Fasting before medical appointment: is 36-40 hours a mistake?

(BuckRimfire) #1

I have a routine annual wellness exam scheduled for Thursday morning. (Trying to break in a new doctor since my previous MD went on time-out for a couple of years to have kids.) I’m supposed to show up fasted for a standard lipid panel and metabolic panel blood draw.

We’re doing IF one or two days a week. So, the question is: if I fast on Wednesday and extend that into Thursday until after my appointment, is being fasted for somewhere between 36 and 40 hours at the time of the blood draw going to change the results in a way that will freak out the doc?

I’m a little curious, so I guess if I do that and the results are bizarre, I can always get a second blood draw after only 12-16 hours of fasting once the results of this come in.


12-14 hrs. is the sweet spot for fasting before a blood test. Lots of posts on here about that if you use the search function.

Why yon earth would you be going in for non essential medical visit at this time? Just because the dr. calls and says time for a yearly, you don’t have to do it now, while things are mostly still locked down or only limited opening hours? I told mine to call me 4th quarter and we would see how that goes.


I don’t know. I’ve read that 12 - 14 hours is ideal. More than that can throw cholesterol numbers off. Might depend on what you are testing for.


I wouldn’t, once you’re in full blown fast most your trigs will be artificially high, possibly REAL high.

(Bunny) #5

Here is an excerpt from a KetoWoman/Dr. Boz Podcast:

Jojo has a question. She would like your thoughts on her recent overall cholesterol being so high at 357. What other tests should she get done? This is her first blood work since starting keto in July. She knows it’s common for this to happen, ie the cholesterol going up, but the more advice she can get, the better.

Right? So why has cholesterol become this marker of worry for the world? And it is because it was linked to heart disease, except they didn’t do such a great job when they first discovered this at linking the two in a correct manner. What I first and foremost remind patients is, cholesterol is the carrier. This is what carries fat from one section to the next. When I put you on a diet that’s 85% fat, guess what? The carrier is going to get higher. The cholesterol is going to get higher. It is not the predictor of heart attacks. You can better predict a heart attack with the size of your waistline. If you put weight on in your tummy, that’s a better predictor of a heart attack than your cholesterol was. So that’s easy. You can do that one at home. Your morning fasting blood sugars, those are a better marker of a heart attack than cholesterol.

Other tests from your doctor? I would encourage every single person who wants to know if they have a risk of a heart attack to look at a calcium score. This is a very high speed, MRI that takes pictures of the coronary arteries. If you have a zero on your calcium score, it is a protector for the next 15 years that you will not have a heart attack. Way better than I can do with that cholesterol, which is going to change depending on what your diet has been for the better part of the previous six weeks before I checked the blood. When I look at a calcium score and it’s zero, I can have a lot of confidence that the inflammation going on in their body is still very low and not depositing calcium into those coronary arteries.

Other markers that are somewhere in between are a Highly Sensitive C Reactive Protein. I say that very specifically a Highly Sensitive C Reactive Protein. This is a marker of inflammation that is designed to specifically predict what the inside skin layer of blood vessels is. In America there’s this cartoon that would happen after school called The Magic School Bus and this teacher would teach you about science and things with the magic school bus. Her magic school bus could get really tiny and she’d drive down the arteries of a human body and teach about anatomy. So if you were driving down the artery and you looked around the skin layer that lines the tunnel, the Highly Sensitive C Reactive Protein helps me know is that inflamed? And that is a predictor of a heart attack. You’re starting to put cholesterol deposits in that layer. Guess what? It’s very inflamed and it’s going to do that even before your blood sugar is high. Before you have a change in your Hemoglobin A1C, which is a predictor of diabetes.

If I needed to know if you are going to have a heart attack and I needed to be the most confident, if I got to grab which one I would look at first, it would be a calcium score in your coronary arteries and I’d vote for a zero. If I don’t get to do that. You don’t need a doctor’s prescription to do that. If you look at any - in America anyway - if you look at any place in America, you can just call up the cardiology team and I think it’s like $25. It’s really cheap. So it’s a quick MRI. It’s a screen for calcium. And if your score is zero, congratulations. If it’s like 250, we’re talking about some significant risks. I have a patient over the last six months who it was like 2,500. So you talk about the question we started this with where they have heart failure, and boy that calcium score is…that’s a delicate equation. We need them carefully monitored by a physician as they make some changes. But instead of focusing on the cholesterol, I would look at those markers instead. …” Ask Dr. Boz Part 2

(BuckRimfire) #6

Yes, I’m planning to ask for a CAC, or if he balks at that a carotid ultrasound, which IIRC is the next best thing? I’m willing to pay for the CAC myself, since I’m pretty curious (even more so for my spousal critter, who’s going in next week).

