Bernstein Apprehension - Especially Endurance Sports

So, I picked up a copy of Dr. Berstein’s book and am toying around with the idea of trying a LCHF diet, I am still not convinced, however, that it is a great idea.

I am currently eating about 150g of carbs a day. The dietitian in my diabetes clinic told me, rather than cutting carbs, bump it up to 200g. She said, "Ya, a lot of people try the LCHF diet and screw up their metabolism. Sure they lose a lot of weight in the short term, but in the long term, they end up heavier then when they started. I get this argument. There must be some level of muscle deterioration when you cut carbs to the point of being on a ketogenic diet.

Besides that, I am a cyclist / mountain biker. I can’t imagine how my energy will wain with almost eliminating carbs. Alright, the first hour should be alright, but, after that, I imagine my energy levels hitting a brick wall (aka bonking).

I am looking at this weekend where I will be riding in the Ride to Conquer Cancer - a 220 km ride over two days. Without carbs, I am beat right out of the gate. Guidelines set by the American College of Sports Medicine indicate that I should be eating 30 - 60 grams of carbs per hour while cycling. That means that I should be eating 250 - 500 grams of carbs during the actual 8 hours of riding.

Anyone have any experience with endurance sports and Berstein?

Doesn’t work for everybody, but the above part is not right. There is no muscle deterioration even on zero carbs per day. Why? Because your body doesn’t build muscle mass from carbohydrate. It builds it from amino acids that your body produces or gets from protein you eat (“essential amino acids”).

What does happen is people feel weaker (usually temporarily) when they start doing very low-carb because of lack of electrolytes and stored glycogen (glucose stored with water molecule in the muscle and liver tissues). The body adjusts quite easily to that.

So here is the way muscle mass and dieting work together, regardless of what kind of diet:

  1. If you are eating at a caloric deficit, it is likely that you will lose some muscle mass (although it can be negligible if you get enough protein and you work hard physically).

  2. If you don’t eat enough protein per day, it is likely you will lose muscle mass, regardless of whether you are eating at a deficit or not.

  3. Energy used to actually “work” the muscles comes from four places: free blood glucose (we’re all familiar with that); stored muscle glycogen; stored liver glycogen (this is what gets “dumped” in the morning during dawn phenomenon and also why you get high BG during stress events); or fatty acid metabolism (ketones produced from stored or free fatty acids).

So, the thing is, while many people in the “traditional” nutritional and sports physiology groups stick to the old “you have to consume carbs to perform,” there is plenty of other evidence out there at this point. The Volek group from Ohio State University has produced good peer-reviewed literature on ketogenic diets and ultra-endurance sports. Summary available from ScienceDirect, with a link to the actual article.

I myself ride (and train for triathlons) at low levels of carb consumption (I’m in between your level and “ketogenic” or Bernstein levels at around 50-70 grams per day of digestible carbohydrate), and once I got used to it and was consuming enough electrolytes, I really quite enjoy it. I haven’t run a triathlon since being diagnosed, so I can’t promise you what it is going to feel like.

I can’t imagine how my energy will wain with almost eliminating carbs. Alright, the first hour should be alright, but, after that, I imagine my energy levels hitting a brick wall (aka bonking).

I would definitely not suggest trying low-carb riding for the first time during an event. I’d want to train to see how my body responds under similar circumstances. One of the advantages of what Volek (and others) call “fat adaptation” is that you don’t “bonk” when your body runs out of stored glycogen…you burn ketone bodies for fuel instead, and this isn’t limited by the amount of consumed or stored glycogen (glucose).

Anyways, it’s something you have to figure out for yourself. Lot’s of Type 1 (and even non-diabetic) athletes are now using keto or Bernstein-like diets and doing fine in endurance sports. But it does take some getting used to. I prefer it myself.


Thanks for the info. You are pushing me further in that direction. But, it still scares the &$@()#$& out of me !!

After 30 years of high-carb, sub-optimal diabetes management, this is one HUGE change !!

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Yes, I had 70 years of normal high carb living before I was dx, and the eventual decision to go low carb/high fat was most definitely scary. I really enjoy this way of eating now and am no longer scared of fats as my bloodwork is always in good shape and diabetes at a good level. You may find your chosen sport improves when you are not weighed down with all that carbohydrate clogging up your system.

