Not being obsessive, but keeping a watchful eye on one's weight is important. Many patients lose weight due to various reasons, one of which is inability to swallow, and choking on one's food regularly is understandably enough to discourage anyone from eating. Losing one's sense of smell does affect to some degree one's appetite, and I have personally found there are certain foods I used to like but now can take them or leave them. I have noticed a definite change in my choice of foods. Although I can't find any data confirming this, I feel sure the sudden change in tastes is connected to Parkinson's. Eating in public is a fairly big problem many fellow sufferer can relate to, as it can be embarrassing, dropping food or making a mess, and quite often I will refrain from eating at a function just to avoid any mishaps. Sometimes, when I am alone at home during the day, I'm simply not hungry, and could easily skip a meal going without eating. However, knowing it is important to eat a well balanced diet, I occasionally have to force myself to eat something, however little it may be.
Then you have the other extreme, where patients put on weight. This is completely understandable, since mobility is often a problem, and lack of exercise or movement, any calories consumed are not burnt off. You've heard the saying "what passes the lips, stays on the hips"!