Low-Carb Diet: Fuel for Brain & Muscle

[pakmingki2]

Hello
im thinking of trying out a low/no carb diet, eating mostly white/lean meat and vegetables.

THe main thing i am concerned about is, how will my brain and muscles get energy without glucose?

 

[Frame Dragger]

Hello
im thinking of trying out a low/no carb diet, eating mostly white/lean meat and vegetables.

THe main thing i am concerned about is, how will my brain and muscles get energy without glucose?

Ketosis.

 

[Shootist]

Hello
im thinking of trying out a low/no carb diet, eating mostly white/lean meat and vegetables.

THe main thing i am concerned about is, how will my brain and muscles get energy without glucose?

I lost 160lbs in 18 months on Atkins (modified). That was 8 years ago. 120lbs is still missing.

But don't fall for the "lean" meat thing. And no (little) vegies allowed. Lots of bacon and cheese though.

Good luck.

 

[stevenstritt]

Fear not! Once your body transitions to burning fat for fuel, you will have all the energy you need for mind and body. I've lived low carb for 10 yrs and will never go back.
Read "Protein Power" by Drs. Dan and Mary Eades for all the details

 

[Moonbear]

Low carb is okay, No carb is bad. If you eat lots of non-starchy vegetables (i.e., go for green beans and broccoli rather than potatoes), you'll still get plenty of glucose for normal function. Though, much of the reason those low carb diets work isn't really cutting out carbs so much as when you reduce carbs and eat more protein and fats, you reach satiety faster on fewer calories.

Just keep in mind that any drastic change in diet should be done under a doctor's supervision. They can monitor that you aren't developing any nutrient deficiencies or stressing your heart, and things like that.

 

[Shootist]

Low carb is okay, No carb is bad. If you eat lots of non-starchy vegetables (i.e., go for green beans and broccoli rather than potatoes), you'll still get plenty of glucose for normal function. Though, much of the reason those low carb diets work isn't really cutting out carbs so much as when you reduce carbs and eat more protein and fats, you reach satiety faster on fewer calories.

Just keep in mind that any drastic change in diet should be done under a doctor's supervision. They can monitor that you aren't developing any nutrient deficiencies or stressing your heart, and things like that.

One CANNOT eat 'lots' of vegetables, on a low carb diet, and hope to lose weight. One cannot consume more than 60 carbs a day and hope to lose weight. In fact ~60 carbs a day is break even. One has to eat < 60 carbs a day. The diet starts off with 2 cups of lettuce and 1/4 cup of green beans (or asparagus, or brussels sprout) as the daily vegetable intake. After 2 weeks you are given the option to add more carbs to your daily intake, but it is an option.

There have been a number of studies in recent years looking into the health impact of extreme low carb dieting. They have all found the diet safe and effective.

You do not have a lower caloric intake. In fact the whole point of the diet is to eat until you are full. My personal experience is eating as much as 4000 calories a day with daily carb intake below 10-20 grams.

The diet works by metabolizing fat into sugar (ketosis). This is an inefficient process. It cost more in energy to release the sugar than the sugar provides in energy. Hence one loses weight, quickly and effectively. A good multi-vitamin (and that's all) is recommended.

Good luck

 

[cfredc]

Low carbers depend on gluconeogenesis (essentially, production of glucose in the liver from amino acids) to supply glucose.

Ketosis is unnecessary unless protein is insufficient or gluconeogenesis is inhibited by chronic dietary carbs or metformin or alcohol.

 

[Monique]

Low carbers depend on gluconeogenesis (essentially, production of glucose in the liver from amino acids) to supply glucose.

Ketosis is unnecessary unless protein is insufficient or gluconeogenesis is inhibited by chronic dietary carbs or metformin or alcohol.

I don't believe that gluconeogenesis is generally sufficient to provide the body's demand for energy substrates. Do you have a source that proves your point?

 

[cfredc]

Dear Monique,

Your intuition is quite natural. After all, eating carbs is universal in your experience.

Many examples of peoples subsisting on no-carb diets exist. The one that comes most readily to mind is the Inuit (Eskimo) people.

Before we brought them pizza and beer, they lived on no-carb fat and protein diets. If you can find the famous (and partly faked) documentary film “Nanook of the North,” you will appreciate just how hard you can work on a no-carb diet.

However, do not quickly switch from carbs to no-carbs. Your body needs time to gradually adjust to the changing diet.

Once switched, you will be free from irresistible physiological carb cravings, but not from learned carb desires.

 

[Monique]

cfredc, I wasn't commenting on the fact that people can live on a no-carb diet. I was commenting on your statement that gluconeogenesis is sufficient and ketosis is unnecessary on a no-carb diet, can you provide a source for that?

 

[DanP]

cfredc, I wasn't commenting on the fact that people can live on a no-carb diet. I was commenting on your statement that gluconeogenesis is sufficient and ketosis is unnecessary on a no-carb diet, can you provide a source for that?

The rate limiting step in gluconeogensis as far as I know lies in the ATP homeostasis. 4ATP are required to convert NH4+ to urea, 6 ATP to convert amino-acid carbon skeletons to glucose, and 1 more for something I can't recall.

ATP is restored through aerobic oxidative metabolism. The liver supply of oxygen is ensured by portal vein, but here the O2 partial presure is pretty low. This limits availablilty of ATP. I believe the numbers quoted is 400g glucose /day, assuming all 02 is used to this process, which is a bit unrealistic. This amounts to something in vicinity of 1600 kcal.

This is enough to power the brain and other cells which cannot oxidize fats as fuel. If you take more kcal from fats, you can get enough energy for a normal day to day life.

I don't know what is the threshold of where ketosis will start, but with 400g / day of glucose ketosis should not be of real significance.

The main problem which I encountered of a permanent low CHO diet is the fact that is quite unable to maintain high performance in power based sports. And I would really dislike to eat so many fats anyway to account for the rest of my energetic intake. Too much fats, no CHO, you pretty much get a imbalance in cholesterol soon enough. This is the last thing a person living today lazy life wants.

I believe in a balanced nutrition. I probably eat 30/30/40 (CHO is 40%).

 

[Monique]

I don't get it, low insulin and high glucagon levels trigger both gluconeogenesis and ketogenesis. Is there a different threshold or kinetics between the pathways?

Also, the low-carbohydrate diet was invented (or at least applied) to treat children with neurological problems. The whole idea was that with a no-carb diet you bring the body in a state of ketosis. The brain then depends on ketone bodies as an energy source, which has been proven to have a neuroprotective effect.

 

[DanP]

I don't get it, low insulin and high glucagon levels trigger both gluconeogenesis and ketogenesis. Is there a different threshold or kinetics between the pathways?

I can't recall too much about ketosis regulation. Ill take your word for it if you say that it will be booted at the same time with gluconeogenesis. Ill look in Frayn's textbook as soon as Ill have a bit of time.

 

[Moonbear]

One CANNOT eat 'lots' of vegetables, on a low carb diet, and hope to lose weight. One cannot consume more than 60 carbs a day and hope to lose weight. In fact ~60 carbs a day is break even. One has to eat < 60 carbs a day. The diet starts off with 2 cups of lettuce and 1/4 cup of green beans (or asparagus, or brussels sprout) as the daily vegetable intake. After 2 weeks you are given the option to add more carbs to your daily intake, but it is an option.

What unit is a "carb" in your definition? 60 carbs? That's a meaningless number.

Perhaps our definition of "lots" of vegetables differs. 2 cups of lettuce and 1/4 cup of green beans sounds like a lot to me.

You do not have a lower caloric intake. In fact the whole point of the diet is to eat until you are full. My personal experience is eating as much as 4000 calories a day with daily carb intake below 10-20 grams.

4000 calories a day?! What weight did you start out with? And what was your caloric consumption prior to starting that diet? Or do you exercise constantly? 4000 calories is an extreme quantity of food, more than double what most people required in a day, consistent with those who become morbidly obese. It doesn't matter WHAT your source of caloric intake is when you're reaching that high of levels...UNLESS you're also doing extreme workouts. Perhaps someone training as an Olympic athlete would need to consume that number of calories or more while doing intensive workouts all day every day.

