CLINICAL GASTROENTEROLOGY AND HEPATOLOGY 2003;1:345–355Exercise and Gastrointestinal Function and Disease: An Evidence-Based Review of Risks and BenefitsLUKE BI* and GEORGE TRIADAFILOPOULOS‡

The benefit of exercise on the gastrointestinal system is unclear. Although exercise

commonly is perceived to improve chronic constipation and has been shown to

reduce the incidence of colorectal cancer, it may cause nausea, reflux, abdominal

cramps, and occasionally gastrointestinal bleeding.

A substantial part of this review is more applicable to trained athletes and

individuals who are highly active and, as such, are at risk to experience the side

effects of exercise. The most significant effects of exercise on gastrointestinal

function occur at higher levels of activity (>70% VO2 max).

Gastroesophageal Reflux Disease (GERD )

Athletes, especially runners, have reported gastroesophageal reflux disease (GERD)

symptoms that limit both their training and competition. Strenuous exercise may

cause belching, abdominal fullness, regurgitation, heartburn, and chest pain in up to

45% to 90% of athletes.

Runners showed the most reflux in duration and frequency whereas only some weight

trainers had evidence of reflux. Cyclists, performing exercise with the least amount of

body agitation, had the smallest amount of reflux.

Significantly more reflux after meals compared with fasting.

Studies in normal volunteers and patients with GERD indicate that an increased

frequency of transient lower esophageal sphincter relaxations is the main mechanism.

Both histamine receptor antagonists and proton pump inhibitors are effective in

treating patients with GERD and they may prevent exercise-induced reflux during

Exercise.

GERD, especially if precipitated by activity, frequently mimics angina-like chest pain in

patients and athletes. Many studies have shown the association of GERD with

noncardiac, angina-like pain.

There is sufficient evidence that rigorous exercise, particularly running, can induce

significant gastroesophageal reflux in trained and nontrained subjects alike, and

medical therapy is effective in reducing reflux frequency and duration. Most exertional

reflux is treatable by modification of exercise habits (e.g., bicycling instead of running)

and fasting before exercise

Gastric Emptying and Gastric Acid Production

Water and electrolyte loss as well as glycogen depletion may limit performance during

severe, prolonged exercise.

The rate of gastric emptying is reduced only slightly at a workload up to 71% of

maximum oxygen uptake.

Light exercise either accelerates or has no effect on gastric emptying whereas severe,

exhaustive exercise beyond a critical number of 70% to 80% VO2 max delays emptying of

liquids and solids. Increased sympathetic tone and the release of catecholamines may

be responsible for inhibition of gastric emptying with vigorous exercise.

Gastric acid secretion decreased, with increasing levels of exercise reaching a 40%

decrease at maximal level of exercise.

Taken together, these studies suggest that mild to moderate exercise has little effect

on gastric secretion whereas strenuous, prolonged activity inhibits gastric acid

production.

Recommendations must be tailored carefully for athletes in different situations

Peptic Ulcer Disease

Study of the link between the incidence of peptic ulcer diseases and the levels of

physical activity. High and moderate physical activity reduced the relative risk for

duodenal ulcers in men. Significant protective effect of physical activity against

stomach cancer only in men reporting moderate to vigorous exercise.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic debilitating disease characterized by

remissions and exacerbations and requires long-term medical or surgical therapy. As

in most chronic illnesses, physical activity may promote overall well-being and

potentially reverse or retard osteopenia and osteoporosis. IBD patients with

osteoporosis have a much higher risk for fractures, which can result in significant

morbidity. These results support a training benefit of low-impact exercise, although

the benefit is rather inconsistent in retarding bone loss in IBD patients.

Constipation and Gastrointestinal Motility

Regular physical exercise has long been advocated as a first-line, standard treatment

of chronic constipation. There has been no scientific evidence supporting exercise

therapy for constipated patients.

The experimental subjects noted a significant decrease in their bowel transit times at

the end of the study. 10 active, healthy adults in a cross-over trial that alternated

moderate treadmill running, resting, and cycling, and showed dramatic acceleration of

whole-gut transit after submaximal exercise. Similar studies with strict diet control

confirm that short- to medium-term exercise has no noticeable impact on bowel

transit across different populations, regardless of age, activity level, sex, and training

status.

