mom tells daughter not to lift heavy

You could either:
1. Talk to the mother. You and her might both learn something from the other.
2. Let it go, it isn't your kid to determine what's best for.

Nothing wrong with lifting heavy (for the individual) The mom should probably talk to the coach to ge an understanding of the program he has her doing.

That said, unless it's a program with a very high coach to athelte ratio she probably should not be lifting for max singles (maybe not even then).

Yes, they apply the same way. They might want to contact a doctor to ensure she gets the green light to do a weight training program at that age, but apart from that all she needs to do to lose BF% is to eat in a calorie deficit. The lifting only helps retain muscle mass while losing weight as eating in a deficit will cause a person to lose both fat, and muscle.

That family needs to see the 12 year olds pediatrician ASAP. I remember my mom took me in before she had me running 10Ks with her when I was 12. He did say that some intense forms of exercise and lifting can stunt growth in some children. He said I was okay to run races with my mom if I wanted.

I wouldn't make this about whether you or your friend are correct. I'd focus on what the coach says. The girl should follow the coach's program, because that's one of the things coaches are for (sure, there are exceptions when a coach is clueless, but I'm assuming this isn't the case here). If the girl wants to play sports, the last thing a parent should do is attempt to stunt that development by trying to make the child stop training for said sport.

I'm a registered dietitian and work in pediatrics. I generally do not teach my clients to calorie count. We talk about calories = measurement of energy, but avoid looking too much at the numbers. The risk of disordered eating and obsession over weight doesn't outweigh the benefits.

What we do focus on is eating a variety of food from all the food groups, especially fruits and vegetables every day, a minimum of 60 minutes of daily physical activity, adequate sleep, and limited sedentary time in front of a screen (exception is school work).

We also talk a lot about body positivity and body image. Instead of mom telling her daughter to stop lifting heavy weights because she wants to be thin like her friends, a better message would be to teach her to be proud of how strong she is and to avoid comparing her body to others. This is incredibly detrimental in adolescence, and much more worrysome than not falling at the 50th percentile weight-for-age.

To answer your question succinctly - it depends.

The long version is this: pediatric weight loss is NOT studied the same way adult weight loss is studied. Recommendations for pediatric nutrition lag behind adult nutrition by several years. A big reason for this is the ethics of research. When we "put kids on calorie restricted diets," we may be harming their development. Some adolescent-teenage boys (depending on weight) need as much as 3,400kcal per day, just for development. That doesn't even take high levels of activity into consideration. So to fund a study with thousands of kids and putting them on a diet that may or may not harm their development is near impossible. I would imagine similar studies focusing on exercise would also be difficult - researchers are always afraid of doing more harm to the study subjects than benefits for the greater good when it comes to children.

My mom had her reservations about me starting out in lifting. Every time she bust my chops I repped her for 3 sets. Nothing will silence a nagging mother like overhead pressing her.