I'm concerned about my brother?

Well first of all. It might be your fault bc she is the one who buys the groceries and lets him. Why don't you talk to your mother about buying healthier foods and talk to your brother about it?

He is going to be extremely sick someday, if not already!

First off pasta was never healthy and neither is any food which is made from grains.

"Fried" foods are fine, if they are cooked in HEALTHY fats -- lard, butter, unrefined oils like olive, coconut, avocado oil. They can be sauteed in this stuff. No problem.

Your brother is overweight most likely because he's consuming a lot of grain-based foods and sugar-laden foods (processed foods).

You cant fix someone else's eating habits... if your brother is concerned, he will do the research to change his own diet. You're only responsible for your diet.

First, where's your father? If he's not in the picture, your mum's mistakes are starting to add up. If he is, can you get him involved?

If not, there's really only one option. Don't bother talking to bro. It sounds like you're a good older sib, but no child will listen to a sib. Given the choice, most kids will eat junk and veg out in front of electronics. Luckily, most kids aren't given this choice. As for mum, this won't help either. She'd have to be braindead not to know these foods are horrible and she's raising a child who won't live very long if something doesn't change.

What you want to do is talk to another adult your mum is close to and who she might listen to. A relative is ideal but if not, a close friend might work. Your mum will be angry if you do this, but honestly, there is no excuse for her lack of parenting, and you're out of options.

EDIT: Yikes, this changes things. Your dad is the one you talk to. He has equal power as your mom, but he's not using it. He should put together a plan for food and also requiring at least one sport, bike rides every day, etc. Then he tells mom either she agrees to this or he's leaving and seeking full custody. It sounds extreme, but it's not, because you're right about the health issues. It also sets bro up for bullying which brings a separate serious problem.

you could try seeing what cps has to say about it

As a starting point, sit down with your mother with scientific evidence to back your concerns and assertively, not aggressively or accusatorily, share your concerns and emphasize you are coming from a place of love and support. Encourage your mother to think about her son's wellbeing and try to get clarification as to why she makes these choices for him. There could be some underlying issues of which you are not aware, so approach with an open-mind and no judgement. Ultimately, if you truly feel your brother's health is in danger, have a conversation with your GP and get some advice.

Inform him about the health issues he could possibly deal being obese. Talk to your mom about it too. She is a grown woman, she has to know better. Tell her that she is the mother and she is supposed to care about you two. If this has no results, then let it be. He will understand one day hopefully. He is still really young. That shouldn't be an excuse but his immaturity keeps him from seeing the truth.

Good luck to you and your brother!

Join him or hide the foods

You are right to be concerned, there are health risks to being overweight such as Diabetes, cancer (endometrial, breast and colon), risk of stroke and heart disease, children who stay overweight are a lot more likely to be overweight when they are adults as well. Being overweight can lead to an early death.