Colorectal Cancer

The role of physical exercise in colorectal cancer prevention has been studied

extensively. nearly all have shown the protective effect of physical activities on widely

varied populations across different study designs. There is less convincing evidence

that physical activity protects against rectal cancer

Even modest levels of exercise (11.3 METh/wk, or equivalent to 1 h of running, 2 h of

tennis, or 3 h of walking at a moderate pace) can substantially reduce colon cancer

risk. Physical exercise exerts an independent protective effect. Perhaps by providing

an immunoprotective effect, exercise enhances the immune response by promoting

T-cell, B-cell, natural killer cell, and interleukin 1 levels.

Gastrointestinal Bleeding

Surveys of endurance athletes revealed a high incidence of different types of upper

(nausea, vomiting, belching, and heartburn) as well as lower gastrointestinal

disturbances (bloating, abdominal cramps, urgency to defecate, diarrhea, and

hematochezia). Running was associated most heavily with gastrointestinal problems.

707 participants of a 1984 Oregon marathon documented an alarmingly high

incidence of lower-tract GI symptoms among the runners who competed

More than one third of runners reported the urge to defecate during or immediately

after running. Bowel movement (35%) and diarrhea (19%) were frequent after

vigorous running and bloody diarrhea occurred in about 1.2% to 2.4% of runners.

Occult bleeding is found in as much as one fourth of marathon runners. Participants

with occult bleeding were significantly younger and also had faster finishing times,

suggesting an association with training status and the amount of exertion.

The mean hemoglobin, hematocrit, and ferritin levels were consistently lower in

runners than in controls. Competitive long distance running induces gastrointestinal

blood loss and may contribute to anemia. Prolonged physical exertion at high intensity

can decrease splanchnic perfusion by 70% to 80% in young healthy subjects because

blood is shunted to the muscles and skin. Although prolonged and intensive physical

training such as marathons can be dangerous, mild regular exercise likely exerts some

protection against lower gastrointestinal hemorrhage.

Interestingly, there has been no direct link between cycling and GI bleeding. The lack

of evidence in this area suggests that prolonged physical vertical bouncing of the

gastrointestinal organs compounded by ischemia in marathon running could play

some kind of role in exacerbating exercise-induced gastrointestinal bleeding.

Liver Disease

Physical activity and regular exercise performance have no adverse effect on liver

functions.

Neurogastroenterol. Mot. (1999) 11, 431±439

The effect of physical exercise on parameters of gastrointestinal function

M. A. VAN NIEUWENHOVEN, F. BROUNS & R-J. M. BRUMMER

Exercise decreases splanchnic blood flow. Therefore exercise may induce alterations in

gastrointestinal (GI) function. In the present study we investigated the effect of high-

intensity exercise on oesophageal motility, gastro-oesophageal refux, gastric

pH, gastric emptying, orocaecal transit time (OCTT), intestinal permeability and

glucose absorption simultaneously, using an ambulatory protocol.

After an overnight fast, the subjects arrived at the laboratory at 08.00. A thin catheter

allowing the registration of oesophageal motility, gastro-oesophageal refux and

intragastric pH was inserted transnasally. Subsequently the subjects received a

standard liquid breakfast (4 mL kg±1 bodyweight, pH = 5.8), and remained seated in a

chair for 60 min.

During this period resting values for oesophageal motility, gastric pH

and gastro-oesophageal refux were obtained. Subsequently the subjects emptied their

bladders, mounted a stationary bicycle ergometer in the cycling trial, or remained

seated in the resting trial. In the cycling trial a warming-up was performed for 10 min

at 100 W. During the final minute of this warming-up a carbohydrate-electrolyte

solution (CES) (2mL kg±1 body weight), was ingested.

Testing procedures

Oesophageal parameters: Two solid-state pressure sensors measured oesophageal

pressure at 13 cm (P1) and 3 cm (P3) above the LES, respectively. The catheter was

connected to an ambulatory data-recorder, thus allowing continuous registration of

pH and pressure.

Gastro-oesophageal refux: A refux episode was defined as a period in which the pH in

the oesophagus, at 5 cm above the LES, was lower than 4.

Gastric emptying: The assessment and mathematical evaluation of 13C-enrichment

was carried out as follows: The drink administered at t = 40 during the exercise

episode contained 150 mg sodium [1±13C]-acetate in order to determine the gastric

emptying rate using the 13C-acetate breath test.

OCTT: The drink administered at t = 0 of the exercise episode contained a

nondigestible soluble carbohydrate allowing the measurement of OCTT via H2

measurement in breath.

Intestinal permeability and glucose absorption: The drink administered at t = 0 of the

exercise episode contained 5 g lactulose 0.5 g rhamnose and 0.35 g 3-O-D-methyl M-

glucose.

Oesophageal motility

The data from the oesophageal motility measurements are displayed in Table 2. The

peristaltic velocity appeared to be increased during cycling, compared to rest. The

number of peristaltic contractions, the peristaltic pressure at P1 and the duration

of the peristaltic contractions at P1 and P3 were lower during cycling.

Gastric pH

There were no significant differences between the pre-exercise, the exercise and the

post-exercise episodes in both median gastric pH (P = 0.767, 0.208 and 0.933,

respectively), and the percentage of time in which the gastric pH was lower than 4 (P =

0.314, 0.889 and 0.612, respectively).

Gastro-oesophageal refux

There were no significant differences between the pre-exercise, the exercise and the

post-exercise episodes in both the number of refux episodes (P = 0.129, 0.610 and

0.786, respectively) and the duration of refux as a percentage of time (P = 0.237,

0.612, and 0.463, respectively).

Gastric emptying and OCTT: Neither gastric emptying nor the OCTT show differences

between the rest and the cycling trials. 13C-TTP in the rest trial was 29.3 min

(17.4±42.2) and in the cycling trial it was 28.7 min (21.6±34.2) (P = 0.33). OCTT in the

rest trial was 117.5 min (105.0±165.0), and in the cycling trial it was 140.0 min

(105.0±195.0) (P = 0.17).

Intestinal permeability and glucose absorption: The lactulose/rhamnose ratio was

significantly higher in the rest trial, compared to the cycling trial (0.015 (0.0076±0.027)

and 0.0067 (0.0017±0.0141), respectively, P = 0.009).

Our study demonstrates that physical exercise has an effect on oesophageal function.

Oesophageal function was measured at 3 cm (P3) and 13 cm (P1) above the

LES. At 3 cm above the LES the oesophagus is entirely composed of smooth muscle

tissue. At 13 cm above the LES, however, the oesophagus also contains striated

muscle tissue. Exercise may lead to a substantial decrease in GI blood flow of more

than 50%.

Therefore exercise may induce alterations in GI-function.

The results of the present study indicate that there are no differences in gastro-

oesophageal reflux, gastrointestinal transit time or gastric pH between a resting and a

cycling trial. The present study demonstrates that the gastric pH does not change as a

result of exercise. the gastric emptying rate was not affected by exercise at a cycling

load of 70% Wmax, which corresponds with approximately 80% VO2max.

Intestinal glucose uptake is a carrier-mediated transport process. Our results

demonstrated a decreased absorptive capacity for glucose uptake in the cycling trial.

Jejunal glucose absorption is also decreased during cycling.

Gut 2001;48:435–439

Potential benefits and hazards of physical activity and exercise on the

gastrointestinal tract.

Peters, vanBerge-Henegouwen, de Vries, et al

“Exercise” is considered as voluntary activation of skeletal muscle leading to short

term effects (for minutes or hours) while “physical activity” is considered as repetitive

exercise periods leading to long term effects (for days, weeks, months, or years).

Hazards

Gastrointestinal symptoms such as nausea, heartburn, diarrhoea, and gastrointestinal

bleeding are common during exercise, especially during vigorous sports such as long

distance running and triathlons. In general, these symptoms are transient and can be

considered protective for critical organ damage: its progressive nature causes the

athlete to reduce exercise intensity or duration.

