I have found that sometimes my workouts are better on down days... but I usually have had some caffeine before the workout. That can make a huge difference. I usually do whatever kind of workout I feel like doing, whether it's an up day or down day, but that tends to leave heavy lifting for the up days. And I don't beat myself up over missing a workout on a down day, if that happens.

I did want to address the hypothyroid question, too. I am (was?) hypothyroid, but my doctor and I are 99% sure it is due to a pituitary problem rather than thyroid. I was diagnosed with a pituitary tumor (prolactinoma) although it was never found on the brain MRI scan. I've been treated with bromocriptine and a small dose of Synthroid, which straightened out the thyroid numbers on my blood work after a couple of months. But as for how this diet may or may not have affected it.... I was just eating very low carb at the time of my initial diagnosis. I changed my diet shortly afterwards to JUDDD, and it has been while JUDDDing that my numbers have improved on all my blood tests. I have also lost about 11 pounds, which I am very happy about. I think that it's a combination of the medications straightening out my hormones as well as the diet.

I hope this info is helpful!