DaveLeeNC

This is an interesting (two part) article related to this general topic.

High-fat, low-carb diets: good for you and your cycling? | CyclingTips

dave

Carbonfiberboy 

The studies I've read, such as the one to which you link, show glucose being produced from infused or consumed glycerol. I know that some tri folks use glycerol to hyperhydrate before an event, consuming about 1g/kg body weight. More is supposedly rather nasty on the digestive system. Anyway . . .

One might assume that gluconeogenesis from glycerol also might happen whenever carb nutrition was absent and blood glucose was low. However human dietary studies don't seem to support this, indicating rather that at least the vast majority of gluconeogenesis is from amino acids. I thought that this study:
Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet
was very interesting as it also helps explain the greater than expected weight loss from low carb diets. It also discusses the variation of protein balance, blood sugar levels, and possible gluconeogenesis with various low or zero carb diets, which I found interesting.

I understand that gluconeogenesis from glycerol takes place, I'm just doubting how much in ordinary situations. I don't think that's really very interesting in any case, since the protein intake of most low carb dieters is plenty high enough to prevent muscle breakdown. I was only trying to be cautionary about keeping protein levels up, above what's normally considered necessary, to allow for gluconeogenesis.

curlyque

Some of the recent science suggests that glycogen, simply because it is the easiest to process fuel source, does not automatically make it the preferred fuel over ketones except in high demand situations such as escape from a dangerous situation, or sprinting to the finish line.

pacemaker

a: Good luck on a 10 gm Carb per day diet, I think that's impossible unless you eat nothing but meat & butter (just two 1/2 cup servings of vegetable has 10gm of carbs). b: gluconeogenesis is the formation of glucose from non-carbohydrate sources, both fat and protein. Fat can be converted into glucose as one person posted, at least part of the fat anyway. A triglyceride molecule can contribute the 3 carbon-chain glycerol molecule; pair it up with another glycerol and you have glucose, the three fatty acid chains left over will be available for oxidation. c: there's an old adage in ex phys: Fats burn in a "carbohydrate flame", meaning you need a little carbs to burn fat. That's why, when you bonk, you can barely move. That's why you can't move even if you're only trying to ride in your aerobic "fat burning" zone. Sure you have plenty of fat, but you're out of glycogen and gluconeogenesis cannot work fast enough to meet demand, thus you shut down.

DaveLeeNC

Pacemaker, thanks for the info.

FWIW, I have on a couple of occasions lived on less than 20 grams of carbs for a couple of weeks. And you are right in that meat and CAREFULLY selected cheese is about it.

dave

tmac100

Thanks pacemeker for the simplified into to biochemistry wrt bonking A reminder of past labs and lectures

Today I pretty well bonked - while walking. Here in Qatar it is HOT and the traffic is on the verge of being "life threatening" - even when you are in a motorcar. That said, to get some training I am walking with the aim of 21K steps per day - spread out over the day.

Before work I usually go 3K to 4K. Today I had the chance of doing 10K before work. Trouble was I started to approach a bonk @ 8K. The reason was obvious - not enough pre-loading because I did NOT anticipate the extra "food" requirements for the extra distance! Simple mistake and potentially serious consequences...

As a Type 1 diabetic for the last 52 (yes that is NOT a typo) years I can recognize the "signs".

Did a quick detour into the college cafeteria and ordered 2 hard boiled eggs, two bananas, some bread (made with cheap flour which has sugar added) and a bottle of water. Two salt packets too

Relaxed with colleagues and basically recovered. Anyone ever try salt on bananas?? On to "scheduled work" and all was well... Later during the day I proceeded to walk some more (in stages of 5K to 7K) and had no further issues - hydtated and "fed".

Ended the day with 26.3K steps. My body was quite happy doing the last 2K steps. The pedometer analysis shows: Aerobic steps 21853 steps. Distance: 22.9 km., and Kcal used 1154.

I am doing this 5 days a week because it is too hot to bicycle here now...

Result of today's escapade:

1. Hydrate!
2. Eat - anything that gives your body glucose and Na and K!
3. Recover and continue!

It seems my body needs the "essentials" and if they are NOT available, there are SERIOUS consequences. Otherwise it seems I can do plenty.

