Global meat production has increased rapidly in recent decades and meat consumption exceeds dietary guidelines in many countries.  Earlier research indicated that higher intakes of processed meat and unprocessed red meat are associated with an elevated risk of type 2 diabetes, but the results have been variable and not conclusive.

Poultry such as chicken, turkey, or duck is often considered to be an alternative to processed meat or unprocessed red meat, but fewer studies have examined the association between poultry consumption and type 2 diabetes.

To determine the association between consumption of processed meat, unprocessed red meat and poultry and type 2 diabetes, the team led by researchers at the University of Cambridge used the global InterConnect project to analyse data from 31 study cohorts in 20 countries. Their extensive analysis took into account factors such as age, gender, health-related behaviours, energy intake and body mass index.

The researchers found that the habitual consumption of 50 grams of processed meat a day – equivalent to 2 slices of ham – is associated with a 15% higher risk of developing type 2 diabetes in the next 10 years. The consumption of 100 grams of unprocessed red meat a day – equivalent to a small steak – was associated with a 10% higher risk of type 2 diabetes.

Habitual consumption of 100 grams of poultry a day was associated with an 8% higher risk, but when further analyses were conducted to test the findings under different scenarios the association for poultry consumption became weaker, whereas the associations with type 2 diabetes for each of processed meat and unprocessed meat persisted.

Professor Nita Forouhi of the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, and a senior author on the paper, said:

“Our research provides the most comprehensive evidence to date of an association between eating processed meat and unprocessed red meat and a higher future risk of type 2 diabetes. It supports recommendations to limit the consumption of processed meat and unprocessed red meat to reduce type 2 diabetes cases in the population.

While our findings provide more comprehensive evidence on the association between poultry consumption and type 2 diabetes than was previously available, the link remains uncertain and needs to be investigated further.”

InterConnect uses an approach that allows researchers to analyse individual participant data from diverse studies, rather than being limited to published results. This enabled the authors to include as many as 31 studies in this analysis, 18 of which had not previously published findings on the link between meat consumption and type 2 diabetes. By including this previously unpublished study data the authors considerably expanded the evidence base and reduced the potential for bias from the exclusion of existing research.

Lead author Dr Chunxiao Li, also of the MRC Epidemiology Unit, said:

“Previous meta-analysis involved pooling together of already published results from studies on the link between meat consumption and type 2 diabetes, but our analysis examined data from individual participants in each study. This meant that we could harmonise the key data collected across studies, such as the meat intake information and the development of type 2 diabetes.

Using harmonised data also meant we could more easily account for different factors, such as lifestyle or health behaviours, that may affect the association between meat consumption and diabetes. “

Professor Nick Wareham, Director of the MRC Epidemiology Unit, and a senior author on the paper said:

“InterConnect enables us to study the risk factors for obesity and type 2 diabetes across populations in many different countries and continents around the world, helping to include populations that are under-represented in traditional meta-analyses.

Most research studies on meat and type 2 diabetes have been conducted in USA and Europe, with some in East Asia. This research included additional studies from the Middle East, Latin America and South Asia, and highlighted the need for investment in research in these regions and in Africa.

Using harmonised data and unified analytic methods across nearly 2 million participants allowed us to provide more concrete evidence of the link between consumption of different types of meat and type 2 diabetes than was previously possible.”

InterConnect was initially funded by the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 602068.

Reference

Li, C et al. Meat consumption and incident type 2 diabetes: a federated meta-analysis of 1·97 million adults with 100,000 incident cases from 31 cohorts in 20 countries. Lancet Diabetes Endocrinol.; 20 August 2024. DOI:10.1016/S2213-8587(24)00179-7

“Compared to prior studies that relied solely on epidemiological data, we integrated multiple layers of information, including epidemiological data, conventional metabolic biomarkers, and cutting-edge metabolomics,” said lead author Fenglei Wang, research associate in the Department of Nutrition. “This allowed us to achieve a more comprehensive understanding of the association between iron intake and T2D risk, as well as potential metabolic pathways underlying this association.”

The study will be published August 13 in Nature Metabolism.

The researchers assessed the link between iron and T2D using 36 years of dietary reports from 206,615 adults enrolled in the Nurses’ Health Studies I and II and the Health Professionals Follow-up Study. They examined participants’ intake of various forms of iron—total, heme, non-heme, dietary (from foods), and supplemental (from supplements)—and their T2D status, controlling for other health and lifestyle factors.

The researchers also analyzed the biological mechanisms underpinning heme iron’s relationship to T2D among smaller subsets of the participants. They looked at 37,544 participants’ plasma metabolic biomarkers, including those related to insulin levels, blood sugar, blood lipids, inflammation, and two biomarkers of iron metabolism. They then looked at 9,024 participants’ metabolomic profiles—plasma levels of small-molecule metabolites, which are substances derived from bodily processes such as breaking down food or chemicals.

The study found a significant association between higher heme iron intake and T2D risk. Participants in the highest intake group had a 26% higher risk of developing T2D than those in the lowest intake group. In addition, the researchers found that heme iron accounted for more than half of the T2D risk associated with unprocessed red meat and a moderate proportion of the risk for several T2D-related dietary patterns. In line with previous studies, the researchers found no significant associations between intakes of non-heme iron from diet or supplements and risk of T2D.

The study also found that higher heme iron intake was associated with blood metabolic biomarkers associated with T2D. A higher heme iron intake was associated with higher levels of biomarkers such as C-peptide, triglycerides, C-reactive protein, leptin, and markers of iron overload, as well as lower levels of beneficial biomarkers like HDL cholesterol and adiponectin.

The researchers also identified a dozen blood metabolites—including L-valine, L-lysine, uric acid, and several lipid metabolites—that may play a role in the link between heme iron intake and TD2 risk. These metabolites have been previously associated with risk of T2D.

On a population level, the study findings carry important implications for dietary guidelines and public health strategies to reduce rates of diabetes, according to the researchers. In particular, the findings raise concerns about the addition of heme to plant-based meat alternatives to enhance their meaty flavor and appearance. These products are gaining in popularity, but health effects warrant further investigation.

“This study underscores the importance of healthy dietary choices in diabetes prevention,” said corresponding author Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology. “Reducing heme iron intake, particularly from red meat, and adopting a more plant-based diet can be effective strategies in lowering diabetes risk.”

The researchers noted that the study had several limitations, including the potential for incomplete accounting for confounders and measurement errors in the epidemiological data. In addition, the findings—based on a study population that was mostly white—need to be replicated in other racial and ethnic groups.

Other Harvard Chan authors included Andrea Glenn, Anne-Julie Tessier, Danielle Haslam, Marta Guasch-Ferré, Deirdre Tobias, Heather Eliassen, JoAnn Manson, Kyu Ha Lee, Eric Rimm, Dong Wang, Qi Sun, Liming Liang, and Walter Willett.

“Integration of epidemiological and blood biomarker analysis links heme iron intake to increased type 2 diabetes risk,” Fenglei Wang, Andrea J. Glenn, Anne-Julie Tessier, Zhendong Mei, Danielle E. Haslam, Marta Guasch-Ferré, Deirdre K. Tobias, A. Heather Eliassen, JoAnn E. Manson, Clary Clish, Kyu Ha Lee, Eric B. Rimm, Dong D. Wang, Qi Sun, Liming Liang, Walter C. Willett, Frank B. Hu, Nature Metabolism, August 13, 2024, doi: 10.1038/s42255-024-01109-5

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