Low-carb and ketogenic diets can be tremendously effective nutrition strategies for weight loss and improving metabolic health. Does this mean they're also suitable for athlete trying to maximize performance and body composition? Not quite. Context matters. When you shift the context from overweight or obese individuals in the general population to high-level athletes pushing themselves hard to perform, the optimal nutritional strategy shifts as well.
For athletes training to achieve a personal best running a 10k, triathlon, or qualifying for the CrossFit Games, your eating strategy will not be the same as a sedentary person simply trying to lose weight.
Remember, exercise is a catabolic process, triggering a release of stress hormones cortisol and adrenaline in order to raise blood sugars to fuel your activity. If you are exercising at a slow pace (less than 65% heart rate) your body has the time to use fat as a primary fuel source. However, as your exercise intensity increases your body quickly shifts to using muscle and liver glycogen (your body’s carb stores) to fuel exercise. You have a limited capacity to store glycogen, which means after about 1-hour of training at a high intensity, you’ll likely have exhausted all your body’s glycogen stores.
WHAT’S THE PROBLEM WITH LOW GLYCOGEN STORES?
High-level athletes training hard need carbohydrates to train effectively at high-intensities, Without carbohydrate, training output falls and so too does the adaptive response to exercise. Carbohydrates are also crucial for keeping glycogen reserves topped up, critical for being able to perform in repeated training bouts. That's not all. Carbohydrates are also crucial for supporting nervous system recovery and for preventing suppression of immune system function following a hard training day, week or month.
The research is clear that if you start your next training session with low or sub-optimal glycogen status, you’ll significantly reduce your capacity to work at high-intensities and your performance will suffer. A recent study of athletes who consumed only 40% of their total calories as carbohydrates and performed “two-a-day” training sessions suffered a significant decrease in their performance during the 2nd session because they did NOT adequately replenish muscle glycogen stores.1
If you are training at high intensity and following a low-carb diet, you are treading a very fine line. Especially if your diet is always low-carb, every single day, no matter what you do in training. Fuel for the required demands; if you're working at high-intensities, restricting carbs will also restrict your ability to perform. If your goal is optimizing your performance potential, eventually you will exhibit signs of overtraining and exhaustion if you're following a 100% low-carb or keto approach.
Overtraining syndrome is when you hit a wall that lasts multiple weeks and even months. You're tired, rundown, unhappy and your numbers in the gym keep sliding backward. This can happen when you train too intensely for too long, with too much volume for too long, or without adequate rest periods or tapers built into your training regime. While you to push yourself hard and train often to be the best (i.e. functional over-reaching), you don’t want to push yourself over the edge into overtraining (or even non-functional over-reaching).
Short-term symptoms of inadequate glycogen repletion include fatigue, reduced work capacity during training, poor recovery and extended delayed onset muscle soreness (DOMS). Long-term symptoms are pronounced fatigue, reduced strength levels, and increased muscular weakness.
HOW CAN YOU IMPROVE RECOVERY AFTER EXERCISE?
To maximize performance during high-intensity training or competition is to ensure you have enough of the right food on board to fuel performance. Before intense training or competition day, you need to ensure your glycogen stores are topped up and you've consumed enough carbohydrate before training, as this is your body's primariy fuel at high-intensity. If you're exercising for more than 60-90 minutes, adding simpel carbs during exericse is a proven strategy to improve your performance.
After training, you want to stimulate the recovery process as soon as possible. The best way to accomplish this is to consume protein + carbohydate in your meal post-exericse. Aim for at least 20-30g of protein and 1-4x the amount of carbs and you'll be ready to attack the gym again the following day.
