Monday, 28 May 2012

Negative Calorie Food: Science Myths and Legends

Celery Cupcakes: A dieters dream?
A popular diet belief is that there are some amazing diet wonderfoods that contain negative calories, like celery. So if you eat lots of them, you will burn extra calories; without even lifting a finger.

The theory goes, negative calorie foods contain fewer calories than they take to digest. Celery is a reported 'negative calorie food'. If one lump (this is a hypothetical example) contains 6 calories, but it takes 10 calories to digest then the body uses 4 calories and does not gain any.

I had some faith in the principal of this idea, it seemed to make sense in my head. Maybe I had just turned my skeptical inquisitive brain off, or maybe, a part of me just wanted to accept that it might be a possibility..
A quick google search revealed a host of information, news articles and blog posts on this subject. Dr Stu posted a blog post summarising some of the literature about negative calorie foods very recently.

Sadly, but predictably, I discovered, there are no scientific studies to support this 'fact', but there is an awful lot of opinion flying around... and here's why it is incredibly difficult to prove or disprove if the statement is true or not:

  • How do you measure how many calories it takes to just digest something? The body is always burning calories, so  how do you measure the number of calories used only in digesting one item of food?
Difficult, there is no 'real' answer to this question.

General consensus is that 10% of your daily calorie output is used in digestion.. This is interpreted to mean that out of a recommended 2000 calories per day for a human lady,  200 calories per day that are used for digestion.

The only way to put any kind of measurement to the energy used during digestion of one meal/food stuff is by measuring 'diet induced thermogenesis' (DIT) which is an increase in energy expenditure above basal fasting level, divided by the energy content of the food ingested (Westerterp et al 2004).

And this is measured, as stated in Dr Stu's blog post, by using a whole body calorimeter (a respiration chamber). More (very interesting) information about how whole body calorimeters work and what they measure here.

But how much of that is used to digest one item, like celery? Do some items of food require more 'digestive energy' as they contain 'tougher' substances (like fibre in celery)?

No-one has tested people eating celery or any other reportedly negative calorie foods specifically, however, from other studies it is concluded that; Protein rich foods, like dairy and meat cause an increase in DIT,  fatty foods cause a very small increase in DIT, and carbs lie in the middle between the two (Mikkelsen et al 2000),. So, proteins use more energy, carbs are in the middle and fatty foods use little energy to digest.

Interesting side observation here, the Westerterp review,  found that when food was consumed with alcohol, this increased DIT. So, alcohol seems to increase the amount of energy it takes to digest something. The relationship between alcohol intake and weight is not clear, a positive correlation between moderate alcohol intake and activity levels has been found (US population) however, as you can probably guess it has been found that, alcoholics exercise less, but also have a lower body weightA more recent and detailed study of 37,000 people, investigated the amount and frequency of drinking alcohol (they did correct for levels of activity, but some information was missing) determined that the people that drank alcohol the least (but frequently) had lower BMI values than those that drink more, less frequently.

I always (maybe presumed in my head) as alcohol is such an incredibly high energy source, (second only to fat in terms of energy density) that there was a link between alcohol and obesity.. but as with most presumptions,  it doesn't seem that clear.

Back to the original question!

Celery contains mostly water and fibre, and Dr Stu's blog explains, although fibre alone hasn't been tested, adding fibre to a meal reduces the DIT.

This means that actually, less energy is used to burn off the calories in the meal that contains fibre. Which goes against the view that low calorie foods take more energy to burn than they contain. This doesn't absolutely answer the question of 'how many calories it takes to digest different food stuffs', but at the moment, it seems to be the closest answer we have

This leads us swiftly on to the next question...
  • How do you measure exactly how many calories the body takes from something? The celery might contain 6 calories, but do you gain all the calories?
Difficult again... View from Susan Jebb from the Medical Research Council's Unit of Human Nutrition Research in Cambridge in response to this question on The Naked Scientists website -

'Not all of the calories that are actually in a food will be absorbed, digested and available for the body to use.  What happens is that the calories which are in food, which will be released if we were just to burn it, as we might do in the bomb calorimeter in the laboratory, those calories cannot all be absorbed by the body.  Some will be lost in the faeces and the remainder will be digested.  About, perhaps, 10% of the total calories we consume might actually appear at the other end of the gut.  Once calories have been absorbed, again, they're not all fully available.  Some will be lost in urine for example.  The final loss of calories happens because some of the energy is fermented by the bacteria in the gut and so, it’s not available to humans.  It’s actually burned off by the bacteria that are living inside us.  And so, the consequence of all of that is that not all the calories that are actually in the food will be available for the body to use.  But in fact, the losses are proportionately quite small.  The calories that you see written on the back of a food pack have already had all of these adjustments made for the amount that will be digested and absorbed.  And so, the calories you see on the packet is actually not the total calories in that food.  It’s the so-called metabolisable energy, the amount of energy which is going to be available to the body.'

So, although celery might lower the DIT, you might not get all of the calories from the celery anyway.
  • How long does it take to chew something, and how on earth do you work out how many calories it uses?
A comment published in the New England Journal of Medicine, suggests that, on average 11 calories per hour are used to chew chewing gum (unspecified number of participants). This value is an average and extrapolated from measurements of 12 minutes of chewing. Unless you chew your food like a cow, for hours on end, the calories you burn chewing celery are going to be pretty insignificant (1-2)?

