Does the Prediabetic Cyclist Need to Worry? (Continued Part 3)
Part 3: What About Me Specifically?
The GTT is a barometer of beta-cell health
How can one tell the difference between athletic hyperglycemia, and an impending beta-cell failure leading to diabetes? The first is age. Late-onset, Latent Autoimmune Diabetes in Adults (LADA) is a slowly progressing form of autoimmune diabetes that can show up in early adulthood. The British Olympic rower, Steve Redgrave was diagnosed with diabetes at the age of 35. Genetics, a strong family history of early-onset non-obesity related diabetes is also suggestive, but not always destiny. Short of genetic testing, Mr. Redgrave could have learned more about his near-term diabetes prospects by a GTT.
The GTT can provide much more useful information than the FBS. The FBS reveals very limited information about the liver’s regulation of glucose during a very short metabolic period of the 24-hour cycle, the fasting period. The two-hour glucose value from a GTT, (two hours after ingesting 75 grams of glucose) can measure beta-cell health by demonstrating the ability of the pancreas to produce insulin.
Someone who has a high FBS, but after two hours of drinking 75 grams of glucose returns their blood glucose level down to the fasting or beginning of the test, has a robust set of beta-cells in their pancreas which can crank out insulin.
There are no long-term studies to foretell the fate of athletic prediabetics. Participants in studies like Dr. Hayashi’s whose participants had an average BMI of 24, (BMI of 23 is the threshold for Asian prediabetic screening) are more similar to the athlete. Let’s look at their diabetes risk by GTT pattern.
Dr Hayashi followed 400 Americans of Japanese descent, about half were prediabetic. He separated the group into five risk categories based on insulin levels at fixed times. Since most doctor-ordered GTT’s don’t include insulin levels, compare glucose patterns. The lowest risk for subsequent diabetes after ten years was among those whose glucose pattern was left most. (3.8%)
Here’s an easy way of interpreting the five GTT curves. Draw a horizontal imaginary line across to the right from the start. (Time zero) Imagine the curve is a tent. The tent with the smallest area underneath has the lowest risk of future diabetes. Why? A roofline tightly cinched down demonstrates the best pancreatic insulin production paired with low insulin resistance.
Any reassurances if I have a solitary prediabetic FBS or A1c?
The gold standard was and still is the GTT. Within the GTT, historically the glucose value at the two-hour mark prognosticates best. If you are worried about any heart damage which comes about from a slightly high glucose, check your 2-hour GTT.
The Baltimore Longitudinal Study of Aging tested 1,401 nondiabetic individuals with the GTT and then followed them for twenty years. The researchers found that “Fasting glucose was not an independent predictor of mortality. Only higher two-hour glucose was a significant independent risk factor for mortality.” In this study, the two-hour glucose value marking low future risk averaged <118 mg/dL. [Metter 2008]
Another study following men (average age 73) with prediabetic FBS, found no increased stroke or heart attack risk among those who had a two-hour glucose <140mg/dL. [Barzilay 1999]
Does the future hold diabetes? No test covers all the bases. Check all three: A1c, FBS, and 2hr GTT to gather all the data. Check out the four year risk in the table below. These risk figures are for non-athletes, which are likely an overestimate for athletes. One prediabetic zone test carries some risk, two more. However, if the GTT glucose value at the two-hour is <140mg/dL, then future risk is low. [Lu] A positive test in the low range carries less risk than one in the high range. [Cavero-Redondo]
No one can guarantee even the athlete that there will be no progression to diabetes because there might be factors which still might be propelling the process onward.
Care to share some proactive tips or blindspots?
If one has a normal patterned GTT, then a high glycemic, high-fructose, or high carbohydrate diet, which frequently is the diet for competitively-minded runners and cyclists can be to blame. During exercise, athletes have no problem disposing of high glycemic food and drinks, whether it’s soft drinks, gels or candy bars. Energy drinks pack both fructose and glucose because the intestines have separate pumps for each sugar. That rush of energy comes from accelerated absorption. Fructose also bypasses the body’s insulin signaling system and can cause liver insulin resistance.
Outside of exercise, decreasing carbohydrates or high glycemic foods may decrease spikes in glucose. Anecdotally, I know of cyclists who have improved their A1c by cutting down fructose, carbohydrates, or sweets.
Recall that athletes experience a “Johnny come lately,” delay in mounting an insulin response to food. Slowing the stomach emptying time can be achieved by listening to your mother’s advice. Chew your food. Eat slower. Eat your leafy green vegetables first. Additional “non-Mom” advice might include taking a fiber supplement or vinegar at the beginning of a meal, drinking tea with the meal or walking afterwards. (Each intervention is detailed in my book, The Thin Prediabetic, available on Amazon.)
