You have lots of faith in politicians, it seems. While they believe they are qualified to make the best decisions for you, decisions in your best interests, they are not actually working in your best interests. They are working in their best interests.
There are some consistent political agendas. If you watch the news, nationwide, across nations, then you can see it. Immunization. Stopping population growth. They are common. What are the common trends in weight? What is on the horizon?
Politicians are great at addressing root causes behind why fat people become obese, right? They are qualified to provide help, to change the fundamentals, right? No. It isn't their area of expertise. It isn't their expertise, but it is their interest. What makes it the area of their interest? Why are they putting tax money into solving that particular problem? If it were an actual solution, there would be a company that makes money from doing it. Texts are so cheap they are nearly free. Imagine a business that was paid real money for something that was effectively free. It is a great business model if it worked. There is a fundamental economic reality behind why it isn't a business - it doesn't work. Fat people (and I'm overweight, I'm the target audience) pay millions a year because they don't want to be fat - go ask Jenny Craig. It is a huge industry, taking money from fat people after convincing them that you can make them human again.
It is weight-ist. Opt in or not, it is a stupid politician being weight-ist.
How secure are text messages? How about the vendor? Are they securing the information? This is medical information. This associates particular medical conditions with a phone number and a persons identity. Is it secure? No way. It is broadcast unencrypted publicly. People are unable to get jobs because of weight. They are considered higher medical risk, and so get less pay for the same job. If you sign up for that list, it is going to go into a HR database somewhere and, God-forbid you ever lose the weight, it is going to be considered against you in the future. It has legal and ethical implications, career spanning implications, that the politicians likely didn't consider.
I'm sure you didn't consider those either.