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  • Sheri Colberg, PhD

How Diets Impact Performance (in Active People with Diabetes)

Many insulin users have chosen to go “low-carb” to better manage diabetes, which may or may not impact how well they perform in athletic events. How do many athletes with diabetes who swear by extreme low-carb diets that are either high in fat (like a keto diet) or higher protein (e.g., Dr. Bernstein) perform? How do their dietary choices impact both their blood glucose management and their ability to be active?

Although I personally choose to follow a more balanced diet with a moderate intake of lower-GI carbohydrates (making up less than 40 percent of my total calories), it’s mostly because I prefer plant-based foods. As a semi-vegetarian (choosing to not eat mammals), I don’t particularly like poultry, fish, and seafood that much either but eat some because it makes managing my blood glucose easier. I avoid most bread and white flour products and strictly limit how much rice, white potatoes, highly processed carb foods, and other rapidly-absorbed, high-GI carbohydrates I eat. Natural, plant-based fiber is a staple in my diet. I also exercise daily doing a variety of activities and experience very few lows when active. I don’t actively eat low carb, but I am carb-conscious and careful with my intake.

Here’s what some other active individuals with diabetes say about their diets and performance (excerpted from The Athlete's Guide to Diabetes, Feb. 2019):

”I eat mostly low carb, but find that I often need to eat more carbs after sports in order to prevent overnight lows. I try to eat 30 percent of my daily calories from carbs, 30 percent protein and 40 percent fat each day.” — Molly M. (Canada)“

I stick to a low-carb diet. I eat a lot of meats, salads, eggs, and nuts. I avoid bread, pasta, processed food, and any type of sugar unless my blood glucose is low. I found that a low-carb diet makes it way easier to control my blood glucose throughout the day, especially during exercise. The more Humalog I use, generally the more tired I feel, and I also gain weight much easier and faster.” — Aaron G. (Minnesota)

“I normally eat a plant-based (vegetarian) nutritional lifestyle. I almost always work out fasted in the morning as I've discovered this is how I feel best and how I can maintain the best control over my blood glucose. I also practice intermittent fasting, with my first meal each day generally at about 11:00 a.m. and my last food intake around 8:00 p.m. My carb intake varies daily, and I don't particularly aim to eat low carb as I eat a lot of fruit, sweet and regular potatoes, and beans. I eat eggs almost every day and rarely eat any kind of dairy product.” — Daniele H. (Pennsylvania)“

I eat reasonably low carb most of the time, though I do “carb up” for race days and tests sometimes (for performance reasons).” — Jennie B. (United Kingdom)

“I have been following a low-carb, high-fat diet for a couple of years. It makes it easier to keep blood glucose levels stable and keeps me full so less tempted to snack between meals. Though I don't eat low enough carb to stay in ketosis. I eat 40 to 60 grams of carbohydrate per day.” — Andrea L. (France)

“I follow the metabolic efficiency diet. I eat about 125 to 150 grams of carbs per day with a diet focused on low glycemic carbs, fiber, healthy fats, and proteins. I avoid white flour and high glycemic foods.” — Conor S. (Pennsylvania)

“I stick to low carb unless in an environment of heavy training (marathon training). Consuming periodic glucose during endurance exercise and events can optimize my performance. I eat no fast food and a healthful diet full of greens and fish.” — Bill K. (Pennsylvania)

“Per Dr. Bernstein’s protocols, I eat low carb, moderate protein. I typically exercise in the morning and do not have active bolus insulin on board. I will eat small portions of dried fruit to bring my blood glucose up to 120 if it’s below that when I start. If I am going to do a race that will last more than 90 minutes, I will use UCAN 60 minutes before the race for slow acting carbohydrate during the event.” — Jason S. (New York)

“I eat low-carbohydrate, high-protein, high-healthful fat meals. I recently cycled from Perth to Sydney, solo and unsupported in a time frame of 20 days, following low carb. As a fat-adapted athlete, this also disproved any theories that such exercise must be performed consuming a high-carbohydrate diet.” — Neil M. (Australia)

“I am, for the most part, on a Paleo diet. My carb intake is ~20 to 40 grams a day. By not needing to cover a large card intake, my boluses are less, thus I am not partaking in an odyssey of hours of either being hugely high or low due to a miscalculation. The law of small numbers is the key here.” — Jay H. (Wisconsin)

“Changing my diet to no starchy carbs has been magic. I dropped Lantus from more than 30 units down to 18 per day since dropping ALL starchy carbs. I eat no breads, pasta, cereal...The carbs I consume include veggies only. Most of my workouts now require no insulin management, and I seldom get low.” — Tom S. (Texas)

“I am carb-conscious. I do not eat low carb but make smart carb decisions. I aim to eat unprocessed, homemade food as much as possible. I love cooking in the backcountry and enjoy finding recipes that are dehydrated, lightweight, nutritious, and carb-rich for trekking days, and fueling.” — Jen H. (Canada)

“I was most helped by switching my diet and way of handling my diabetes to the Dr. Richard K. Bernstein method. I spent 47 and a half years stuffing glucose in my face all day long when I was skiing, hiking, or swimming just to keep my blood sugar above 100 (5.6) and then having it fly up to the 200 to 300s later. Now that I'm eating very low carb, this problem is greatly minimized. Eating this way has significantly flattened my blood glucose graph and prevented the precipitous, scary lows of the past. I'm so thankful to have found this way of handling type 1 diabetes.” — Mary Alice (California)

"I tend to eat low on the glycemic index and very little gluten. I substitute bean noodles for wheat, and quinoa is a staple. I eat a lot of slow-cooked meals with beans and vegetables. Breakfast is usually full-fat Greek yogurt. During trail races, I eat hard-boiled eggs and potatoes, items that provide nutrition, but don't require a bolus. I don't drink sports drinks or anything with sugars that need insulin. For low correction, I eat dried fruit which I find is kinder on the stomach than simple sugars in sports drinks. I don't eat Gu or other sports gels. The less insulin in my system around exercise the better. This is not to be mistaken for low-carb or low-calorie diet; it’s just low-GI.” — Blair R. (California)

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