Alternate-Day Fasting Improved My Fasting Blood Sugar

Seth Roberts

A few days ago, I gave a talk at a Quantified Self Meetup in San Francisco titled “Why is my blood sugar high?” (PowerPoint here and here). My main point was that alternate-day fasting (eating much less than usual every other day) quickly brought my fasting blood sugar level from the mid-90s to the low 80s, which is where I wanted it. I was unsure how to do this and had tried several things that hadn’t worked.

Not in the talk is an explanation of my results in terms of setpoint (blood sugar setpoint, not body fat setpoint). Your body tries to maintain a certain blood sugar level — that’s obvious. Not obvious at all is what controls the setpoint. This question is usually ignored — for example, in Wikipedia’s blood sugar regulation entry. Maybe Type 2 diabetes occurs because the blood sugar setpoint is too high. If we can find out what environmental events control the setpoint, we will be in a much better position to prevent and reverse Type 2 diabetes (as with obesity).

A few years ago, I discovered that walking an hour per day improved my fasting blood sugar. Does walking lower the setpoint? I didn’t ask this question, a curious omission from the author of The Shangri-La Diet. If walking lowered the setpoint, walking every other day might have the same effect as walking every day.

I was pushed toward this line of thought because alternate-day fasting seems to lower the blood-sugar setpoint. After I started alternate-day fasting, it took about three days for my fasting blood sugar to reach a new lower level. After that, it was low every day, not just after fast days. My experience suggests that the blood-sugar setpoint depends on what your blood sugar is. When your blood sugar is high, the setpoint becomes higher; when your blood sugar is low, the setpoint becomes lower. Tim Lundeen had told me something similar to this.

If you tried to lower your fasting blood sugar and succeeded, I hope you will say in the comments how you did this. I tried three things that didn’t work: darker bedroom, Vitamin B supplement, and cinnamon. Eating low carb raises fasting blood sugar, according to Paul Jaminet.

12 thoughts on “Alternate-Day Fasting Improved My Fasting Blood Sugar”

  1. Could you describe what you eat on the eating / fasting days in more detail ?
    I’m interested in how you use this along side strategies such as your flaxseed consumption and vitamin D supplementation.
    I’ve tried alternate day fasting and have had some success with it in the past for weight reduction.
    There are lots of different fasting plans – from my reading, the essential element seems to be going for 16+ hours without any food, so you don’t completely have to abstain from food for a full day.
    I like a daily 19/5 schedule personally : skip breakfast , have a late lunch, then a normal dinner, which is pretty easy to stick to. In the 19 hours, I consume only water.
    Seth: Before I started alternate-day fasting, I ate only one normal meal per day — already coming close to your 19/5 schedule. While doing alternate-day fasting (which I am doing now), I eat normally (for me) on the meal days (low carb, vaguely paleo) and on the fast days I eat butter and flaxseed oil and a few other things, about 700-800 calories. I take Vitamin D3 at 8 am every day.
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  2. Is it the fasting that matters, or having successive days with very different diets? What if, say, I ate only fish on the ‘fasting’ days, and my normal diet, minus fish, on the ‘eating’ days? Anyone here want to try that out?

