Does Eating Red Meat Increase the Risk of Diabetes?

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No matter how often I write articles defending the place of red meat in a healthy diet, there are always people who get bent out of shape whenever a new study is published with a different twist on the same old “red meat is killing us” story.

Although I can’t say addressing these (often ridiculous) studies is the most exciting undertaking, I wanted to write about this one because it’s a prime example of the limitations of observational evidence, and what happens when you control for even the most simple confounding variables.

Does red meat really increase your risk of diabetes? Read this to find out!

The study in question is titled “Associations between red meat intake and biomarkers of inflammation and glucose metabolism in women,” and was conducted by Walter Willet and a group of other Harvard researchers. (1) Using data from the Nurse’s Health cohort, they identified a positive relationship between red meat intake and higher levels of plasma C-reactive protein (CRP), ferritin, fasting insulin, and Hb A1c, after adjusting for demographic, medical and lifestyle factors. CRP (and sometimes ferritin) are markers for inflammation, and elevated fasting insulin and hemoglobin A1c indicate impaired glucose metabolism.

Limitations of Observational Evidence

Right off the bat, there’s a glaring weakness in this study that has been largely glossed over by many media reports: all but one of these associations disappeared after adjusting for BMI. As the study authors mention, excess body fat is the biggest risk factor for type 2 diabetes, so it shouldn’t come as a surprise that people with higher BMIs have less-than-ideal biomarkers for glucose metabolism. Additionally, it’s common for people who are overweight or obese to have have underlying chronic inflammation, so it makes sense that people with higher BMIs would tend towards having higher levels of inflammatory biomarkers.

A more accurate title for this study would probably look something like this:

whsource tweet

But that wouldn’t garner nearly as much press, would it?

This study is also a classic example of “if you look for something hard enough, you will probably find it.” The association between red meat and biomarkers for inflammation and glucose metabolism has already been studied on numerous occasions, and the results have been inconclusive. But from the researchers’ perspective, there must be an association between red meat and these unfavorable biomarkers, so they felt it was necessary to try yet again to establish this relationship. This type of confirmation bias can be a big problem in epidemiology; the China Study is a case in point.

I don’t want to imply that all observational evidence is worthless. That’s not true. Epidemiology can study trends and associations that are nearly impossible to evaluate with clinical trials, and these observational studies can be valuable for generating hypotheses. They only become a problem when we start treating these hypotheses like conclusions, and base public policy or nutritional advice on them. (For further discussion on this, I recommend checking out this recent paper on the limitations of observational evidence in nutrition.)

So, what of the hypothesis that red meat contributes to (or even causes) inflammation and impaired glucose metabolism?

Red Meat and Inflammation

I’ve already examined the relationship between red meat and inflammation at length, and although a few different mechanisms have been proposed by which red meat could cause inflammation, none of them really hold water. Additionally, a clinical trial that came out just a couple months after the Willet study was published actually found that regular red meat consumption decreased markers of inflammation. (2)

In this study, a group of older women living in retirement communities were given two 80g servings of red meat per day to consume six days per week for four months, in combination with resistance training. Compared with the control group, the red meat group actually ended up with significantly lower levels of interleukin-6 (an inflammatory marker) by the end of the study. If red meat caused inflammation, eating it twice a day for four months probably wouldn’t produce these results.

Red Meat, Iron, and Glucose Metabolism

One relationship that the Willet study brings up is the link between heme iron consumption, iron metabolism, and glucose metabolism. If you recall from earlier, only one association didn’t lose significance after adjusting for BMI, and this was the association between red meat intake and serum ferritin.

Ferritin is a marker for iron stores, so on the surface, this may seem like just a side effect of consuming more heme iron. But ferritin is also an acute-phase reactant (like C-reactive protein) that can be elevated in chronic inflammation even when iron levels are completely normal, so it’s not sound to assume that elevated ferritin is related to iron intake from meat. I frequently see patients in my practice with high ferritin and normal iron levels, so it’s necessary to test other iron markers like iron saturation, TIBC, UIBC and serum iron to determine what’s going on.

