Veronica Hackethal, MD
September 21, 2017
Eating red meat or darker cuts of poultry may be associated with increased risk of type 2 diabetes, with higher levels of consumption linked to higher risk, according to new results from the Singapore Chinese Health Study, published in the American Journal of Epidemiology.
The trial is one of the largest to evaluate meat consumption and diabetes risk in Asian populations.
"Compared with those who ate the least amount, those with the highest levels (approximately one serving a day) of red meat or poultry consumption had a 23% and 15% increased risk of diabetes, respectively," lead author Woon-Puay Koh, PhD, a professor at Duke-NUS Medical School, Singapore, commented by email.
Results also suggest that different types of meat may have different effects on type 2 diabetes risk. Varying levels of heme iron, which is found only in meat, may be involved.
"After adjustment for heme-iron content in the diet, the red-meat/diabetes association was still present, suggesting that other chemicals present in red meat could be accountable for the increase in risk of diabetes," Dr Koh explained.
"Conversely, the association between poultry intake and diabetes risk went away, suggesting that this risk was attributable to the heme-iron content in poultry." The darker cuts of poultry, such as chicken thighs, have higher heme-iron content than breast meat, she noted.
Results also indicate that the increased diabetes risk associated with red meat and poultry was reduced if they were substituted by fish or shellfish. "Replacement of red meat and poultry with fish/shellfish may reduce type 2 diabetes risk, and it is worth testing this theory in experimental studies," she added.
Asked for outside comment, Keith Ayoob, EdD, a nutritionist and associate professor emeritus at Albert Einstein College of Medicine, New York, noted several strengths of the study, including the long-term follow-up, the large study population, and face-to-face dietary interviews.
But, he said, it's still a big leap to say that consumption of heme iron increases the risk of type 2 diabetes.
Rather than advocating one particular dietary pattern or nutrient over any other, Dr Ayoob emphasized overall lifestyle: physical activity, controlling portion size, and food preparation that stresses lean foods over fried and fatty ones.
"It's not about one food, it's about a lifestyle. That's where I'd put my money as a clinician. Would I tell someone to eat more fish? Yes. Would I tell them to eat lean red meat? Yes. I'd take a lean strip steak over fried chicken breasts, hands down."
Is Heme Iron One of the Culprits?
Past studies in Western populations have linked red-meat consumption to increased risk for type 2 diabetes, but results in Asian populations are varied.
That may partly be due to different dietary patterns. Compared with Western populations, Asians tend to eat less red meat overall — more pork and less beef — and more poultry and fish or shellfish. Cooking styles also vary, which may have an impact on diabetes risk. Asians also develop type 2 diabetes at a lower BMI than Western populations.
To further investigate the issue, the researchers conducted a cohort study that included 63,257 middle-aged and elderly Chinese adults in Singapore (mean age, 55.2 years; 57.3% women). At the beginning, participants were interviewed and self-reported their usual diet over the past year on a questionnaire developed and tested just for this population. At two follow-up interviews, participants self-reported physician-diagnosed type 2 diabetes. Participants were followed for an average of 11 years.
Results showed that the highest intake of red meat and poultry was significantly linked to type 2 diabetes, compared with the lowest intake (red meat multivariate adjusted HR, 1.23; P for trend < .001; poultry HR, 1.15; P for trend = .004).
Risk of type 2 diabetes was not significantly linked to eating fish/shellfish (HR, 1.07; P for trend = .12).
Replacing one serving per day of red meat or poultry with fish/shellfish was linked to 26% and 22% lower risk of type 2 diabetes, respectively.
Analyses adjusting for heme iron intake showed that the association with poultry disappeared, and only red meat intake remained significantly associated with type 2 diabetes (HR, 1.13; P for trend = .02).
Other studies have suggested a link between dietary heme iron intake and increased type 2 diabetes risk.
"A high intake of red meat, which contains high concentrations of heme iron, can lead to heme-iron accumulation in our body," Dr Koh noted.
While the mechanism remains unclear, Dr Koh explained that keeping the right balance of iron in the body is critical: too little can lead to anemia, while too much can increase oxidative stress and damage tissues. In particular, the insulin-producing cells of the pancreas tend to be sensitive to oxidative stress.
That suggests that heme iron may be mediating the increased type 2 diabetes risk with poultry, but more may be going on with red meat.
Other components in red meat, like advanced glycation end products, may also contribute to insulin resistance. And eating red meat can promote inflammation. These other factors may muddy the picture, which could explain why heme iron seemed to only partially mediate the link between red-meat consumption and type 2 diabetes.
Describing the key take-home message for the public in a press release from her institution, Dr Koh concluded: "We don't need to remove meat from the diet entirely. Singaporeans just need to reduce the daily intake, especially for red meat, and choose chicken breast and fish/shellfish or plant-based protein food and dairy products to reduce the risk of diabetes.
"We want to provide the public with information to make evidence-based choices in picking the healthier food to reduce disease risk."
Improve Overall Lifestyle: Help People Eat 'Beyond the Headlines'
Dr Ayoob said the observational nature of this Singapore study means that the results can be used only to generate a hypothesis, not prove that consuming heme iron causes increased risk for type 2 diabetes.
Other factors may explain the results.
For example, people who ate more red meat were less likely to exercise, and being sedentary could have contributed to increased risk of type 2 diabetes.
Also, the study lumped pork and beef together, which could affect results. Finally, levels of heme iron may vary based on types of meat consumed: fatty cuts of red meat may have less heme iron than leaner cuts and chicken.
And one of the biggest limitations is that researchers assessed dietary intake and physical activity only at the beginning of the study, he pointed out.
"The taking of dietary data only once at baseline is a red flag for me," he said, "I'm a nutritionist, and I've changed my diet in 20 years. I can't imagine that other people haven't. That's just unrealistic.
"The study is too vague and has too many unknowns to draw conclusions that can help in clinical practice," he said, "A good study helps people like myself counsel patients. Poor studies add to confusion. I have to help people eat 'beyond the headlines,' so they don't feel they have to change their diets after every study."
The authors and Dr Ayoob report no relevant financial relationships.