Incidence rates during prolonged exercise vary mostly from 20% to 50%, depending on

factors such as mode, duration, and intensity of exercise, type of symptom, age,

training status, sex, dietary intake, occurrence of gastrointestinal symptoms at rest,

and method of investigation. In particular, exercise intensity seems to be an

important factor provoking gastrointestinal symptoms.

The mechanisms by which exercise causes gastrointestinal symptoms are not well

known. Decreased gastrointestinal blood flow, increased gastrointestinal motility,

increased mechanical bouncing, and altered neuroendocrine modulation are

postulated. All of these mechanisms are associated with exercise intensity.

While most gastrointestinal symptoms do not hamper the athlete’s health,

gastrointestinal bleeding may be a serious problem.

In addition to gastrointestinal symptoms, unfavourable effects of exercise on liver

function and peptic ulcer disease have been reported.

Benefits

The potential benefits of physical activity concern mainly effects on cancer risk,

cholelithiasis, gastrointestinal haemorrhage, inflammatory bowel disease, diverticular

disease, and constipation.

GASTROINTESTINAL CANCERS

To date, the risk of oesophageal, bile duct, or gall bladder cancers have not been

examined in relation to physical activity. Concerning stomach cancer, the data are

controversial: one study reported a reduced risk while two did not. No relationship

between physical activity and risk of pancreatic cancers has been found, whereas

rectal cancer risk was unrelated to physical activity in the majority of studies.

In contrast, there is overwhelming evidence that physical activity reduces the risk of

colon cancer: there is consistent evidence that physically active men and women are

at a reduced risk of colon cancer (up to 50% reduction in incidence).

Studies analysing dose-response relationships suggest that more intense activity may

confer greater protection against the risk of colon cancer than less intense activity.

The primary postulated mechanism is that physical activity reduces intestinal transit

time which would limit the time of contact between the colon mucosa and cancer

promoting contents.

Two recent large prospective studies showed a relative risk (RR) of cholelithiasis of

0.63 in men and 0.69 in women when comparing the most active with the most

inactive subjects, whereas sedentary lifestyle (watching television or sitting) resulted

in an increased risk (RR 1.11–3.32). A clear dose-response relationship was observed,

independent of several potential risk factors, strongly suggesting that (symptomatic)

cholelithiasis can be prevented by physical activity, even beyond its benefit for control

of body weight or diet.

GASTROINTESTINAL HAEMORRHAGE

The only study which examined gastrointestinal haemorrhage and physical activity

was a prospective cohort study with three years of follow up in 8205 elderly

subjects.

Only severe gastrointestinal haemorrhage was investigated. For those participants

doing the activity at least three times per week, RR was significantly lower for

walking (0.6) and for the summary variable (0.7) in comparison with sedentary

subjects, independent of several other risk factors such as age, sex, mobility, body

mass index, or health status. The RR for gardening (0.8) and vigorous physical

activity (0.7) was not significantly lower. The authors hypothesised that a relatively

increased gastrointestinal blood flow in physically active subjects reduced the risk of

gastrointestinal haemorrhage. One should keep in mind that the findings of this

study were restricted to severe haemorrhage in elderly subjects and that no data are

available for less severe forms of haemorrhage or for younger subjects.

INFLAMMATORY BOWEL DISEASE

A limited number of studies have investigated the preventive effect of physical

activity on Crohn’s disease (CD) or ulcerative colitis (UC). Sedentary and physically

less demanding occupations were associated with a higher risk of inflammatory

bowel disease than physically demanding occupations.

While the preventive effect of physical activity remains inconclusive, it has become

clear that physical activity is not harmful for patients with inflammatory bowel

disease. Physical activity should be promoted as these patients have muscle

weakness and are at risk of osteoporosis. This risk is especially high with

glucocorticoid medication, which causes muscle atrophy and weakness,

osteoporosis, and osteopenia. In addition, physical activity may reduce disease

activity and improve physical health, general well being, perceived stress, and

quality of life.

