Exercising In The Heat And Gut Function

Research in recent times has uncovered that a sizable proportion of endurance athletes are likely to experience, to some extent, digestive tract difficulties or tumult during their training and events, particularly during circumstances of high temperatures (Prado de Oliveira et al., 2014).

The impact of strenuous physical activity in hot weather on a person’s digestion can be significant, as up to half of athletes have reported a range of digestive issues of varying degrees of severity, although the exact rate of prevalence may vary.

It has been discovered that nearly all ultra-marathon runners experienced at least one gastrointestinal complaint (Stuempfle et al., 2015); with nausea being the most common ailment.

This particular pathway is responsible for supplying catalysts that can cause heat-related illnesses, like suppressing appetite, loss of weight, and reducing the desire to drink liquids. It can disrupt the process of the body maintaining a healthy temperature, resulting in poor health, lack of satisfactory performance, and a decrease in the pleasure of the occasion.

In particular, intense physical effort (such as a large rise in the body’s interior temperature above 39°C, reduced blood flow to the stomach, strenuous pressure on the heart and vessels, and dehydration) when running in hot weather can have a detrimental impact on the gastrointestinal system’s defensive capabilities and performance.

This can eventually cause gastrointestinal permeability that is momentary compared to exercising in chillier settings (Snipe et al., 2018; Costa et al., 2020; Walter et al., 2021).

Your body and gut when exercising in heat stress

When athletes do intense or long-term exercise in warm conditions, they often experience problems in their digestive systems.

Blood circulation is redistributed from the digestive organs to the skeletal muscles (for continued physical activity) and to the appendages of the body to help with cooling the body and controlling the temperature. This results in a range of negative outcomes, including:

  • reduced splanchnic perfusion (or, less blood flow to the abdominal organs, including the stomach, liver, and intestines),
  • gastrointestinal ischemia (or, reduced gut blood flow),
  • epithelial cell injury and tight junction damage to the gut itself and,
  • a “leaky gut”, where endotoxins or bacteria escape from the gut and enter the blood circulation.

Leaky gut

Apart from this, athletes may suffer inhibited stomach emptying, causing a variety of disagreeable symptoms, such as feeling nauseous and off balance, abdominal distress, passing of gas, belching and swelling, and a need to have a bowel movement (van Wijck et al., 2011; Costa et al., 2017; Walter et al., 2021).

These are not necessary when running in the sand dunes of the Sahara!

Disrupted GI function can affect individuals in different ways. At times, directly after finishing a race stage, the need for intense healing may be present (over 0-4 hours), or the reactions might be delayed (4-48+ hours).

Severe endotoxemia can generate immune and inflammatory responses that may result in septic shock, systemic inflammatory response syndrome, and/or heat stroke, so it has to be taken seriously.

Women may be more vulnerable to GI symptoms

Additionally, women may be more prone to gastrointestinal symptoms while participating in physical activity. Hormone changes during the menstrual cycle, as well as changes in how sensitive the body’s organ systems are (i.e. gut pain) and how quickly food moves through the digestive system, all contribute to this.

It is especially important to be aware of this during periods, which is when estrogen and progesterone levels are low, and in the luteal phase of the menstrual cycle, when estrogen and progesterone are high (Lei et al., 2017).

Carbohydrate use increases but the absorption rate decreases

Working out in high temperatures can significantly alter the metabolism of carbohydrates.

Studies have found that when exercising in a hot climate, the body uses carbohydrates at a higher rate than in more moderate temperatures. Glycogen stored in the muscle is consumed at a rate of 25% greater, leading to higher levels of lactate in the bloodstream.

It was pointed out before that heat stress decreases the circulation of blood to the stomach. This could reduce the body’s ability to take in carbohydrates (as well as other nutrients), potentially decreasing the breakdown rate of the ingested carbohydrates by up to 10%.

The probable cause of these elements might be guessed to be the taking in and releasing of ingested glucose by the liver, the delivery of glucose to the muscle, emptying of the stomach, and the absorption of glucose in the intestines (Jentjens et al., 2002). Everyone reacts differently to these situations, so the outcome will vary for each person.

Though one tends to take in more carbohydrates while working out in hot weather, the intestine has a limited absorption capacity. Hence, simply eating more carbohydrates is not the only answer.

This emphasizes the importance of becoming accustomed to the heat (and potentially adapting your digestive system). It is suggested, based on current evidence, that approximately 30-60g of carbohydrates should be consumed each hour.