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Keep in mind, as you read the Bernstein book, that this is not a binary take-it or leave-it proposition. I’ve enjoyed a carb-limited diet for the last five years. Bernstein recommends a strict adherence to a 30 grams/day carb budget. I’ve varied in the last five years from less than 30 grams/day to up to 100 grams/day. I’m currently eating about 50-75 grams per day. My point is that many of us employ Bernstein-style tactics but with less strict adherence to his limits and still derive large benefits. Discover where your carb-limit balance lies!

I am not an endurance athlete but you should check out the story of Timothy Olson. He is a carb-reduced runner who won the 2012 Western States ultra-marathon in a course record time of under 15 hours! This 100-mile through-the-night course runs from the Squaw Valley ski resort over the Sierra Nevada to Auburn, California. He does use carbohydrates strategically (something called “goos”) before, during and after the race but his primary diet removes most grains and would be considered by many to be “lower” carb. On one website someone published Tim’s answer to his race-day fuel:

Tim’s Reply: “Maybe i’m low carb to most because i don’t eat grains, but i still use carbs for racing and hard training sessions. During training i use 1 to 2 goos for 3-5hr runs. For races, i take about a goo an hour.”


I can see myself easily getting down to 90 grams quickly. Similar to Timothy Olson, I use Clif Bloks - 8 grams of carbs per blok with no grains.

I was as skeptical as you, @Michael_Birch, about trying a much lower carb or LCHF diet. In my case, the price of sticking with a 100-120g carb/day diet was a fair amount of weight gain from the added insulin doses I that I needed. After frustration about my weight and zero success losing it (when prior to diabetes, I could easily maintain my weight at a desired level!), I gave in and tried a very low carb approach. While it has NOT been a resounding success on the weight-loss side, my BG management has become MUCH easier using around half the total insulin I was taking before (and not just from bolus insulin, my basal insulin requirements also dropped in half!). While I am unsure if my diet is technically LCHF - I think I have a more even distribution between fat and protein - I’m definitely staying low carb most of the time. I aim for closer to 50g/carbs a day, rather than Dr. Bernstein’s 30g - I found I was uncomfortable when I tried for lower than that for more than a day or two at a time. I also ease up and eat more carbs on the weekends - a habit I may yet modify going forward.

As for exercise, I find that I nearly NEVER go low since after I adjusted my doses after going low carb. I’ll see a mild drop during exercise, but after 20 minutes of exercise, that drop starts to vanish – in fact, the one problem I’ve had is that frequently I’ll see a big rise in BG around an hour after I exercise now. I honestly don’t recall the last time I’ve had to eat fast glucose to correct a low – they’re that infrequent!

All-in-all, I have found the approach much more successful than I’d imagined, though, in my case, there is still plenty room for improvement.


Hey, me too! I’ve been doing the low-carb thing for a year now, and I’m still uneasy with it, even though it is mostly working well for me. However, I’ve come to realize that most of my issues with it are on my side, not the physiological side :slight_smile: I’ve always struggled with “bonking” during rides.

All the sudden, since diagnosis, a bonk feels dangerous where it used to feel annoying. I used to think… “hey, I’m out of energy, should have planned better and brought more gels.” Now I think… “OMG, I’m having a low and I’m going to fly off the next bridge like a drunk and plummet to my doom…”

For me, and this is just my experience, exercising while fasted and exercising on low-carb is completely doable, if I prepare correctly. I still bring gels in case I go low. In fact, I actually use gels at each hour interval during a longer ride so that I won’t go low. On those days, I guess I’m not low-carb in reality, although my body doesn’t seem to know the difference. Also, when I’m feeling poorly (like today, actually) from exercise, it’s often because I’ve forgotten to consume enough electrolytes. It is critical on a very low-carb diet to get enough potassium, magnesium, and sodium.


LCHF can also be ketogenic, which it would be at the level of carbs you are talking about.

Read Volek and Phinney’s “Art and Science of LC Performance.”


