One of the major criticisms of low-carb nutrition is the assertion that carbohydrates are NEEDED by the body to power effective workouts.
Does science actually back this idea up?
Are there other alternatives to carbs? Let’s have a look.
There’s no doubt that the majority opinion is that carbohydrate is the superior fuel, especially with results from studies like the 1939 Danish endurance test , and the Second World War ‘Pemmican’ study .
But the one weakness of these types of studies is DURATION i.e. a couple of days to a week! This is hardly long enough to really assess the effect of low-carb/ketogenic diets on performance.
We know that a body that burns fat as its primary source of fuel requires different enzymes to function than a carbohydrate metabolism. Synthesizing the correct enzymes in sufficient quantities to become a fat-burner takes a little time. Only THEN can we truly access the effects of a low-carb diet on exercise performance.
Once adapted, exercise performance is as good as ever. The truth is that if you are working out for less than an hour (as we do with THT workouts), the body doesn’t rely much on stored carbohydrate (glycogen) for fuel, ketones can easily take care of it.
One 8-week, metabolic ward study by Dr. Stephen Phinney  tested the above hypothesis i.e. that there is no detrimental effect on exercise performance after fat adaptation has occured.
“Treadmill performance testing of these subjects included determinations of peak aerobic power (VO2max) after a 2-week weight maintenance baseline diet, and again after 6 weeks of the ketogenic weight loss diet. Endurance time to exhaustion was quantitated at 75% of the baseline VO2max.”
The endurance test was undertaken during…
- baseline, maintenace diet
- 1 week into the ketogenic diet
- after 6 weeks on the ketogenic diet
|Exercise parameters of Vermont study |
|Baseline||Week 1||Week 6|
|Endurance time (min)||168+||130||249+|
LPM, liter per minute *week 6 < baseline, P < 0.05 +week 6 > baseline, P < 0.01
Phinney Nutrition & Metabolism 2004 1:2 doi:10.1186/1743-7075-1-2
Some interesting observations here. Yes, the subjects did see a decrease in endurance after 1 week on the ketogenic diet but lets see what happens after 6 weeks.
Endurance time on the keto diet was significantly INCREASED over the baseline value. Also, the oxygen/energy cost of the test was significantly DECREASED compared to baseline. According to conventional wisdom; that’s not supposed to happen!
Now, the subjects did lose weight, in fact, they lost an average of 22lbs! However, this was compensated for by making the subjects wear a backpack during training, which weighed the same as the weight they had lost.
An interesting point is that the keto diet employed in this study was quite low fat and low calorie! A higher fat content can MORE than cope with the demands of weight training AND intense cardio sessions like HIIT.
Secondly, as far as energy expenditure goes, weight training is not as costly as long cardio sessions. Short bursts of energy with longer break times in between for a total of 40-50 minutes can easily be supported by a ketogenic diet.
A second study   was carried out by Phinney to correct for weight loss and possible fitness improvements of the subjects. Already highly-trained, competitive bicycle racers adapted a high-fat diet (83% of total calories) which was carefully designed to prevent weight loss.
While this study didn’t show actual improvements in performace in the keto group (as expected), it did corroborate the position that fat is AS GOOD an energy source as carbs for athletes.
Aside from the studies, there is also the information we have about inuit populations surviving off diets virtually free of carbohydrate. I thought the following from Dr. Phinney was an interesting historical note…
“One of the earliest documented demonstrations of physical stamina during a ketogenic diet was the Schwatka 1878–80 expedition in search of the lost Royal Navy Franklin expedition…The leader of this expedition, Lt. Frederick Schwatka, was a graduate of both West Point and Bellevue Hospital Medical College. His summary of the expedition was published as a news article in the New York Herald in the Fall of 1880…In one notation, Schwatka provides an interesting insight into his weaning from their initial supply of carbohydrate-containing food. ‘When first thrown wholly upon a diet of reindeer meat, it seems inadequate to properly nourish the system, and there is an apparent weakness and inability to perform severe exertive fatiguing journeys. But this soon passes away in the course of two or three weeks.’ “
In summary, the point I’m making is that BOTH carbs and fats are good energy sources. Which one you use is simply up to you. I feel that for reasons of a boosted anabolic hormone profile AND the preservation of lean muscle mass, low-carb (or carbohydrate cycling to be more exact) is more advantageous for the bodybuilder.
