Ask Dr Jonny
By Jonny Bowden, MA, CN, CNS

December 14, 2006



Q. Is it true that a low-carb diet decreases your physical endurance and makes it harder to work out? I’ve heard conflicting reports. - Sam, New York

A. You’ve heard conflicting reports because there are conflicting reports. As the saying goes, “God (or in this case 'truth') is in the details.” Let me explain.

Among conventional doctors and nutritionists, the majority opinion is that carbohydrates have to be a large part of the daily diet if optimum performance is to be maintained. (Of course, majority opinion also made Clay Aiken a star and gave us “The Tyra Banks Show”). The consensus view in this case, however, is based on a long list of published studies performed over the last century that link muscle glycogen stores to high intensity exercise, bolstered by the common perception that many people following “low carbohydrate diets” frequently complain of lightheadness, weakness and fatigue.

The other side of that argument lies in our ancient history. Many hunter-gatherers (the Inuit, for example) existed on diets in which an actual carbohydrate was a rare as a Beethoven String Quartet on Paris Hilton’s i-pod. There have also been many reports of European explorers living with native hunter-gatherer societies and adapting to their meat-and-fat diet with absolutely no ill effects. In some cases, great feats of physical endurance and stamina were accomplished on these virtually carb-free diets.

How do we account for these seemingly contradictory results? One researcher, Dr. Stephen Phinney, decided to test what happens to exercise capacity on a ketogenic diet under rigorous scientific conditions. (A ketogenic diet is one that is so low in carbohydrates that the body goes into ketosis, and begins to use ketones as an alternative fuel source to glucose, an adaptation that works quite well for many people).

Phinney’s studies were pretty involved, but here’s the Cliff’s Notes version: After a period of adaptation (which took from one to two weeks), exercise performance was just fine, thank you. The only thing that was slightly depressed was sprint capability. Phinney did one study on untrained subjects and another on highly trained athletes. In both cases, there was no loss of VO2 max despite the virtual absence of dietary carbs for 4-6 weeks.

Here’s the bottom line, according to Phinney (and interpreted by me). Number one: If you’re looking at how an athlete performs in the first few days after going on a low carb routine, forget it. They’ll suck. There’s a period of adoption of at least one and maybe two weeks before performance gets back up to previous levels. (Many of the studies dissing low carb diets just didn’t go long enough to see that happen).

Number two: Phinney optimized mineral intake. In a lot of the “low carb” diets studied, folks just didn’t take in enough potassium (and sodium.) Phinney made sure that they did. It makes a huge difference in the cardiovascular reserve and in the preservation of lean body mass.

Finally, number three, all “low carb” diets are not created equal. Phinney found that the protein dose was critical. Effective preservation of lean body mass and physical performance happened when protein was in the range of 1.2 to 1.7 grams per kilogram of body weight (pay attention- it’s 1.2- 1.7 kilograms of body weight, not per pound!) The best results came when there was plenty of dietary fat. The headache and fatigue sometimes felt by people who take on a “low carb high protein diet” frequently happens when people are eating way too much protein and not enough fat.

Finally, when all is said and done, you’ve got to consider what the definition of “low carb” is in the first place. If you’re an athlete, there’s no real need to be on a ketogenic diet (the ultimate “low carb” approach), but there’s an awfully big spread between “ketogenic” and “carb loading”. You can get all the benefits of lower carb eating by just reducing carbs to a reasonable number, making sure you’re eating enough fat, and keeping protein to about 20% of calories (OK maybe 30%). For goodness sake, the current head of Atkins Nutritionals, Dr. Stewart Trager, is an ironman triathelete. Even he downs about 100 grams (or more) of carbs a day, hardly a ketogenic diet. But compared to the national average of 300 or more grams of junk carbs, that’s technically still a “lower carb diet”. As I said, “God is in the details”.

Thanks for all your questions!  Keep them coming – please send to askdrjonny@charlespoliquin.com!  Maybe yours will be next week’s featured question!

Poliquin Performance is pleased to have Dr. Jonny Bowden as a member of the Poliquin Performance team!  Jonny Bowden is a board certified nutritionist, life coach, seminar presenter and former certified personal trainer.  His newest release “The 150 Healthiest Foods On Earth” (Fairwinds) will be available January 2007.  Purchase Dr. Jonny Bowden’s latest CD sets, including “Change Your Body, Change Your Life: Diet Boot Camp”; “23 Ways To Improve Your Life” and “9 Essential Steps To Weight Loss” in our on-line store soon!  Please visit Jonny at http://www.jonnybowden.com!

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