If you've got another training bout within the next 4 hours, then consuming high-glycemic index (GI) carbs immediately after training can be very helpful. High GI carbs enter the bloodstream quickly, allowing you to rapidly replenish glycogen stores in the first 30-60 minutes after training when glycogen synthase enzyme activity is elevated and allows for optimal replenishment.(2) In China, a recent study examined the effects of high-glycemic meals after exercise on performance in runners. The results showed athletes consuming high-GI meals post-training had significantly improved work capacity during their subsequent run four hours later.(4) Root vegetables make a great post-workout carb choice, especially if you bake them, which naturally raises the glycemic index of these foods. Great starchy carb options include sweet potatoes, yams, yucca, plantains, carrots, beets, parsnips, etc.
If you are on the go and don’t have time to sit down for meal, try adding some dried fruit to your post-workout nutritional arsenal. Dried fruit is very high-glycemic, and while not ideal as a midday snack when sitting at your desk, it’s a great option after vigorous activity. Try 2-4 Medjool dates for 36-72g of carbs, or half a pack of dried mangos (1.5oz provides 36g of carbs).
The total amount of carbs you consume post-training depends on a few variables: your genetics, current body-fat percentage, training phase, etc. Aim for one gram of carbs per kilogram bodyweight in the first hour after exercise (divide your bodyweight in pounds by 2.2 to achieve your weight in kilograms).(2,3) This can be repeated every two hours for up to 6 hours post-training for elite level trainees and sports that require two-a-day training, such as triathletes, Olympic weightlifters, and Ironman competitors.
WHAT HAPPENS IF YOU WAIT TO CONSUME YOUR CARBS POST-TRAINING?
Carbs directly replenish glycogen stores and after exercise your capacity to soak up carbs and top up glycogen is heightened. Research shows that if you wait several hours post-training you will reduce your glycogen repletion rate by as much as 50%(5) Not consuming enough carbs after exercise can also exacerbate inflammation, depress immunity, and lead to prolonged muscle soreness.(6) In real-life terms, the meals you consume over a 24-hour period will be sufficient to top up your glycogen stores. It's only if you're performing two-a-day training sessions, or training multiple times within a 4-6 hour time frame, that you need to really think about loading in high-glycemic carbs to maximize recovery.
If you follow low-carb, high fat (LCHF) or ketogenic diet you can still benefit by incorporating more carbs than normal post-training, without affecting your capacity to burn fat.(7) For most, adding more carbs before intense training, as well as in the post-recovery meal, is a great way to boost performance and recovery. The truth is, during high-intensity exercise the research is clear that LCHF or VLCK diets impair top end performance.(8) Adding more carbs to your nutritional aresnal is likely the added boost you need to upgrade your performance.
Remember, if you’re gearing up for a 10k run, triathlon, CrossFit Games or your competitive season, fatigue is directly related to muscle glycogen depletion when exercising at higher intensities. For optimal athletic performance, refuel with the right amount of carbs post-exercise and take your game to the next level.
Dr. Marc Bubbs ND, MSc(c), CISSN, CSCS
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1. Ivy JL et al. Muscle glycogen storage after different amounts of carbohydrate ingestion. J Appl Physiol. 1988 Nov;65(5):2018-23.
2. Jentjens R, Jeukendrup A. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med. 2003;33(2):117-44.
3. Ivy JL1.Glycogen resynthesis after exercise: effect of carbohydrate intake. Int J Sports Med. 1998 Jun;19 Suppl 2:S142-5.
4. Wong SH et al. Effect of glycemic index meals on recovery and subsequent endurance capacity. Int J Sports Med. 2009 Dec;30(12):898-905.
5. Jentjens R, Jeukendrup A. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med. 2003;33(2):117-44.
6. Flakell PJ et al. Postexercise protein supplementation improves health and muscle soreness during basic military training in Marine recruits. J Appl Physiol 2004;96:951-956.
7. Burke LM, Hawley JA, Angus DJ, et al. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med Sci Sports Exerc 20002;34:83-91.
8. Antonio J, Kalman D, Stout S, et al. Essentials of Sports Nutrition and Supplements. International Society of Sports Nutritionists. Humana Press, NY 2008.