One little side-note: the idea that drinking extra water or fluids helps you create more breastmilk is a myth. Here's what Dr. Sears says: "Because milk-making hormones help your body conserve water, failing to drink enough water will not affect the fluid content or volume of your milk." So, lactating can cause you, yourself, to require more fluids in your own body to keep you from dehydrating, but drinking extra water will NOT mean you are able to physically create more breastmilk. Only frequent nursing and pumping can trigger the "Supply & Demand" response to encourage your body to produce milk. Secondly, many babies at your son's age go on intermittent nursing "strikes" as they become more and more alert and distracted by the world around them. The want to look around, smile at you, tilt their heads back and see how the room looks upsidedown, poke you, babble, squirm and get moving. It doesn't mean they want to wean. I would stick with attempting to nurse him as often as you can at the breast for at least another few weeks to make sure this isn't just a temporary strike. If he refuses to eat at noon, don't force it, but try again 30-45 minutes later. He may refuse again or be hungry enough this time to buckle down and nurse. And don't immeadiately whip out a bottle- offer the breast first as the default method for feeding. My daughter would go through phases almost daily at that age, of refusing to nurse for 1 or 2 feedings and then snuggling in later on for a decent session, then refusing the next one after 2 minutes. She's 10.5 months now and we got through her strikes and are still nursing well. Just make sure you aren't giving up nursing because of your busy baby's new interest in the world! Especially if you want to keep him on breastmilk. Nursing obviously is the best way to keep up supply.
If he really prefers the bottle and won't nurse after a couple weeks of continuing to offer the breast 1st, then don't worry about pumped milk causing obesity. It is still the ideal food, and the fat balance, mixed or not, will be healthiest for him no matter what!!! Good luck!