There have been a few queries on the forum regarding the effect of consuming carbs around a workout and inhibition of GH release. Some 'gurus' are apparently recommending avoidance of carbs post workout because it allegedly suppresses growth hormone.
What does the science say?
Carbs before exercise:
GH is often, but not always elevated during exercise. Consuming carbohydrates before exercise can[1], but does not always[2], diminish growth hormone elevations during exercise. BTW, one study has shown that consuming 25g of whey and caseinate proteins 30 min before a strength training session significantly decreased serum GH and testosterone levels, and increased serum insulin during the workout[3].
However, consuming whey (or essential amino acids) before a workout has been shown to boost protein synthesis. So if it's muscle growth you are after, then take your pre-workout aminos or whey.
Carbs during exercise:
Consuming carbohydrates during exercise can[4,5], but does not always[6], diminish growth hormone elevations during exercise.
Carbs after exercise:
Williams et al took a group of resistance-trained men and had them perfom high, moderate and low volume workouts, each performed twice and followed immediately post-exercise by either a placebo or carbohydrate-protein supplementation. "Levels of growth hormone rose significantly after the greatest volume of exercise only. Those of insulin and glucose rose significantly after supplementation only... Supplementation had no effect on the lactate, growth hormone or cortisol responses to resistance exercise."[7]
Koeslag et al found that, after a 2 hr bout of running in men who had followed a low-carb diet for 48 hours, 100g of glucose 2 hours after the run had little effect on post-exercise GH release. 100g of soluble starch had "equivocal" effects, meaning it showed large variation among subjects[8].
Kramer et al had resistance-trained men consume either a protein-carbohydrate supplement or placebo for 1 wk each. The last 3 days of each treatment, subjects performed resistance exercise and consumed the supplement 2 h before and immediately after the workout. Growth hormone, and testosterone were significantly elevated immediately postexercise. Growth hormone response on day 1 was significantly higher during supplementation, but not on days 2 and 3. Post-exercise testosterone declined below resting values during supplementation. Cortisol decreased immediately postexercise on day 1; the response was diminished on days 2 and 3. Glucose and insulin were significantly elevated by 30 min during supplementation and remained stable during placebo. Insulin-like growth factor-I was higher during supplementation on days 2 and 3[9].
To examine the effect of carbohydrate and/or protein supplements on the hormonal state of the body after weight-training exercise, nine experienced male weight lifters were given water (Control) or an isocaloric carbohydrate (CHO; 1.5 g/kg body wt), protein (PRO; 1.38 g/kg body wt), or carbohydrate-protein (CHO/PRO; 1.06 g carbohydrate/kg body wt and 0.41 g protein/kg) supplement immediately and 2 h after a standardized weight-training workout. Venous blood samples were drawn before and immediately after exercise and during 8 h of recovery. Exercise induced elevations in lactate, glucose, testosterone, and growth hormone. CHO and CHO/PRO stimulated higher insulin concentrations than PRO and Control. CHO/PRO led to an increase in growth hormone 6 h postexercise that was greater than PRO and Control. Supplements had no effect on insulin-like growth factor I but caused a significant decline in testosterone. The decline in testosterone, however, was not associated with a decline in luteinizing hormone, suggesting an increased clearance of testosterone after supplementation(10).
So pre- and peri-WO carbs may inhibit GH release during exercise, while post workout carbs either have no effect or may even increase GH after a workout.