Too Much Exercise Can Damage Your Gut

By Katherine Schreiber

Many people still believe that too much exercise
isn't a bad thing—and that, if you're going to
be addicted to anything, exercise is the
healthiest drug of choice. A growing body of
evidence is proving these assumptions wrong,
however. One recent study adds to this pile of
proof by demonstrating a link between
excessive physical activity and impaired gut
functioning.

A team of Australian researchers led by Ricardo
Costa systematically reviewed research into
exercise-related gastrointestinal dysfunction
and injury conducted over the past 20 years.

Costa's team found that as exercise intensity
and duration increased, so too did the risk of
exercisers' guts being damaged or otherwise
impaired. The damage appeared to arise from
injuries to intestinal cells, causing the gut to
leak disease-causing molecules normally
contained within the intestine into excessive
exercisers' bloodstreams. People who
experience this so-called "leaky gut" often feel
nauseous, have aches and pains in their
stomach and bowel area, and experience
cramps, bloating, and gas.

Exercising for two or
more hours at 60
percent
VO2max seems to
be the tipping point
for exercise-related
gut issues to occur,
as Costa et al.
found. (VO2max is a
term for how much
oxygen a physically
active person is able to utilize during intense
exertion. 60 percent of VO2max means that a
person is exercising at 60 percent of their
maximum capacity to utilize oxygen—in other
words: at a moderate to strenuous pace.
VO2max varies based on age, fitness levels, and
sex. More conditioned athletes can perform
without feeling the need to stop at higher
VO2maxes.) High temperatures also appear to
raise the likelihood that exercisers will
experience such problems.

Costa et al. are careful not to dissuade people
who have no history of gastrointestinal issues
from ever engaging in strenuous exercise—nor
do the researchers recommend that individuals
struggling with gastrointestinal issues avoid
exercising to be on the safer side. They do,
however, caution exercisers to be aware of the
potential risks inherent in pushing oneself too
hard for too long (i.e. for more than two hours,
especially in heat). And while they recommend
that folks with GI problems stay away from
extreme exercise (and avoid exercising in
extreme weather conditions) Costa et al.
actually point to evidence in their review that
low to moderate levels of physical activity can
help individuals struggling with GI issues to
manage their symptoms.

This research adds one more entry to the often-
overlooked but still growing list of downsides to
excessive exercise. Other negative
consequences of too much time spent exerting
oneself include heart problems, impaired
immunity, increased risk of injury, overtraining
syndrome, loss of menstrual cycle in women
(which may court osteopenia or osteoporosis).