Dear Mark: Low Energy on Primal Challenge

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Updated on April 11, 2014

Calendar Dear Mark,

I’m finding that I have low levels of energy in the evenings only. Could this be because my body is still adapting to primal living and adjusting to less carbohydrate intake? How long does this usually last? I’m also finding that after my sessions of intense Muay Thai training, I don’t have the energy the next day to do much of anything regarding exercise. (My Muay Thai routine includes two hours of jumping rope, calisthenics, ab work, sparring, focus mitt work and pad work in 92-93 degree heat three days a week.) Any suggestions?

Though this scenario has some pretty specific points I’ll address, the issue of fatigue seems to be a common theme in many reader questions, especially since we began the Primal Challenge.

First off, the time a person needs to adjust to a lower carb diet depends a lot on very individual factors, including how glucose dependent that person has become over a lifetime. If you’re coming down from a very high carb intake (say, 300-400 grams a day), I recommend taking it slowly. Spend a week at 200 grams and then reduce intake to 150 grams. If you can hold it at 150 for a week or so and still feel good, you can gradually decrease to 100 or fewer if you want. Track how you feel as you reduce your carbs. And during this time, try to keep everything else the same (duration of sleep, exercise routine, etc.). Trying to do too much at one time will not only set you up for fatigue, it seriously muddies the picture as you try to understand what’s behind your low energy. For the purpose of the Primal Challenge, assess the changes you’ve made this month. Make sure you’re not overdoing it in any one area, and dial back slightly if fatigue is throwing a wrench in your efforts.

True physiological adjustment to a lower carb diet can take two to three weeks as a significant shift in gene expression gets underway. (see my post on the Context of Calories and how ketosis increases with a drop in glucose intake. (Also see this great review.) And that’s if you’re wholly consistent in your low carb routine. You’ll derail the process if you go for 400 grams of carbs on a “bad day” in the interim. Not everyone will get deep into ketosis, and that’s fine. Not everyone needs to. The main point is this: you need to be in a place where you’re making the normal 200 grams a day of glycogen from fats and protein and then you are able to easily get any “emergency” glucose for the brain from dietary protein. That’s the main reason protein is high on the PB diet…you don’t really need that much, but you have it there to be used for fuel in the event glycogen runs out (and you don’t want to tear up precious muscle to achieve that). Gluconeogenesis (where the liver converts protein to glucose), by the way, is fueled by fat. Be sure you’re getting enough total calories and that you’ve added enough protein and fat into your diet to keep you well-fueled.

Secondly, I’d like to stress that duration of exercise makes a world of difference. There’s an essential reason I recommend a person stay at or below an hour for intensive workouts. The reason “less than an hour” is so critical here is that the body can only store 200-300 grams of glycogen per day on a low-carb plan. That’s enough carbo/glucose fuel to get you through an hour or less of intense workout effort, but it’s generally not enough for 90 minutes or two hours, especially in the kind of heat our reader describes and especially several days a week. The fact is, two hours of intense cardio work (whether it’s running or Muay Thai) will leave the body lethargic or craving carbs. Very possibly both. If you keep the same workout under an hour, no matter how intense, the body doesn’t begin tearing down muscle for glucose. Moreover, it recovers efficiently by burning fat and restocking that 200-300 grams of glycogen for the next day. Especially if weight loss is a goal, working with (not against) your body’s physiology will bring the best results. Occasional longer very low level (like 60% max HR) fat-burning hikes are part of a PB-style exercise program, but when you cut back your harder workouts to well under an hour (all other PB elements in place), you’ll get better results.

A good point to consider: if your workout leaves you feeling like you’re unable to do anything that night or even the next day, you’re working yourself too hard. “Rest periods” between intensive workouts are intended for productive healing and muscle building, not for getting over extreme fatigue.

Thanks for all the great questions and updates on the Primal Challenge. Keep it up everybody, and keep the questions coming!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.