Hey Nicole, If you are a member of this forum you probably know a lot more about baby and toddler nutrition than most pediatricians do. Period! I can't believe he/she told you to feed sugar...but what they also support is the parents' feeding kids processed grains (beginning with grain cereals, on up into the idea that mac and cheese is a nutritious childhood meal...), which are essentially sugars in a simple form, too.
I have had to let go of a LOT around my 2-y.o. girls' weight. They are the lowest-weight babies I have ever found on Curezone or any other forum. At one year, they were about 13.5 lbs, at 2 more recently they were not yet 21 pounds! But, they have met all their milestones just fine, talk up a storm, and are pretty well-balanced emotionally. We have yet to have a complete meltdown from either of them (I am sure it will come!).
We switched pediatricians because the first ones (large practice, so I had the same experience with many different doctors there...) could not get beyond that not-being-on-the-chart-for-weight. They were telling me I did not have enough milk, to supplement, etc. -- which was simply not true -- and encouraging me to put weight on by starting cereal early, etc. Our most recent doctor is a family doctor who also practices homeopathy and who is more open to other ways of thinking than the first pediatricians (and I don't think there is anyone more wed to their ways than a pediatrician -- the most unpleasant of all doctors in my opinion, both from what I remember as a child and have found as a mother...). He has concerns, but has been OK with how they are as the ultimate determinant, rather than how much they weigh or don't weigh. He also pointed out that we never come in for sick visits whereas other kids come in several times a year.
None of this I say with any smugness. But, I do believe that feeding high-quality fats (coconut, olive, flax seed oils, for instance) and meats, and then vegetables, and then lastly some whole-grain carbs, has been a good strategy for us. i.e. take the "food pyramid" and prioritize it backwards, so to speak. (The USDA way seems to have done a marvelous job at creating a nation of obesity!)
We are also lucky to be able to get fresh goat milk and farm eggs, which I use a lot. And I do try to let them eat some fun kid things, too if we are out at a birthday party or something (though I can always tell a difference when they eat lowfat, high-sugar stuff).
The old doctor ran an endocrine test on Merry when she was 9 months (without telling me that the blood test was for such a test and not for something else...). It came back perfectly normal, and would not let her stick Annie later because they are identical and I was pretty pissed about the first stick. But, the new doctor is now suggesting we do another endocrine panel that looks at growth hormone, and this is where I appreciate OTJ's insights -- I am just NOT going to let them draw blood from my girls when they are absolutely fine. I mean, who is going to feel better in that situation? The doctor, for sure. But at some point it all got a lot easier when I made the decision to let my daughters just be themselves in their skinny little bodies (and besides, I would not "do" anything if they were tested and something came back abnormal...I am not going to give them growth hormone, for sure).