Kurt G. Harris MD

PāNu means paleonutrition. The "paleo" here signifies "old" and not necessarily paleolithic. The PāNu approach to nutrition is grounded on clinical medicine and basic sciences disciplined by knowledge of evolutionary biology and paleoanthropology. The best evidence from multiple disciplines supports eating a pastoral (animal-based) diet rather than a grain-based agricultural one, while avoiding what I call the neolithic agents of disease - wheat, excess fructose and excess linoleic acid.

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There are no essential carbohydrates, even for athletes

Despite current nutritional dogma dating from the 1970's, carbohydrate consumption is completely unnecessary for your energy (or any other) needs. Fat is the primary way we store energy in our bodies, and eating fat is the evolutionarily preferred food source in a food-abundant environment.* During aerobic exercise, the predominant fuel source is fatty acids, supplemented by glycogen stores.

It is possible to eat no carbohydrates at all and still do plenty of physical work. Any carbohydrates needed not provided from glycogen or food can be produced in abundance via gluconeogenesis. Glucose provided this way makes you literally burn fat, and keeps your insulin levels low.

You have about about an hour or more of exercise in your liver and muscle glycogen.

If you are a lean runner, you have enough energy in your body fat to walk about 800 miles.

You simply don't need to eat carbohydrates to exercise.

Try this:

Once you are adapted to low carb intake (it may take 6 weeks or more, so go slowly) your mitochondria, including in your muscles and your brain, will literally proliferate and be more energy efficient. Gradually start doing your workouts with less and less carb consumption prior to exercise, to the point where you are solely working out in the fasting state. By fasting state I mean no food for at least 12 hours. Now, most people think I am a lunatic when I suggest this, but hear me out.

I have talked about intermittent fasting as a complement to low carb eating to keep your insulin levels low. One reason they are complementary is once you are off the glucose/insulin hormonal yo-yo, your ability to tolerate fasting is increased immeasurably. On a very low carb diet you are literally never hungry, in that desperate way you are when you are carb-dependent. Intermittent fasting is absolutely the best way to keep your insulin levels as low as possible (more on why that is good in the future)

Working up to fasting workouts slowly, and once you have been on a low carbohydrate regimen for several months, you will find that your performance (running time, max lifting) eventually equals or exceeds what you could do before with a meal 2 hours before, as your body becomes more adapted to fatty acid metabolism and less dependent on glucose .

Now here is the good part. When you race, you have new mitochondria and your newly efficient fat-preferring metabolism. Add a moderate carb load and some GU bars if its a long race, and you will be faster than you were before. Glucose is now your nitrous oxide, not your primary fuel.

When you want to climb K2, you train in Leadville, Colorado, where the air is thinnest. Training at 10,000 feet is harder at first but more effective. Same with fasting workouts. 

*When food was abundant in paleo times, it was often because there were large mammals rich in fat stores. Humans ate the fat, and it was adaptive for them to be satiated because food was abundant. No insulin response to make them store the fat, just use it for fuel and waste the rest. Conversely, when fruits were available they were much less calorie dense than their modern versions and in many environments only seasonally available. Fructose seems to work the opposite of saturated fat - the hormonal signal to the body is to store it and keep eating more. That may be why fructose is sent straight to the liver to be converted into triglycerides. Eating lots of high density fructose-laden food year-round in a food abundant environment is not something we are adapted to. The paleo enviroment we need to emulate is the one metabolically closest to our current condition of food abundance - high fat consumption.


Reader Comments (16)

the idea of fruits appearing before winter, triggering insulin to spur fat storage, is intuitively appealing to us residents of temperate climates. but is this the climate in which our ancestors evolved?

June 1, 2009 | Unregistered Commenterjeff klugman

Hi Jeff

This paragraph is part heuristic, but based on reasonable inferences. Trying to describe 2 million years of evolution in one paragraph is always a bit cartoon-like. We know that fructose has some uniquely bad metabolic properties for humans that all seem to cluster around fat storage and with it come some metabolic and hormonal effects that would not be adaptive (and clearly aren't) if fructose were supposed to be our primary food source. I think some combination of much lower potency compared to modern frankenfruit and seasonal availability combine to explain how the negatives of fructose could have been adaptive in some circumstances. Remember, all fauna have co-evolved with our foods - fruit is sweet so animals will eat it and the plant does not care if that is good for us- the opposite evolutionary strategy to cereal grains which were and still are trying to poison our guts to discourage consumption.

How much of our relevant evolutionary history involved eating the modern versions of what people now call fruit? very little.

How much have we evolved towards carnivory as the transition from the tropics to the savanna to ice age europe where sapiens and neandertalensis had the same diet as top level carnivores like wolves?

A lot in my opinion.

