A recent paper provides further evidence that type 2 diabetes (T2D) is associated with increased intake of heme iron, which occurs naturally in certain animal products and is added to certain meat substitutes to enhance their flavor.
In August, Frank Hu, MD, PhD, of the Harvard T.H. Chan School of Public Health, and co-authors wrote in the journal Nature Metabolism that those with the highest heme iron intake in the study had a 26% higher risk of type 2 diabetes than those with the lowest intake, as measured by a multivariate-adjusted hazard ratio (95% CI, 1.20-1.33; P < .001 for trend).
“Eating more plant-based foods and reducing heme iron intake from red meat should be considered a strategy to reduce diabetes risk and prevent chronic disease,” Hu said in an interview with Medscape Medical News.
“High heme iron intake has also been associated with an increased risk of cardiovascular disease and even certain cancers, such as colorectal cancer,” he added.
The article builds on findings Hu and colleagues published last year in the American Journal of Clinical Nutrition about a possible association between red meat consumption and type 2 diabetes risk.
When asked by Medscape Medical News to comment on the new paper by Hu and co-authors, Marilyn Tan, M.D., director of the Endocrine Clinic at Stanford University School of Medicine in Palo Alto, California, pointed out the limitations of studies aimed at examining how dietary choices affect health in general.
“Many studies have pointed to associations between various dietary factors and certain disease states, but in studies that rely solely on epidemiologic data, the associations do not prove causation,” Tan told Medscape Medical News in an email. ”In addition, the The rest of the diet may be very diverse except for the specific dietary components being studied.”
Diet studies in general also don’t perfectly control for other key lifestyle factors, such as exercise, sedentary time, and sleep quality, she said.
But Tan also noted that Hu and co-authors took extra steps in their study of hemoglobin iron and diabetes risk, such as controlling for certain health and lifestyle factors.
Tan wrote that they also used metabolic biomarkers, including small molecule metabolites from food and chemical breakdown, to further elucidate some of the possible mechanisms underlying the association between heme intake and diabetes risk.
“The attributable risk of diabetes associated with heme iron calculated in the study is noteworthy and appears to be dose-related,” she wrote.
Study design
In this study, Hu and co-authors examined 36 years of dietary-reported data from 204,615 adults who participated in the Nurses’ Health Study I and II and the Health Professionals Follow-Up Study. They categorized these results into five groups based on heme iron intake.
In the lowest quintile, there were 2,554/1,052,982 cases of type 2 diabetes in terms of person-years of follow-up (about 2.4 cases per 1,000 person-years), Hu told Medscape Medical News. In the highest quintile, the number was 5881/1,047,447 (about 5.6 cases per 1000 person-years).
Hu and colleagues reported that across studies, people in the high-heme iron group reported eating about eight to 10 servings of unprocessed red meat per week, while people in the low-heme group reported eating about two to three servings per week.
Pooling the results of the studies yielded a high heme iron quintile with an estimated median heme iron intake of 1.5 mg/day and a median of 0.7 mg/day for the low heme group. There are no established standards for heme iron intake.
According to Hu and co-authors, people with higher total and non-heme iron intakes reported being more physically active, more likely to use multivitamins, and less likely to smoke cigarettes than those with lower intakes. They also ate more grain fiber, magnesium, fruits and vegetables. People with increased heme iron intake were typically less physically active, were more likely to smoke, and ate less grain fiber, magnesium, fruits, and whole grains and more red meat, poultry, and fish.
Hu said he and his co-authors took these factors into account in their statistical analysis.
Turkey sausage vs. the occasional steak
When asked to comment on Hu’s paper, Dariush Mozaffarian, M.D., a cardiologist and director of the Food as Medicine Institute at Tufts University in Medford, Massachusetts, offered a different take on the findings, focusing on the paper’s analysis of processed meat and type 2 diabetes.
In the paper, Hu and co-authors noted that heme iron intake accounted for more than half of the association between unprocessed red meat and diabetes risk, “but it explained only a small part of the association with processed red meat.” They say, “The deleterious association of processed red meat with type 2 diabetes risk may be attributable to high levels of other compounds, such as nitrates and nitrites.”
The medical community’s advice on diet focuses primarily on saturated fats, but Hu and co-authors’ paper, as well as other studies, suggest that there are other factors at play, such as inflammatory compounds, Mozaffarian said.
With that in mind, it’s best to reconsider the emphasis on fat content, which can mislead people into thinking highly processed foods are healthy choices, he says.
Turkey sausage and low-fat deli meats may not be better than steaks or burgers made from fresh meat, he said. He disagrees with many paleo-diet proponents who believe red meat is essential and with critics who believe it is very harmful.
“The main message for patients is that red meat deserves neither an aura of health because it’s something you have to look for, nor the devil’s condemnation for being the worst thing in the food supply,” he says.
Hu and his co-authors report that they were supported by an American Heart Association postdoctoral fellowship, the Canadian Institutes of Health Research, the Novo Nordisk Foundation, and the National Institutes of Health.