rely on the popular media for their information.

The question of how best to measure energy (and also power) is a theme to which we shall return in a forthcoming article.

Technical footnote:

What the above Royal Society quotation does not explain is the reason why the joule is a better unit than the “calorie” (in all its variations).  This is because, whereas the value of the “calorie” is determined experimentally (by heating water), the joule is defined in terms of other SI units.  Thus, since energy = force x distance, a joule is a newton times a metre, or in other words the quantity of energy needed to accelerate a mass of one kilogram at a rate of one metre per second squared over a distance of one metre.  Similarly, a joule can be directly related to the watt (1 W = 1 J/s).  By contrast  the “calorie” is simply an unrelated anomaly that – unfortunately – has gained some currency in the popular media and some parts of the weight-watching industry.  It should be phased out as soon as possible, and the FSA should be helping in this – rather than prolonging its life.

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15 Responses to Joules on the menu, please

  1. philh says:

    'Weight watchers' have a point system which combines a measure of the amount of saturated fat with energy intake. It actually works out that a point is about 300 kJ (actually its 70 kcal but I round it to 300 kJ) or 4 g of saturated fat. It works by reckoning both e.g. a meal with energy content of 1.2 MJ and 8 g of saturated fat would be about 6 points.

    The daily allowance during a fat reducing diet varies with body weight but it's about 30 at 100 kg. The WW regime is aimed at 10% loss in body mass over 8 weeks.

    It's just a pity they don't seem to recognise how much easier all this is in SI units!

  2. michael worstall says:

    Great submission . Concur absolutely with the point being made. I have suggested this approach many times to the FSA and never been given the courtesy of a reply let alone actioning this simple idea.

    Recommend that the technical footnote be amended to show the correct unit symbols. As ISO 1000 points out unit symbols are always printed in upright font even if the surrounding text is being printed in italic. [Quite right. We have amended it accordingly - Editor]

  3. Russell Partridge says:

    An excellent and coherent disposition in favour of using the joule, again indicating the logical interconnectedness of the SI measurement

  4. David Brown says:

    People often claim that they want to stick with imperial measures because they “understand” them. But calories are a great example of a unit that people claim to understand, when in fact they do not. Advertisers prey on our lack of understanding to promote “calories” as being bad (hence low-calorie foods from the weight-loss industry), and “energy” as being good (for example energy drinks). How many consumers really appreciate that calories and energy are the same thing? Surely with soaring obesity rates there is a need for a public education campaign. That cannot be undertaken seriously without retiring the woefully outdated energy unit “calorie” and replacing it with the international standard joule.

  5. philh says:

    The apparent refusal by the FSA to replace the calorie with joule may be motivated by the same thinking as the department of health resisting the centilitre in place of the "unit" of alcohol.
    Government departments tend to draw upon the techiques of advertising for publicity campaigns. They are more used to manipulating public perception rather than informing it.
    The calorie and "unit" are buzz words used to connect with an otherwise apathetic audience who lack curiosity or interest in a proper understanding.
    The aims of such campaigns may be laudable but it raises the question as to whether the ends justify the means.
    A weak understanding of basic science must underpin a poor understanding of basic nutrition. Like the wider issue of a single system of measurement, it isn't the only factor but it should at least be recognised as a key enabler.

  6. 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 he states "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 almost four decades later the British Science Association doesn’t support this.

    Considering this position, does the BSA support the speedy completion of metrication in the UK?

  7. A says:

    Has the BSA given any reason for not having a position on this? Surely it would work in their favour somehow if they supported this proposal. Don't say that this is another ignorant refusal against progress. Seems to be a British trait which needs to be stopped.

  8. The British Science Association (BSA); no reason was given.

    In the letter dated 17 March, Sir Roland Jackson the Chief Executive of the BSA did go on to express his personal views about this matter.

  9. Use joules says:

    It's now the responsibility of health departments to 'Shed Calories'.
    The statement below is from the Food Standards Agency's website
    "[Thursday 30 September 2010]
    Responsibility for nutrition policy will transfer tomorrow (1 October) from the Food Standards Agency to the Department of Health in England and to the Welsh Assembly Government in Wales.
    These changes will mean that the health departments in these countries will be responsible for:
    *nutritional labelling
    *nutrition and health claims, dietetic food and food supplements
    *calorie information in catering establishments
    *reformulation to reduce salt, saturated fat and sugar levels in food and *reducing portion size (including in catering)
    *nutrition advice, surveys and nutrition research
    The Department of Health will also be responsible for supporting the work of the Scientific Advisory Committee on Nutrition (SACN).
    In England, the transfer to Defra of food labelling and food composition policy (where not related to nutrition or food safety) has already taken place.
    The devolved administrations are considering whether they want to make any other alterations to their current arrangements for food policy."

  10. Ezra Steinberg says:

    So, they mention England and Wales, but who now has responsibility for food labeling in Scotland and Northern Ireland?

    Let's hope this is an opportunity for the organizations newly responsible for nutritional labeling to be persuaded to adopt "joules" instead of "calories" or "kilocalories".

  11. Ken Cooper says:

    "Who now has responsibility for food labeling in Scotland and Northern Ireland?"

    Food labelling policy in Scotland & Northern Ireland is currently still the responsibility of the FSA.

    Unfortunately, I cannot see the recent changes in England & Wales having even the slightest effect on the use of "calories" in food labelling

  12. Philip says:

    19 February 2011
    Today's Daily Mail has an article - Health Secretary Andrew Lansley, says Calories on menus could come into effect as early as September.

    "Mr Lansley set up the Food Network, a collection of food industry leaders and consumer bodies, to draw up voluntary measures to improve the health of the nation under a so-called ‘responsibility deal’."

    The Department of Health has NOT had a public consultation on this.

  13. Submitted by Philip [Wellcome Trust: Killing off the calorie] says:

    Readers will be interested in the following online article: Killing off the calorie, Jennifer Trent Staves chomps through the history of the calorie.

  14. Philip says:

    The British Nutrition Foundation's Education News (issue 61, March 2012) has an excellent poster, it shows plates of different meals and the energy values are in kJ.
    The word calories does not appear. The values in kcal are shown as a supplementary unit. I have an paper copy of the poster. The following link may assist, however I don't see an online version of this poster called Small change, big difference:-

  15. Philip says:

    Use joules ...
    The editor of the Wellcome Trust’s education resource the ‘Big Picture’ has sadly failed to use the SI unit for energy.
    On page 3 of the latest issue, which is about plants, there are the following:
    “387 calories in 100 g table sugar”, and "77 calories in 100 g of potato”

    It’s disappointing that, in what is an excellent publication for schools and colleges, the editor has used ‘calories’; failing to give the energy values in SI units.


    [BigPicture Issue 24 Summer 2016 published by The Wellcome Trust,
    ISSN 1745-7777.
    Address: The Wellcome Trust, 215 Euston Road, London, NW1 2BE and]


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