June 2, 2009 | Unregistered CommenterKurt G. Harris Md

I found your posting very interesting and wanted to share with you my own experience. what you have come to learn with a medical and biochemistry background I also learned blindly with self-experimentation. Having lived in the epicenter of vegetarianism (Santa Cruz CA) I was pretty brainwashed for many years about what was good nutrition. I moved to the tropics some time ago and I realized that my "mild" candida and endometriosis symptoms were worsening. I think that the climate exacerbated these illnesses along with a diet high in sugars. I cut out all sugar for about 6 months and practiced specific Yoga exercises and both cleared up %100. I became interested in learning the sources of nutrients and wading through the nonsense in most books I ended up concluding that all those nutrients that are now sold to us in pill form (ALA, CLA, vitamin E, glucosamine) are all found in REAL food.

Once My system was cleared of most things on your list ( I can´t resist a good bowl of home made chili once a month and I do consume cheese and yogurt) I realized that as a side benefit I had a much greater athletic endurance. I could make a lot more effort and not feel fatigued. I could go to the pool and swim 2 hours in the morning on an empty stomach, having not eaten since dinner the previous night, and feel strong and lucid. My nutritionist friend was in horror . I told her that fat is a much more consistent energy source for me and there was a look of disbelief in her face. I am asked what the secret is to my lean and muscular build and once I tell them, I can see the person´s eyes glaze and tune me out. That was not the answer they were looking for.

As much as people complain about the beef here in Panama being "tough" all the cows live their lives in fields eating grass until the truck rolls up to takes them to slaughter. There are no hormones and few antibiotics and I am leaning to like beef. Adding beef along with locally produced coconut oil and palm oil has increased my intake of saturated fats.This is year 3 on this eating regimen and I can honestly say that I have never felt better and plan on continuing with this experiment.

I look forward to your next posts

June 12, 2009 | Unregistered Commenterclara

Hello Clara

Thank you for your interest. My experience in the training effects of Paleo/LC eating was also acquired accidentally. I noticed after about a 18 months of LC eating that a morning workout ( 3 mile run plus 40 minutes of weight training) was quite easy with no breakfast, just an extension of the hunger free fasting I was already doing several days a week. After some reading and further theorizing, I and some more athletic associates began experimenting with fasting workouts and we've had nothing but positive results. Glad to hear your success story.

June 13, 2009 | Registered CommenterKurt G. Harris MD

GU or Hammer gel in addition to an electrolyte tab (salt) and a 1/4 protein, 3/4 carb drink (perpetuem - http://www.hammernutrition.com/za/HNT?PAGE=PRODUCT&PROD.ID=4047) is a standard for ultra runners. I have been using a similar diet on long training runs (3+ hours) and mountaineering efforts (8+ hours). Following a low-carb, paleo diet, downing this stuff seems questionable. Any advice? I've considered trying to shift to real food (paleokit - http://paleokits.bigcartel.com/) but I'm not sure if this is too difficult to digest while maintaining 60-70% max HR. Thanks in advance.

June 25, 2009 | Unregistered CommenterNed

Hey Ned

I am more into paleonutriton as a health idea than a fitness enhancer. I don't think lots of multihour steady state exercise does anything to
improve your resistance to disease or your general health. I am somewhat with Mark Sisson that it may do just the opposite.

That, said, I totally get the challenge of competition and I personally run a bit ( 10-12 miles a week) just because it feels good to do it.
I only train in the fasting state, but if I were trying to win a race, I would load with some source of glucose.

I used to climb in my younger days. If I did so now, I would probably carry those paleo kits or zone bars if they were gluten free. Better yet, a big chunk of cheddar cheese and a tin of sardines. I must say that for climbing, your metabolic headroom and the ability to function safely on an unintended bivouac will be greatly enhanced if you do fasting workouts and only supplement with carbs on the real climb.

If you want competitive performance enhancing advice, try Chris at conditioning research or Robb Wolf -they are more real competitive athletes than I am.


June 25, 2009 | Registered CommenterKurt G. Harris MD

Kurt, thanks for the feedback. I do follow Robb Wolf's site, but I value your input as you have a slightly different viewpoint. Yes, ultras may not be health enhancing, and I don't plan on doing them forever, but I am driven by the challenge! Thanks again and I really enjoy your site. It has served not only as a great resource, but a place I sent friends who want to know why I eat the way I do.

June 26, 2009 | Unregistered CommenterNed

Thanks for spreading the word, Ned

I try hard not to claim happiness, longevity or eternal life effects with my dietary ideas.

wouldn't avoiding alzheimer's, cancer and coronary disease be plenty enough?

Some factions of the fitness crowd behaves as if they will never die or even age and I find that a bit creepy. Maybe I am just jealous of their performance, but if you are a climber you know what I am talking about - the "good" reason to do these athletic pursuits is to live, not to live forever.

Climbing and running on a treadmill could not be more different activities on a philosophical level. I have no argument with athletic pursuits even if they might kill you - just the superstition that running marathons makes you immortal - it sounds like an exaggeration but in the 80's the whole culture thought that.

If you are a well trained athlete and are LC and in or near ketosis most of the time, I think you can put any non-wheat fuel that your body can burn into it when you do the "real thing" like climbing or ultramarathoning - that is not the time to be an ascetic and you are not doing that pursuit for physical health reasons anyway.