Can someone run a marathon on ketones? I don’t know, nor do I care. I won’t be running one any time soon 😉 . If YOU are and you feel they help, eat them. I know from some online buddies that it certainly is possible for them to complete one while in ketosis. However, it would take a ward study to actually prove it.
I’m really not that interested. As long as I can lift the iron and perform my cardio come cutting time, I’m happy 😀 .
 Christensen EH, Hansen O: Zur Methodik der respiratorischen Quotient-Bestimmungen in Ruhe and bei Arbeit. Skand Arch Physiol 1939, 81:137-71.
 Kark R, Johnson R, Lewis J: Defects of pemmican as an emergency ration for infantry troops. War Medicine 1946, 8:345-52.
 Phinney SD, Horton ES, Sims EAH, Hanson J, Danforth E Jr, Lagrange BM: Capacity for moderate exercise in obese subjects after adaptation to a hypocaloric ketogenic diet. J Clin Invest 1980, 66:1152-61.
 Phinney SD, Bistrian BR, Wolfe RR, Blackburn GL: The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation. Metabolism 1983, 32:757-68.
 Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL: The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983, 32:769-76.
 Stackpole EA, ed: The long arctic search: the narrative of lieutenant Frederick Schwatka. Mystic CT. The Marine Historical Society 1965.
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I agree. I’ve been doing a very low carb usually no more than 20g per day and it totally got me ripped last year. The best one that works for me is protein based on my lean weight and the rest fat. My abs just started coming out all of a sudden and the definition was there. I tried just about every diet out there and this one is the best. I have more enery of this diet than I do when I add carbs. I actually started adding more protein to my diet and some more carbs for a month now and I put on more muscle but my fat percentage also went up. I started the low carb again as of today for the summer and will probably be doing the GLAD diet come winter. Also, when I eat carbs, I’m always very bloated and and very uncomfortable, with the high fat, I don’t have these problems. Maybe I’m carb sensitive. I’m going to compete for my first time next year in April in either the fitness or figure category and this is the diet I’ll be using to cut up. Love all yours articles!!
Same story as Josephine here, except I’ve also noticed that I don’t get nearly as cold in the winter as I used to since going low-carb. Strange, huh?
Great research. I’ve been on the Anabolic Diet for a few months, but it’s hard not to eat carbs when they seem ubiquitous in modern society. Plus my parents don’t like that I’m eating so much fat. I’ve noticed that carbs now make me feel tired and less satisfied, however, and hopefully any cravings will soon be completely gone.
Anywho, this is just the type of research I wanted to see. I don’t know how you find all of these, studies, but keep it up. Great article.
I find no drop in performance without carbs. The only carbs I eat are from lots of green veggies (broccoli, cauliflower, asparagus, cabbage, spinach etc, and the occasional apple. I weight train 5 days a week for 1 hour per session and get good pumps and finish the hour feeling great! I usually have a slurp of extra virgin olive oil a few times a day, get a very good one and they taste quite nice. I eat lots of full cream (no milk) cheese and leave the fat on my steak. I never feel bloated anymore and don’t crave junk or bread or pasta etc. I have been eating virtually no carbs for over 6 months, previously low carbs but I cut out wheat and grains as an experiment.
All I can say is it works for me.
Jimmy More got an interview with world-class Swedish triathlete Jonas Colting.
He credits his low carb diet for his results.
