A recent study is one of the largest looking at the association of red meat consumption, both processed and unprocessed, and the risk of developing Type II diabetes (T2D). The study used data from the Nurses’ Health Study (NHS), NHS II, and Health Professionals Follow-up Study (HPFS), with over 5 million person-years of follow up, and 22,761 T2D cases. This is a powerful study, and adds to decades of research looking into any association between red meat consumption and negative health outcomes.
They found:
Comparing the highest to the lowest quintiles, hazard ratios (HR) were 1.62 (95% confidence interval [CI]: 1.53, 1.71) for total red meat, 1.51 (95% CI: 1.44, 1.58) for processed red meat, and 1.40 (95% CI: 1.33, 1.47) for unprocessed red meat.
And this is pretty much how this study has been reported in the media – that there is about a 50% increased risk of T2D with too much red meat consumption. But let’s delve a bit deeper into the data to put the risk into perspective. For example, it has been misreported in the media that:
A new study says eating just two servings of red meat weekly increases the risk of developing type 2 diabetes by 62%, reported Fox News Digital.
Incorrect – the 62% is the comparison between the highest and lowest consumers of red meat, eating red meat daily vs not at all. The risk decreased with lower red meat intake, disappearing at 1 serving per week, but at 2 servings per week the risk was small and uncertain. This is consistent with previous data showing that the risks of red meat consumption is only statistically robust when you get to daily consumption.
A study published in 2022 looked at all the data regarding red meat consumption and disease risk published to date (so it did not include the current study) and found that they methods generally used tended to overestimate the risk. They took a “burden of proof” approach and found a wide range of uncertainty when it comes to the amount of red meat consumption that is healthy (zero measured risk). They found, for example, that the zero risk amount of red meat did include 0 g per day, but the error bars extended to 200 g per day.
The bigger problem with this data, however, is that it is correlational only. It is not able, by itself, to demonstrate cause and effect. Of course, we are limited to observational data with risk factors such as diet. Large and long term controlled studies of dietary red meat are simply not feasible and we will likely never see them. Observational studies can also still be powerful, but we have to recognize their limitations. With the current study the researchers found:
“Of note, individuals who reported consuming red meat most frequently within each cohort were more likely to eat less fish (or) fruit and (more) calories, weigh more, and engage in less physical activity,” added Lichtenstein, who is also the director of Tuft University’s Cardiovascular Nutrition Laboratory. “This suggests they had poorer overall diet quality and were less likely to engage (in) healthy lifestyle behaviors.”
When controlling for body mass index, they found that explained half of the association with red meat consumption and risk of T2D. That does not mean, however, that red meat explains the other half. We still have the other factors listed above – consuming less fruit and fish and engaging in less physical activity. Perhaps these factors explain the other half.
I am also always very suspicious when I see such associations. If you are someone who eats red meat daily, does not eat much fruits or vegetables, and does not exercise – what other poor lifestyle habits might you have? The rule of thumb for observational studies is that it is very difficulty to identify and control for every possible confounding factor.
This is also why, in order to close the loop on cause and effect with observational studies finding only a correlation, we need evidence of a mechanism. How could red meat consumption cause T2D? What we have now is mostly speculation and preliminary data. The heme in red meat might stress the insulin producing cells of the pancreas. There may be various pro-inflammatory mechanisms of eating red meat. These are currently hypotheses to be explored, not conclusions. A recent systematic review looking at some of the possible mechanisms related to insulin and glycemic control found:
The results of this meta-analysis suggest red meat intake does not impact most glycemic and insulinemic risk factors for T2D.
Where does all of this leave us? Even though I think the data is far from certain, and the confounding factors of other lifestyle factors are likely dominant, it is reasonable to limit red meat, and especially process meat, consumption. This conclusion is based not only on the data but on the general principle that when it comes to diet, everything in moderation is a good approach. Plus, red meat consumption is associated with increased calorie consumption and BMI. Further, it is pretty well established that eating sufficient fruits and vegetables are key to an optimal diet – if you are eating red meat every day, you are probably not getting enough plant-based calories.
Even taking this data (and previous studies) at face value, eating one serving of red meat per week appears to be healthy. Eating red meat and especially processed meat every day probably isn’t. I don’t think this data is robust enough to establish exactly where the line is, however. For most people it is likely good advice to say – limit your red meat consumption to something less than every day, and make sure you eat enough plant calories. If you have a family history or other risk factors for T2D, you may want to limit red meat consumption more. Of course, addressing those other risk factors is also important, and may be more important.
I do think there is a risk to overstating the association between red meat and T2D as it may make some people think that they can do this one thing to mitigate their risk, rather than addressing all of their risk factors. Too much focus on red meat may also cause people to make unhealthy changes to their diet, by substituting in more high glycemic index foods like white carbohydrates. Demonizing individual foods, rather than emphasizing balance and moderation, may ultimately be counterproductive.