Does It Matter What
You Eat After Exercise?
Many of the health benefits of aerobic exercise are due to the most
recent exercise session (rather than weeks, months and even years
of exercise training), and the nature of these benefits can be greatly
affected by the food we eat afterwards, according to a study published
in the Journal of Applied Physiology.
"Differences in what you eat after exercise produce different
effects on the body's metabolism," said the study's senior
author, Jeffrey F. Horowitz of the University of Michigan. This
study follows up on several previous studies that demonstrate
that many health benefits of exercise are transient: one exercise
session produces benefits to the body that taper off, generally
within hours or a few days.
"Many of the improvements in metabolic health associated
with exercise stem largely from the most recent session of exercise,
rather than from an increase in 'fitness' per se," Dr. Horowitz
said. "But exercise doesn't occur in a vacuum, and it is
very important to look at both the effects of exercise and what
you're eating after exercise."
Specifically, the study found that exercise enhanced insulin
sensitivity, particularly when meals eaten after the exercise
session contained relatively low carbohydrate content. Enhanced
insulin sensitivity means that it is easier for the body to take
up sugar from the blood stream into tissues like muscles, where
it can be stored or used as fuel. Impaired insulin sensitivity
(i.e., "insulin resistance") is a hallmark of Type II
diabetes, as well as being a major risk factor for other chronic
diseases, such as heart disease.
Interestingly, when the research subjects in this study ate relatively
low-calorie meals after exercise, this did not improve insulin
sensitivity any more than when they ate enough calories to match
what they expended during exercise. This suggests that you don't
have to starve yourself after exercise to still reap some of the
important health benefits.
The paper, "Energy deficit after exercise augments lipid
mobilization but does not contribute to the exercise-induced increase
in insulin sensitivity," appears in the online edition of
the journal. The authors are Sean A. Newsom, Simon Schenk, Kristin
M. Thomas, Matthew P. Harber, Nicolas D. Knuth, Haila Goldenberg
and Dr. Horowitz. All are at the University of Michigan. The American
Physiological Society (APS: www.the-aps.org) published the research.
The study included nine healthy sedentary men, all around 28-30
years old. They spent four separate sessions in the Michigan Clinical
Research Unit in the University of Michigan Hospital. Each session
lasted for approximately 29 hours. They fasted overnight before
attending each session, which began in the morning.
The four hospital visits differed primarily by the meals eaten
after exercise. The following describes the four different visits:
1. They did not exercise and ate meals to match their daily
calorie expenditure. This was the control trial.
2. They exercised for approximately 90 min at moderate intensity,
and then ate meals that matched their caloric expenditure. The
carbohydrate, fat, and protein content of these meals were also
appropriately balanced to match their expenditure.
3. They exercised for approximately 90 min at moderate intensity
and then ate meals with relatively low carbohydrate content,
but they ate enough total calories to match their calorie expenditure.
This reduced-carbohydrate meal contained about 200 grams of
carbohydrate, less than half the carbohydrate content of the
4. They exercised for approximately 90 min at moderate intensity
and then ate relatively low-calorie meals, that is, meals that
provided less energy than was expended (about one-third fewer
calories than the meals in the other two exercise trials). These
meals contained a relatively high carbohydrate content to replace
the carbohydrate "burned" during exercise.
The exercise was performed on a stationary bicycle and a treadmill.
The order in which the participants did the trials was randomized.
In the three exercise trials, there was a trend for an increase
in insulin sensitivity. However, when participants ate less carbohydrate
after exercise, this enhanced insulin sensitivity significantly
more. Although weight loss is important for improving metabolic
health in overweight and obese people, these results suggests
that people can still reap some important health benefits from
exercise without undereating or losing weight, Dr. Horowitz said.
The study also reinforces the growing body of evidence that each
exercise session can affect the body's physiology and also that
differences in what you eat after exercise can produce different
The research team is now performing experiments with obese people,
aimed at better identifying the minimum amount of exercise that
will still improve insulin sensitivity at least into the next
January 29, 2010