Higher intakes of red meat tied to greater risk of type 2 diabetes, study finds

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Many observational studies have linked a high intake of unprocessed and processed red meats with an increased risk of type 2 diabetes.

Yet the quality of such evidence, while statistically significant, has been deemed low by some research groups owing to the limitations of observational research, such as relying on unreliable self-reported food intake, for example.

In research, statistical significance describes a high level of certainty that a difference or relationship between two things (e.g., meat intake and diabetes risk) does exist and isn’t owing to chance.

Now, new research from the Harvard T.H. Chan School of Public Health provides strong evidence that higher intakes of red meat – just two servings per week – increases the risk of type 2 diabetes later in life.

Here’s a breakdown of the study and its findings.

About type 2 diabetes

Type 2 diabetes occurs when cells in the body become resistant to the action of insulin, the hormone that clears glucose (sugar) from the bloodstream. As a result, blood glucose levels remain higher than what’s considered normal.

The chronic disease, rising rapidly worldwide, is the leading cause of illness and death globally. It increases the risk of heart disease, stroke, kidney disease, blindness, nerve damage, Alzheimer’s disease and certain cancers.

The latest study findings

The study, published online this month in the American Journal of Clinical Nutrition, included 216,696 participants, 81 per cent female, from the ongoing Nurses’ Health Study, Nurses’ Health Study II and Health Professionals Follow-up Study in the United States.

Participants were followed for up to 36 years, during which time their diets were assessed every two to four years and health data was collected every other year.

By the end of the follow-up period, in each separate study and when the studies were combined, intakes of total red meat, processed red meat and unprocessed red meat were all associated with a higher risk of developing type 2 diabetes.

Participants who consumed the most total red meat (two servings per day) – versus the least (about two servings per week) – were 62 per cent more likely to develop type 2 diabetes during the study period.

One serving of unprocessed red meat is equivalent to 3 ounces (85 g) of beef, pork or lamb. One serving of processed red meat is equivalent to one ounce (28 g) of bacon or 1.5 ounces (45 g) of hot dog, sausage, salami or deli meats.

Lower intakes of total red meat were also tied to an increased risk of diabetes. Compared to people who ate less than 1.4 servings per week, those who consumed two to three weekly red meat servings were 18 per cent more likely to develop type 2 diabetes.

Each additional daily serving of red meat increased diabetes risk further – 46 per cent for processed red meat and 24 per cent for unprocessed red meat.

To arrive at these findings, the researchers controlled for many other potential risk factors including smoking, alcohol intake, physical activity, family history of diabetes, diet quality and socioeconomic status.

The researchers also estimated the effect of replacing one daily serving of total red meat with other protein sources.

Swapping one serving of meat with a serving of nuts or legumes was tied to a 30-per-cent lower risk of type 2 diabetes. Replacing one meat serving with one dairy serving reduced the risk by 22 per cent.

Limitations, strengths

The study was observational and does not prove that eating red meat directly causes type 2 diabetes.

Even so, the study has a number of strengths that reinforce the reliability of its findings.

These include its large sample size, decades long duration, repeated measures and a robust analysis of dietary intake which provided a more accurate representation of usual food intake.

The researchers also made extensive adjustments for other possible diabetes risk factors.

According to an editorial that accompanied the study, “all in all, the study may arguably be the best evidence to date on the relation between red meat intake and type 2 diabetes”.

How red meat may affect diabetes risk

Saturated fat in red meat has been shown to reduce insulin-producing cells in the pancreas and insulin sensitivity. The type of iron in red meat, heme iron, can increase oxidative stress and insulin resistance.

Processed meats can contain high amounts of nitrates, which are also thought to promote insulin resistance.

High intakes of red meat have also been linked to excess weight; weight gain from early to middle adulthood is strongly connected to an elevated risk of type 2 diabetes.

Takeaways

The findings suggest that eating no more than one serving of red meat per week is sensible to help lower type 2 diabetes risk.

They also indicate that replacing a daily serving of red meat, processed or unprocessed, with a serving of plant protein – e.g., 28 g of nuts or 100 g (about one-half cup) of beans, chickpeas or lentils – can protect against type 2 diabetes.

Besides improving health, swapping red meat for plants also considers the environment and animal welfare.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD