Yeah, we just told you to pump iron, but you also need to eat it. "If you don't have enough of this mineral, your body can't get enough oxygen to your cells, which slows down your metabolism," explains Samantha Heller, R.D., a nutritionist at the New York University Medical Center. Most multivitamins contain around 18 mg (the RDA for adults); you can also get your fill by eating three to four daily servings of foods rich in iron, such as lean red meat, chicken, fortified cereal, and soy nuts. If you're feeling symptoms like fatigue and weakness, ask your doctor to test you for anemia (it's a simple blood test) at your next physical.
This may explain why the fat-burning effects of eating more protein were confirmed in a study published in the American Journal of Physiology. One group was fed a high-protein diet (just over 1 gram per pound of body weight per day) while the second group consumed an amount closer to the lower recommendation of the RDA (recommended dietary allowance). The group eating the higher-protein diet burned the most fat.