Post-exercise Supplement Reduces Muscle Loss
One of the main challenges for people who want to lose weight
is to get rid of the fat without losing muscle. The good news is
that a post-exercise supplement can help to minimize the loss of
muscle during a restricted-calorie diet.
In one study, a group of ten active young women took part in two
separate seven-day trials separated by at least one week [1].
The women cycled at approximately 65% of their VO2peak on four
days (day 1, 3, 4, and 6). On day seven, they performed a ride
to exhaustion at approximately 75% of VO2peak.
In trial one, the women took a carbohydrate-protein supplement
after exercise. For trial two, they consumed a placebo supplement
that contained no nutrients. Nutrient intake over the course of
the week was the same; it was only the timing that differed.
The women lost weight during both trials: 3.1 pounds (1.4 kilograms)
during the control condition, and 1.5 pounds (0.7 kilograms) when
using the supplement. Unfortunately, the researchers didn't measure
body composition, so we don't know how much of the lost weight
came from muscle and how much came from fat.
Nitrogen balance was positive on day five and six when the women
used the post-exercise supplement. Without the supplement, nitrogen
balance was negative.
Nitrogen is found in foods that contain protein (such as fish,
meat, poultry, or dairy produce). Nitrogen balance represents the
difference between the amount of nitrogen you consume, and the
amount of nitrogen you excrete.
A positive nitrogen balance is
thought to indicate an anabolic state (muscle growth) while a
negative nitrogen balance indicates catabolism (muscle loss).
Although the positive nitrogen balance suggests that using the
supplement after exercise helped to preserve muscle, there are
problems with using nitrogen
balance to estimate muscle loss.
Moreover, we know that protein metabolism in women varies according
to the phase of the menstrual cycle they're in [2, 3]. For five
of the women, the trials occurred on successive weeks, and for
the other five, on successive menstrual cycles. This may have influenced
the nitrogen balance measurements.
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Reference
1. Roy, B.D., Luttmer, K., Bosman, M.J., & Tarnopolsky,
M.A. (2002). The influence of post-exercise macronutrient intake
on energy balance and protein metabolism in active females participating
in endurance training. International
Journal of Sport Nutrition and Exercise Metabolism, 12,
172-188
2. Lamont, L.S., Lemon, P.W., & Bruot, B.C.
(1987). Menstrual cycle and exercise effects on protein catabolism. Medicine
and Science in Sports and Exercise, 19, 106-110
3. Bisdee, J.T., Garlick, P.J., & James, W.P. (1989). Metabolic
changes during the menstrual cycle. British
Journal of Nutrition, 61, 641-650
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