I really can't advise spoon feeding lumpy foods at all. Your son should be feeding himself finger foods, it is much safer than spoon feeding lumpy foods and generally better accepted by the child.
Also realistically breastmilk or formula has far more calories and fat than almost any food. As long as your son continues to get enough breastmilk or formula he won't loose weight.
http://www.borstvoeding.com/voedselintroductie/vast_voedsel/rapley_guidelines.html#choke
Many parents worry about babies choking. However, there is good reason to believe that babies are at less risk of choking if they are in control of what goes into their mouth than if they are spoon fed. This is because babies are not capable of intentionally moving food to the back of their throats until after they have learnt to chew. And they do not develop the ability to chew until after they have developed the ability to reach out and grab things. Thus, a very young baby cannot easily put himself at risk because he cannot get the food into his mouth in the first place. On the other hand, the action used to suck food off a spoon tends to take the food straight to the back of the mouth, causing the baby to gag. This means that spoon feeding has its own potential to lead to choking – and makes one wonder about the safety of giving lumpy foods off a spoon.
It appears that a baby's general development keeps pace with the development of his ability to manage food in his mouth, and to digest it. A baby who is struggling to get food into his mouth is probably not quite ready to eat it. It is important to resist the temptation to 'help' the baby in these circumstances since his own developmental abilities are what ensure that weaning takes place at the right pace for him. This process is also what helps to keep him safe from choking on small pieces of food, since, if he is not yet able to pick up small objects using his finger and thumb, he will not be able to get, for example, a pea or a raisin into his mouth. Once he is able to do this, he will almost certainly have developed the necessary oral skills to deal with it. Putting foods into a baby's mouth for him overrides this natural protection and may increase the risk of choking.