How to Train Your Gut

fueling gut hydration microbiome Mar 14, 2023
Gut image for Dr Stacy Sims

Females suffer more GI issues than their male counterparts. Here’s how to get the fuel you need without the GI distress you don’t.

Women are no strangers to GI distress. Research shows we’re more prone to symptoms like bloating, stomach cramps, and constipation, partially because of monthly hormonal shifts in menstruating women and also because females have slower motility through the stomach and intestine than our male peers. Though research is somewhat mixed, women also may be more likely to suffer GI distress during exercise, especially abdominal cramps, side stitch, flatulence, intestinal bleeding, the urge to have bowel movements, and diarrhea, than men.

This can make it especially challenging to get the energy you need during exercise, especially for longer endurance events and/or during super hard efforts like CrossFit workouts. That’s why it’s important to understand your physiology and, importantly, to train your gut to meet the challenges you’re asking of it.

Duration and Intensity Matter

When it comes to fueling for exercise, duration and intensity matter. You can walk the dog, take an easy bike ride, and lift some weights without worrying too much about what you eat. Once the efforts get harder and longer, digestion becomes more finicky. 

On the endurance side, different types of upper and lower GI symptoms occur in about 45 to 50% of athletes. Research shows that 43 percent of triathletes reported serious gastrointestinal problems. It all comes down to where your blood needs to go. When you start exercising more intensely, your body shunts blood flow from your gut to your working muscles. This causes your gut to become a bit hypoxic, or low in oxygen, which increases the activity of what are known as submucosal neurons, vital regulators of water, electrolyte secretion, and local blood flow to your gut. These GI changes decrease absorption through your intestinal cells you and you can end up with greater risk for diarrhea, intestinal cramping, delayed gastric emptying (extra pressure in the stomach- “slosh” factor), and some bleeding of the stomach and colon may result (which is why some individuals experience blood in the urine and stool). Dehydration can decrease blood volume and make all of this worse.

So, what’s an athlete to do? First think carefully about what you put into your gut, especially during exercise. Also, train your gut! That means drink and eat the way you plan to compete, so you’re not suddenly trying to put lots of calories in during activity when your gut is not accustomed to processing them. 

Hydration First

First things first. Prioritize hydration. Athletes are often eating when they should be drinking, and they think they’re bonking when they’re really getting dehydrated. When you’re out there feeling the wall approaching, it’s very often because you have a big drop in total-body water and your blood is turning thicker, not because you don’t have enough fuel to burn. For more on how to properly hydrate, check out my blog Hydration is Power. Harness Yours.

Take In the Right Calories

You have enough stored carbohydrate to run for about two hours (depending on pace, intensity, and fitness levels). The main goal of eating during long or more intense exercise is to keep your blood sugar concentrations topped off, so you have a steady stream of energy to keep going (this is especially true for women as we rely more heavily on blood glucose than stored glycogen). How much is enough?

As you might expect, many of the laboratory studies on this topic have been performed on young, well-trained men. In research you see these men are able to burn through and hit optimum performance at about 78 grams (312 calories) an hour of carbohydrates from mixed sources (meaning a combination of sugars, rather than just one kind; the body absorbs a combination better).

The results from these studies trickle down and leave many athletes with the impression that the more calories you can consume, the better your performance will be and the longer you’ll be able to go. That’s not really true, especially for women. I know some women who can approach that super high-carb mark, but not many, and even then, only through years of practice and training, because they compete in super-ultra-endurance events.

Women are better off aiming for a calorie range and not taking in all their calories in the form of carbs because it works far better with your physiology. Inside your small intestine are specific receptors that assist with the digestion of carbohydrate, protein, and fat. It’s best to feed your body a steady stream of mixed macronutrient foods to avoid overloading any one macronutrient receptor at one time, which is what often happens when you keep taking in carbohydrates the whole time. Carbohydrate overload makes you feel bloated, gassy, and uncomfortably full—not good for performance. A better range for most active women is 0.9 to 1.15 food calories per pound / 2 to 2.5 food calories per kg of body weight per hour running or 1.3 to 1.6 food calories per pound / 3 to 3.5 food calories per kg per hour while cycling or participating in another nonjostling sport. When in doubt, err toward the lesser amount. Consuming more than your gut can absorb, the excess just remains in the stomach or intestinal tract too long, causing nausea, pain, and discomfort (which, of course, impairs performance).

