The singer and actress signed a $4 million spokesperson deal with Weight Watchers in May after giving birth to her daughter Maxwell Drew Johnson.
Simpson tweeted about her progress as the company's newest celebrity face, writing: "What we put in our bodies mirrors our Self-Worth!"
She added a hash-tag followed by the word "inspired".
Simpson previously posted on Twitter that she has embraced better drinking habits now that she is a mother.
In July, it was reported that Simpson is planning to release her own wedding dress line. The launch will allegedly coincide with her upcoming nuptials later this year.