Losing weight from running?

Sometimes it takes quite a while for something to really sink in to my tiny brain!!! And sometimes I have to consider the very outside extremes of an argument to be able to understand it completely.

So - considering the "burning fat zone" argument. It makes complete sense to me that our human energy comes from two sources - our body fat and the sugars (glycogen) in our blood. But - how, when , where and why??? I read somewhere today, that when we are at our most inactive - when we are sleeping - that our bodies almost solely use fat to provide basal energy, almost no blood sugars at all - that is why we don't feel tired or lacking energy while sleeping!! :) - but during the last bit of a 5K race, most of our energy is being provided almost solely by blood sugars and not fat !! That is why we feel exhausted at the end of hard 5K!!

So - at what stage of our lives do our bodies use mostly fat as a source of energy - and that is when we have a slightly elevated heart rate , more than when we are resting and less than when we are exercising strenuously . So - if we REALLY want to lose as much fat as we can when exercising, we must exercise at quite low heart rates - elevated just a little more than we walk briskly. Personally , I find it difficult to run and keep my heart rate low over a period of time - so this morning I ran/walked 10Klm at only a 30 second/30 second ratio of running to walking. This is VERY easy!! My average HR turned out to be only 116 over the period involved - 1 hour and 20 minutes. At the end, I felt that my body had had a good workout over that time - but I was very far from being "exhausted" which suggests that I could have gone on for longer. I'm going to keep on doing this at least once per week - and stretch the time out a little more. I seem to have reached a plateau as far as weight loss is concerned - hoping that this will kick it into gear again!! :)

8 Replies

  • That's why they say that the long slow runs are best for weight loss! I seem to have reached a plateau too and need to make sure I don't do too much comfort eating during the winter. ..

  • On the whole the only thing that matters is calories. There are tiny differences between fat, protein and carbs, but they aren't worth considering if you aren't stick thin anyway.

    If you deplete glycogen on a run, it'll be replaced fairly rapidly when you eat. If you use a bit of fat when you run, when you next eat, the calories that would have gone into replacing glycogen go to fat instead. So the best weight loss runs are those that use the most calories.

    HIIT and weightlifting (both anaerobic exercises) are very good at using calories, but there's nothing like a long run to add up the numbers.

    I put a bit of weight back on during my last holiday and I'm having real problems losing it again. Too much comfort (and Christmas) eating.

  • I found that mixing it up over the week helps, and then resting at the weekend. Mon/Wed/Fri I do a 30 minute treadmill run at 10.5km so its 5Km in about 28 mins (580-600 cals). Then follow that with 20 mins circuit (290-310 cals) and 20 mins swimming (160-180 cals).

    Tuesdays is SPIN class (50 mins 700-730 cals), and Thursday is Body Balance (50mins 330-350 cals) for flexibility.

    Saturday and Sunday is couch potato time (or time to relax with the family).

    While running on its own was great to start with (and running outdoors was wonderful) your body gets too comfortable so you have to start looking at what your doing on the other days that you don't run and help that along. Then the shift of weight will change, and your boredom level will also.

    For winter this year I have joined a gym so that I can continue to run without getting wet or blown away in the wind. Its also helping my pacing which is great.

  • As I understand it, which may be vastly oversimplified, your fat provides "slow" energy, your sugar/glycogen provides "fast" energy and certain cellular stores (ATP & such things) provide "burst" energy. The ATP stores are so small that we can ignore them for any kind of cardio work. There is a maximum rate at which cells can use the "slow" energy from fat. After that, the balance has to be made up from the faster stores, primarily sugar/glycogen.

    When you are sleeping, your energy requirement is low and can be provided entirely from fat. You thus burn all fat, but only at a very low rate, so you don't get thin by sleeping unless you hibernate and don't eat.

    When you operate at low levels of exertion (walking, slow running etc), your energy requirement approaches the maximum that can be provided from fat. You have effectively limitless stores of fat and so you can walk all day without a snack if you stay within this level.

    Once you get towards the top end of the rate of energy that fat can provide, you start to have to dip into other forms. These forms are faster but their supplies are more easily exhausted. So, as you run faster, you reach a point where you run out of sugar. At that time, you are forced to slow to your "fat burning" energy rate or to use emergency measures (protein can be converted to sugar, for example, but it's very inefficient and you don't really want to be burning your muscles if you can help it). The more glycogen you can store or the faster you can derive energy from fat, the longer you can go before you hit this point.

    The ideal rate for fat loss is fast enough to be burning fat at your highest level but slow enough that you can keep it up for a long period without running out of sugar. Ideally, this means that you work as hard as you can sustain for the period of your workout, but towards the top end, you are only increasing your fat burning very slightly because most of the extra energy is coming from sugars.

    There is also the effect of exercise on post-exercise energy consumption. If you do HIIT, for example, you will rapidly deplete your glycogen because in the "working" periods you are blasting so hard that only sugar can provide the energy. This will tend to mean that your muscles will mop up any sugars from your blood for some time afterwards to restore their stores, which will help to stop you replacing the fat that you used. You may use less, but it stays off. Similarly, more muscle means a higher rate of "resting" fat usage, so as your muscle increases your body fat % tends to come down.

    All in all, it's ridiculously complex, but a combination of long slow runs, HIIT and muscle-building exercise should be the best way to burn fat and keep it off. I think.


  • -Yes - that is also basically my understanding - and you have stated it very well! :)

    Now that I have a "good" HRM and can more easily and more comprehensively look at my HR's during a run, I can see that I have been running too hard, with HR's way too high on average. We should do some runs at these levels of exertion - but not every one!!! :)

  • I'm coming to the same conclusion, hence after Sunday's 10km I am entering a bit of a smart training period before I go back to HM training I think. The one thing I have noticed and read up on is, as I understand after a very taxing run that has depleted your glycogen stores the body seems to replace it. It does this by using liquids to take the stores back to the muscles. This is why after a long hard run I have anything up to 1 - 1.5lb weight gain that's goes as the muscles are restored and the water is no longer needed. That's why it's so important to hydrate properly after a long run. The thing I'm not sure about is where this fits in with weight loss? As I would personally like to lose some weight but find it so difficult on thyroid replacement tablets and being a middle aged woman. Trying to read around the subject it seems to be your a serious runner and don't need to lose weight or your a dieter trying to run. The information for the people in the middle is a bit sparse.

  • I guess that it really does boil down to a couple of things - firstly calories in versus calories out :) -- but also this concept of trying to exercise in such a manner that the calories out come largely from fat stores. Of course, if the calories in exceeds calories out , then fat will be layed down regardless - however, if not, then it seems important to exercise in such a way that fat is consumed while exercising - as blood sugars are very readily and quickly replaced after a run ( hence little fat lost then)

    This at least makes "sense" to me - as opposed to the varying new and conflicting "studies" that we read almost every day

    It also involves time -- I am certain that if we went on a 100 mile walk , we will have lost weight at the end of that ( provided we don't munch on chocolate bars along the way!! :) )

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