The real reason being overweight is bad for your health:

[BrotherIvan]

19. Hypothyroidism

There is an unknown epidemic of hypothyroidism in developed countries. Why? Hypothyroid sufferers are prone to infectious diseases and have weak immune systems. Before the advent of antibiotics and other treatments, they succumbed to infectious diseases such as TB, pneumonia, or flus. In countries where TB was treated, there was a huge upsurge in heart disease, diabetes and cancer (all previously linked to hypothyroid) because they lived longer than before and were able to manifest the long-term symptoms.

These people had offspring where before they were removed from the gene pool. Now we have a rash of obesity, infertility and reproductive problems, joint and muscle pain, arthritis, acid reflux, sleep apnea, migraines, anxiety, depression, heart disease and cancer. Since the advent of the TSH and synthetic hormones, patients are not diagnosed and under treated. You can walk down the street or the mall and see untreated hypothyroids EVERYWHERE. It's as plain as day in puffy bodies and puffy faces. What we think of as fat or chubby people are all manifesting very clear symptoms of hypothyroid. And suffering a host of ailments all while they are shamed for being fat and lazy. It's too damn bad that the medical community has willfully allowed this to happen.