Confuzed

If any random person reading this can help me ... please do!

How much should I be eating? Last year I saw a nutritionist in an attempt to trim down ahead of my first half-marathon for 2009. Her advice was a low GI diet, with around 1300 to 1500 calories a day. In terms of exercise, on an average week I do:

3 x running sessions (two 30-40 mins, one 60mins)
3 x swimming sessions (three pool, one surf)
Pump x 2
Bikram x 2

Obviously I double up sometimes :)

Anyhoo, I spoke to a friend of mine who is a PT who worked out my base metabolic rate (or something) and she said based on those figures (which included height, weight, activity level, age) I should be eating more like 2,000 calories a day!

What the? And she suggested that I wasn't eating enough, which was slowing my metabolism down, which was why I was having trouble with random weight gain.

Does this sound vaguely plausible? I'm so confuzed. Situation normal really, but if I'm doing the absolute wrong thing, I'd love to know!

Argh.