node_access rebuilding gobbles up all memory

if you rebuild the node access table you'll run out of memory quickly. Problem is this code:

$result = db_query("SELECT nid FROM {node}");
while ($node = db_fetch_object($result)) {
node_access_acquire_grants(node_load($node->nid));
}

That means all nodes are loaded. The problem is that loaded nodes are cached and thus the memory is depleted.