This is an important point, because the study authors imply that increased iron consumption from red meat could contribute to impaired glucose metabolism, causing the positive association between red meat intake and biomarkers such as fasting insulin and Hb A1c. As I’ve talked about pretty extensively in the past, iron overload is certainly harmful, and even high “normal” iron stores can lead to metabolic issues. However, making this connection assumes that the additional heme iron obtained from the increased red meat consumption is actually causing iron overload, and this is unlikely for a few reasons.

First of all, this study speaks mostly in terms of relative red meat consumption – the quartile of subjects who consumed “the most” red meat had higher levels of these biomarkers. But did you notice the absolute amount of red meat consumed? According to the paper, women in the 95th percentile for total red meat consumption only consumed 141g (or 0.31 pounds) of total red meat per day. A third of a pound of red meat per day is not a lot, and although this amount of red meat provides more iron than the same amount of chicken or fish, it’s unlikely to cause iron overload, especially for premenopausal women who have higher iron requirements.

Further, even if the amount of iron in a third of a pound of red meat were excessive, the body has mechanisms that regulate iron absorption so that if the body is replete in iron, additional iron isn’t absorbed. These regulatory mechanisms break down in disorders such as hereditary hemochromatosis, but for most people (and again, especially premenopausal women), iron intake from reasonable amounts of red meat would not cause iron overload. So it’s unlikely that the high serum ferritin observed in the highest consumers of red meat is due to the heme iron content of meat.

In summary, I still haven’t seen any convincing evidence that red meat contributes to inflammation, and there’s actually evidence that red meat decreases inflammation. And although iron overload can contribute to impaired glucose metabolism, red meat consumption does not cause iron overload in the absence of a disorder such as hereditary hemochromatosis. That said, if you do have iron overload, it’s a good idea to limit red meat consumption.

I hope you’ve enjoyed this latest installment of “don’t take observational red meat studies at face value”! Please feel free to share your thoughts in the comments. 

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  1. John says

    I’m very interested in the iron issue, but I do question how much red meat in general contributes to iron overload. One thing that seems to get overlooked is that non-heme iron comes both naturally, and in supplemental forms (from both vitamin supplements and from fortification). According to USDA data, the average intake of iron was around 14 grams a year per individual, with grains being the biggest source (this was before fortification). Currently, the average American gets about 21 grams a year, with less meat consumption, and much of the extra due to fortification. And a lot of the supplemental iron forms have been engineered to increase absorbtion. While I do think it’s wise for those worried about iron overload to shift some of their protein intake to things such as eggs, dairy and gelatin (like bone broth), I think removal of fortified grains should be stressed over reducing red meat.

    • Lance says

      One of the most common causes of excess iron is the regular consumption of alcohol. Alcohol consumed on a regular basis will increase the absorption of any iron in your diet. Eating processed food products like cereals and white breads that are “fortified’ with iron, is also a major contributor of iron overload. The iron they use in these products is inorganic iron and far more dangerous than the iron in meat. Multiple vitamins and mineral supplements often have iron in them. Alcohol and excessive vitamin C both will increase the absorption of iron (in any form)

      But, I do agree that the “fortified grains” would be a great place to start. In fact, I suspect many realize that reducing/eliminating processed grains would be of great benefit to most (for many reasons other than iron overload).

  2. chip says

    You know, if it is from Harvard that it has to be right. Ha! As a MD myself, I would like to see you, Chris, to make contact with those authors and get a comment. I tend to agree with most of what you put out and right about but would like to see a counter comment from those guys. You may find some common ground and clear some of this up. Thanks!

  3. says

    I’ve never seen a nutritional study reported on in the mainstream media that was worth reading. Often, the headlines are intentional skewed and don’t even summarize the gist of the story either. They know that many people only read the headlines.