Robb is very cool in that he is anti-grain. He may be a bit constrained by his CF affiliation but he seems to have modified Zone to be pretty close to a PaNu type diet. I am highly skeptical of quantitative titration of macronutrients a la zone as a health measure, but as you say, Robb is more perfomance oriented.

Just more rambling, but that's my opinion


June 26, 2009 | Registered CommenterKurt G. Harris MD

In your post you said:

"During aerobic exercise, the predominant fuel source is fatty acids, supplemented by glycogen stores"

"Once you are adapted to low carb intake (it may take 6 weeks or more, so go slowly) your mitochondria, including in your muscles and your brain, will literally proliferate"

Source please?

I really liked your blog. I do my self practice a low carb/high fat diet and I feel great.


July 2, 2009 | Unregistered CommenterMiguel Angel

Hi Miguel

Here are a few re: Mitochondrial function in the brain with ketosis. Happens quicker than 6 weeks actually - just being conservative





July 2, 2009 | Registered CommenterKurt G. Harris MD

From what I understand, mitochondria mutate slowly, which is partially why there are so few disorders with them. Wouldn't encouraging them to mutate faster increase the risk of those disorders? (Not that isn't possibly better than many modern illnesses, but just a point)

August 28, 2009 | Unregistered CommenterAnn

hi -

I think carbs are needed for certain heavy training in sports such as tennis, which involves a lot of intermittent sprinting. I found that out by trying to train on VLC (around 10-20g carb/day 70-80% fat), even after a whole year I could not keep up, and eventually got a leg injury. Swimming and walking seems fine on no carbs, but tennis is a problem. I could train as long as I had 3-4 days rest in between, but usually I only had 2.

It would seem that my legs need glucose, and faster than it is getting replenished by gluconeogenesis. My arms and upper body strength do not suffer, but multiple sprinting - forget it. That is when the heart rate goes above a certain level, the exercise is then anaerobic, and glucose is needed. I think I have that right?

Taking a lot of protein in a protein shake beforehand somewhat helps but again the body can only do so much gluconeogenesis on demand, so there needs to be breaks between points or sprinting. Nothing really compares to carbs for replenishing glycogen for this kind of sport. Other sports seem to be more fat-burning.

September 4, 2009 | Unregistered CommenterLouisa

Mitochondria are capable of processing carbs, triglycerides and proteins. Your basic requirement for glucose is for those cells that go without mitochondria. The idea that glucose is the superior fuel for your muscles is a myth. It is just that your body needs 4 to 6 weeks to adjust to a low carb diet. After this period there is NO difference in performance.

As a matter of fact, cancer cells don't have mitochondria. So they rely on glucose to be able to grow. And they want to grow fast! Don't feed your cancer!

November 1, 2009 | Unregistered CommenterAndré

This reminds me of when I had a job with plenty of medical and nutritional textbooks lying about. Having just started on a low-carb diet, I checked one that said something like this:
'From anthropological studies (of the Iniut and so on), it appears that the required dietary carbohydrate intake for humans is zero.'
Great, right? Ah! But the sentence that followed immediately was:
'Nonetheless, health experts recommend at least 300 grams of carbohydrates a day to avoid adverse effects such as ketosis.'
I've remembered it to this day, almost word for word, because it was such a complete non sequitur. 'You don't need any dietary carbohydrates at all ... but you should eat at least 300 grams worth of carbohydrates a day.'
And to say it again, just because the whole experience was so weird: evidence says you need ZERO dietary carbohydrates, but anyway we'll insist that you should eat at least 300 grams per day.
Dr. Harris, this being a first post, let me thank you for the great work you do for all of us with this site. Without people like you, we'd all still be eating crap.

November 6, 2009 | Unregistered CommenterEric

Hi Kurt,

I've just started reading your blog and I am currently following intermittent fasting where I usually fast twice per week (24h at a time). Some of the topics you've discussed are eye opening and challenge the conventional approach to nutrition that we have been force fed all these years.

My sporting background is endurance related, specifically Ironman triathlon (taking a break at the moment) which involved 20h+ of training per week and racing 9h+ which consists of 3.8km swim, 180km bike, 42.2km run.

Relating this back to your post, it is just not possible to compete in such a race without CHO for fuel. It requires CHO loading leading into the race and a constant trickle of CHO during the event to be competitive and not hit the wall so to speak. My general CHO requirements during competition range b/w 70-100g/hr depending on intensity.

Perhaps the term "athletes" is a tad too generic in your blog title. Sure, I can certainly cycle of 3h, approx 100km without any CHO but athletic performance starts to deteriorate close to or beyond this length of time.

Any thoughts?



How much experience do you have training on a VLC regime for at least, say, 6 months?

December 19, 2009 | Unregistered CommenterMark

Hi and excuse me for butting in but I have been recently reading about a father son endurance bicycling team experimenting with just that. The father insists on the normal carb load while the son is zero carbs and having interesting success with fat loading before a race while fully keto adapted. He has more even energy levels wilt no "wall" effect. I will try to find it again.

December 22, 2009 | Unregistered CommenterAlan
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