Don't Eat Too Much Red Meat!

Summarized by Robert W. Griffith, MD
February 12, 2004

Introduction

There's an inherited disease known as hemochromatosis, in which a large overload of iron occurs in the body. And such patients commonly develop type 2 diabetes - it occurs in as many as 65% of them. So it's not surprising that scientists have wondered whether too much iron in the body could be a risk factor for diabetes. Some early small studies suggested this might be the case, so recently Harvard researchers conducted a large study to try to confirm or refute this; their results are published in the American Journal of Clinical Nutrition.

What was done

The subjects in the study were drawn from the large Health Professionals' Follow-up Study. In 1986 over 50,000 male health professionals aged 40 to 75, drawn from across the USA, completed detailed questionnaires on their medical history, diet, and possible risk factors for major diseases like diabetes or heart disease. There were questions on consumption of 131 individual food items, and also about blood donations.

Over the next 12 years, general health was verified every 6 months and dietary habits every 4 years. Subjects reported their weight, smoking habit, and physical activity level every 2 years. If diabetes was reported, an additional questionnaire was sent, and blood sugar levels requested. A new case of diabetes was diagnosed if the fasting glucose level was over 140 mg/dL (7.8 mmol/L) or there was a random glucose level over 200 mg/dL (11.1 mmol/L).

What the results showed

A total of 33,541 subjects provided complete questionnaires, including a history of blood donations. There were 1168 new cases of diabetes diagnosed during the 12 years of the study.

The diets were evaluated for total iron intake, total heme iron¹, heme iron derived from red meat, and heme iron from non-red meat sources. The subjects were divided into 5 equal-sized groups depending on their intake of total iron (these are called quintiles). Quintiles were also formed for heme iron and non-heme iron intake.

After allowing for differences in age, body mass index (BMI), and other diabetes risk factors, there were no differences between the five quintiles for total iron intake in the likelihood of developing diabetes. However, in the case of total heme iron, there was a clear trend, suggesting that those with the highest heme iron intake were about one-and-a-quarter times more likely to develop diabetes than those with the lowest intake.

The researchers did separate analyses for heme iron derived from red meat and from non-red meat sources, such as chicken or fish. Those men reporting the highest intake of red meat heme iron were about 1.6 times more likely to develop diabetes than those with the lowest intake. On the other hand, there was no such effect of different intakes of non-red meat heme iron.

There were no links between the amount of blood donations and the risk of developing diabetes. (The scientists measured this because they thought that increased frequency of blood donation is known to reduce total iron stores in the body.)

Comment

This study showed that neither total iron intake nor blood donations were linked to a change in the risk of developing diabetes. Increased heme-iron intake from red meat, however, was clearly associated with an increased risk of diabetes. However, the fact that other sources of heme iron weren't linked in this way suggests there may be some additional factor in red meat contributing to the increased risk.

The fact that blood donations had no effect on the likelihood of diabetes also suggests there may be an additional factor in red meat that bears some of the responsibility. This will doubtless be researched further. In the meantime, it seems clear that too much red meat isn't good for you (as we've been hearing for years from those advocating heart-healthy diets). Get your iron from other, healthier sources, such as lentils, peas, and spinach!

Source

• Dietary iron and blood donations in relation to risk of type 2 diabetes in men: a prospective cohort study. R. Jiang, J. Ma, A. Ascherio,  et al., Am J Clin Med, 2004, vol. 79, pp. 70--75

Footnotes
1. There are two types of iron found in foods: heme and non-heme. The body absorbs heme iron more easily than non-heme iron. Heme iron is found in animal products (meat and fish), and non-heme iron in plants (e.g. vegetables, fruit, grains), and in supplements.

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