But, my point is that while you eat until you are full, you reach satiety (that feeling of fullness) on fewer calories when you're eating more fat and protein. Those are the foods that send the satiety signals.

But, you MUST have SOME carbs in your diet. This is why the original "no carb" diets have been modified to now be "low carb" because they weren't safe when they cut out all carbs. That was the gist of my post, that low carb and no carb are not the same thing.

Either way, my other point is the most important...any major change in diet should be supervised by a physician. Part of the reason dietary advice from any generic source is useless is that none of us knows what weight people are starting at, what percentage body fat they are, what their current habits are, what's realistic, what their energy usage is in a day (do they sit at a desk or do they do construction work or are training for a marathon), whether they have any dietary restrictions already due to allergies or intolerances, if they have any known metabolic disorder, are they diabetic, do they have any other pre-existing condition, etc. Or, they may not even know they have some condition that might contraindicate a particular diet or going beyond a certain caloric restriction, but might discover it when a diet exacerbates the problem.

This is the difficulty. For an average person who is generally healthy and just a little overweight, these diets are safe, but probably not necessary. On the other hand, someone who is obese or morbidly obese and in need of a diet to get healthy again is already, by definition, not healthy. As much as they need to lose weight, they also need to lose that weight while being supervised so they don't put their health at greater risk. These are people who may be developing diabetes, or heart disease already. A diet that might be healthy for one may not be healthy for another.

 

[IcedEcliptic]

I don't get it, low insulin and high glucagon levels trigger both gluconeogenesis and ketogenesis. Is there a different threshold or kinetics between the pathways?

Also, the low-carbohydrate diet was invented (or at least applied) to treat children with neurological problems. The whole idea was that with a no-carb diet you bring the body in a state of ketosis. The brain then depends on ketone bodies as an energy source, which has been proven to have a neuroprotective effect.

AFAIK the threshold is nearly identical. In practical terms such as this diet, Ketosis is a guarantee.

 

[DanP]

AFAIK the threshold is nearly identical. In practical terms such as this diet, Ketosis is a guarantee.

Where is ketosis regulated ? At what points ?

 

[Monique]

Where is ketosis regulated ? At what points ?

Here is a link with the TCA cycle and how gluconeogenesis and ketogenesis is related to it:

source: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=endocrin&part=A43#A81"

AcetylCoA can only enter the TCA cycle when it is bound to oxaloacetate, however, when blood glucose levels drop the oxaloacetate is used for gluconeogenesis. This means that when demand for oxaloacetate is high, its levels will drop, AcetylCoA can no longer enter the TCA cycle and its levels will rise. This triggers the formation of keto acids through beta-oxidation.

One thing I don't understand: when AcetylCoA can no longer enter the TCA cycle, it would mean that oxaloacetate cannot be produce. Since AcetylCoA needs oxaloacetate to enter the cycle, there appears to be a negative feedback for gluconeogenesis?

 

[IcedEcliptic]

Here is a link with the TCA cycle and how gluconeogenesis and ketogenesis is related to it:

source: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=endocrin&part=A43#A81"

AcetylCoA can only enter the TCA cycle when it is bound to oxaloacetate, however, when blood glucose levels drop the oxaloacetate is used for gluconeogenesis. This means that when demand for oxaloacetate is high, its levels will drop, AcetylCoA can no longer enter the TCA cycle and its levels will rise. This triggers the formation of keto acids through beta-oxidation.

One thing I don't understand: when AcetylCoA can no longer enter the TCA cycle, it would mean that oxaloacetate cannot be produce. Since AcetylCoA needs oxaloacetate to enter the cycle, there appears to be a negative feedback for gluconeogenesis?

No confusion, this does exert negative feedback on the TCA cycle.

