Nettles are rich in several nutrients, including iron, vitamins C and E, calcium and magnesium. The mechanism for how it helps burn belly fat isn't fully understood. It is believed to nourish cells better, which curbs cravings and hunger. Nettles are often paired with fennel, because fennel curbs hunger and boosts energy. Both are available as supplements. Fennel is also a common cooking herb and comes ground or in seed form. You can also buy nettle tea, fennel tea or a tea made with a combination of these herbs.