    Seth: There’s lots of research about intermittent fasting in animals, such as rats. In this research, the successive days do not have different diets, in the sense that what is eaten on the fast day (the little that is eaten) is the same sort of food that is eaten on the non-fast days.
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  3. I believe that intermittent fasting helps by improving insulin sensitivity. Things like fasting improve the sensitivity of insulin receptors in the muscles, allowing the muscles to take in greater amounts of glucose from the blood stream.
    That’s the problem with insulin resistance in obese people. They are consuming tons of sugar (and carbohydrates), but they can’t get the sugar into their muscles because the insulin receptors are not sensitive. All that energy available and they can’t get it into their muscles to burn it off.
    As I understand it, high intensity training (i.e. exercising your muscles until “momentary muscular failure”) is also very good for improving receptor sensitivity. When we thoroughly deplete glycogen in our muscles, it triggers our body to improve receptor sensitivity so that we will be better able to quickly restore glycogen levels in the future.
    I tried doing one 24-hour fast per week, but now I do a daily 16-hour fast (a la Leangains). I do all my eating during an 8-hour “feeding window.” This is a reasonable compromise for me. I start eating at 12 noon and stop at 8 PM.
    My next step is to give up diet soda, which I currently drink outside my feeding window (for the caffeine). They have found that artificial sweeteners also reduce insulin sensitivity. This may be sabotaging my results to a degree.
    Seth: “Intermittent fasting helps by improving insulin sensitivity.” Well, maybe. Why should improving insulin sensitivity change the body-sugar setpoint? It isn’t clear why. In the realm of body weight, there is a similar issue. Just because exercise burns calories does not imply it lowers the body fat setpoint. Certain sorts of exercise do lower the body fat setpoint, but that had to be figured out.
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  4. Quick question: Seth, how do you measure you blood sugar levels? Thanks
    Seth: I use Abbott’s Freestyle Lite meters with butterfly test strips. They work well. No pain when I prick myself on my arm. Only a tiny amount of blood is needed. The test strips cost about 50 cents each.
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  5. I have been doing a similar self-experiment for about 3 years now. I have accumulated quite a lot of blood sugar data, and my numbers are similar to yours. My situation and A1c numbers are also similar.
    I’ve learned a few things in my experiment, which I’d like to share:
    1. Blood sugar meters have terrible reproducibility, but some are better than others. Avoid Reli-On meters altogether. I’ve had pretty good luck with True-Track meters (and the USB port is very handy for downloading data). Whatever meter you are using, buy a full box of strips, and take 10 or so readings from the same prick. You will see significant variation in the readings. It’s expensive, but if you do 40 or so successive readings, you’ll be able to calculate the statistical variance of the meter.
    2. If you get an unusually high or low reading, take another using the same prick. Take a third. The variance will surprise you. If I were injecting insulin, I’d never trust a single reading.
    3. I use the inside tip of my left pinky finger. Least innervation and highest vascularization.
    4. A reading when you first wake up will tell you more about liver insulin insensitivity than all the readings you take throughout the day. Mine ranges from 75 to 110. If I’m doing something right, it will be in the 80s. More commonly, it will be in the mid 90s.
    5. Exercise helps tremendously. I like to rock climb at the local gym, because it’s the only activity I truly enjoy. It’s very intense, short duration, and probably not very aerobic (I hate aerobics) but it can get your heart rate up for short bursts . Climbing for an hour after work, fasting afterwards, and then going to bed early usually, but not always, will keep me in the 80s the next morning.
    6. A per Jack Kruse’s recommendations, wearing blue-blockers after sunset seems to help. (They also work tremendously well for eliminating jet lag.)
    7. My fasting blood sugar seems to creep up during allergy season (spring and fall). When I’m sneezing and hacking, the sugar is almost always around 100 rather than 85. (I’m very interested to know if a hookworm infestation will lower this.)
    8. Stress definitely raises blood sugar. Both long-term annoying stress and sudden, unexpected stressful situations seem to aggravate it. Mine once shot up from 90 to 157 after I was hit with an unexpected bill from a hotel front desk.
    9. Read Dr. Bernstein’s book. It is loaded with good information.
    10. I’ve found that cutting back somewhat on protein lowers fasting blood sugar. Fat (lard and/or coconut oil) doesn’t seem to have much of an effect., unless large amounts are eaten before bed. That seems to increase liver insulin insensitivity.
    11. The most fascinating thing I’ve discovered is that cold thermogenesis (see Dr. Kruse’s blog) really lowers blood sugar quickly and effectively. If mine’s over 100 in the morning, I jump into a tub of 50 to 60 degree water and soak for 20 minutes. That reliably drops it to the 70s or low 80s. This effect last anywhere from 90 minutes to 5 hours. From what I’ve been reading, cold does not cause an insulin release, but rather a release of TXIP.
    12. I supplement with Mg and D3. Active liopoic acid often seems to have an effect, but it’s hard for me to isolate the cause/effect as of yet.
    I have not tried alternate day fasting, just reduced eating or skipping dinner, and that definitely seems to help. After reading this post, I will try alternate day fasting.
