Where do the calories go from...?

I was just thinking about this on my long run today and now it's bothering me!

I ran 12.5 miles which should in theory be around 1200 calories burnt. But where does your body take the calories from while you are running? In other words, where do they all disappear from?!



  • i think  mine definately  come from my backside as mine has at this stage has totally disapeared, infact im thinking of having implants,everywhere else looks normal except this area.image
  • Mine go from my brain.  I'm thick as mince after a long run image
  • (please note this is not guaranteed to be accurate)   i think it depends on how your run is, if your HR is low then you generally will burn fat, as it increases then you will start to burn glycogen which come from carbohydrades.

    i think i generally burn them from my upper body as my thighs are still the same size as when i started running...

  • Calories go from the wine left in the bottle , not the glass you are drinking now- tis very strange phenomenon {sp}
  • I think you may have it the wrong way around MD6. When you begin to run, you use up sugar in the form of Glucose which is present in your blood. The normal level is 90mg Glucose/100ml of blood. As you begin to run your muscle cells begin to respire more - using up Glucose to produce energy in the form of ATP - they will use up this Glucose.

    In the Pancreas, there are little groups of cells called Islets of Langerhan. These respond to changes in blood glucose. In the case of running, your blood glucose will fall too low. So the hormone Glucagon is released. This binds to Liver cells - Hepatocytes - and causes them to turn stored Glucose in the from of Glycogen into Glucose which then enters the blood stream. When this store of Glycogen is used up, then you start to burn fat (Lipids).

    Your body doesn't particuarly want to burn fat, it would much prefer Glucose as it is produces energy less efficiently. This can be measured by looking at the RQ value or Respiratory Quotient. This is calculated by:

    RQ = CO2 Produced / O2 Used Up

    Lipids have a value of about 0.7, carbs (ie glucose) have a value of 1. This means respiring lipids produces more CO2, which is not good as it affects blood pH and other bad things.

    Hope this is comprehensive, you guys just helped me revise for my A-level bio exam on thursday image Any more questions, throw em my way and I'll give them a bash.
  • Thanks ShleyBey, that's taken me back to my A level biology revision from 20-odd years ago!

  • But MD6 is correct that at lower levels of energy output fat is predominantly burnt. According to the diagram in Noakes the crossover point when carbohydrate usage overtakes fat is about 35% VO2max. That is of course until you have depleted all the available glycogen stores when you have to revert to fat anyway. The scientific reference quoted is Brooks, one of the papers he wrote is this one:


    although this paper seems to say 45% VO2 max is the turning point.

  • Ah thanks Joe, I didn't realise that. So that means it would be better to do, say, a 2hour run really slow at like 12min/mile, than a 20min run at 7min/mile? Sort of longer runs at a much lower heart rate would give better fat burning?

    Do you know why this is? I was under the impression Lipids were a much poorer substrate for respiration, so why would the body preferentially respire it? Anything to do with, that since it's at much lower heart rates it can be assumed not as much energy needs to be produced/CO2 production is less of a concern, so the body tries to conserve its Glycogen reserves? I had a browse through that link you posted, and it seemed to be saying Lipids were respiring till more energy was needed than they could provide and then more and more Glucose respiration took place, have I got that right?

  • Ah, so i am right but wrong at the same time??? I'm with betty79, it must go from the brain,  as after reading that my head is starting to hurt...image
  • You were absolutely right MD6, my bad.
  • Well there are two ways of looking at it, a slower run burns more fat calories but at the same time it burns fewer calories. I read that someone walking in the fat burning zone still burns fewer fat calories than someone running and fewer calories overall.

    Also when you run faster you take longer to recover and burn calories after you finish running. ]

    Fat burning zones are used a lot by gyms as a way of making scientific the fact that you shouldn't be out of breath or sweating so people feel like they are doing well.


  • SB

    The main thing I take from the science is that people are right when they say that if you want to get rid of excess fat you are better off going for a long walk than a run, as fat is what you will mainly burn at walking speeds. You would have to be running very slowly indeed to get down to this threshold pace. But you've raised a good point, and to quote from 'Better training for distance runners' by Peter Coe and David Martin

    1. carbohydrate is a less efficient form of stored energy than fat as fat has a higher proportion of C and H.

    2.  as intensity increases the lower proportion of stored O in fat becomes a liability thus favouring carbs

    3. fats are higher in energy per unit mass than carbs

    There is also some stuff about how much CO2 is produced by burning different fuels.

