His malnourishment could make his friends worry more about him. For example, Sakura might start to be more motherly towards Naruto, constantly trying to get him to eat proper meals. His relationship with Sasuke could also change as Sasuke might initially look down on Naruto for being weak because of the malnourishment, but then as he sees Naruto's determination to overcome it, he gains a new respect for him.
Well, it would likely slow down his progress. Malnourishment means his body doesn't have the proper nutrients to build muscle or increase stamina. In ninja training that involves a lot of running, jumping, and fighting, Naruto would get tired easily. He might not be able to keep up with his peers in sparring sessions or obstacle courses.
Well, his friends might start to feel like he's drifting away. Since he's hiding his strength, he can't fully participate in training or battles as they expect. For example, Sakura might think Naruto is being lazy or not trying hard enough, which could create some tension between them.
His relationship with Sasuke would become more complex. Sasuke, as an Uchiha, might feel threatened or intrigued by Naruto having the Sharingan. They could have a new level of rivalry or a new form of cooperation.
With Sasuke, it could either drive a wedge or bring them closer. If Sasuke blames himself for Naruto getting injured while protecting him, he might distance himself out of guilt. On the other hand, it could also make Sasuke realize how much Naruto means to him and he could become more committed to their friendship.
His apathy can strain his relationships. His friends might feel neglected. For instance, Sakura could be confused and hurt as Naruto no longer shows the same eagerness to be part of the team.
Well, Naruto being cold could really put a strain on his friendships. His friends like Sakura and Kakashi would be concerned. Sakura might try to use her medical skills to check if there's something physically wrong with him. And Kakashi could attempt to have heart - to - heart conversations to break through that cold exterior. Since Naruto is usually so warm - hearted, this change would be quite a shock to them all.
Some friends might feel betrayed. If they are very clan - oriented, they could see Naruto's leaving as a sign that he doesn't value the clan and by extension, their friendship. However, his true friends like Sasuke or Sakura might understand his reasons. Sasuke, who has his own issues with his clan, might be more empathetic. Sakura, who has seen Naruto's determination, could support his decision in the long run.
His friends might respect him more for having a useful new skill.
Well, it would be a huge blow to his friendships. Naruto's friends are drawn to his big heart and strong emotions. An emotionless Naruto would not respond in the same warm way. He might not share in their joys or sorrows. Sakura, for instance, would miss his determination and the way he used to encourage her. His friends would have to work hard to reach out to him, but they may also start to drift apart because the emotional connection is no longer there.
It could make him very distrustful at first. He might have a hard time believing that others truly care about him. For instance, when his friends try to be nice, he might think they have ulterior motives.