Heat’s impact on the body’s ability to digest food

The difficulty with this is that everyone responds differently to physical activity in warm weather. Athletes describe their symptoms as anything from minor and insignificant to quite painful and disruptive to their performance.

It has been observed that a sizeable portion of individuals who experience hard-to-bear signs make use of non-steroidal anti-inflammatory drugs (NSAIDs) (Schwartz et al., 1990).

Exercising in the heat can reduce gastric emptying rate. When the core body temperature rises, the movement of material through both the stomach and gastrointestinal tracts lessens.

This can affect the amount of CHO being actively moved and the speed of absorption in the digestive system. Essentially, if you try to keep a precise diet and hydration plan, it might not go as expected.

Blood flow to the gut is critical

What is the connection between perspiration caused by high temperatures and the digestive system? When there is a reduced amount of bodily fluid during physical activity (especially in your blood vessels), the flow of essential blood, oxygen, and nourishment to the digestive system can be affected.

If fewer oxygen and nutrients are sent to your intestinal tract, its performance can be weakened. An example of what may occur to the boundary between your gut and bloodstream, the intestinal barrier, when you work out in the heat is a good illustration.

The cells that line your intestines are usually closely connected to each other, which stops harmful materials from entering your system. Despite this, when under heat duress during physical activity, the boundaries of the tight junctions become weaker, providing a gateway for molecules to cross into the bloodstream.

Bacteria are among the most significant of these intruders. The amount of lipopolysaccharide in the blood is usually determined by scientists for usefulness in assessing the number of bacteria that have entered the body.

Lipopolysaccharide is an intricate scientific term for endotoxin, which is a major element that is found in the walls of certain bacteria. Your body can detect endotoxins, which then trigger the production of molecules with inflammatory properties to ward off the infection.

It is generally advantageous to have an increase in inflammatory molecules to avoid the spread of foreign entities within the body, yet a drawback of this heightened inflammation is the possibility of obstructions of organ functionality and early exhaustion.

There is also a link between an increase in endotoxins in the bloodstream during long-term physical activity and the feeling of queasiness in the stomach, especially nausea.

The activity of blood flow can also be observed in the GI tract by fluctuating motility, which is the process of muscle contracting and relaxing that allows food to move through the digestive system.

During exceptionally vigorous activity, blood is sent towards the legs, as they require more oxygen, which deprives the gut of blood and oxygen.

The lack of oxygen in the gut can possibly become more serious in hot temperatures and if there is a lack of water. In the end, having reduced blood flow to the intestines can result in problems with gut movement; specifically, lower oesophagus and stomach muscle strength.

If you’ve ever experienced a sensation of food seeming to feel like a weight in your stomach while running in hot weather, there is likely an issue with your intestines not moving correctly.

Multiple types of sugars

Research has shown that consuming food items that are easy to take with you and contain carbohydrates (like drinks with both glucose and fructose), can be advantageous in hot weather.

Due to an increased rate of carbs being burned from the ingested beverage and increased fluid availability (Jentjens et al., 2006), exogenous oxidation rates are higher.

It is a good idea to select items that have more than one type of sugar rather than depending solely on one kind of CHO. This might yield the highest possible utilization of transport, taking into account the restrictions that have been noted.

Additionally, cravings can transform during a competition such as Marathon des Sables, which makes it necessary to have a variety of food and snacks, like sweet and savoury items.

It is commonly understood that dehydration resulting from physical activity (also referred to as ‘exercise-induced hypohydration’) leads to a breakdown in the gastrointestinal barrier.

This has nothing to do with heat stress and can make it even worse when it comes to being able to digest and assimilate important nutrients. It is essential to become accustomed to the heat and keep yourself hydrated during event preparation, which is yet another reason why.

Fueling for ultra-marathons

General recommendations for endurance and ultra-endurance events suggest that athletes should have 30-60 grams of carbohydrates every hour and consume 400-800 millilitres of fluids each hour.

Research has demonstrated that participants who complete a single-stage ultra-marathon generally take in more carbohydrates than those who do not finish the marathon (~1g/kg/hr versus ~0.6g/kg/hr of CHO respectively; Stellingwerff, 2016).

Despite being achievable up to 90g/hr, consuming such large amounts for longer periods might be too much and result in gastrointestinal uneasiness and discomfort during the later part of the race (Tiller et al., 2019). This may be an issue for events that occur in several stages.