So, due to lack of evidence, I would summarise that we do not have a conclusion as to if negative foods do exist or not. The DIT studies suggests food high in fibre does not take increased energy to digest and can lower the energy used to digest other foodstuffs, however, as the calorific content of celery is pretty low anyway, if eaten alone, fewer calories could be taken by the body than are used in eating it.

One thing is for sure unfortunately, if you are dieting, you are going to get fewer calories from a stick of celery than a slice of cake.

... as always, please share any extra information below!

I created this blog post after spotting a brief exchange on Twitter, between @tkingdoll and @noodlemaz, about negative calorie foods, like celery that reportedly contain fewer calories than they take to digest.


Westerterp KR: Diet induced thermogenesis. Nutr Metab (Lond) 2004, 1:5.

Mikkelsen PB, Toubro S, and Astrup A. Effect of fat-reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein, and carbohydrate. Am J Clin Nutr 2000 72: 5 1135-1141

Levine J, Baukol P, Pavlidis I. “The energy expended in chewing gum.” New Engl J Med. 1999 Dec 30; 341(27): 2100.

Friday, 18 May 2012

Happy Scientists

It's Friday and although I will be working over the weekend, I am feeling pretty cheerful. Lab life can get you down sometimes, a never ending stream of failed experiments, things to do, late nights, early mornings and a lack of appreciation. Personality clashes, politics and unwanted work are themes from any work life.

But, sometimes, labs can be the most fun place to be, a source of comedy, fun and practical jokes. 

Here are some things that have made me SMILE and kept me HAPPY over the past 2.5 years. The people you work with can keep you going.  Please share your sad times and good times (practical joke tales encouraged) and keep laughing.

When it all goes horribly wrong (does it get any worse than boiling western blots with students?!).......

Someone might give you a special gift

Look away!

You might win a prize

Supervisors can make or break you....

Someone always has cake

You never know when your desk might get covered in balloons

The badge everyone wants...

Tuesday, 15 May 2012

Making Lab Life Easier With Technology

Working in a laboratory can be stressful, and cause tension (see my post about lab post-it notes and the radio). Can new technologies help make life easier, by saving time and enabling easy sharing of work? Or is sticking with old-fashioned paper methods better? (I have already posted about how I like the idea of e-lab books)

I get really annoyed that labs are at the forefront of new discoveries, new science and THE FUTURE, but often work in an old-fashioned way with paper notes and old equipment (my computer is currently on its last legs, I am pretty sure it isn't going to survive 'the thesis').

In the lab I work in, we are pretty old-school. Order numbers and prices are found on a computer, written down on paper and then put back in a computer. Excel files and written lists are used to keep track of what comes in and where it is kept in the lab, but these are not available to update on a computer. But saying all this, in general, it seems to work well.. so why change it?

  • Time. Searching for things can take a lot of time - searches can be quickly done on a computer. Time can also be saved for writing papers and theses as all the information, if online can be accessed easily. Time that can be spent doing stuff can be wasted finding things.
  • Traceability. Paper can get lost, things logged in a database can be searched, so you can remember exactly what antibody you used 3 years later. If you have an e-lab book, maybe you can link directly to the antibody, reagents and ingredient lists from a book (again, time saving). Eventually, I also think that published papers should link back to original work (values and pictures), e-lab books would allow that to happen.
  • Sharing. Others can easily see if there is any of compound XYZ in the lab (and where it is)
  • Supervisors that don't work in the lab, can keep up to date with projects easily
BUT there are so many apps, gadgets and toys out there? How can you know what is good and what is a waste of time?

There is a big investment in time and energy when you start using a new device, app or database. Information has to be put in and people have to learn how to use it, so the benefits of it have to be good (or, it needs to be pretty) to encourage people to devote their time to it. It isn't until people actually use these things that you can judge (or read reviews) to see if they are any good or not.

I came across a system that seems to offer all the things above, LabGuru, at a conference a few weeks ago.

LabGuru offers a database for individuals, (for free) and/or labs. I had a play with the system at the conference and it seemed to cover all the questions I had. It allows you to input projects, experiments, equipment, log where you have stored things, create timetables for using equipment.. pretty much everything you do in a lab.

I'm organised, but I could be more organised and I think software like this might be useful. I have just over a month left in the lab, before I finish to start writing my thesis and I have promised myself I am going to plan out my time and experiments using LabGuru over the next few weeks and see how it goes. They do have an ipad app, that allows you to update experiments and projects as you do them, however, I am lacking an ipad so I do not know if I will be able to experience LabGuru's full potential.

Which leads me to another interesting question, I wasn't aware (as I am surrounded by ipad-less people) that people took ipads into the lab? Do you? How do you use it? Or do you just use it to play angry birds when waiting for an experiment?

I shall report back how I get on.... would be interested to know if others use apps or other methods to share information within a lab and keep organised?

(also, I have nothing to do with LabGuru, I am not being paid, or given stuff by them, I just genuinely think this)

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