As for glycolysis and gluconeogenesis, the citric acid cycle is regulated by the energy needs of the cell, mainly the rate of oxidative phosphorylation to replenish cellular ATP. Therefore, ATP and NADH exert a negative feed back control on citrate synthase (the first step in the cycle that feeds acetyl-CoA into it) and iso-citrate dehydrogenase, the first step in generating reductive power. This two allosteric regulations completely shut down the cycle when ATP synthesis is no longer needed and NADH starts to accumulate. Because both the Krebs cycle and oxidative phosphorylation are localized in the mitochondrial matrix, there is an immediate diffusion-controlled feed back mechanism to the key enzymes in both pathways. In addition, this allosteric control shuts down the cycle under anaerobic conditions, where NADH and FADH2 can no longer be oxidized by the electron transport chain components (complexes I & II).

A second regulatory mechanism is the feed back control of citrate on glycolysis and fatty acid synthesis. High citrate concentrations are indicative of high acetyl-CoA levels slowing down glycolysis while accelerating fatty acid synthesis reduces acetyl-CoA levels. Excess oxaloacetate not needed in the Krebs cycle (e.g. anaerobic conditions) will then be funneled into gluconeogenesis. The absolute concentration of oxaloacetate is the major focal point in metabolic coordination between energy household and biosynthetic demands by linking the metabolisms of carbohydrates, lipids, and amino acids together.

http://www.whatislife.com/reader2/Metabolism/pathway/tca.html

This does not answer your question Monique, and you clearly do not need this, but for others needing an interactive tutorial: http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html

 

[DanP]

One thing I don't understand: when AcetylCoA can no longer enter the TCA cycle, it would mean that oxaloacetate cannot be produce. Since AcetylCoA needs oxaloacetate to enter the cycle, there appears to be a negative feedback for gluconeogenesis?

I checked prof. K. N Frayn's textbook today (Metabolic regulation - a human perspective) and yes, this is also the conclusions he does reach:

The major regulation appears to be delivery of fatty acids to the mitochondrion for oxidation. Beyond that, the availability of oxaloacetate may limit entry of acetyl-CoA into the TCA cycle. HMG-CoA is synthase is also regulated by by covalent modification by succinyl-CoA, a TCA cycle intermediate. Succyinyl-CoA competes with acetyl-CoA and can be displaced when acetyl-CoA concentration is high. Glucagon lowers succyinil-CoA concentration and so stimulates ketogenesis.

I personally wonder whatever the negative feedback on gluconeogenesis might be an adapatation for survival during prolonged starvation. Gluconeogenesis proceeds mostly on expense of proteins. In starvation, this would be mainly proteins coming from the skeletal muscles. Now, if in starvation, the brain starts gradually to use preferentially ketone bodies instead of glucose, it means that that the body can get away with less glucose produced de novo. So it makes sense to have a negative feedback on gluconeogensis, if only for conserving the proteins of the body. It would be a precious adaptation IMO.

 

[Count Iblis]

Is such a low carb diet bad for the kidneys due to the high protein intake?

 

[Proton Soup]

Is such a low carb diet bad for the kidneys due to the high protein intake?

no. and the protein doesn't need to be as high as you might imagine. depending on your goal, you could simply fill in the remainder of calories with fat. with low [STRIKE]cal[/STRIKE]carb/ low fat, you'll end up burning a lot of your own fat reserves to generate energy. and excessive protein intake will end up feeding things like gluconeogenesis.

an example of low [STRIKE]cal[/STRIKE]carb/low fat:

Am Fam Physician. 1990 Nov;42(5 Suppl):51S-56S.
Approaching the protein-sparing modified fast.

Seim HC, Rigden SR.

University of Minnesota Medical School-Minneapolis.
Abstract

The protein-sparing modified fast is a safe and effective method for losing a large amount of weight relatively quickly. This diet should be used in combination with an exercise program, behavior modification and patient education. Caloric intake is in the range of 400 to 800 per day. Candidates for the diet should be generally healthy; they should have at least 40 lb to lose or be at more than 120 percent of their ideal body weight.

PMID: 2239650 [PubMed - indexed for MEDLINE]

 

[Count Iblis]

I see! Well, I think I'll just stick to my high carb, low fat diet.