In contrast, the majority of ultra runners don’t tend to rely only on a sports drink or gel to nourish themselves. They usually prefer energy-dense, fatty foods and things that have a salty taste and are full of sodium.

Research has demonstrated that during an ultra-marathon of 100 miles, the people who completed the race had an average fat intake of 98 grams, whereas those who did not finish the event had an intake of 19 grams, according to Stuempfle et al., 2011.

This implies that some level of acceptance of both carbohydrates and fat may be necessary to finish an ultra-race efficiently (Tiller et al., 2019).

Beat the heat to help your gut

It should now be evident that warm weather can cause digestive problems. In minor instances of gastrointestinal distress, an athlete may need to reduce their activity level to resolve the issue; nevertheless, more profound situations can lead to them abandoning the competition.

What other steps can you take to reduce the effects of high temperatures on your digestive system? There is no guaranteed way of avoiding digestive problems in hot temperatures, but you can use the following techniques to lessen the chances.

Get used to it. Getting used to operating in the warmth is the most important step to take. If you have not dealt with heat-related issues before, there will be greater reductions in the flow of blood to the gastrointestinal tract, which could worsen any digestive problems.

For those of us living in hotter parts of the world, we are already used to the hot temperatures, but people living in cooler places have to figure out an effective way to get their bodies used to hotter temperatures.

You might want to try out working out while wearing extra layers, relaxing in a hot sauna, or taking a warm or hot bath following your usual workout routine.

It is advised that workout sessions intended to help with getting used to the heat should run for a minimum of an hour, though if you’re not familiar with being in the heat, you may need to work up to it slowly.

The amount of time it takes to see physical and performance enhancements from these types of protocols can vary, with some being visible within just a few days and others not until two weeks have passed.

Suggestions for creating a useful and hazard-free heat acclimatization program can be acquired from the Gatorade Sports Science Institute.

Cool yourself down. Research compiled in the Scandinavian Journal of Medicine and Science in Sports and Exercise revealed that both consuming cold water or an ice slurry beverage (internal) and using cooling vests, ice packs, etc. (external) are capable of diminishing body temperature and enhancing capacity when in hot temperatures.

In researching the digestion of runners, one investigation did not detect any change in gut-related problems among participants who consumed water of different temperatures (cold, cool and tepid) during a two-hour physical exercise in hot and humid weather.

There were minor signs that stomach troubles might be reduced when drinking cold water, but perhaps the sample group was too petite (12 individuals) and the physical activity session was too brief to detect a gain amid the noise in the data.

Drink enough (but not too much) to prevent dehydration. When it is hot and humid, perspiration increases, which can speed up the dehydration of the body during physical activity.

Be mindful that the lack of hydration can reduce the blood supply to the gut, which can cause digestive problems. The chances of being handicapped increase when you perspire and drop over 3 to 4 per cent of your body weight.

This implies that you do not have to restore all of the moisture lost due to perspiration during physical activity, as it is natural to experience some degree of dehydration.

You could aim for replacing about half to three-quarters of the energy expended during extended exercise sessions (which last longer than two hours) depending on how your digestive system is feeling.

Try using an online calculator to discover your usual amount of sweat lost. In most situations, you should be able to take in enough fluids by simply following your thirst when doing exercise that doesn’t last longer than two hours.

Try a probiotic (maybe). Probiotics are living microorganisms that have positive effects on a person’s health and metabolism when taken in.

Research into the purported advantages of probiotics on athletes has generated inconsistent results; however, one particular study has presented encouraging findings when it comes to exercising in hot weather. A group of ten male runners went through a 10-week period in which they were given either probiotic supplements or placebo pills.

The probiotic was composed of nine different kinds, mainly from the Lactobacillus and Bifidobacteria categories. The men had a 10-week period in which they ran until they were exhausted under hot temperatures.

After that, for a further 10 weeks, they changed over to the alternative treatment and repeated the same steps. The group that consumed the probiotic was capable of engaging in strenuous activities for a longer length of time than the control group (37:44 minutes in comparison to 33:00 minutes).

Furthermore, their blood contained fewer endotoxins after probiotic supplementation.

It would be prudent to keep expectations in check since the two treatments did not differ when it came to gut symptoms and another investigation did not turn up any advantage when endurance-trained males consumed Lactobacillus casei for a week before running in the heat for two hours.


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