Hi, Cinnamon. These opinions are strictly my own, or at least those of MY five personalities and no others
IMHO your trainer is full of it. For a number of reasons:
Number 1, minimal cardio will reduce your cardiovascular fitness, which is something you absolutely DO NOT want for health reasons. As you have indicated, you do not wish to "lose weight", but cardio work is important for heart, circulatory and respiratory health, not just burning calories. And I don't care what the muscleheads out there say, muscle training and the resultant mass-building IS NOT cardio training and cannot substitute for it.
Number 2, your trainer is just that, a trainer, and unless he is a registered dietitian or nutritionist he has no business at all giving nutritional advice. In fact, reputable fitness certifying bodies (including the American Council on Exercise {ACE} {I am ACE certified in group fitness instruction}, the American College of Sports Medicine {ACSM}, the National Strength and Conditioning Association {NSCA}, the National Academy of Sports Medicine {NASM} and a whole host of others) specifically forbid trainers and GFIs from attempting to offer advice or counsel outside their scope of certification and training. If I were you, I'd check out his certifications and academic training, and the less he has of each of these (and I'll bet he doesn't have much) the less I'd listen to him.
Number 3, I agree with you - at your height, if you were to increase your caloric intake that much you would be at great risk of building fat stores that you do not want. Strength training is not a big calorie burner, and the degree to which fat-free muscle mass raises your resting metabolic rate has been grossly overstated in previous years, primarily by trainers who are strength-oriented.
IMHO, it would be worthwhile for you to bring in a heavy-lifting protocol if you have not done so already (more on what "heavy lifting" means in a minute) while keeping your cardio output AND your caloric intake constant (and keeping your healthy food choices exactly as you have listed), and then YOU listen to YOUR body in terms of what it might need for additional fuel and what macronutrients (carbs, protein, healthy fats, etc.) you need. I found over the years that as I began lifting heavier and heavier, my body told me what it needed (and in what quantities) through my taste buds: I would crave carbs here, extra good protein there, and my appetite for crap (refined concentrated sweets, bad fats and the demon salt) plummeted. Pay attention to the muscle mass that you build and your own changes in appetite if any, and make changes from there.
Heavy lifting is relative to the individual exerciser, as I'm sure you know; what's heavy for one person might be light for another, AND what was heavy at one time becomes light as you build strength. A protocol that incorporates weight loads that nearly completely fatigue the muscle group after 8-12 reps would be a good one for you, and I'm sure others here (are you listening, LauraMax?) can chime in with their ideas for gym strength routines.
JMHO - I'm sure others will have their own as well.
a-Jock