    These seem to be the main factors for starting with fat then crossing to carbs, according to this book anyway.

  • Joe Volcano wrote (see)

    The main thing I take from the science is that people are right when they say that if you want to get rid of excess fat you are better off going for a long walk than a run, as fat is what you will mainly burn at walking speeds.

    If that is true then you should  just stay in bed because then an even higher percentage of your calories burned will come from fat!

  • Ah ok, thanks Joe. So....

    Fat obviously is a larger molecule, therefore breaking it up will release more energy. It is therefore more efficient as more energy is released per unit. But, respiring fats produces more CO2. So when you're exercising, your cells are respiring more producing more CO2 anyway. So to correct this, your body starts respiring more glucose to reduce CO2 concentration in the blood?

    Sorry for all the questions Joe, but I'm off to medical school if I get the grades in the summer, so this sorta stuff is really interesting to me image
  • tricialitttricialitt ✭✭✭

    Part of the problem is the limited supplies of available carbohydrate, so once this has run out, you have to switch to fat, whatever the intensity- naturally, you are likely to be able to maintain continuous excercise for long enough to get into this zone, if you're going slowly!!!!- Someone else posted a different thread about a strange smell they give off post long- run- and I reckon this is due to fat metabolism kicking in, and Ketones being excreted as a by product.

    I think I read somewhere that on average this is after about 90minutes, but must vary from person to person

    Good luck with the exams SB- just be aware that there's quite a bit of "pseudo science" in running (and other sport) literature, so something presented as "gospel" in the running world may be deemed downright WRONG by conventional science (ie your exam marker!!!)

  • SB/tricialitt

    Yes there is a lot of pseudo-science on here but I certainly wouldn't put Noakes who is one of the world's foremost experts on the science of running  in that category, especially as every statement he gives is backed up with a reference to the latest scientific journals, one of which I cited. He is professor of exercise and sports science at Cape Town University and former president of the South African Sports Medicine Association.


    Martin, the other author I cited, is professor of health sciences at George State University.

    One thing about Noakes in particular though is that he quotes a lot of leading edge science, some of which is contradictory. So in that respect you could argue that despite his knowledge his book is not necessarily conventional science.

    Personally I am not an expert on human biology and I don't want to put SB off his exam revision by misquoting something.I skipped the CO2 bit as I didn't fully understand its significance. Stick to the recommended texts for your course and get a good result in the exams.

  • Ah - no offence - but I would NEVER take something I had read on t'internet and use it in an exam, let alone use it in preference to what was in my course. Even if it's right, it doesn't mean the exam board know that's it's right !!! image

    I was just interested in the topic, Human Biology is very interesting to me. It just so happened I had literally just finished revising respiration and metabolic processes, so I thought I'd chip in.
  • I have an interesting conundrum - whenever I do my long runs I seem to put ON weight, only to see it generally come off a day or so later....is there a biological theory for this, or is it just that I probably overeat afterwards!!!! image

  • This whole walking vs running thing for fat loss is a bit of a non-arguement in my book.

    Walking, like any moderate exercise burns fat. It true that it burns a higher percentage of 'fat calories' than running, but its all relative. It is just more economical a fat burner than running, although running will burn more calories overall and keeps your metabolism high and burning calories for several hours afterwards.

    But running gives many more added benefits as we all know.

    Sprinting is the king though. It burns fat even more economically than walking and doesn't have the catabolic (muscle burning) effect that running does. Also, like weight lifting, it elevates your metabolism to such a degree that you are still burning more calories than usual up to 2 days after your session (depending on the intensity of your workout).
  • I put a couple of punds on after a long run and then it goes as well - is that water retention repairing the muscle tears?  Just interested
  • Dr.DanDr.Dan ✭✭✭

    For weight loss, what matters is how much energy you burn and not which stores it comes from during the exercise period itself. Whether it comes from carb stores or fat stores isn't important ... if you use your fat stores and leave your carb stores intact, then you'll simply top up the fat stores from ingested carbs/fat over the next few days. If you use your carb stores rather than your fat stores, then you'll use more ingested carbs to directly top up those stores and convert less into fat. It's all the same in the end.

    But running slowly and  "in the fat burning zone" can teach your body to preferentially burn a higher % of fat over carbs ... which saves glycogen stores and increases endurance and recovery.

Sign In or Register to comment.