(Fashionistas, for the record, are apparently citizens of the country of Fashionistan, where no one is allowed to look at real women, ever.)
Jessica has apparently "ballooned" all the way up to a size twelve, from her size one a few years ago. For those of you unfamiliar with how American dress sizes work, it's like this: an average healthy adult woman is usually anywhere from a size five to a size sixteen. By way of comparison, if you visit your nearest Chinatown, you'll probably find a shop where the ducks have been hanging in the window too long, until they've become an orange jerky-like substance. Those ducks are a size one.
Just as astrology can be applied to almost everything in life, it can be of tremendous use when trying to lose weight. I've never had a client come to me exclusively for help with this, but the matter comes up surprisingly often in consultations. Although the details will be individual to every person, there are a number of astrological guidelines that generally apply.
First of all, forget about your Sun Sign. Although it can be an influence, I've seen too many chubby Aries and slim Tauruses and such to know that the Sun Sign should be, if not the last place to look, then low on the list. Unless, of course, you have Leo Rising or Leo on the sixth house cusp, which your Sun would rule.
Your Moon is a much more reliable indicator as to body weight. Even so, one should be cautious of too many generalizations. In other words, if you have Moon in Pisces (for example) you aren't automatically prone to emotional overeating. Depending on the aspects to your moon, that placement could just as easily lead to emotional under-eating.
A more reliable indicator of weight is the Ascendant: its sign placement, planets aspecting it, and the condition and placement of the planet ruling it. The Ascendant also rules your general appearance, posture, coloring, and a lot of other things people don't like about themselves that they can't change.
The most important thing to keep in mind when trying to lose weight with astrology is not so much the birth chart, as the planetary transits happening to it at any given time. Even a perfect diet and exercise routine (if there were such things) could go wrong if you started them at the wrong time.
The best time to start a weight loss routine is when Mars is transiting either the First or Sixth House of your birth chart. The First House starts at your Ascendant, and the Sixth House (which rules diet, health, and routines) is almost on the opposite side of your chart from the First House. Since Mars makes it around the Zodiac in about 18 months, this means that, most of the time, your "diet transits" can last for at least a month and a half. For most people's purposes, that's more than enough time to get a new habit ingrained.
Weight loss is also often the surprisingly good side of a Saturn transit. A supportive aspect to the Ascendant and/or Sixth House ruler can be of tremendous help when it comes to applying self discipline, and an aspect to your natal Venus or Jupiter can curb impulsive eating, overeating, or your fondness for snacks.
An astrologer who knows what they're doing can help you time when to commence a new diet and/or exercise regimen, and can help you understand what factors in your birth chart are helping or hurting the situation.
Perhaps the single most important thing to keep in mind is this: On the one hand, the fashion industry has dictated for about the last fifty years or so that "underfed" is a good look. On the other hand, biology has dictated for about the last million years that having a little "excess" weight is an attractive thing. It indicates good health, a plentiful supply of resources, and the means to bear and raise children (in the area of extra boob and bum matter).
And besides, if most straight males are honest with you about it, they'd prefer a woman with a little excess weight over one who's underweight. Unless of course you're trying to catch a man who takes all his advice from fashion magazines... in which case, your relationship may have much larger problems than just your dress size...