<human>: Could you distill the essence of the text into 1-3 sentences?

So a few months ago my sister in law (SIL) came to visit, and she started my parents in law (PIL) on Shakeology. They used it for a month but stopped because of other things. They lost a few pounds using it, but I'm positive they gained it all back once they stopped using it. 

My PIL aren't huge, but they can stand to lose a little weight. My SIL is big and she is on Shakeology so she can make her self happy by saying she is doing something healthy. 

I'm close with PIL and they are like my parents since I cut my parents out of my life. My husband and I are becoming healthy, working out often and tracking calories. The best way to lose and maintain weight is to make it a lifestyle change. 

I found out a few days ago they are starting it again and spending hundreds of dollars on it. I want to tell them that it's just a tool to help with weight loss and they don't really need it at all to lose weight.

I asked my husband if we should tell them and he agreed but hasn't brought it up again. I don't want to be the annoying daughter in law telling them what is right and what isn't; but at the same time I don't want them doing something that won't be worth it in the long run.
<bot>: Not sure if I should tell my PIL that Shakeology won't help them keep the weight off in the long run?