How low-carb does an athlete with diabetes really need to go?
By Sheri R. Colberg, PhD, FACSM
There has been a lot of interest recently in going “low-carb” to better manage diabetes, particularly type 1. At present, a large clinical study (1) is being undertaken in Scandinavia to examine the effects of very low-carb eating on blood glucose levels in adults with type 1 diabetes. For years, a very low-carb diet championed by Dr. Bernstein has been the main one followed by some with diabetes, until the last decade when fad weight loss plans like the LCHF (low-carb, high-fat, or Keto) and Paleo Diets have been become mainstream not just for losing weight, but also for their purported ability to boost to athletic performance and improve blood glucose management.
All these eating plans are very low in carbohydrates, but differ in the types of non-carb macronutrients or foods they recommend. Dr. Bernstein’s plan advocates higher protein intake and only 30 grams of carbs daily. The LCHF Diet gets 70% of calories from fat, 15% from carbs. Paleo Diet eating focuses on “natural” foods that nomadic early man supposedly ate (higher protein). Honestly, LCHF diets remind me of the no-carb, starvation regimen that everyone with type 1 diabetes had to go on to survive for a few months or years after diagnosis back before insulin was discovered in 1921. Have we really come full circle back to that diet in mainstream eating for diabetes? This question is particularly relevant to athletic individuals with diabetes. We have often preached the importance of carb loading (think “pasta party”) for endurance athletes prior to events. Can they perform at the top of their game while eating very few carbs?
At least one study in type 1 diabetes has shown that it’s possible to balance blood glucose levels and prevent lows while doing long-duration endurance events and consuming 75 grams of carbs per hour, like many nondiabetic endurance athletes do (2). For intermittent sports like soccer and rugby, it also appears that ingesting 30 to 60 grams of carbs per hour has the greatest impact on performance when fatigue or hypoglycemia are more common, such as towards the end of a game (3) (although this has only been studied in nondiabetic athletes).
That said, it also appears possible to adapt to using more fat as a fuel after becoming keto-adapted from low-carb eating. Highly-trained, keto-adapted ultraendurance athletes have extraordinarily high rates of fat oxidation, but their use of muscle glycogen and its repletion during and after a 3-hour run are similar to athletes on high-carb diets (4). Some questions remain as to whether this improves performance in most events; likely, it does not, but performance is likely at least maintained (5). For instance, keto-adapted, off-road cyclists experience greater fat use, but higher heart rates at the same workload during training following LCHF diets containing only 15% of daily calories from carbs (6). With their average calorie intake, though, this amounts to nearly 150 grams of carbs daily, much more than many low-carb advocates allow in their diets.
To my knowledge, no studies to date have been conducted on keto-adaptation and performance in exercisers with diabetes. However, I recently surveyed over 275 active individuals with diabetes to collect information to update my 2009 book (7), Diabetic Athlete’s Handbook, as a second edition is coming out in Spring 2019. I was surprised by the large number of athletes claiming to be following very low-carb dietary regimens. Based on their responses, it appears entirely possible to undergo fat adaptation and exercise regularly—at least when engaging in endurance type training and events. These exercisers worry less about getting hypoglycemic during events as they have lower levels of insulin on board, but many others accomplished the same reduction in the risk of lows simply by not taking bolus insulin within a few hours of being active (even if eating more daily carbs).
There are several caveats to these survey results. All normal dietary patterns by these active individuals (most with type 1 diabetes) were self-reported, and I did not analyze their actual daily carbohydrate intake. Some claimed to eat only 20 grams of carbs a day, but it’s possible they weren’t including carbs from every food, including the many avocados (12 grams of carbs per medium one), olives (2-3 grams per 10 olives), and nuts they were consuming. Any carbs taken in during activities, even if taken to prevent or treat lows, count towards daily total intake. What’s more, if an average active individual consumes about 2,000 calories per day, getting 15% of calories from carbs (like most LCHF diets advocate) still equates to 75 grams per day, which is not nearly as low as the 20-30 daily grams many of these athletes claimed to be eating.
So, how low-carb do athletes with diabetes really need to go? In all likelihood, it depends on the sport and level of athlete. Sure, most of us can benefit from avoiding or limiting our intake of refined carbs and foods with a higher glycemic index to better manage our diabetes, but going to the extreme of avoiding nearly all carbs may not be necessary. If you do decide to try a lower-carb diet, keep in mind that adapting to training with fewer daily carbs requires several weeks, so don’t just cut carbs for a few days and expect to feel good during any type of exercise.
- Lennerz, B.S., A. Barton, R.K. Bernstein, R.D. Dikeman, C. Diulus, S. Hallberg, E.T. Rhodes, C.B. Ebbeling, E.C. Westman, W.S. Yancy Jr, and D.S. Ludwig. Management of type 1 diabetes with a very low-carbohydrate diet. Pediatrics May 7, 2018. doi: 10.1542/peds.2017-3349. [Epub ahead of print]
- Adolfsson, P., S. Mattsson, and J. Jendle. Evaluation of glucose control when a new strategy of increased carbohydrate supply is implemented during prolonged physical exercise in type 1 diabetes. European Journal of Applied Physiology 115:2599–2607, 2015
- Baker, L.B., I. Rollo, K.W. Stein, and A.E. Jeukendrup. Acute effects of carbohydrate supplementation on intermittent sports performance. Nutrients 7:5733–5763, 2015
- Volek, J.S., D.J. Freidenreich, C. Saenz, L.J. Kunces, B.C. Creighton, J.M. Bartley, P.M. Davitt, C.X. Munoz, J.M. Anderson, C.M. Maresh, E.C. Lee, M.D. Schuenke, G. Aerni, W.J. Kraemer, and S.D. Phinney. Metabolic characteristics of keto-adapted ul-tra-endurance runners. Metabolism 65:100–110, 2016
- Burke, L.M. Re-examining high-fat diets for sports performance: did we call the “nail in the coffin” too soon? Sports Medicine Auckland New Zealand 45: 33–49, 2015
- Zajac, A., S. Poprzecki, A. Maszczyk, M. Czuba, M. Michalczyk, and G. Zydek. 2014. The effects of a ketogenic diet on exercise metabolism and physical performance in off-road cyclists. Nutrients 6:2493–2508, 2014
- Colberg, Sheri. Diabetic Athlete’s Handbook. Champaign, IL: Human Kinetics, 2009
Sheri R. Colberg, PhD, is the author of Diabetes & Keeping Fit For Dummies. She is Professor Emerita of Exercise Science from Old Dominion University and an internationally recognized diabetes motion expert. She is the author of 12 books, 25 book chapters, and over 300 articles. She was honored with the 2016 American Diabetes Association Outstanding Educator in Diabetes Award. Contact her via her websites (SheriColberg.com and DiabetesMotion.com).
The above tips come from my latest book, Diabetes and Keeping Fit For Dummies. It offers all the guidance and step-by-step instruction you need to make exercise a priority in your diabetes management. This informative, down-to-earth guide shows you how to incorporate exercise into your routine, even if you haven’t been in a gym since high school. Get it online at Amazon.com or Dummies.com/store.