There's no getting around it: Your weight can and will be held against you in the workplace. If you're overweight, potential employers are more likely to pass you by, partially because they believe weight-related health issues such as diabetes and high blood pressure will cost them a lot of money and keep you from doing your job to the best of your abilities. Your current boss might give that big promotion to someone else for the same reasons.
It's hard to argue that point. It's been estimated that more than two-thirds of the U.S. adult population is overweight or obese, and studies have shown that those people cost their employers billions annually -- statistically, they have more accidents, take more sick days, are more likely to be less productive and cost more to insure.