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Glucose Tolerance Test

Discussion in 'Low-carb Diet Forum' started by New_Blood, Sep 7, 2018.

  1. New_Blood

    New_Blood Prediabetes · Newbie

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    Hi all,
    Just wanted to ask your advice about taking a GTT.

    First, a little background about me. Last May I had a blood test which came back with a HbA1c of 5.9% (41) which is prediabetic. This could have major implications for my job, so since then I've been reading this forum extensively trying to figure out the best way to manage this. For the last 4 months I've been:
    • Eating low carb
    • Intermittent fasting (2 x 24 hr fasts a week, plus skip breakfast every day)
    • Exercising 1 to 1.5 hrs a day
    • Checking blood sugars in the morning, as well as 1 and 2 hours after meals
    Generally when I get up first thing in the morning my BS is 4.5 - 5.5 but sometimes rise to 5.5 - 6.0 by mid morning (dawn effect??). After meals it's mostly under 6.0 at 1 and 2 hrs, which I guess just reflects the low carb meals I've been eating.

    Anyway, I now need to take a GTT for work and it would save me a lot of headaches if I can pass it first time. I've read that eating low carb can cause you to fail a GTT and that you should introduce some carbs back into your diet a few days before the test. Just wondering what kind of carbs and how much? I was thinking some slow carbs like oats or muesli, but not sure of how often and serving size.

    Other things I'm considering are:
    • Some light exercise a few hours prior to the test
    • Doing the test in the late afternoon, so no dawn effect
    • Had read that that small amounts of alcohol can suppress your liver releasing glucose, so maybe a glass of wine with breakfast (yay! ... finally a good reason to drink in the mornings :))
    I'll be taking the test next week, so any tips or advice would be greatly appreciated.

    Cheers
     
  2. kitedoc

    kitedoc Type 1 · Well-Known Member

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    If you plan to stay on a low carb diet long term why not stay with that before the GTT ?
    Who knows how long you would need to be back on a higher carb diet to influence the test results anyway?
    I have not heard of any job that would be threatened by being pre-diabetic?
    Sure there are some where a definite diabetes diagnosis could be a problem.
     
  3. sally and james

    sally and james Family member · Well-Known Member

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    The figure of 130g of carbs per day for at least three days before taking the test, come to mind. Probably read it on here at some point over the past few years. I'm not sure that the type of carbs are so important, but if you have a slow release, it possibly just takes a bit longer to build up the effect, an effect that may linger to the time of the actual test.
    Sally

    ..... and totally off topic, just realised that this will be my 1,000th post.
     
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  4. britishpub

    britishpub Type 2 · Well-Known Member

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    What job could be impacted by being Pre-diabetic or even T2D ?

    Anyway, I did an OGTT earlier this year and passed, without taking any particular steps beforehand. If you had an HbA1c of 41 previously, you are on the cusp so you may have been able to pass a GTT on the same day that blood was taken.

    General guidance for preparing for a GTT if you have been eating low carb is to eat a slightly higher amount (130g a day) in the 2 or 3 days running up to the test.

    If your fasting glucose test is above 6.1 but below 7 they will note it as Impaired fasting glycaemia which is pre-diabetes, so based on your recent testing it may not be an issue for you.
     
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  5. New_Blood

    New_Blood Prediabetes · Newbie

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    Thanks for the replies.
    Pilot.
    T2D would mean immediate grounding and a minimum couple of months off while they sort out whether your licence can be re-validated. Pre-diabetes, while not disqualifying, would make your yearly medical a lot more onerous (stress ECGs, multiple specialist reports etc). Apart from that, they may make it a condition on your licence that you take statins, which I'd really, really like to avoid.
     
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  6. Bluetit1802

    Bluetit1802 Type 2 (in remission!) · Guru

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    The guidelines are to eat 130g carbs in the 2 to 3 days before the test. No idea what sort of carbs. The test is a fasting one. I believe it is a 12 hour fast beforehand. The reason for the carbs is because on very low carb our pancreas has no need to produce a lot of insulin. Suddenly giving it a blast of 75g of pure glucose catches it unawares so there is a liklihood of failing the test.

    I can't see how on earth they can make it a licence condition that you take statins.

    Edit to add. Exercise on an empty stomach can cause your liver to dump glucose. Personally I would avoid it.
     
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  7. Indy51

    Indy51 Type 2 · Well-Known Member

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    This is the advice I have on file from Dr Michael Eades:

    Carbing up for OGTTs

    Following a low-carb diet makes one a little glucose intolerant, which is the reason that the instructions for a glucose tolerance test always include the admonition to eat plenty of carbs in the week before the test. Why? Because all the macronutrients–glucose, fat and protein–are broken down by enzymes during the metabolic process. And all the enzymes necessary for the metabolism of the various macronutrients are made on demand but not immediately.