  4. Andy says

    Hi Chris – thanks for another awesome post. I bought your book a week ago and my wife and I are now on day 6 and going strong. I had been wheat free for a couple years already – the difficult part has been avoiding chocolate and butter. We buy grass fed beef (a whole cow once a year), so we get high quality meat. I love liver and eat that a few times a week; our farmer has so much of it as nobody seems to like it. My family eats everything and we make good stews with bones and cartilage. We even make dried meat and dried sausage with it. Please could you help with three questions:
    1. We home-cure our meat. In your book, you state that cured meat is on the MODERATE list, but this home cured with vinegar and sea salt and hung up to dry. Assume this is not a problem.
    2. When we pan-fry (or BBQ) our meat, I go for a medium-rare temperature. Can you validate that meat which is more rare is better for a person?
    3. Lastly, some of out cuts come with nice and tasty fat on the side. Should I be trimming this, or can we enjoy it?
    Thanks very much
    Andy

    • says

      Andy,

      Hopefully Chris won’t mind if I step in and answer some of your questions…
      1) “home-cured” meat as you describe, as well as jerky prepared without sugar, should not be a problem, as long as it is in a dry atmosphere…
      2) yes, the lower the temperature of cooked meat, the better, as carcinogens created thru heat are avoided, as long as you are not using vegetable oil as a cooking medium… there are always exceptions to every rule however, as an example, I would never undercook pork or poultry …
      3) as for the fat, beef fat (tallow) is saturated fat, and good for you in “reasonable” amounts…

      I should mention that, in America, ALL salt is considered “sea” salt, and can be labeled as such… I prefer Himalayan salt, both for the mineral composition, and the flavor…

      Arnold (MR PALEO) http://www.misterpaleo.blogspot.com

      • Andy says

        Thanks Arnold.
        Yep, we are in CO, so quite dry here. We can eat the meat after 4-5 days of hanging in a meshed-in open air box.
        We have just moved over to Himalayan minerals now.
        Nice website you have. Good info.
        Cheers!

    • Lance says

      If someone is concerned about gout and/or elevated uric acid levels, they would be better served focusing on the reduction of foods/drinks containing fructose. Here’s a article stating that the consumption of just two servings a day of a sugar sweetened soft drink increased the risk of developing gout by 85%

      http://www.bmj.com/content/336/7639/285

    • says

      Purines come substantially from the breakdown of fructose in the liver, so avoiding sugar, agave, high fructose corn syrup and a few vegetables like asparagus will tend to avoid gout.

  5. Chris says

    My wife’s cousin is currently at Harvard in the graduate program in public health and when I shared the article on why veggie & vegan diets are bad she tried to argue otherwise. She is a vegan and not a very healthy one at that. Unfortunatley her undergrad education at another Ivy League school was wasted as she was unable to critically think and just put forth a whole slew of outdated arguments – i.e. sat fat being bad was one. She even mentioned Walter Willet and she finally let go of her attempt at a discussion when I posted an article by Robb Wolf. Her issue was that PubMed did not have any articles on paleo and that real world evidence i.e. first hand accountants of folks who’ve had their lives altered for the better meant nothing. She reminded me a bit of the pony tailed guy in Good Will Hunting who is regurgitating a bunch of information from his texts without any critical thought. Robb did not speak of Willet in a good light and now with Chris not doing so here, I have to say that I’m not impressed either.

    • Lance says

      Green tea and rosemary reduce iron absorption. The polyphenol in turmeric (known as curcumin actually acts as an iron chelator). Clinical studies have also shown quercetin, rutin, chrysin bind to iron. Milk thistle and its flavonoid constituent (i.e., silymarin) have iron chelation properties, as does cranberries, pomegranate, and R lipoic acid.

      • Andy says

        Thanks Lance – that is good to know. So popping 2 tumeric capsules with some POM juice after easting a steak should work :)

        • Julie White says

          Hang on there, surely we need to be far more careful about hampering iron absorption. I am a UK thyroid patient and struggle to keep iron levels optimal as do many people I speak to on thyroid forums. I really don’t think we should strive to hamper absorption unless we have test results suggesting a possible overload

          • Dawn says

            I agree Julie.
            I am also a UK thyroid patient and have a great deal of trouble holding on to my iron. I also suffer from inflammation but I don’t put it down to red meat :).