Now to get to Perth (AU) in July and bicycle across to Peterborough/Adelaide ... I am heartened to know that folks have been doing that for about 100 years now - and without gels, fancy cooking and sleeping gear and just (originally) with SS bicycles with 28" wheels

curlyque

"It has been claimed that carbohydrates serve as a primer for fat catabolism ("fats burn in a carbohydrate flame"). However, as pointed out by Robergs and Roberts [22], this is an incorrect contention. In skeletal muscle, fat certainly does not burn in a carbohydrate flame, as skeletal muscle does not have sufficient quantities of the enzymes to convert glycolytic intermediates into molecules that can be transported into the mitochondria to supplement citric acid cycle intermediates."

"In comparison with glucose, the ketone bodies are actually a very good respiratory fuel. Indeed, there is no clear requirement for dietary carbohydrates for human adults."

"Contrary to popular belief, insulin is not needed for glucose uptake and utilization in man. Finally, both muscle fat and carbohydrate burn in an amino acid flame."

Metabolic Effects of the Very-Low-Carbohydrate Diets: Misunderstood "Villains" of Human Metabolism
Anssi H Manninen

Metabolic Effects of the Very-Low-Carbohydrate Diets: Misunderstood "Villains" of Human Metabolism

Carbonfiberboy 

This link is to an argument, not a study. The argument contains cites of studies, however the studies which are cited do not support the argument. Some of the most anti-scientific cites are to books to which we do not have access. A common feature of nutritional arguments which arise from an ideological basis rather than a scientific one, as well as other anti-scientific arguments, is that they cite the opinions of others who then cite their opinions: a circle jerk in a closed system.

In an obvious example, type 1 diabetics would certain take issue with the claim you make that they could lay down their insulin and walk. This is a religious claim, not a scientific one.

Pacemaker is correct. Bonking is real. Diabetes is real.

curlyque

This discussion takes place in a playground....

tmac100

Today ... no bonk. Walked almost 31000 steps and felt pretty good for most of it. What did I do to prevent the bonk?

1.Lots of water - even when I felt I did not need any. Forced it down. Urine was never yellow.
2. Pre-loaded adequately on foods. This pre-loading seemed to work. Tested blood sugars regularly (every 2 hours as usual and times for 30 minutes after a 5K or 7 K walking stint. Lowest was 4.3 (so ate a banana with a bit of salt) and a candy. Now before bedtime it is 8.3 and I have also learned how to take reduced amounts of Toronto and Lantace insulins at the same times as before - just reduced by about 20%

The bit of salt on the banana tastes better than one would think.
Works for me. Now to see what happens with blood sugars tomorrow and walking almost 31K steps. Granted, I should be training on a bicycle, but with ~40 C temps and aggressive traffic NO WAY. On the work bus home it was almost side-swiped at the front end by an aggressive driver in a 4X4 Land Cruiser who was changing lanes. An applied Pauli Principle: 2 objects cannot be in exactly the same place at exactly the same time

bartolomei

Authors of the above study say (not prove) that "Because fat is a thermoneutral ingredient, ie, it does not increase diet-induced energy expenditure," from which they conclude it does not stimulate gluconeogenesis. Still, they mention other studies in which energy expenditure was not significantly different among different diet compositions.

In any case, I think during a low-carb (<10% energy) diet, neither protein nor fat are able to provide enough glucose to replenish glycogen stores, because people on low-carb diet who do not even train report they have ketones in urine, and, significant ketogenesis and ketonuria occur only after glycogen stores are depleted.

RR3

10% is about 350 kCal for me.

My experience does not support your statement that ketogenesis occurs only after glycogen stores are depleted. It is quite straightforward to be in a state of ketosis and still not be glycogen depleted. I do it all the time and I do not rely upon urine analysis. I test my blood ketone levels (and glucose and lactate). Peter Attia has some data posted as do other blggers.

