I'm inclined to think it's because of emotional issues your improving health is bringing up, versus a physical side effect.
Consider your childhood---were your caregivers unhealthy? Although you may be consciously feeling better about your health, you may have some sense of being disloyal to your family's unspoken code on how to live your life.
And/or, your unconscious mind is angry at you for doing it, because it may feel that whole 'unworthy of any good thing' your caregivers or significant folks in your young life impressed upon you based on the projection of their own issues which your behavior triggered, is important to maintain.
Your unconscious mind has probably been enforcing that 'shouldn't feel good about myself' with your destructive lifestyle, and you're cutting that off at the knees. It no doubt believes feeling that way is essential for your long term survival, somehow. Younger kids don't do logical thinking, and that was when your unconscious mind 'figured' this out. It doesn't realize you've grown up, and that conclusion was based on faulty harmful 'information' delivered by your projecting caregivers or who ever.
And/or some unconscious part of you believes you deserved to be punished, again from faulty programming from your caregivers, based on their issues. And rather take the abuse from your caregivers, you decided to punish yourself because they might go too far. And it let them have one less thing on their probably already way full plate. Kids are like that. They try to make things better for their parents because it makes their lives easier, too.
And those are just a couple reason for your anger being brought to the surface now. Maybe even something as simple as being angry at yourself for all the lost wasted years of unhealthiness. The detoxing obviously triggered some emotional issues.
Maybe a good counselor can help you wade thru it, or maybe you can wade through it yourself, if you can allow the notion that your life as a child is very much reflected in the choices you make today.