I go to the gym as well as run very often.
But I feel that I'm losing more weight and becoming more skinny.
How do I maintain my bulk and tone while training for a marathon?

Are you sure you are losing muscle now? Marathoners and triathletes often have muscle loss (catabolism) and the only way to minimize it is to continue weight lifting and make sure you take in enough protein.

Yea, simply eat more and lift heavy.

also try to eat right away after you are done running / lifting; at most 30 minutes. On top of that eat lots and lots of slow digesting carbs / protein. Think potatoes, corn, pasta, wheat bread, and cottage cheese.

As long as you eat as much as you burn, you should not be losing weight; in the grand scheme of things. Otherwise, if you are losing weight, some maybe muscle lost along with lots of fat lost.

Everything that's mentioned in this thread are great ways to minimize catabolism. I've got a lifting buddy who does marathons, and he definitely loses some mass but always comes back and hits it hard. The muscle returns within a month or two.

Hi Brad,

All the info above is very relevant especially protein intake, marathon runners requirements are one of the highest of any sport! Protein supplementation could help but I prefer the natural approach make sure your meals and snacks contain some form of protein. Good sources are meats (obvious I know), peanut butter (spread on toast good combo carbs + protein), nuts, fish etc..

You will find however your body will adapt to the training you are doing so it's inevitable you will lose some bulk the same way heavy weight training would increase your size.

Fuelling the body before, during (if possible) and after exercise is key to performance and recovery after your training thus minimising potential body mass reductions due to insufficent calorie intake.

Hope this helps.