Keep in mind that your nerves will be sending a flock of butterflies into your belly during the actual event, and whatever you eat needs to be familiar and very easy to digest. (For an example see my Salty Balls recipe at the end of this blog.)

Watch the Gels

I’ve ruffled a lot of feathers over my 20-plus years in the sports nutrition field. But the topic that tends to rile people up the most is my stance on energy gels, which in a nutshell is no. I understand that energy gels are a super convenient, calorie-dense, easy-to-put-in-the-pocket fuel source. They are also one of the most detrimental fuel sources for performance.

To understand why, consider the nutritional breakdown of a standard gel. One packet generally ranges from 100 to 120 calories per serving, typically about 20 to 40 grams of carbs, and is composed of maltodextrin and fructose with a bit of sodium, potassium, flavorings, and preservatives. If you read the label, you’ll see that most directions state that a gel must be consumed with 2 to 4 ounces of water. Do you know why? Because a gel is a very concentrated carbohydrate (specifically a 73 percent solution). By recommending water, the companies are trying to water down the concentration of the solution, so your body can effectively get it out of your stomach and into your gut, where it can be absorbed for energy.

It’s all about osmolality (the concentration of dissolved particles such as electrolytes in your blood plasma) and the concentration of carbohydrates. The higher the carb concentration, the higher the osmolality, and the slower it leaves your stomach and your intestines. By nature of how concentrated the gel is, it will sit in your stomach and increase osmotic pressure, drawing water into the stomach to bring down the pressure and allow the solution to exit your small intestine. This backward flow of fluids from the bloodstream into the gut can effectively start dehydrating you. Even when you drink the amount of water recommended on the label, the concentration of carbohydrate remains unchanged and outside of the range of osmolality for fluid absorption.

This problem is compounded by maltodextrin, which is made with the building blocks of glucose rather than straight glucose. Maltodextrin is used because it doesn’t affect osmolality the same way as the simple sugars glucose, fructose, or sucrose do. So, a gel can actually contain quite a bit of maltodextrin and still get shuttled out of the stomach quickly. Sounds appealing. There’s just one problem. Maltodextrin can overload a key “gate” in the small intestines; thus, it creates the same high-osmolality environment as fructose—complete with the same increased lag time and undesirable results.

In the end, you don’t get the fuel you need, you compromise your hydration, and your belly is upset to boot. I’ll note that this can happen with the new generation of isotonic gels, which are designed to deliver quick carbs during exercise and can be consumed without water. Though they are isotonic to the blood, they’re not to the intestines. They are still high in carbohydrate (i.e., 22 grams, mostly from maltodextrin, in 60 ml of fluid), making them roughly a 13 percent solution, which will still impact gastric emptying.  

Of course, the human body is not an algorithm, and there are definitely outliers within physiology. There are talented, elite athletes who do get by on gels and water, but as we dig a bit deeper into these success stories, it becomes evident that these athletes do not just use gels; they use them in collaboration with other racing foods. If you really need that quick hit of energy, I recommend glucose tablets instead. 

The “Salty Balls” Recipe

  • 1/2 cup natural peanut butter (or any kind of nut butter)
  • 1/3 cup brown rice syrup.
  • ½ teaspoon vanilla
  • Dash of cinnamon
  • 1 tsp instant espresso
  • 1/2 cup whey protein isolate.
  • 1/4 cup crisped rice cereal or dry oatmeal.

Put the nut butter,  brown rice syrup, vanilla, and cinnamon in a microwaveable bowl. Microwave for ~1 min until the syrup is bubbly-hot. 

Stir to combine and add the whey protein, crisped rice cereal or oatmeal, and if using, the instant coffee. 

Throw a sprinkle of salt on top and freeze until needed (makes ~10 balls, ~140 kcal/ball)

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