Well … an update. I finally got my head around this LCHF idea. The initial jump terrified me as I am so used to using carbs to manage my blood sugar. So, I cut my basal down from 45U to 30U per day and cut the carbs right as close to zero as I could. I cut out all grains, root vegetables, sugars and processed foods. Within less than a week, I cut my basal again to 25U.

To my surprise, right away, I am seeing the best sugar control that I have seen in almost three decades. I am now on day 8 and am feeling great.

Also, I tried cycling - no carb. What a dramatic change. After an hour and a half of intense riding, my sugar levels only dropped slightly, and bounced back up following the ride.


Thanks for giving us an update. Your surprise and pleasure in regaining blood glucose control mirrors my start of a low-carb high-fat way of eating six years ago. That was year 28 of my diabetes.

After slowly falling off the LCHF wagon during the holidays, I restarted better eating habits 11 days ago. My total daily dose of insulin, average BG, BG variability, and weight have all gone down. It still seems magical to me.

It’s good to read that this way of eating does not compromise your ability to enjoy cycling. A LCHF diet is so potent for me, you, and others, I’ve always wondered why doctors do not at least raise this tactic for interested patients.

Some people will criticize LCHF as unsustainable. I’ve been at it for almost six years. Sometimes I slack, like around the holidays, but when I return to my base habits, my blood glucose is stellar.

Good luck to you! I hope your initial success blossoms into a long-term way of eating.


Dr. Bernstein actually explains why Dr.s recommend a high carb diet and it funny to me that we are still in a practically stone age rut about it. It’s because diabetics were developing or dying from heart disease and Dr.s thought it was because of fat in our diets when in reality it was high BG’s which were damaging our hearts so in the mid 1900’s they put all diabetics on a high carb, low fat diet and the recommendations haven’t changed since then.


Try reading “The Ketogenic Diet for Type 1 Diabetics” by Keith Runyan, MD. The author is both a T1 Diabetic, medical doctor, and ironman distance triathlete who follows a strict Ketogenic lifestyle. As long as you eat the proper amount of protein you won’t lose muscle mass, and as long as you have fat on your body you won’t run out of energy lol

I switched to a 20 or less carbs a day ketogenic diet and I have more energy than I have ever had as a diabetic and my BG instantly got worlds better. I rarely, if ever, have lows <65 or highs >170 anymore. So sad it took me so long to hear about this way of life. My stress level has been cut down by probably 80% too since I no longer fear debilitating lows even while working out.


It depends on the intensity of the exercise. Fat metabolism and glycogen are not the same and they are not interchangeable.

Anaerobic glycolysis forms 2 ATP molecules from each glucose molecule, and it also creates lactic acid and oxygen debt. Aerobic glycolysis and forms 36 ATP molecules per glucose molecule, but no oxygen debt.

Ever notice how the winners in the Olympics in the 10k race are out-of-breath? Hint - they aren’t relying much on fat metabolism for that effort.

Yes, you can run slowly with fat metabolism. But at some point as you increase your speed, ultimately your body turns to other forms of energy.

There is a difference between how these two guys are running their races.

Michael, great to have your very positive feedback.

I ran a very slow 10 km running event last weekend. In fasted state. Waking blood sugar was 84, just before the event I was 92. At completion i was 100. My blood sugar tends to go up during exercise. I did a 1 unit correction when I got home, and blood sugar was in the 80s for the rest of the day…

I love low carb eating, and I combine it with intermittent fasting. It hasn’t helped me lose weight (I can thank for that failure a dead thyroid and being a middle aged woman), but it has made diabetes a manageable condition, that doesn’t consume all that much of my energy, attention, and time. I shoot up my basals morning and night, a small dose of fast acting to catch the dawn phenomenon, and some days that’s it! Coasting all day… glancing at my freestyle libre only occasionally to be sure that the low hills and shallow valleys of my blood sugar stay that way.


I ordered that book last week and expect to receive it today. Hopefully he has some good information.

For that matter, I emailed Dr. Runyan on Friday with questions about my ketone levels. He responded within about an hour and sent me a very thoughtful email. From my experience with Canadian doctors, this idea of communicating with patients - not even his own patient - outside of billable hours is completely foreign.

So thankful for his feedback !!

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