Eating chocolate is not exercise
From NHS - Thursday September 15th 2011
Many newspapers overreacted to a story on chocolate today. “Dark chocolate may be as good for health as
exercise,” reported the Daily Mirror. “Chocolate gives you a workout,” claimed the Daily Express.
“How dark chocolate 'boosts fitness in the same way as jogging,'” the Daily Mail said.
These misleading headlines refer to the findings from a small study in 25 mice. The relevance of these findings
to humans is uncertain.
The research looked at the effect of a chemical found in cocoa called epicatechin on the animals’ muscle
performance. The study found that mice receiving epicatechin for 15 consecutive days performed better on a
treadmill test of endurance compared with mice that didn’t. These findings provide evidence that giving mice
epicatechin can lead to increases in their muscular performance that are similar to those obtained by regular
Contrary to the statements made in the news reports, it is unclear whether the chemical would have the same effect
in humans, and further research would need to investigate this.
Also, epicatechin is found in dark chocolate, but chocolate was not tested in this research. It is unclear how much
would need to be consumed to get the levels that were given to these mice, or the appropriate level of epicatechin
needed to get a similar response in humans.
This study focused on muscle performance, and did not compare epicatechin with exercise for other established
exercise-induced health benefits, such as stress reduction and improved cardiovascular health. Epicatechin is just
one compound found in dark chocolate. Chocolate can also contain a lot of fat and sugar, the health implications of
eating too much of which are well established.
To sum up, the study does not show that eating dark chocolate is beneficial, or that it is a substitute for
exercise in humans, attractive though the idea is. Regular exercise is known to reduce the risk of developing many
diseases including diabetes and heart disease and is an effective part of maintaining a healthy weight.
Where did the story come from?
The study was carried out by researchers from the University of California and was funded by Cardero
Therapeutics, Inc. The research was published in the peer-reviewed medical journal The Journal of
Most of the news coverage of this study highlighted the key fact that it was carried out in mice. However, most
reports tended to overstate the benefits of chocolate by suggesting it might be an equivalent or a substitute for
exercise in humans. Such statements are not backed up by this study.
What kind of research was this?
This laboratory based animal study in mice investigated whether epicatechin (a natural substance found in
dark chocolate) can induce changes in the muscles of mice that are equivalent to the effects of regular exercise
Muscular endurance is known to be greatly enhanced by regular exercise through increasing the number of
mitochondria (the small powerhouses in every cell responsible for producing its energy) and the number of small
blood vessels (capillaries) delivering oxygen to the muscle cells to fuel energy production. The authors were
interested in finding a natural product that could mimic these beneficial effects and potentially be used to reduce
the muscle fatigue and the wasting effects related to ageing.
The researchers chose to test epicatechin because other recently published research suggested that consuming
small amounts of dark chocolate is linked with a reduced risk of cardiovascular disease in adults. Epicatechin is
the main flavonoid (a class of natural chemical found in plants) present in dark chocolate.
This small animal study was an appropriate first step in testing the theory that epicatechin can improve
exercise performance. Future studies would need to be done in humans only after careful consideration of any
potential safety issues to test whether there is a similar association.
What did the research involve?
Using mice, the researchers examined the effect of low doses of epicatechin in the presence and absence of
exercise on: exercise performance; muscle fatigue; muscle capillarity (the number of blood vessels serving the
muscle) and number of mitochondria.
The research was carried out in 25 one-year-old mice. All animals performed an initial exercise test on a rodent
treadmill, the speed of which was gradually increased at regular intervals until the mice reached the point of
exhaustion or were unwilling to run any more. Running time, distance, average speed and power were all recorded at
the start of the study as a measure of fitness and muscular endurance. After the initial exercise test the mice
were randomly divided into four groups to receive: water; water and exercise; epicatechin; or epicatechin and
exercise, for a period of 15 consecutive days.
All groups were fed a standard diet without limitations.
Those assigned exercise performed 30 minutes of moderate exercise five times a week for a total of 15 days.
Those assigned to receive epicatechin were given this in solution (1.0mg/kg of body mass) twice daily (morning and
On the 16th day the mice were retested on the treadmill to assess any changes in their performance. Forty-eight
hours after the final treadmill test the mice were sacrificed and their hind leg muscles dissected and examined for
changes related to muscular endurance ability. These included the number and density of capillaries in the muscle,
the number and density of mitochondria, and the presence of components essential to the function of
What were the basic results?
Mice receiving epicatechin on its own performed significantly better on all aspects of the treadmill test
(duration, average speed, distance, power and total work rate) than mice on water, and mice who received water and
Mice that also exercised while receiving epicatechin also performed significantly better on all aspects of the
treadmill test than mice receiving water only, and mice who exercised and received water.
The improvement between the two treadmill tests in the epicatechin only group was similar to that seen in the
epicatechin with exercise group. For example, mice in the epicatechin only group were able to run for an extra 160
seconds after receiving epicatechin for 15 consecutive days compared with an improvement of 154 seconds in the
epicatechin and exercise group. The water only, and water plus exercise groups showed no improvement, and actually
ran for less time in the second treadmill test (42 and 61 seconds less, respectively). Similar patterns were seen
in the other treadmill measures including distance run and average speed.
In all cases the density of capillaries in the dissected muscles was higher in the epicatechin-treated groups
compared with the water-treated groups. An increase in the density of muscle mitochondria, as well as components
essential to the internal processes of the mitochondria, was also observed to be significantly higher in the groups
receiving epicatechin compared with those who did not.
How did the researchers interpret the results?
The researchers report that these findings may have “the potential application for clinical populations
experiencing muscle fatigue”.
The main findings of this study are that 15 consecutive days of epicatechin treatment resulted in improved
treadmill performance, more capillaries serving the leg muscles and more mitochondria in one-year-old mice. These
effects are usually achieved through regular exercise.
The following points should be considered when interpreting the results of this study:
- The study was very small, using just 25 mice. Hence, it represents an initial proof of concept study that
epicatechin may be linked to muscular performance. Studies on humans would be necessary to confirm this
association in people and assess whether the positive effects would be large enough to be of benefit to someone
with the significant muscle fatigue associated with old age.
- The study assessed just one compound of dark chocolate, epicatechin, and did not test the effect of feeding
the mice chocolate as a whole product. Hence, news stories suggesting chocolate is just as beneficial as
exercise are misleading.
- This study focused on just one aspect of health - muscular performance. It did not assess whether
epicatechin was better or worse than exercise for other elements of health. Exercise has many benefits outside
of improving muscle endurance, such as improving cardiovascular health, and reduces the risk of developing many
diseases such as diabetes and heart disease.
- The authors describe the level of epicatechin given to the mice only as “low-dose”. It is not clear how
much dark chocolate humans would have to eat to ingest a similar level of epicatechin as that tested in this
study and what the additional effects on the body might be in terms of weight gain.
- The excess consumption of chocolate (a calorie-rich food) can lead to weight gain and obesity unless it is
offset by regular exercise. This study does not suggest chocolate is an adequate substitution for exercise in
the general population, merely that a specific extract from it shows signs of improving muscle function in
This small animal study provides evidence that giving mice epicatechin can lead to increases in muscular
performance similar to those obtained by regular exercise. Further studies will be needed to confirm these findings
in people. This study does not show that chocolate consumption is beneficial, or that it is a substitute for
exercise in humans. Exercise is known to be beneficial to the body in numerous ways and is an effective way of
maintaining a healthy weight.