Extended fast and blood work

#1

I am scheduled to have blood work done the end of this week. Should I do a 3-4 day fast before, or just the usual overnight (12 hrs.)?

(Michelle) #2

I’m curious about this as well. Our yearly blood work is the end of August and I’d like to plan my fast. Of course 12 hour fast is required, but I’d be curious to see blood work after EF.

(LeeAnn Brooks) #3

I believe the recommendation is to just do the 12. Extended fasting can throw off the results.

#4

@oukid Yes, EF will throw off the results. Last time I had bloodwork done I happened to be on the final morning of a 5-day fast. My LDL was much higher than usual and of course my sugar was low (I think it was in the upper 50s). I think that’s typical for both LDL and blood glucose, so if the results will matter to anyone other than you, you should probably do a normal overnight fast (and no more) before the test.
For more details on how fasting affects cholesterol results, look at Dave Feldman’s site. He’s shown that most folks show a drop in cholesterol if they eat plenty of fats in the day (days?) before a blood test, but I don’t remember the details.

#5

Thanks you Anniegirl9 & Madeleine. Will definitely check out Dave Feldman’s site.

(Todd Gamel) #6

I agree with Anniegirl19, you want to get the most accurate lab work possible, and an extended fast prior to blood work can schew your numbers and give your false readings.

(Victoria Mc Coy) #7

Anybody know if labs other than cholesterol can be skewed by an EF prior? I just got results back (blood drawn morning of 3rd day of EF) that shows my fasting insulin going UP(!) from previous labs. April = 11; June = 17. How? Lots of fasting, strict Keto with IF on eating days. I am losing weight, but lowering my insulin is a goal too. Any science-y people who may have insights? @brownfat @richard @carl @OldDoug @devhammer?

#8

Hmm… that’s annoying! I don’t have any ideas for you (sorry) but am following this because I’m curious what feedback you get.

(Alec) #9

Madeleine is right, Dave is the go to person on this. He knows more about it than probably anyone else on the planet.

(Todd Allen) #10

Victoria, your increased insulin result while deeply fasted seems quite unexpected to me. My first thought is what other differences were there between the two tests? Were they performed by the same lab? Different labs can use different assay methods with different reference ranges making it hard to compare results. Were the blood draws performed at the same time of day? Circadian rhythm might have an impact, for example some of us have a very pronounced dawn effect with a marked increase in blood sugar early in the morning due to a rise in stress hormones. And higher blood sugar likely leads to higher insulin. Poor sleep can greatly aggravate blood sugar swings and probably insulin response too and when fasting I often experience impacts on my sleep. Many other forms of stress (mental, physical, injury, illness, etc.) could also lead to swings in stress hormones, blood sugar and insulin as well.

(G. Andrew Duthie) #11

IIRC, @richard has mentioned that insulin is pulsatile in nature, so a single test may not provide a perfect picture, because you may hit a high point just when the blood draw is done.

So I would not panic about it, personally.

(Doug) #12

Victoria, good comments above - it can fluctuate somewhat. Still, going from 11 to 17 is a big enough change, and in the unexpected direction, that it’s mighty confounding to me. I’d say get at least one more test in the future. There would be a larger pattern, then, and more evidence if your level actually did go up, or if the 17 was just an outlier, and/or a bad/skewed test result.

This kind of thing makes me want to beat my head against a wall - all the more reason for “keeping calm…” I guess. :slightly_smiling_face:

(Victoria Mc Coy) #13

Different labs, Todd, so that could be a factor. Roughly same time of day. And definitely a more stressful time (re-org at work) on the second draw. Thanks for your thinking on this.

(Victoria Mc Coy) #14

Yep. At least my weight loss hasn’t stalled, but I was expecting any change in insulin to be down, so… I’m going with the new lab, increased stress + pulsatile hormone factor. Really appreciate your thoughts on this. Keeping calm; ketoing and fasting on.