    If you are on a high carbohydrate diet, then you will have plenty of enzymes on hand to deal with the carbohydrates you consume. If you switch to a low-carbohydrate diet, it takes a while to manufacture the enzymes in the quantities needed to deal with the extra fat and protein that your metabolic system hadn't been exposed to. This deficiency of protein/fat metabolizing enzymes is the reason people starting a low-carb diet become so easily fatigued–they've got plenty of enzymes on hand to break down carbs, they just don't have the carbs to metabolize. Once they produce the enzymes necessary to deal with the load of protein and fat, which takes a few days, they become low-carb adapted and no longer feel fatigued.

    Once people become low-carb adapted then the same thing happens if they go face down in the donuts. They don't have the enzymes on board to deal with the sudden influx of glucose, and, as a consequence, their blood sugar spikes higher than it would on a person eating the same amount of carbohydrate who is already carb adapted.
     
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  8. Brunneria

    Brunneria Other · Moderator
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    While i would go with the info @Indy provides, i think (in your situation) i would be tempted to do a trial run just to see what happens.
    Depending on the result, it will either set your mind at rest, or it will encourage you to ‘carb up’ as much as poss before the test.

    Basically a DIY glucose tolerance test is ever so easy.
    Instead of breakfast, quickly glug enough lucozade to provide you with 75g of glucose.
    Then sit around for the rest of the morning (no running about burning that glucose up), and monitor your blood glucose to see what happens.

    If you want to do a GTT properly, you can find all the precise specs with a google search, but my rough instructions above will give you a clear indication of what your work GTT holds in store. Then you can decide whether to stuff those carbs or not.

    (A word of caution: ‘carbing up’ doesn’t work for some people, including me. I have tried it, and saw no improvement in carb handling after 10 days. But i expect your carb handling capacity will be much better than mine, since you are not even Pre-D)

    Hope that helps.
     
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  9. DCUKMod

    DCUKMod I reversed my Type 2 · Moderator
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    It's interesting that they use an OGTT, as opposed to HbA1c these days, although I can see they're looking at spot checks, rather than loner term impacts.

    Does everyone have an OGTT? If I were to retrain as a pilot, would I have an OGTT annually?

    We have at least one commercial airline pilot member here, although he is T1, so the requirements would be very different.

    Are, or were you carrying any excess baggage around your midline? If you do, and you could manage to trim up, that can make a difference too.
     
  10. New_Blood

    New_Blood Prediabetes · Newbie

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    I've tested this quite a bit and in my case it's really unpredictable. Sometimes it rises by more than 1.0, other times it drops slightly. Whilst I wouldn't risk doing the test within a couple of hours of exercise, would I have a better test result if I exercised say 5 or 6 hrs beforehand?

    Everyone is tested for fasting glucose every 5 years (more often as you age). If you have a result over 5.5 you have to do a GTT. If that indicates you have IFG or worse, then you'll have to do a GTT yearly. If you are diagnosed with IGT or T2D you'll have to test your HbA1c several times a year.

    None at all, which is the really odd part. My BMI has dropped from about 25 to 23.5. At the moment my waist is around 82 cm.

    Great idea! I'm doing a 24 hr fast today (dinner to dinner) but will give this a go tomorrow and let you know how it goes.
     
    #10 New_Blood, Sep 7, 2018 at 9:39 PM
    Last edited: Sep 7, 2018
  11. New_Blood

    New_Blood Prediabetes · Newbie

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    Got up this morning and did the pretend OGTT. These were the results (readings every 30 mins):

    FBG 5.3
    12.0 10.6 8.0 5.6

    The spike at the start is a bit of a worry, but it seems I would have passed. In any case, I think I'll take the test in the afternoon because my BS is always lower then. Was also thinking about having a couple of shots of vinegar before the test as I had read somewhere (Jason Fung?) that this can blunt the spike.

    PS Thanks for all the replies so far. I do appreciate that my problems are pretty minor compared to others who post on this forum, and hope I haven't taken up too much bandwidth :)
     
  12. pollensa

    pollensa · Guest

    You seem to have it all in good perspective as I see it. Good informative post. It all seems based on individuals, and what one should or should not do, so much and many options out there from personal experience if of any help not a doctor,

    Mornings, Dawn Phen. I find when getting up I drink 4 glasses of water, have brisk 10min at 5.7klm on the tread, wait 15 mins and bingo, my levels by doing this are consistently normal. Thats not to say it works same for all.

    I also sip cider vinegar night before a test, sometimes a slurp of red wine, I see levels norm doing this also.

    Test times, I find late afternoon for myself personally is best.

    Exercise seems to work differently for individuals as I read, it can upt levels, for some it brings them down, I have taken a balance due to this and as within, before any test, I do only 10 mins brisk exercise walking, and have a lull of 15 mins before the test or even longer, and I dont have reaction of any higher results.

    Sorry not in position to know if introducing carbs will make any difference, I have not heard of this, interesting to note thank you for raising this area.

    Hope this helps, and good luck with your test.
     
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