DIVERTICULAR DISEASE

Diverticular disease was more prevalent among subjects with sedentary occupations

than in more active occupations. An increase in colonic motor activity via hormonal,

vascular, and mechanical aspects, leading to a reduction in colonic transit time, was

postulated as an underlying mechanism.

CONSTIPATION

Several cross sectional studies have shown an inverse independent relationship

between constipation and physical activity. Underlying mechanisms are unclear but

a favourable effect on colonic motility, decreased blood flow to the gut,

biomechanical bouncing of the gut during running, compression of the colon by

abdominal musculature, and increased fibre intake as a result of increased energy

expenditure have all been reported.

Biological mechanisms

The mechanisms by which exercise and physical activity influence the

gastrointestinal tract are poorly understood although decreased gastrointestinal

blood flow, increase in gastrointestinal motility, increased mechanical bouncing, and

neuro-immuno-endocrine alterations are postulated. However, most of the

described mechanisms have only been investigated after acute bouts of exercise.

Whether or not these mechanisms are predictive of the long term effects of physical

activity remains to be elucidated.

GASTROINTESTINAL BLOOD FLOW

During exercise, blood will primarily be shunted to the skin and exercising muscles at

the expense of the gastrointestinal tract. 60–70% decrease in splanchnic blood flow

in humans exercising at 70% of maximal oxygen consumption (V~O2max). At

maximal exercise intensity, splanchnic blood flow may be reduced by about 80%.

Ischaemic damage has been proposed as a causal mechanism of gastrointestinal

bleeding during and after exercise. Although gastrointestinal blood loss is transient,

increased faecal á1 antitrypsin and lysozyme concentrations after exercise have

been found, indicative of local mucosal damage with an inflammatory response. In

theory, critical ischaemic levels and accumulation of metabolic waste products may

induce malabsorption, hypersecretion, and increased gastrointestinal permeability

with endotoxaemia. Findings for the effect of exercise on absorption and acid

secretion are inconsistent: both a decrease or no change in absorption and acid

secretion have been reported. Exercise induced increases in intestinal permeability

and mild leakage of endotoxins into the portal circulation have only been found at

higher intensities.

GASTROINTESTINAL MOTILITY AND BILE SALT METABOLISM

Data on the effect of exercise and physical activity on gastrointestinal motility are

scarce and mostly indirectly obtained and limited to acute exercise

MECHANICAL BOUNCING

The frequency of most gastrointestinal symptoms is almost twice as high during

running than during other endurance sports such as cycling or swimming, where up

and down movements are more limited. The mechanical vibration of the body is

more than doubled in running compared with cycling. The way in which this

bouncing of the gut affects gastrointestinal function is still unknown.

NEURO-IMMUNO-ENDOCRINE ALTERATIONS

Many hormones associated with gastrointestinal function at rest (secretion,

absorption, and motility) alter during exercise, in terms of plasma concentrations:

cholecystokinin, vasoactive intestinal peptide, secretin, pancreatic polypeptide,

somatostatin, peptide histidine isoleucine, peptide YY, gastrin, glucagon, motilin,

catecholamines, endorphins, and prostaglandins.

With respect to immune function, the current opinion is that physical activity of

moderate intensity may protect against infections by inducing changes in the activity

of macrophages, natural killer cells, lymphokine activated killers cells, neutrophils, and

regulating cytokines. Severe exercise, however, can result in a transient reduction in

natural killer cells and production of free radicals, which temporarily increases the risk

of infection. Knowledge of optimal intensity and duration of physical activity for an

optimal immunomodulating effect in athletes and in patients with gastrointestinal

related diseases is lacking.

Conclusions

Strenuous exercise may induce gastrointestinal symptoms such as heartburn or

diarrhoea, which may deter people from participating in physical activity. Repeated

gastrointestinal bleeding during training and competition may occasionally lead to iron

deficiency and anaemia. However, these and other symptoms can often be prevented

with appropriate precautions.

Physical activity, mostly performed at a relatively low intensity, may also have

protective effects on the gastrointestinal tract.