Unfortunately, you are probably exposed to some chemicals in your house every day that can change your hormone balance and lead to changes in insulin resistance, fat cell accumulation, and decreased metabolism. All of these can lead to weight gain. Here is a list of the most common ones: BPA is in the plastic used to make water bottles and other bottled drinks, phthalic acid is in plastics and beauty products, and atrazine is in herbicides that get into foods. PFOA is in many nonstick pots and pans.