Strategies to decrease the post meal increase in blood sugar:
◎ Cut out fruit juice and other sources of corn syrup or fructose-based sugar.
◎ Limit carbohydrates to times during or immediately preceding exercising or decrease overall.
◎ Slow stomach emptying time by eating slower, eating vegetables first, taking a fiber supplement or vinegar at the beginning of a meal, drink tea with meals.
◎ Take a walk immediately after eating.
Still, it is difficult to say for any one individual whether these strategies will change the trajectory for diabetes or even whether they were ever at risk for progression to diabetes.
This leads us to the second point. Recall the WHO’s earlier concern regarding the ADA’s lowered bar for prediabetic diagnosis? At the same level of hyperglycemia, someone who does not have any metabolic diseases and regularly exercises is at lower risk for progressing to diabetes compared to their sedentary or overweight brethren.
Athletes are not immune as all of us are individuals.
Dr. Haslacher from Vienna studied 47 cyclists and runners in their sixties, whose average 5.6% hemoglobin A1c was near the cutoff to prediabetes. After three years, about 42% went from normal glucose levels to prediabetic hemoglobin A1c levels. At the same time, half that percentage reverted from prediabetic A1c levels to normal levels. One prediabetic went on to diabetic level A1c.
Many straddle either side of the A1c cutoff fence of 5.7%, bouncing back and forth. Some progress, yet others return from the prediabetic range to normal.
If your A1c is in the prediabetic range, but you have low insulin resistance and a normal glucose response after 2 hours of the GTT, then the same level of hyperglycemia is less worrisome compared to your sedentary or overweight brethren. [Chia]
This leads us to the second point. Recall the WHO’s earlier concern regarding the ADA’s lowered bar for prediabetic diagnosis? Someone who does not have any metabolic diseases and regularly engages in aerobic exercise is in the lowest risk group for progressing to diabetes.
What am I possibly missing?
Physically active people still might have risk factors which if unrecognized might steadily worsen their glucose. Recognizing and addressing sources can make progression less likely.
Here are of a few underrecognized sources of insulin resistance: high-fructose sugar consumption, a potbelly even with normal BMI, chronic inflammation such as gingivitis, chronic stress, chronic insomnia, binge alcohol drinking, low testosterone levels, Polycystic Ovarian Syndrome, or smoking. High blood pressure and elevated triglycerides are signs of insulin resistance.
Underrecognized sources of insulin resistance:
◎ Lack of regular strength training
◎ High consumption of high-fructose sugar (soda and juices!)
◎ Protuberant belly even with normal BMI
◎ Chronic inflammation (gingivitis?)
◎ Chronic stress
◎ Chronic insomnia
◎ Binge alcohol drinking
◎ Low testosterone levels
◎ Polycystic Ovarian Syndrome
◎ Smoking
I wish to place an asterisk on the first item. Dedicated aerobic exercise without strength training provides fertile soil for insulin resistance. Hyperglycemia under these circumstances might indicate insulin resistance coming with age-related muscle loss. Don’t forget resistance training is required to stave-off insulin resistance from atrophying strength or Type 2 muscle fibers, sarcopenia. (Subject of my book, The FIRST Program, available on Amazon.)
A final upbeat parting thought.
Regular exercisers are among those most health-conscious. Even within this group, there is a tendency to misidentify or incorrectly rank the predictors of longevity and health. Ultimately, what we seek is neither low glucose nor other favorable biomarkers, but a healthy and disability-free life. By far, the most accurate predictor of a future free of disability or death is fitness level.
“Cardiorespiratory fitness is inversely associated with long-term mortality with no observed upper limit of benefit. Extremely high aerobic fitness was associated with the greatest survival . . . . The adjusted mortality risk of reduced performance was comparable to, if not significantly greater than, traditional clinical risk factors, such as CAD, diabetes, and smoking.” — JAMA Network Open.
Regardless of whether fitness studies measure agility, physical strength, or aerobic stamina, physical fitness performance outpredicts any laboratory test for longevity.
While some young athletes have later been diagnosed with slow-onset Type 1 diabetes, in mid-life or later, a majority of the fit who encounter hyperglycemia as an exercise-related phenomenon aren’t destined for diabetes, premature strokes or heart attacks. Higher blood sugar in this group does not have the same future negative health implications as the majority of prediabetics who are not fit. To be sure, check to see if all your bases have been covered.
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