What’s on your Labor Day menu this weekend? Maybe a juicy grilled steak, barbecue chicken wings, or a fresh spinach salad.
A surprising new study in mice has found that iron-rich foods such as those could increase appetite and lead to overeating. That may be true especially of the steak, the authors note, as our bodies absorb iron more readily from red meat than from other sources.
“Eating too much is a risk factor for almost every age-related disease: obesity, diabetes, cardiovascular disease, Alzheimer’s disease, and more,” says Don McClain, senior author on the study, which appeared in the Journal of Clinical Investigation, and director of the Center for Diabetes, Obesity and Metabolism at Wake Forest Baptist Medical Center in North Carolina. “It turns out that high iron levels have been associated with all those as well.”
McClain, biochemist Yan Gao, and colleagues set out to determine if and how iron might cause overeating. In a series of mouse studies comparing animals fed different amounts of dietary iron, the researchers found that iron directly suppresses a hormone that regulates appetite. And they pinpointed where the action is happening — in fat cells.
When we’ve had enough to eat, fat cells in our bodies produce leptin, the “satiety hormone.” Leptin travels in blood up to the brain, where it shuts down the desire to eat. McClain’s team found that in response to iron, fat cells turn off the production of leptin, so the brain does not receive the “I’m full” signal.
Instead, it hears something else. “When leptin levels fall, one of the signals to the brain is, ‘We might be starving. We should go eat more,’” says McClain.
While most of the work was done in mice, the team verified their results with 76 human blood samples. Iron levels in the human blood were directly associated with leptin levels: When iron stores in the body were high, leptin levels were low, and vice versa.
This and other studies provide compelling evidence that both high and low amounts of iron are bad for our health. Luckily, there are simple interventions to fix either condition: People can avoid excess iron in their diet; in extreme cases, blood donation can reduce iron levels. Conversely, added dietary iron and pill supplements can increase levels.
But we still don’t know the iron sweet spot. “Textbooks define ‘normal’ iron within a range of 20-fold,” says McClain. “We think within that range there’s a much narrower window of optimal iron for health, and we’re trying to define what that level is.”