The interplay of exercise and ketosis ? Part II - The Eating Academy | Peter Attia, M.D. The Eating Academy | Peter Attia, M.D.

bartolomei

How do you know you are not glycogen deleted? If your blood glucose and lactate are normal, it means you produce enough glucose (via gluconeogenesis), but this does not mean glucose comes from glycogen.

In the blog mentioned, Attia speculates about glycogen stores during ketosis, but he does not actually prove/measure them.

RR3

Because I can put out 290 watts for one hour despite being in ketosis. Makes sense?

When bonked or when my working muscle glycogen is depleted, I struggle with half that power and can't do it for long.

Is that sufficient evidence?

If not....

Second, elevated blood lactate is synonymous with anaerobic metabolism. At 290 watts, my blood lactate is 4 mmol/L when fitness is good. Neither the power level nor the lactate level would be possible if I were depleted and my blood ketone level was 1.6. Thus, I was in ketosis.

I'd take a muscle biopsy if you pay the labs? Attia did report Respiratory Exchange Ratios in some of his posts....this is proof.

Gycolysis and Beta Oxidation are not mutually exclusive processes and those with flexibilty can switch from one to the other more easily than the typical type 2 diabetes patient eating a typical standard american diet.

bartolomei

At which percent of carb intake?

Null66

I have been trying to find out how to "train" glycogen stores. So far the best I've found is riding in a depleted state, such as first thing in the morning w/o eating.

Does anyone have any idea how to extend your glycogen stores?

RR3

zero carb intake on rides less than 75 miles or so

bartolomei

OK, but in general, are you on a low-carb diet?

Carbonfiberboy 

The usual thing is to do as you say, or any variety of other methods such as polarized training, thus attempting to increase the amount of fat contribution to power laid down at moderate intensities. On a 4 hour ride, one might have only 1 hour at or above LT, where there is almost no fat contribution and energy comes from glycogen and a little from food. To reduce glycogen use during the other three hours, we can train to reduce the amount of glycogen used by increasing the fat contribution. We can also eat more calories as long as those calories can be moved into the muscles. There are a variety of eating strategies mostly focused around maltodextrin and fructose.

For short events, I think we are stuck with just trying to eat more if we think our glycogen might be insufficient.

Many studies show that caffeine increases the proportion of fat used for energy.
Energy Beverages: Content and Safety
Is caffeine banned at the Olympics

However, ingestion of ~500mg of caffeine before an event can produce a urine concentration that could result in banning.

RR3

In general yes, I am on a low carb diet.

However, there is a certain amount of carbs of specific types that I will eat on long rides. Tomorrow I will do a 400k and although I could do it without eating anything, I chose not to simply because it is more fun and easier to eat just enough. I would say I am fat adapted. I just do not need to eat as much. Some low carb athletes will keep carb intake down even on long endurance events. I am probably going to burn 10,000 calories tomorrow of which 6-7,000 will be fat, 1500 will be stored glycogen and liver glucose and maybe 2000 or so from eating. The food will be primarily carbs but there will be fats and proteins. I will also have BCAA in my mix after after the first 123 miles. I have found that modest carb intake during such events is helpful and it does not shut down beta oxidation provided I do not start eating until around 30 minues into the event and provided I do not eat sooner than a couple hours before. So, I do not eat breakfast before a 4 am Brevet.

My typical breakfast might be coffee or expresso with either grass fed heavy cream or coconut oil. Four farm gathered eggs and a few slices of local organic bacon. Probaby no lunch. Maybe a small square of 90% Lindt Dark chococlate or some Macadamia nuts during the afternoon. Dinner might be an Arugla Salad with goats cheese with Balsamic and Olive oil. Maybe a sweet pototo once in a while. Fish, grass feed beef, lamb or venison. No grains generally, none.

RR3

https://www2.bio.ku.dk/bibliotek/phd/...%F8rgensen.pdf

Just ride your bike every day.

Never take more than two days off in a row.

MinnMan

Yeah,the one time I really bonked I had NOTHING - then both legs cramped and I HAD to stop. Pouring out sweat, etc. A long drink and a cliff bar brought me back to something like functional, and I limped back to the ride start. I do not want to repeat that.