I think it has to do with your metabolic rate, which "peaks" around 27 for men, and thence diminishes, gradually...(it "starts" high gear as you hit puberty)...
I believe for females, the "peak" is reached around 36-40 years (where's Audeo when you need something definitive?) and I think they "start" around 20...
If you cannot "process it" at the fantastic rate that simple metabolism gives you (of course this is greatly assisted by physical activity), then you tend to lose the appetite...
As for "allegies", with our four, we had a gamut of them, and were fortunate to be seconded to a good allergist that tested each of them (expensive...thank God for being a Canuck with Public Healthcare to pick up the costs!)...
Amongst those "discovered" were: dogs, cats, milk, food colouring peanuts, nuts, soy products, corn (and all corn derivatives), peas, apples, fish, tomato paste, etc etc...
A merry mess!
With the oldest, I was about to the point of wanting to "drive her through the wall", when we finally got this diagnosis....when she was "dried out" (14 days abstinence) (it was Christmastime, many years ago!) and we sent her back to school, within 20 minutes, the Principal was on the phone, asking if we had put her on Redelin, or some like drug...she was positively "normal"...
as the "tests" are non-specific, you are supposed to "dry out", then "test" each food item in small quantity (once!) and observe "reaction"...she came home from school, ate a 3/4" cube of medium cheddar, as was an idiot for seven long days....(this was the one with peas, corn products, apples, tomato paste...quite a "challenge"
Allergies do "fade" with time, tho' I'm not anxious to "test" Dougie with his peanut/soya/fish/nut allergies, as these are potentially "deadly"
Other things are simply "acquired" tastes...
Or so I have come to "believe"...
Lifter