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How to fuel when you are insulin resistant, prediabetic, or diabetic

A big motivation for many endurance athletes to enter and continue with the sport is the wellness benefit. Cardiovascular exercise can be especially beneficial for those with insulin resistance or prediabetes/diabetes. During exercise, the muscles become highly sensitive to insulin to be able to take up as much cell-fueling glucose as possible. Fueling for triathlon, especially when racing, must involve intake of simple sugars for best performance, which can seem like an unhealthy choice for those with sugar metabolism issues. The good news is that, with some planning, wellness goals and performance goals can both be obtainable.

Note that if you are a diabetic on insulin, special considerations apply and you should consult with your doctor and a registered dietitian to obtain personalized recommendations.

Isn’t sugar bad?

Added or refined sugar is not good for us on a regular basis. It can have negative effects on weight, blood sugar control, and blood pressure. During endurance athletics, however, simple sugars are critical for performance. When participating in prolonged endurance events, blood sugar levels that go below a certain threshold will negatively affect performance. The best way to keep those levels up is to utilize fast-acting (also known as simple) sugars (gels, blocks, etc.). The good news is that this is not detrimental to overall wellness, since it only needs to happen during training and racing. Those who are insulin resistant or have diabetes should follow careful carbohydrate counting and limited simple sugar intake all the rest of the time. The other factor to consider is the difference in the body’s metabolism of sugar during exercise. The uptake of sugar during exercise happens differently than during rest, so blood levels of glucose typically will not rise above threshold during exercise.

For endurance sports, regular intake of carbohydrates needs to be on the higher side, but this can be done in a healthful way. There are many nutritious foods that contain a lot of carbohydrate in the form of natural (versus refined) sugar or starch: fruit, low-fat milk and yogurt, legumes, and whole grains. Fueling before and after training should include all three macronutrients (carbohydrate, protein, and fat) for the body to adequately recover.

Will eating carbs make my blood sugar spike?

There are many modifiers of blood sugar response, and exercise is one of them. For example, when sugar is ingested during exercise, there is little or no insulin or glucose spike. However, when not exercising, it is normal for blood sugar levels to increase after eating carbohydrates. This can be considered a “spike” when more simple carbohydrates are consumed. Transient changes in blood sugar concentration in response to eating should not be confused with chronically elevated blood sugar. Moderate “spikes” in blood sugar are normal while chronically elevated blood sugar indicates prediabetes or diabetes. Following carbohydrate ingestion, insulin is released to help the body remove glucose from the blood. The insulin “spikes” that we see in healthy individuals are happening so that storage of glucose can occur in the appropriate tissues. Chronically elevated blood glucose (type 2 diabetes) develops because insulin becomes less effective. Glucose concentrations stay higher for longer periods, especially when being inactive. This is why athletes with insulin resistance should control their portions of carbohydrates during the times when they are not exercising.

The 3 main keys to success

Endurance athletes have an increased energy expenditure compared to those who are less active. Therefore they have higher calorie needs, which means higher carbohydrate needs. The timing of carbohydrate intake in relation to exercise, distribution of carbohydrates throughout the day and the choice of carbohydrate-containing foods are key factors to consider.

1)    Timing of carbohydrate intake

Endurance athletes who are insulin resistant still need to consume similar amounts of carbs during and after exercise compared to healthy athletes. Carbohydrate needs during exercise are about 30-90g/hour depending on exercise duration. Post exercise, it is recommended to consume about 1 -1.2g/kg of body weight of carbohydrates (about 0.5 g of carbs/pound of body weight). For example, a triathlete who weighs 150 lbs doing a 3-hour bike ride will need about 60g of carbs per hour during the bike ride (180g of carbs total) and about 75g of carbs in the meal or snack post workout. This can seem like a lot of carbs, especially for someone with prediabetes or diabetes. However, carbohydrate intake during prolonged moderate to high intensity endurance exercise (>60 minutes) will be used as a fuel during that activity and will not have negative health effects. Similarly, carbohydrate intake immediately after endurance exercise will be used to replenish glycogen stores in the liver and muscles and will not affect blood sugar control.

2)    Carbohydrate distribution throughout the day

To meet carbohydrate needs without negatively affecting blood sugar control, endurance athletes should consume enough carbohydrates during and after exercise since intake of carbohydrates at those times will not affect blood sugar control. The rest of the day, they should aim to eat several small meals and snacks to distribute their carbohydrate intake throughout the day and avoid consuming too many carbohydrates at one time, which could negatively affect blood sugar control.

3)    Types of carbohydrates

As discussed previously, simple sugars like sports gels and sport drinks are the preferred fuel during prolonged endurance exercise, even for athletes with prediabetes or diabetes. The rest of the time, athletes should choose mostly whole food carbohydrate sources such as fruits, starchy vegetables, whole grains, and legumes. These foods are high in fiber, which not only helps with blood sugar control but is important for overall health.

The bottom line

Endurance athletes who are insulin resistant or diabetic should still follow a diet that is higher in carbohydrate, if the timing of the intake and distribution of carbohydrates throughout the day is optimized. They should choose simple sugars during prolonged exercise and focus on whole food, high-fiber carbohydrates in controlled portions the rest of the day.

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