Exercise + weight loss + low carb questions

Hi there,

I have a couple of questions for the exercise/diet/low-carb physiology experts out there …

After three months away from home (bad sleeping —> worse than usual BGs + excessive hunger —> Hba1c up to 6.9 from 6.3 + about 10 extra pounds of weight), I’m attempting a more serious low-carb trial, with the goals of getting back to my usual weight and investigating the impact of a lower carb diet on my A1c.

My first question is more a general request for advice on the weight-loss front (re. frequency and content of meals + anything else that seems relevant). I work out at quite a high intensity most days (cardio + strength, masters rowing) and continued to do so during my weight gain phase, so adding in more exercise isn’t something I’m inclined to do.

The second question is a bit more specific. I know that on a relatively high-carb diet, the body uses glucose as its primary fuel and that very low-carb (ketogenic) diets will result in fatty acids / ketone bodies being used instead. What I’m wondering is if the fuel “choice” is an either/or thing — particularly with regard to intensive exercise — or if we can go back and forth between the two. If an athlete has been on a ketogenic diet for several weeks, will his/her body continue to favour fat as its fuel source, or, in the sudden presence of higher-than-usual glucose, will it revert back to glycolysis? I’ve read that glycolysis is preferable, performance-wise, for sprints and other anaerobic activities — not that I do any serious racing, but I’m curious.


Good for you. So my understanding of low carb diets is that your body becomes accustomed to switching back and forth between carb burning and fat burning. Everybody burns fat overnight, but if you are carb adapted, you will tend to prefer carbs. When you start a low carb diet (like Atkins), you will shift to become fat adapted. This is the source of the Atkins flu as your body switches, you sometimes feel tired. I will tell you that after this first phase and become fat adapted, you readily shift to burning fat and you do feel energized on a low carb diet and extended aerobic exercise is easy. And I do weight lifting, serious weight lifting.

As to whether you will be as competitive as when you are carb adapted, I can’t answer that. It does seem at least worth trying, does it not?

Thanks, BSC! That’s helpful. You’re one of the people I was hoping would weigh in on this topic. :slight_smile:

Did you notice any difference in your weight lifting power or stamina after going low carb?

Well, I can’t really compare, but I’ve done well on low carb (for a non-athlete). I started low carb in 2006. That was when I started Bernstein. I picked up weightlifting soon after. I will tell you that soon after diagnosis, through calorie restriction I dropped from 210lbs to 175lbs, but it left me skinny fat and still with poor control. I now weigh 205 lbs with the same waist size as when I was 175. Given that I am an old man, that seems pretty good. I don’t do a lot of endurance, but for a while I was doing the equivalent of 25-35 miles on the elliptical every week while on low carb, no problem.

Chiming in on this a bit late Heather, but for high intensity anaerobic activities involving glycolytic pathways, carb based fuels are the only thing that can be used by your cells, whether it be circulating glucose or muscle/liver glycogen stores. Fat and protein simply can’t be burned anaerobically. The metabolic pathways don’t exist for Humans.

Athletes adapted to high intensity or moderate/high activity for longer periods will have higher levels of stored glycogen in ther muscles to draw from. Marathon runners store upwards of 800g of glycogen in their muscles, about 400%, IIRC, more than the average person.

Whether or not your own activity level necessitates an increased reliance on carb based fuels just depends on how much you do an how long you are doing it for.

Not late at all! Thanks, FHS … science teachers rock! :slight_smile:

On the topic of stored glycogen, how much does the average liver store?

heather, I could be touching on your first part question and maybe way off base (I am not the exercise /diet/low carb expert ) … your extra weight seems to be a concern for you ?
Has your thyroid level been checked lately ?

Your liver typically stores about 100 grams of glycogen and your muscles about 350 g. The glycogen in the liver is typically used to stabilize blood sugar. Should exercise needs exceed that, then the liver will start a process called gluconeogenesis and convert protein in your body into additional glucose. In non-conditioned person, glycogen stores will last 8-10 minutes of maximum anaerobic activity. In a well-conditioned athlete (like the marathoner FHS talks about) that may enable 30 minutes of max intensity activity. Now this is not 8-10 minutes of sustained endurance exercise, this is 8-10 minutes of combined 100 m sprints. If you do weight lifting, your combined max intensity exercise will generally not exceed about 5-10 minutes. If you do “intervals” for 20 minutes, you sprint for a minute and wind down for 2 minutes, you only spend a total of 6-7 minutes. When you do aerobic exercise, your body naturally burns fat for fuel and on a low carb diet, you can fuel much of your energy needs from fat.

Thanks for that additional info, BSC. That’s useful, as cardio intervals and heavy weights are indeed part of my program.

Nel, I have had my thyroid tested recently — it’s always my first suspicion when weight and energy levels are at issue. Anyway, it’s fine. I think this is a pretty clear case of overeating. When I don’t sleep well (which I wasn’t while out of town), I get chronically hungry (from what I’ve read, interesting things happen w/ leptin levels and insulin resistance when we don’t sleep). I felt like I was eating constantly, and though I didn’t pig out on carbs, they were certainly a significant part of the mix. I kept up my usual activity level — even improved my fitness, I think — but the weight crept on. Some of it might be new muscle mass … but definitely not most!

As I posted on someone else’s low-carb thread, my first five days on low carb (about 35 grams per day) have resulted in excellent blood sugars, about which I’m very encouraged. I’m not so sure what’s happening weight-wise, however. I think I need some guidance about protein and fat requirements in the realm of low-carb weight loss.

I had a sense , you would have checked out the thyroid …I have been very lucky in the " steady weight " department…so far that is ; not a good sleeper and talk to myself a lot, when I think of food first…and not necessarily hunger pangs …just thoughts. I am for certain eating less ( carbs, fat, protein ) , than during my younger , more active days ( I mean before I turned 70, ha, ha !) .
Hang in Miss Rower .