            I have to supplement iron. Why has iron suddenly got a bad rap? Is it another of those wierd trends that start? Our body has been handling meat and iron for thousands of years without having to give blood to control it. Iron overload is connected with an illness and not every person can develop this.

            Cook in iron pots and give your body some blood cells :)

  6. Ginny Risley says

    I believe that regular blood donations (every 56 days) will help keep iron in check, and also saves lives. Thanks for the thorough article!

  7. says

    Chris, I know it’s not easy to be reactionless to such media releases, especially when they come from people who don’t really know what they’re talking about…We need to keep promoting this message of lower carb consumption and higher real food consumption…it will eventually pay off…

    Science will follow! I’m really sure about that because there are a lot of existing studies and even more emerging studies…They just need to become more visible.

  8. PC says

    I have problems with red meat, it usually gives me an inflammatory type response, but then I suspect I am more full of inflammation (due to stress) than the average person is. I do okay with broth made from lamb shanks, and chicken and turkey seem to agree with me.

  9. Sarah says

    Love to know WHY someone as educated and erudite as you are, Chris, is STILL using BMI and referring to it as, albeit obliquely, “a measure of body fat”, when anyone who’s been in the low-carb game for even a short length of time knows that BMI has as much to do with telling you how much fat you’re lugging around as your shoe-size does!

    This is another major reason these studies fall down (the fact they’re always complete BS anyway (and I STRONGLY suspect Big Pharma has a hand in most – if not all – of them, as it’s got no interest in seeing a healthy populace – has it…?! Just think of all that lost revenue!)) is that they ALL rely on BMI as a measure of obesity, when we all know it’s perfectly possible for someone weighing 16 stone to have less fat than someone weighing 8.

    The sooner we dispense with BMI as a measure of obesity, the better, I say!

    • Mark says

      You are correct that BMI is useless as a measure of body composition of an individual. It is, however, a pretty good indicator of obesity over a whole population — which is what it was invented for, and how Chris was using it.

  10. newbie says

    Thank you for bringing this study to your readers’ attention.
    Your analysis is clear.
    I would like to ask for your opinion about the relevance of the elevated ferritin. When the other markers were controlled for BMI, their association with red meat disappeared. Let’s assume that iron stores are normal in these post meno women (TIBC, %sat, sFe), then what would cause the increase ferritin as an APR? As I read the results, even low BMI women without metabolic syndrome had higher ferritin with higher red meat intake. Just asking for your thoughts, in a more general way, about high ferritin with normal iron stores, in leaner healthy women. I realize the answer is not in the study material.
    Thanks for considering this question.

    • Cat says

      Just though I’d chime in here, in case you’re overlooking that greater red meat consumption is associated with higher ferritin for the basic reason that red meat has more iron than other meat people tend to eat (chicken, fish, etc), so if you eat more iron-containing meat, you will have higher iron stores, ie/ higher ferritin. Higher ferritin does not necessarily mean pathologically high (I don’t have access to the numbers, so I don’t know how high the numbers were, but to be honest, most women I know have problems with LOW iron, and need to increase their red meat intake.) So on an individual basis, it’s best to test a range of iron store measures, as Chris mentioned. In the study, it’s difficult to say what’s going on without seeing the numbers, since just having ‘higher’ ferritin isn’t necessarily a bad thing. It could be good, actually, if everyone else’s ferritin is too low.

      • newbie says

        Thanks for taking the time Cat.
        If you are absorbing more from the red meat, and since humans don’t have a “rate limiter/overload exceting mechanism”, your stores should increase in proportion to the elevated absorption.
        Basically, though, my question is – What is the significance of high ferritin (say 150 – 250 range, which is still considered normal in Canada), in a metabolically
        healthy lean postmeno female population with normal or even low normal iron indices?