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  7. As an adjunct, you might also check out this study, which points to benefits of glucose control from regular blood donation. The Wikipedia page on blood donation has a couple more references, including the Finnish study pointing to lower incidence of Type 2 diabetes.
    As for “set points”, maybe it doesn’t really change the set point. Maybe it just keeps the system from reaching equilibrium most of the time? In any case, that might be a distinction without a difference–if it works, who really cares why.
    Seth: That’s very interesting about blood donation. In your “maybe it doesn’t really change the set point”, what is “it”? If by “it” you mean alternate-day fasting, I guess you mean that frequent meals (more frequent than alternate-day fasting) may raise fasting blood sugar not because they change the set point but because they keep the system from reaching equilibrium most of the time. Then my question is what you mean by “equilibrium”. “who really cares why?” — I think the history of science shows that theories (which answer “why” questions) are often really helpful. Theories may suggest or motivate new experiments, for example.
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  8. I don’t think Jaminet is right about this, but the requirements for keeping fasting blood sugar low via a low carb diet is pretty restrictive and thus most people saying they are low carb are probably cheating enough to cause the problem. I did it for a while after going to the doctor and finding out I had a high fasting blood sugar. It seems to be predicated on what you ate or drank the day (or night) before, and it doesn’t necessarily make any kind of sense.
    For instance, when I found out I had the high fasting blood sugar, I had been experimenting with a tablespoon of honey before bed (improves sleep). Well, the honey had to go, but a chocolate bar with 20g of sugar in the afternoon didn’t seem to cause any problems. I was carrying around a jar of ghee at the time to help make calorie requirements.
    Low carb does make you insulin resistant, and in context, this is a good thing because it keeps the glucose reserved for the brain. So, Jaminet and others are probably seeing blood sugar rising during the time it takes for the body to switch this particular insulin resistance off. Peter did a series on palmitic acid a while back, which is how I was informed of this: https://high-fat-nutrition.blogspot.com/
    I got bored with the whole thing. I ran out of blood test strips and eventually decided I want more muscle. I suppose I should get some more, because I’m certainly eating a lot more carbs. The problem is, I can eat to make the testing look good, but I’m not improving my quality of life when I do that. When I eat and gain muscle, the improved quality of life is noticeable.
    Seth: Higher blood sugar levels are correlated with greater risk of several major diseases, such as stroke. This is why I believe high fasting blood sugar is a bad thing. I agree that fasting blood sugar is not the perfect way to measure blood sugar; HbA1c is better. When I started alternate day fasting, I didn’t notice any decline in quality of life — if anything it improved because I had more free time.
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  9. walking shortly after a meal (about 15-20 minutes) which prevents a post-meal spike in blood sugar; and cinnamon. my last blood sugar reading was 87; i also eat a fair amount of avocado and minimize starches/sugars
    Seth: You found that adding cinnamon made a noticeable difference? I haven’t heard that before about avocado.
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  10. I had wondered if you have tried walking for different amounts of time and frequency after you discovered that it lowered your blood glucose to find the lowest amount for the benefit. And are you still walking while doing alternate day fasting?
    Seth: Yes, I walked varying amounts. I found I needed to walk about an hour to lower my fasting blood sugar the next morning. Thirty minutes wasn’t enough. I am still walking while doing alternate day fasting.
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  11. Is the amount of walking one hour in total throughout the day or does it need to be one continuous hour?
    Seth: Close to continuous. Maybe 2 30-minute bouts will work. But scattered walking didn’t help.
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  12. Replying, yes by “it” I meant ADF. In the model I’m contemplating, “equilibrium” is reached by eating ad libitum every day. Now, if one starts eating ADF instead, does this affect set point? Or does it just pull the system away from equilibrium without affecting set point at all?
    If I have a helium balloon in my living room, it will naturally rise and stay at the ceiling. But if I bat it downwards regularly–say every three seconds–it will spend no time at all on the ceiling. Is that because my batting somehow affected the tendency of helium balloons to stay on the ceiling? No–it just prevents this equilibrium from occurring.
    One key question is whether the set point sticks upon discontinuing ADF for a while. If it sticks, even for a month or two, that would be interesting.
    Regarding “why”, I just meant that if ADF really affects longevity, as a practical matter, maybe I should be doing it, whether or not set point is the mechanism.
    Seth: Alternate-day fasting may or may not change the blood sugar level that the body “defends” (= the setpoint). As far as I can tell, it does change the set point. My experience suggests that the defended level changes in a few days, not a month. The helium balloon analogy does not involve a regulated system. Sorry, I don’t understand what you mean by “the model I’m contemplating”.
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