@senna was spot on. Determining his normal daily caloric intake is Step 1 because you know this is what he needs to maintain his current weight at 140. At this point, the goal should be to add 500 calories to this number.
For example, if he is taking in 2000 calories per day, the new goal should be 2500 per day. This should be THE NUMBER until he starts to plateau at a higher weight. Then you can adjust higher from there.
Does he have an end goal weight by a certain deadline? For example, does he want to gain 15lbs by Spring Season/March 1st? If so, he has about 16 weeks, so all he needs to focus on is gaining one pound per week.
Training Strategy - is his current training strategy designed to gain Strength and Size? It could be his current strategy is more Strength and Endurance or Strength and Power based and that is why the muscle growth isn't occurring. Maybe ask his trainer? Lastly, lifting 3 days per week, especially during the off-season, is light on volume. Really needs to be 5 days per week.
Other factors to consider:
- Daily Protein, Carb, and Fat intake (all of these are on the labels.) These can be used to make sure the weight gain is healthy and diversified.
- Desired Body Fat Composition (measuring this will help to make sure the weight he is putting on is "good" and will have a positive impact on performance)
- Food Scale (Purchasing one of these to understand portion sizes)
- Rules of thumb
- Food will always be better than supplements (if possible)
- Protein - "The less legs the better." (Fish = best. Chicken = second best. Cow = 3rd Place)
- "Eat a Rainbow Often" - Different colored vegetables. Variety is good for every meal.
- Carbs - complex is greater than simple.