I had an hsCRP at my last exam a year ago and it was 0.2, so I’m pretty happy with that. If they repeat it, that would be great.

(BuckRimfire) #7

I din’t realize trigs went up when fasting. Weird. I thought that measurement mostly came from conversion of dietary carbs to fat in the liver.

I have noticed that my blood sugar goes up when fasting after exercise, but I’ve forgotten what it does at the same time of day if I don’t exercise or if I exercise when not fasting, so that means nothing.

Anyway, I will aim to be around 12 hours fasted for the blood draw.

(Bob M) #8

All kinds of stuff changes. This shows going the “other way”, from fasting 4.5 days to eating a ton (of high fat, heavy on the saturated fat such as cups of cream) for the three days, but it shows what happens:

In CT, USA, I was able to find a CAC scan for $100. I had to pay myself (insurance would not cover it).

(Bob M) #9

Oh yeah, got a 0.4 for CRP in a later, more “normal” test. CRP changes quite a bit.


Yup, mine was pretty extreme but I went in once like 4-5 days fasted. My trigs are usually in the 30’s-40’s. They were 260 I think! Told them their test screwed up which of course they denied (it was a work health discount thing) ate for two day and went back to re-test, all normal again. They were like “Wow, it did mess up, nothing changes that much that fast!” Suckers! They know NOTHING!

(BuckRimfire) #11

Hah! See, pulling a stunt like that is right up my alley. But not this time…


14 hrs I have found to be a sweet spot and yes it does change if longer as your body if moving from a conservative mode of autophagy in to progress mode. I pressured my Cardiologist for a CAC, especially after having a full run of test(carotid artery test, leg vascular test, stress test, heart ultrasound test , culminating in heart catheter) all of which really did not find anything overly exciting! He finally agreed, wrote the script was not covered by insurance but needed a script in my area cost of $250! Was worth it as I found out roughly my LAD was 260 ish of my 320 ish score! This is the widow maker spot and put me on Notice! So yes CAC and a good panels of blood work to include Nuclear Cholesterol makers even if your doctor is not good at reading it! Get Baselines!

(BuckRimfire) #13

At 12-13 hours fasting, I think all my blood test numbers, including ApoB at 117 mg/dL, were near median or better except total and LDL cholesterol, which have bounced up somewhat. Not a concern to me, since my trig/HDL ratio is even lower than previously measured, and combined with ApoB seems to say that my LDL is in the harmless “pattern A.” My doc wrote a referral for a CAC before seeing anything, which I consider the acid test, but if he has any concerns about the lipid panel I’ll try using that as leverage to get him to order a more sophisticated NMR lipoprotein test, too.
LipidPanel2.pdf (101.6 KB)

(BuckRimfire) #14

If my newly elevated LDL leads my doc to recommend a statin, I’m going to delay/deflect that with a request for NMR cholesterol analysis, as well as waiting on the CAC.

(UsedToBeT2D) #15

Doctors can prescribe all they like. It is your decision whether or not to take their advice.

(ben) #16

according to the feldman protocol 12-14 hours is best IF you’ve prepared three days before the blood test

(Bob M) #17

I think the Feldman protocol works fairly well (for many people) if what you want to do is get lower TC and LDL. For me, though, I actually got “better” results (at least from a doctor who believes in the lipid hypothesis point of view) by using a normal test. The first two were Dave Feldman’s test (4.5 days fasting, then 3 days high fat then “official” test). The third was a “normal” test:


You can see that my values were “better” on the third test: lower TC, LDL; higher HDL; about the same trigs; glucose lower; CRP lower.

And these values change all the time. Another example, two weeks of difference. These were both “normal” tests:


I got a super high insulin on the first test, so I took again two weeks later (and got lower but still high). Insulin is another marker that for me is highly variable.

(BuckRimfire) #18

Of course. They may also be able to refuse to continue seeing you if you are sufficiently uncooperative, though. Not exactly sure what the policy of that clinic is. So, my goal is not to seem TOO confrontational, while also not buying any statins.

This guy is pushing 70, so “long-term” may be limited by his retirement anyway, but he claims he likes working and getting paid, so I hope to string him along for at least a few years. He looks younger, for what little that’s worth.

(BuckRimfire) #19

I wonder if the comment there to avoid coffee also applies to black tea. I’ve been drinking a little coffee lately (most days, but typically only a small cup) but I almost always drink lots of black tea each day. So, if it’s the caffeine, I’m getting plenty.