I'm considering doing CrossFit. Any advice?

I'm sick of being overweight. I'm borderline obese now at a BMI of 30 (6' tall, 225 lbs).

I am not a huge fan of gyms, but there's a crossfit gym in my town, and I need to make some big lifestyle changes.

My weight has yo-yoed for years. In my teens I was 215. In my early twenties, 150. In my late twenties, 185. Around 30, I was 205, started cycling with a racing bicycle, and dropped to 170. Got hit by a truck, and went back up to 200. Went on a zero carb diet and dropped to 158 for 9 months until I became hypothyroid due to the nutritional deficiencies of that way of eating. Went up and down many times since then, but steadily climbing upward to where I am today. I can't take this anymore. I have a desk job at a computer for 40 hours a week, and I'm becoming very depressed.

Do you have any advice for someone who is overweight trying to start crossfit?
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I'm considering doing CrossFit. Any advice?
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