As a person with type 1 diabetes who exercises regularly, I can tell you it's pretty much of a guessing game. I have some strategies that I use to keep my glucose in range for my spin class, aerobics, kick box, hiking and other workouts, but they are far from fool-proof -- and I've yet to find any really solid advice on BG management during these sweat-fests.
So I for one am really intrigued to see the first-ever official guidelines on managing exercise with T1D published in The Lancet journal last week as a 14-page report titled “
The new info-packed paper honing in on exercise was compiled by an international team of 21 researchers and clinicians, including some familiar names like JDRF's Artificial Pancreas lead Aaron Kowalski, and Drs. Bruce Bode of Atlanta Diabetes Associates, Anne Peters of USC Keck School of Medicine, and Lori Laffel of Joslin Diabetes Center.
It offers "guidelines on glucose targets for safe and effective exercising with T1D, as well as nutritional and insulin dose adjustments to prevent exercise-related fluctuations in blood sugar."
So what did these experts come up with? Well, let me just say that it's a comprehensive and informative paper -- explaining everything from the physiology of diabetes and exercise and the body's differing metabolic responses to aerobic vs. anaerobic activity, to sports energy drinks and the relative benefits of a low-carb, high-fat (LCHF) diet.
Disclaimers, and a Green Light
The authors are careful to make a few important disclaimers, first and foremost that one-size recommendations do not fit all, so strategies should be built around exercise types and individual aims, and should take into account "various factors including glucose trends, insulin concentrations, patient safety, and individual patient preferences based on experience."
The other main disclaimer is the simple fact that there are VERY FEW studies from which they were able to draw. "Several small observational studies and a few clinical trials have been published to date that help to inform the consensus recommendations presented here. More studies are needed to determine how to best prevent exercise-associated hypoglycemia... and how to manage glycemia in the recovery period after exercise."
They also state what seems obvious to most of us: "In general, aerobic exercise is associated with reductions in glycemia, whereas anaerobic exercise might be associated with (an) increase in glucose concentrations. Both forms of exercise can cause delayed-onset hypoglycemia in recovery."
Still, they make a big point of saying that despite concerns around fluctuating BG levels, exercise is highly recommended! "Active adults with type 1 diabetes tend to have better chance of achieving their (target A1C) levels, blood pressure targets, and a healthier BMI than do inactive patients... (and experience) less diabetic ketoacidosis and reduced risk of severe hypoglycemia with coma."
"The overall cariometabolic benefits outweigh the immediate risks if certain precautions are taken."
Gotcha, good news.
"However, older women who are active appear to have higher rates of sever hypoglycemia with coma than those who are inactive." (well, crap! bad news for me)
Which Exercise, and How Much?
The authors note that all adults with diabetes (either type) should be getting in 150 minutes of accumulated physical activity per week, with no more than two consecutive days of no activity.
They make detailed mention of aerobic activities (walking, cycling, jogging, swimming, etc.), resistance or strength training (free weights, weight machines, elastic resistance bands), and "high-intensity interval training" that involves intervals of exercise and rest.
But the consensus is: "It is unclear what the most effective forms of exercise for improvement of cardiometabolic control in type 1 diabetes are."
A few specifics they could provide are:
- Exercise can increase glucose uptake into muscle by up to 50 times
- Hypoglycemia develops in most patients within about 45 minutes of starting aerobic exercise
- Individuals who are aerobically conditioned have lower glucose variability than do those who are unconditioned
- The risk of hypoglycemia is elevated for at least 24 hours in recovery from exercise, with the greatest risk of nocturnal hypoglycemia occurring after afternoon activity
- Weight lifting, sprinting, and intense aerobic exercise can promote an increase in BG that can last for hours; although a conservative insulin correction after exercise might be prudent in some situations, over- correction with insulin can cause severe nocturnal hypoglycemia and lead to death
- High-intensity interval training has been associated with a higher risk of nocturnal hypoglycemia than continuous aerobic exercise in some cases
Starting Glucose for Exercise
Again with a lot of disclaimers about taking all the personal variables into consideration, the report recommends the following for kicking off exercise:
Starting BG below target (<90 mg/dL)
- Ingest 10–20 grams of glucose before starting exercise
- Delay exercise until blood glucose is more than 5 mmol/L (>90 mg/dL) and monitor closely for hypoglycemia.