        • Cat says

          Ah I see, thanks for clarifying. I don’t really know the answer, except maybe how healthy is ‘healthy’? Since inflammation (even subclinical) can elevate ferritin, without actually increasing iron stores, that could be the cause: http://www.sciencedirect.com/science/article/pii/S1878764912001155
          The other markers of iron status would be low or low-normal. If the ferritin is still technically within range, this type of thing would be subclinical, so most likely ignored by doctors (or so I’ve found).
          These diagrams could be useful for eliminating possible conditions: http://www.haematologica.org/content/94/3/307/F1.large.jpg
          http://www.haematologica.org/content/94/3/307/T1.expansion.html

          • newbie says

            Still trying to get a framework for understanding if any pathology is present is this scenario.
            Read the material you suggested – no other markers of inflammation in these healthy lean women, ie,
            ESR, hsCRP, WBC, albumin are normal, not HC carriers.
            The reason I am stuck on this is that Chris has so often has made a point of focusing on high (yet still normal) ferritin as a disease indicator, I’m trying to discern if he is alluding to HC as the disease to be watchful for, or if there is something else to be watchful for in patients with high ferritin and no other inflammatory markers. Thanks for your input.

            • Cat says

              OK, well good luck then! I’m pretty sure Chris only uses the high ferritin as a starting point that needs further testing to find out if there’s something wrong. If nothing is found, it could be the early stages of subclinical inflammation, with nothing showing up, or maybe nothing is wrong at all, and it’s just normal variation.

  11. Wenchypoo says

    Once again, everybody’s getting bent out of shape over a study that MAY NOT apply to them! These researchers use what they can get easily from the nearest grocery store, which is CONVENTIONAL meat–laden with antibiotics, and all manner of other drugs and chemicals, fed using grains, soy, and nowadays gummy candy, and all but the gummy candy sprayed with pesticides and GMO’d to within an inch of its life.

    They start out with inferior meat at best, then expect us to believe them when they find the meat supposedly causes other health problems. How do they REALLY know it was the meat? Why couldn’t it just as easily have been the drugs or soy WITHIN the meat? Anything fed soy will automatically be suspect for diabetes-related findings, because soy is a known hormone disruptor.

    Grass-fed, pastured meats will certainly deliver much different findings. I’m beginning to believe the researchers know this, and are afraid of the results from using such meats. If you eat grass-fed and pastured meats, none of these so-called “studies” will apply to you, so quit freaking out!

    Eating Paleo means we avoid a vast majority of the drugs, GMOs, pesticides, anti-nutrients, and other problems found in food that help to generate “studies” and the hysteria that follows (and also sells papers/magazines and generates website hits).

    • Katy says

      Thank you for addressing the very important aspect of the quality of the red meat consumed, although I think it should have been one of the first and most obvious aspects about the lack of credibility of this study. Of course a piece of grain-fed meat with a high omega 6:omega 3 ratio will cause a higher level of inflammation than a piece of meat from a 100% grass fed animal with a much lower omega 6:3 ratio.

  12. says

    What about the difference between grain-fed beef and grass-fed beef? My understanding has been that grain-red beef (high Omega-6 to Omega-3 ratio) would be somewhat inflammatory (unhealthy) whereas grass-fed beef (with a favorable ratio of Omega-6 to Omega-3) would perhaps be anti-inflammatory, therefore healthy.

  13. says

    Like my old man used to tell me … don’t believe everything you read. I guess there are medical studies that will crop up every now and then and where it concerns my and my family’s health, I make sure I understand clearly the results of such a survey and when it goes against my own personal belief, I have simply got to try and find a satisfactory conclusion. Can red meat cause or worsen diabetes? I have got to dig deeper.

  14. Dee b says

    I want to live a long time, so I eat what my ancestors ate. High fat, high protien diet, no candy (expensive), drink water often (again, saves money). All my grandparents/uncles/aunts lived well into their 90′s eating what today’s medicine says will kill me. I’ll go with actual experience, instead of all these new theories. Red meat, pork, chicken, turkey, some cheese. Potatoes, pasta or rice as a small side dish. A couple of slices of bread. And a small fresh salad with dinner. Water, tea or coffee. No milk, no soda, small juice only with breakfast, I’ll live forever.

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