Is he gassy with all dairy, or mostly whole cows milk? If it is a problem digesting milk proteins, you might have some success with yogurt, which has been cultured; the culturing helps to break down some of the milk protein so it's easier for some people to digest. The same is true for cheeses, although some are easier than others for the digestive system to handle. If yogurt is OK, try to find full-fat yogurt, like Stoneyfield Farms, which is also organic and SOOOOO creamy!
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If not, I'd go ahead and get rid of all dairy till your appointment, and supplement with other good-fatty foods already mentioned, like avocados (Natalie LOVES guacamole!
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, butter (sometimes tolerated where other dairy is not - but you'd have to find out if it would be OK for him), olive oil, dark meat chicken (fattier than white meat), flaxseed oil, and fish oil. Coconut oil is also EXCELLENT and great for high-heat cooking, which olive oil is not.
I've also heard of people having great luck with goats' milk; it's available at many health food stores.