Mastering Long-Distance Swimming With Type 1 Diabetes

People with diabetes can’t access glucose data in the water, which adds complexity to blood glucose management in a sport like endurance swimming. A long distance-swimmer with T1D and his dietitian discuss the best way to fuel with type 1 diabetes; their advice might surprise you.

These days, it’s quite common for people with type 1 diabetes (T1D) to excel in land-based sports such as football, cycling, and running. But might long-distance endurance swimming be just too tough with T1D? Not for New Zealander Paul Spurway. 

Diagnosed with T1D at age 18 years, Spurway used exercise as a key component to managing his condition from the beginning. He was initially a long-distance runner until his knees put an end to that in his late 30s. So, he switched to the swimming pool. He then connected with a group of long-distance outdoor swimmers and decided to give that a go, despite the extra glucose management challenges. 

“In the water you don’t have access to your glucose data. You can’t prick your finger. The challenge is making sure you’ve got enough fuel in the body, not only to keep the engine working but also to keep the sugars under control. It takes a lot of trial and error,” Spurway told diaTribe.  

So why does he do it? “I find it very rewarding mentally and physically,” he said, “and with the right checks and controls in place, it’s something that can be very enjoyable.”

Soon after he switched from running to swimming and while he was living in London, Spurway’s diabetologist referred him to a multidisciplinary diabetes exercise clinic within the National Health Service’s Imperial College Healthcare NHS Trust. There he met Siân Rilstone, a dietitian who specializes in diabetes and sports nutrition. 

Rilstone recently authored a paper, along with Spurway and two other clinicians, about Spurway’s experience. In it, they detail his nutritional requirements, insulin adjustments, and other considerations before, during, and after his swims. 

“Paul was our first endurance swimmer,” she told diaTribe. “There is no published data about T1D and endurance swimming. A lot of our work with him was trying different things and making sure he had the technology so that he was safe and able to monitor his glucose levels.”

One key to any endurance sport, including swimming, contradicts the advice often given to people with T1D to limit carb consumption. With endurance sports it’s important to get lots of carbs. 

 “Whether you have diabetes or not, you need to fuel, and carbohydrate is the preferred fuel source during exercise,” Rilstone explained. “Of course, it’s more difficult in T1D because if you’re eating large amounts of carbohydrate and you’re struggling to control your glucose, of course that’s going to affect your performance. On the other hand, if your glucose levels are fine but you don’t have enough available carbohydrate, then you’re going to be exhausted. So it’s a real balancing act.”

The amount of carbs for people with T1D, however, may need to be somewhat less than the 90g per hour recommended for long-distance swimmers. It may be closer to 60g/hour, with individualized insulin adjustments made accordingly. These feedings are given to the swimmer from support boats.   

For one eight-mile UK swim, Spurway consumed either warm lime shots or caffeine gel with Gatorade, warm ovaltine, or warm coke every 40 minutes throughout. The first two feeds totaled 32 grams of carbs each, with fewer carbs (11-15g) in subsequent feedings. That morning he took his usual Lantus dose and breakfast bolus about three to four hours ahead of the race so that there was no more insulin “on board” that could drop his blood sugar. 

Training far in advance is crucial. “You obviously have to build your fitness, but you’ll also need to learn what to do with your insulin and carbohydrate,” Rilstone said, “which means that testing is really important, and this is why continuous glucose monitoring (CGM) is a total godsend.”

CGMs aren’t currently funded in New Zealand’s health service nor were they for most people with diabetes under the United Kingdom’s NHS at the time Spurway was living there. But, for several of his longer swims, Rilstone and the team temporarily fitted Spurway with an Abbott Freestyle Libre CGM. Someone on the boat would scan the device to get his glucose reading at the same time as he took the feedings. 

Over the years, Spurway has completed dozens of long-distance swims in England and New Zealand. He also once swam from France to Morocco through the Strait of Gibraltar, about 20 kilometers (12 miles). For nearly all of these swims, he has “nailed” the blood sugars, keeping within target range most of the time. 

Next up, he’s planning to tackle the Lake Taupō swim of 40.2 kilometers (about 25 miles), New Zealand's largest lake in the center of New Zealand's North Island. It is the caldera of the Taupō Volcano, a large supervolcano. For Spurway, it’s not about winning a race. 

“Some events are competitive,” he said. “I’m not at the front of the pack. I’m sort of mid-pack. I do it for the achievement.”