Quote Originally Posted by btchance
I have a question in the opposite direction, how do you know you are too low on body fat, and what is an approximate number?

I ask this because 6mo ago I was measured by the nutrition doctors at the university at 17%, while their recommended bottom number was 21, although they didn't think 17 would be a problem. I have since started exercising a lot more, and have dropped down a couple of sizes without losing any weight or eating differently. Now I have started to have irregular periods, which the doctors attribute to stress, but I don't know about that as I have been similar stress levels for years, and this actually started during a break from most of the stress. This is worrisome to me because I already have pretty small bones. When I broke my arm in multiple places when I was 20, they actually did a bone density scan because the density looked pretty light on x-ray, and when they operated, the surgeon said my bones were the size of an 11yo, so this is definately something I'm worried about.
When you start missing periods & are nowhere near menopause you can assume your body fat is getting too low. I know because I struggle with this problem myself. Eat, my dear, eat. Your body is putting on muscle & replacing the fat. Even though the scales read the same it sounds like this is what's going on. Muscle will have you burn up more energy...good if you want to lose weight, bad if you're trying to maintain. Don't be afraid of the food, your body is telling you it needs it.An example for you: last week I cycled 525km because I'm in training for a major 200km hill ride event in Jan 06. I wear a heart-rate monitor which tells me how much energy I burn up. For me to maintain at 50kg (112lbs) I require about 4,000kcals/day. This is double the average. If I fall below 50kg I lose energy & my periods mess up.
If you're at risk of osteoporosis (thin bones) the last thing you want your body thinking is that you're starving it because it will take calcium & minerals from your bones. Vicious circle.
Good luck!
Yasmin.