Link with to Jimmys blog where you can hear an interview with Jonas.
hmm, so i generally eat low carb anyways – do high fat to keep weight on (i love peanuts, so usually go with those) and also do an occasional ‘weekend carb load’ every other weekend (meaning, eat a lot of crap), but this is all because i tend to shrink rapidly without some kind of light carb intake…
*however* regarding ketogenics and energy, you may find more interesting studies in the world of epilepsy – the ketogenic diet and approach was actually first used to treat epilepsy (with strong results for seizure control in children) a long, long time ago – and they only happened to notice that it had a strong effect on weight control with high energy levels (meaning no loss of muscular tissue, but rather lower body fat etc)…
I am 6 weeks into my low Carbs/high Fat/Carbs loading life style(Don’t like the word Diet). I have tried 60, 40, 20 grams of Carbs to see how my body adjust and to see what is best for me. I am still able to lift heavy and do cardio on the low carbs day and I love the look and the fat burning feeling. I am more weak on the 20 grams of Carbs but I see more cut from it and muscle may be a lttle flat. When I carb up I am very strong but it’s true I do feel a little boated (Squat and bench on those days). I use 20 grams on my day off lifting and 40 grams when training and I find that does the trick. Mark I have one question is Dextrose power ok to bump up the Carbs on the carb loading days.
Thanks for alway providing good reading and motivation for us.
The point at which the body switches over to primarily glucose oxidation is called the Lactic Threshold, and it roughly corresponds to 75% of VO2 Max in trained individuals (so the study was conducted at the LT). Performance above the LT requires a ready supply of glucose, with Liver glucose playing a major role. So once in ketosis, exercise above the LT up to the VO2 Max threshold will suffer, while exercise below the LT will not. Note that ketones do not get used by muscles for fuel to any significant degree (being mainly reserved for the brain).
If you look at any non-beginner marathon training program, you’ll see that you need to do three basic types of training runs.
1.) Intervals at VO2 Max pace, which is roughly the pace you can sustain for 11-minutes and no more. Research has shown that this tyep of workout increases mitochondria density in Type IIA fibers the best.
2.) A 25-30 minute run at just above the LT, which turns out to be just about the pace you can hold for 25-30 minutes and no more. Same study shows that this increases mitochondria density in Type I fibers the best.
(Ref: Dudley, G. A., P. C. Tullson, and R. L. Terjung. Influence of mitochondrial content on the sensitivity of respiratory control. J. Biol. Chem. 262: 9109-9114, 1987)
3.) A long run at 65% of VO2 Max pace to full fatigue. This run likely is responsible for making Type IIA fibers act more Type I like (eg. the Type IIA mitochondria adapt to convert fat more readily into ATP).
I am on a cyclic ketogenic diet, and I am training for a marathon while also continuing to lift weights to add muscle mass. For my aerobic training, I do VO2 Max interval runs (timed miles) on Sunday after my carb up while Liver glycogen is still available. I then do a 30 minute run on Tuesday at just above my Lactic Threshold pace (I eat an extra 25-40g of low GI carbs at lunch that day). Then I do my long endurance run on Thursday (completely in a ketogenic state by now). I then do a 48 hour carb up on Friday and Saturday.
The point is, glucose may be needed, even by endurance atheletes, but there’s no reason a cyclic ketogenic diet cannot provide it. Interestingly, I’m aware of no studies that have specifically looked at the effects of a cyclic ketogenic diet on endurance atheletes (and I have looked).
I am not sure if you have ever mentioned this in any of your blogs, but i was wondering if sugar alcohols should be counted when calculating net carbs when on the mans diet.
@Zack. Yes, count sugar alcohols – most are bad news. Some are ok like erythritol. For more, see my post here
@David. Thanks for your input. Yes, CKD’s are certainly sufficient for weight training. You’re right to have extra carbs on the Tuesday. I advise some people who feel performance is starting to suffer to implement a mid-week carb spike.
@Ian. Yes, dextrose is ok. In fact, high GI carbs have been shown to be better at refilling muscle glycogen than low GI ones (at least for the first 24 hours of a carb up). Just don’t dump 100g into you at 1 time. 50g of carbs at a time works well.
@Dave. Yes, I’ve heard about epileptics being put on ketogenic diets before – haven’t really studied it much though. Thanks.
@Rikard. Thanks man.
@Josephine, Sean, Ben, & Alan – Thank You! 🙂
I know a real difference has been made in my progress after I’ve stopped eating so much grains & carbohydrates. I’ve also felt a great deal more energy.