Male 50 5"7" 125 lbs. I run 10 miles three days per week and do weights three days. I watch what I eat, no fried foods, no saturated fats. I want to gain 10/15 lbs but want to keep toned with no change to belly or abs. Any suggestions.
You will probably have to back off on the running. At the level you are, the running causes your body to use muscle to sustain itself. Your diet should not have to change except make sure you get 1 to 1.5g of protein per pound of body weight. Also, adjust your weight training. Come up with a four or five day split and train heavy.