I'm the lightest I've ever been for starting out a pregnancy (5' 5" around 113lb), which had me concerned I might have a hard time conceiving. Now that I am, I have family secretively telling DH to make sure I am eating...if they only knew. I really dislike that people think I don't take good care of myself in regards to eating, when it's the opposite that's true.
Pregnant or not, I eat foods high in good fats and steer clear of the low fat/non fat options. I crave foods (mushrooms, onions, kale, asparagus, beet tops, garlic, pasta) sauteed in butter every few days and go with it, figuring my body needs the extra fats and nutrients.
In the past I've never had a problem gaining the appropriate amount of weight and I don't expect it to be an issue this time either. From the beginning of this pregnancy, I am hungry way more frequently and for a variety of foods. So I just go with what my body's telling me I need. Hoping if I keep that up, that I will be able to stave off the nausea I experienced a few weeks my last pregnancy. My midwife believes morning sickness is caused from low blood sugar and/or lack of protein and I did notice that correlation for myself.