Starting BG near target (90–124 mg/dL)
- Ingest 10 g of glucose before starting aerobic exercise
- Anaerobic exercise and high-intensity interval training sessions can be started
Starting BG at target levels (126–180 mg/dL)
- Aerobic exercise can be started
- Anaerobic exercise and high-intensity interval training sessions can be started, but beware that BG levels could rise
Starting glycemia slightly above target (182–270 mg/dL)
- Aerobic exercise can be started
- Anaerobic exercise can be started, but beware that BG levels could rise
Starting glycemia above target (>270 mg/dL)
- If the hyperglycemia is unexplained (not associated with a recent meal), check blood ketones. If blood ketones are modestly elevated (up to 1·4 mmol/L), exercise should be restricted to a light intensity for only a brief duration (<30 min) and a small corrective insulin dose might be needed before starting exercise. If blood ketones are elevated (≥1·5 mmol/L), exercise is not recommended and you should be treating your high with the help of your HCP
- Mild to moderate aerobic exercise can be started if blood ketones are low (<0·6 mmol/L) or the urine ketone dipstick is less than 2+ (or <4·0 mmol/L). BG should be monitored during exercise for further increases. Intense exercise should be initiated only with caution as it could promote further hyperglycemia
These are primarily aimed at maximizing athletic performance, the authors explain, and "are based largely on studies done in highly trained healthy individuals without diabetes, with few studies done in people with type 1 diabetes."
Basically, for intense exercise, they say that various carbohydrate and insulin adjustment strategies can be used, including reducing your pre-exercise bolus insulin dose by 30–50% up to 90 minutes before aerobic exercise, and/or consumption of high-glycemic (fast-acting) carbs during sport (30–60 grams per hour).
The optimal recipe here will vary by individual, but a general rule of thumb for "nutritional distribution of the total daily energy intake" is:
- 45–65% carbohydrate
- 20–35% fat, and
- 0–35% protein, with higher protein intakes indicated for individuals wanting to lose weight
The authors state: "The major nutrients required to fuel performance are carbohydrates and lipids, while the addition of protein is needed to help foster recovery and maintain nitrogen balance."
For protein intake, they suggest:
- Eating 1-2 to 1-6 grams per kilogram of body weight per day, varying with training type and intensity
- Eating ~20-30 grams of protein in addition to carbs immediately following exercise to promote muscle protein synthesis
They also point out that low glycemic index foods are a better choice before exercise, whereas high glycemic foods after exercise can enhance recovery. They even cite a study with proof of that, in which adults with T1D who ate low-GI carbs two hours before a high intensity run did better than those who ate more sugary stuff.
When it comes to low-carb, high-fat diets in people with T1D, they simply state that "long-term studies have yet to be done on the health, glycemia, or performance effects... (and) a concern with these diets is that they could impair the capacity for high intensity exercise."
Recommended Liquids for Exercise with Diabetes
They even have a lot to say on what we should be drinking.
Water is the most effective drink for low intensity and short-duration sports (ie, ≤45 min), as long as BG is at 126 mg/dL or higher.
Sports beverages containing 6–8% carbs and electrolytes "are useful for athletes with type 1 diabetes exercising for a longer duration (and) as a hydration and fuel source for higher intensity exercise, and for prevention of hypoglycemia. However, over-consumption of these beverages can result in hyperglycemia." Ya think?
Milk-based drinks containing carbs and protein "can assist with recovery after exercise and prevent delayed hypoglycemia"
Caffeine intake in athletes without diabetes has shown improvements in endurance capacity and power output. Caffeine intake (5–6 mg per kg body mass) before exercise attenuates the decrease in glycemia during exercise in individuals with type 1 diabetes, but it might increase the risk of late onset hypoglycemia.
Insulin Dosing Strategies for Exercise
And what about adjusting insulin? Should you be tweaking your bolus or basal doses?
Here's a rundown of what the paper says on that:
- Bolus dose reductions "require planning in advance and are probably only appropriate for exercise with a predictable intensity performed within 2–3 hours after a meal"
- Reduction in the basal insulin dose for patients on multiple daily insulin injections "should not be routinely recommended but can be a therapeutic option for those engaging in considerably more planned activity than usual (eg, camps or tournaments)"
- Where practical, a basal rate reduction, rather than suspension, should be attempted 60-90 minutes before the start of exercise
- An 80% basal reduction at the onset of exercise helps mitigate hyperglycemia after exercise more effectively than does basal insulin suspension, and appears to be associated with a reduced risk of hypoglycemia both during and after the activity; optimal timing is yet to be determined
- We propose a time limit of less than 2 hours for insulin pump suspension on the basis of rapid-acting insulin pharmacokinetics (meaning how the drug moves through your body)
To address nocturnal hypoglycemia, the consensus statement recommends about a 50% reduction of bolus insulin dose for the meal following exercise, "along with consumption of a snack with a low glycemic index at bedtime."
"Consumption of a snack alone, without changing basal insulin therapy, does not appear to entirely eliminate the risk of nocturnal hypoglycemia, and alcohol intake might increase the risk," they add.
... All very useful tidbits for managing this incredibly complex condition! And doing so while also concentrating on your workout, for God's sake.
So, all you athletic types with diabetes out there -- what are your thoughts here?