Yes, evidence does suggest that women being overweight before menopause decreases a woman's risk of breast cancer. But this is by no means a recommendation to pack on any extra pounds.
Women who became overweight in adulthood have a higher risk of breast cancer. Also, women whose bodies are "apple"-shaped (i.e., women who carry their extra weight in their abdomen, rather than on their hips and thighs) have a higher risk of breast cancer.
Furthermore, most women who gain weight before menopause tend to keep those extra pounds on after menopause. Being overweight after menopause increases breast cancer risk by about 20% to 60%.
If extra fat cells are present after menopause, the fat cells produce estrogen. Higher levels of estrogen can stimulate the growth of estrogen receptor-positive (ER-positive) breast cancer.
Your best bet for avoiding breast cancer is to maintain a healthy weight throughout your lifetime.