Tag Archive for: heme iron

The FFQ: Still Too Vague

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I spent a long time examining validation and reliability studies on the Food Frequency Questionnaires (FFQ). It was interesting to compare the original validation studies with a new FFQ that was published in early 2024; researchers asked subjects in those studies that began decades ago to participate in this recent validation study.

The Stats

I learned more about a variety of statistics that I don’t typically encounter: coefficient of correlation, and then attenuated and deattenuated coefficient of correlations, and more. The researchers concluded that the “study showed that the FFQ used in prior studies has reasonably high reproducibility and validity in measuring food and food groups intakes among both women and men.” I disagree.

The coefficient of correlation is important (COC) because it gives an indication of the association of the variable with a standard, in this case a 7 Day Dietary Recall. The best COC is 1.0 or -1.0, which means it’s perfectly correlated or not correlated with the standard. A COC greater than 0.8 is considered a strong relationship, but a relationship of 0.6 – 0.79 is considered moderate.

The COC for most categories of food was well below 0.6. How can that in any way be valid? It may be reproduceable, but you’re reproducing the same mistake over and over again.

How Dangerous Is Meat?

High level analytics like this aren’t my area of expertise, but logic dictates that you can’t get precision even with large numbers of subjects. This is especially true when using FFQ data to correlate nutrition with disease. Remember the study on red meat intake and type 2 diabetes? The Hazard Ratio was only 10% per 100-gram serving of red meat. If the meat intake is moderately correlated, how much does any error of intake impact the HR?

Whether researchers are trying to estimate how much of each type of meat a person eats or trying to calculate the heme-iron content of that meat, the FFQ doesn’t have enough precision to be used in determining those values. Remember, the increase in HR was 10% per 100 grams—that’s 3.3 ounces—of unprocessed red meat per day. If a patty were 100 grams, a reasonable size, and you ate six patties every day, that would be 600 grams or over 1.5 pounds of hamburger patties per day. Would that raise the HR to 60% based on that single answer? What about a vegan who gets no heme iron? Would they never get type 2 diabetes? We know that’s not true either.

One more thing: People under-report what they eat. It can be 100 to 200 calories per day, or even up to 500 calories per day. No after-the-fact adjustment of the food intake can make up for that kind of imprecision.

The Bottom Line

What we’re left with is this: There may be a relationship between red meat, and subsequently, heme iron intake, and the risk of type 2 diabetes, but we don’t know how much. That’s about it. We’re going to need much better studies to nail that down before we make a pronouncement. For now, you’re probably safe eating red meat, especially if you keep this in mind: eat better, eat less, and move more.

What are you prepared to do today?

        Dr. Chet

References:
1. Am J Epidemiol. 1985;122(1):51–65.
2. Am J Epidemiol. 2024;193(1):170–179

Is Red Meat Linked to Type 2 Diabetes?

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The next study actually precedes the heme iron paper, not only in time but in size—with close to 2 million subjects! This was an attempt to check on whether red meat, chicken, or processed red meat, such as bacon and sausage, are associated with type 2 diabetes. This was a Herculean task that would never be possible without the type of computers available today; just examining the results of the observational studies alone was amazing.

The researchers used a statistical technique called a federated meta-analysis to test the relationship between meat consumption and type 2 diabetes that allows the nutritional data to be analyzed while preserving the anonymity of the subjects. One of the problems was that the data for meat intake had to be standardized among the 31 countries covering the Americas, Eastern Mediterranean, European, South-East Asia, and Western Pacific.

With 1.9 million adults selected for the study, there were just over 107,000 people diagnosed with type 2 diabetes. The median follow-up time was 10 years. The range of meat consumption in all categories was as little as 0 grams up to 110 grams per day. One thing that surprised me as I looked at the medians was that the European processed meat intake far exceeded that of the U.S.—Americans love their hot dogs and cold cuts and sausage and bacon, but apparently not as much as Europeans do.

They found that eating more of each type of meat increased the diagnosis of type 2 diabetes. The Hazard Ratios were:

  • 10% greater risk for each 100 grams of unprocessed red meat
  • 15% greater risk for each 50 grams of processed red meat
  • Only 8% greater risk for every 100 grams of chicken

The increased risk was found in North America, Europe, and the Western Pacific regions. Repeated covariates such as age, gender, or BMI were tested to explain the differences with other regions, but no clear answers emerged. The conclusion? Eating red meat is a risk factor for developing type 2 diabetes across all populations, and processed meat even more so.

Why Meat?

I often criticize these types of studies because they don’t give any reasons or even guesses as to why the results turned out as they did. They couldn’t explain it but gave one possibility that many people don’t consider: red meat and chicken with skin contains fat, and processed red meat has other chemicals used in processing, but what they have in common is protein. If people aren’t eating enough carbohydrates, they are more likely to make glucose from the amino acid remnants of the protein. That’s why people who claim to eat few carbs and starches will end up with prediabetes and fatty livers. I give the authors credit for that.

The real problem, in my opinion, goes back to data collection: almost all studies used a food frequency questionnaire. That’s the topic I’m going to cover next week.

What are you prepared to do today?

        Dr. Chet

Reference:  Lancet Diabetes Endocrinol. 2024; 12: 619–30

Iron from Meat and Type 2 Diabetes

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The abstract begins simply enough: “Dietary Haem iron intake is linked to an increased risk of Type 2 Diabetes.” Haem iron is another word for heme iron, iron sourced from animal meat. But let’s get back to the statement. The first question that pops into my mind is this: how did they measure iron intake from all sources, especially when you consider the scope of the study?

The research team examined data from over 200,000 potential subjects from three large studies of healthcare professionals; some of the subjects were followed for as long as 36 years. Researchers wanted to examine associations between iron intake from all sources and the risk of type 2 diabetes. They also examined blood markers in a subset of close to 38,000 subjects: insulin, lipids, inflammation, and uric acid levels.

They found that heme iron intake resulted in a Hazard Ratio of 26% increased risk for the development of type 2 diabetes when comparing the highest quintile with the lowest quintile of heme iron intake. The heme iron intake was also correlated with poor blood profiles such as high insulin, hs-C-reactive protein, and lipid levels. Nothing from non-heme sources.

Is it time to reduce meat intake? That’s not my initial question. My question is how’d they do that? How did they measure the heme and non-heme iron levels in over 200,000 people? We’ll hold on that for now and look at a study with almost 2 million subjects on Saturday.

What are you prepared to do today?

        Dr. Chet

Reference: https://www.nature.com/articles/s42255-024-01109-5