Ever got to the point where your body takes over? My tummy is tummy okay doing more than should be but legs and arms are like straws.
Only realised today, and it isn't bad but my arms are starting to grow fluff. It's a natural reaction for protection. Not that I really care what y'all think whether I was Bigfoot but it is really fluff, it's interesting knowing what's happening and why.
Where your body loses weight (and stores it) is almost entirely a function of genetics. All the ads/products that show people targeting their core for a six pack is nothing but snake oil/smoke and mirrors.
There is also a gender based component to fat storage as well. Woman (on average) tend to hold weight in their lower body (thighs and buttox in particular), while men develop more of a pear shape with weight being concentrated through the mid section.
When you say that your arms are beginning to grow fluff, as your referring to fat, or body hair? The former is explained by the above (genetics.... perhaps lack of muscle tone due to minimal resistance training). As for body hair, that can be a bit more complicated - the first question would be: Did you always grow hair in these areas? Are your prone to hair growth on the body overall? If the answer is no, then in all likelihood, your hormone levels are out of whack. Unexpected hair growth (for both men and woman) tend to be the result of excessively high androgen levels - this is exacerbated for people who use steroids. I shave my upper body twice a week, but the hair on the top of my head seems to be losing its battle with baldness.
I'm going to assume that your not on steroids, and would guess that caloric restriction/deficit has sent your endocrine system for a loop. Ask your doctor for blood work, and check your thyroid, estrogen, prolactin and testosterone levels in particular. Progesterone (steroid, but not in an anabolic sense) can also cause unexpected hair growth, particularly if it is being topically applied.
Probably nothing to worry about, but that's my 2 cents as an armchair medical doctor.