A liquid protein preload has generally been shown to decrease energy intake at an ad libitum meal compared to water( 1 ) or an isoenergetic carbohydrate preload( 2 ). However this has not been investigated in conjunction with exercise. Ingestion of protein and carbohydrate drinks post-exercise has become common practise amongst athletes and physically active individuals and their effects on appetite and energy intake is of interest, particularly to those on a weight management programme. To investigate whether protein induced satiety was evident when drinks were ingested in a post exercise context; the present study compared two isoenergetic drinks, differing in macronutrient content, and a low energy placebo drink.
Using a randomised double blind, counterbalanced design, 9 healthy males completed 30 min continuous cycling exercise at 63 (4) % VO2 max, followed by five, 3 min intervals at 86 (4) % VO2 max, separated by 2 min rest. 10 min post-exercise, subjects ingested 500 ml of one of three drinks each made up with low-energy lemon squash: a placebo drink (PLA) (15 kJ, 0.3 g protein, 0.6 g carbohydrate); a whey protein isolate drink (PRO) (528 kJ, 30.3 g protein, 0.6 g carbohydrate, 0.1 g fat); a sucrose drink (CHO) (528 kJ, 0.3 g protein, 30.8 g carbohydrate). This drink was ingested from an opaque bottle and through a straw. 60 min post-drink ingestion, subjects were provided with a homogenous ad-libitum lunch, consisting of pasta, cheese, tomato sauce and olive oil (1.88±0.03 kcal·g−1). Visual analogue scales of appetite ratings (hunger, fullness, desire to eat, prospective food consumption, satisfaction) were completed pre-exercise, post-exercise, post-drink, pre-meal, post-meal, 30 min post-meal and 60 min post-meal. Drinks were rated for sensory characteristics (pleasantness, after taste, saltiness, bitterness, sweetness, creaminess, refreshing, thickness, stickiness, fruitiness) immediately post-ingestion.
Energy consumed at the ad libitum lunch was lower after PRO ingestion (5732 (959) kJ) than PLA ingestion (6398 (497) kJ) (P=0.025), but was not different after CHO ingestion (6137 (1041) kJ) compared to either PRO (P=0.747) or PLA (P=0.889) ingestion. When the energy content of the drink ingested was added to the energy consumed at the ad libitum meal there was no difference between the trials (PRO: 6270 (959) kJ, PLA: 6413 (497) kJ, CHO: 6665 (1041) kJ; P=0.302). There were no main effects of trial (P>0.05) interaction (P>0.05) for any of the measured subjective appetite ratings. With the exception of sweetness, which was rated greater for the CHO drink compared to the PRO drink (P=0.038), there were no differences in the sensory characteristics of the drinks (P>0.05).
These results demonstrate that the addition of whey protein isolate to a drink ingested 10 min post-exercise reduces energy intake at a subsequent post-exercise meal. This effect was not observed with the ingestion of a sucrose drink. Protein ingestion immediately post-exercise might enhance the adaptive response to an exercise training programme (e.g. myofibrillar/mitochondrial protein synthesis) and the present findings suggest that this adaptation might be possible without effecting gross energy intake relative to ingesting nothing post-exercise.