Category: Fact or Fiction?
The straight dope on nutrition myths, trends, and fads
Red meat: Not so bad after all?
A lot of people I know have cut back on meat–specifically red meat–in an effort to make their diets healthier. I think there are lots of good reasons to eat less meat. But regular readers of this blog will know that I’ve long been suspicious of this idea that “red” meat is any worse for you than “white” meat.
See also: Meat and mortality: What’s color got to do with it?
This idea that red meat is unhealthy is self-reinforcing. Because we’ve all convinced ourselves that this is true, studies which find a link between red meat and some sort of disease are much more likely to be published and get a lot more press than studies which find no such link. Never mind that what we categorize as “red” and “white” makes absolutely no sense, either nutritionally or zoologically.
So I consider it my duty to point out that a recent meta-analysis published in the Nutrition Journal found no association between eating red meat and risk of prostate cancer. And while I’m at it, I’ll remind you that a widely-cited report linking red meat and cancer risk was later found to contain significant errors and omissions. The authors later acknowledged that they had overstated the risks. Of course, the retraction got way less press than the error.
A more rational approach
If you want to make your diet healthier, I suggest a color-blind approach to meat. Don’t worry about whether it came from a cow or a chicken. Instead:
- choose meat that is raised on healthy feed and without hormones or antibiotics
- right-size portions: a 3 ounce serving is the size of a deck of cards
- avoid fried or charred meats (See also: Tips for healthier cookouts)
- avoid processed meats with added salt and/or nitrates
- add lots of vegetables
Your thoughts?
Red meat and cancer: dumbing down the science
At this morning’s session on Diet and Cancer, Dr. Marji McCullough gave an epidemilogist’s-eye view of the relationship between cancer and diet. Her main point was that focusing on overall dietary patterns (such as higher fruit and vegetable intake) rather than individual nutrients and foods (such as broccoli sprouts or soy) appears to be the most effective way to reduce cancer risk.
Throughout her talk, she was careful to point out the limitations of the research and how hard it is to collect and intepret data in the extremely messy experimental model known as “free living humans.” So I was a little disappointed to hear her single out “red and processed meats” as one of the only food groups for which there is consistent evidence of a link with cancer.
First of all, it always irritates me to hear “red and processed meat” discussed as a single food group. My friends, there is a world of difference between a hot dog and a bison steak.
Cured meats and cancer
There does appear to be a link between cancer and high consumption of processed (i.e. cured) meats like hot dogs, sausages, salami, and cold cuts–most likely due to nitroasamines formed from the nitrates used to cure these meats. Incidentally, nitrosamines are deactivated by vitamin C and the link between cured meat consumption and cancer risk disappears in those who eat a lot of vegetables. That’s right: Those who eat the most cured meats but also the most vegetables have no increased risk of cancer.
But, I digress. Back to (uncured) red meat.
Cooking methods and cancer
McCullough suggested that red meat consumption might contribute to cancer because heat-heat cooking methods (such as grilling) create harmful compounds. Hang on a minute. Maybe the problem isn’t red meat. Maybe the problem is charred meat. After the talk, I had a chance to chat with Dr. McCullough and she admitted that from the existing data, most of which was collected 20 and 30 years ago, researchers can’t really distinguish between the type of meat and how it was cooked. Nor can they separate Big Macs from flank steak…nor beef from bison…nor grass-fed from corn-fed. It’s all just “red meat.” And what kind of red meat were Americans eating most of in the 80s and 90s?
Dumbing down the science?
For folks who eat most of their red meat in the form of char-grilled, high-fat, fast-food burgers, telling them that they can cut their cancer risk by cutting back on “red meat” may be good public health policy. But in over-simplifying the prescription this way, we may be throwing the baby out with the bathwater.
Is there any evidence to suggest that lean, grass-fed red meat, prepared in a way that minimizes formation of HCAs and PAHs increases your risk of cancer? No, there is not. (Click for tips on how to reduce harmful compounds) In fact, compared with poultry, red meat is higher in monounsaturated fats and lower in omega-6 fats–two qualities that red meat has in common with the cancer-protective Mediterranean diet pattern.
Fructose: Poison, Nutrient, or Both?
Given the escalating rhetoric on fructose, I think it’s time to revisit a couple of basic facts and try to regain some perspective.
Fructose is not a toxin. It is not a man-made “chemical.” The fact that is it metabolized in the liver does not mean that it is a poison.
Fructose is a naturally occurring mono-saccharide (sugar) found in fruits, vegetables, nuts, grains, eggs, dairy products and other whole foods. It has been part of the human diet since the beginning. Presumably, our bodies are well-adapted to it. In fact, there might be an evolutionary advantage to the ability to metabolize sugars through multiple pathways–including one that does not lead to an immediate rise in blood sugar.
All nutrients are potentially toxic
As the National Academy of Sciences states: “All nutrients can have adverse effects when intakes are excessive.” That’s why tolerable upper limits (ULs) have been established for many nutrients. The NAS recommends that you don’t exceed 45mg per day of iron, for example. But no-one is suggesting that iron is a poison or that it should be avoided at all costs. Maybe if we had a tolerable upper limit for fructose, we could all relax a little bit.
How much fructose is too much?
According to a recent analysis, Americans are now consuming somewhere between 38 and 73g of fructose a day. A third of that comes from sweetened beverages. The rest comes from other processed foods as well as grains, fruits, vegetables, eggs, cheese, and other whole foods.
It seems clear that current sugar intake is excessive and making us sick. Many argue that it’s fructose, specifically, that’s doing most of the damage. Fine: For the sake of argument, let’s just say that the current average intake of 55g of fructose (or around 10% of total calories) is enough to overload the liver and contribute to obesity and other ills. That suggests that somewhere between 0 and 55g per day is a threshold at which fructose ceases to be a useful (or at least harmless) nutrient and starts to be a problem.
Seeing as it doesn’t seem possible, necessary, or even desirable to reduce fructose consumption to zero, I think it would be useful to start looking for that threshold.
What is the tolerable upper limit for fructose?
Bias in Research Not Always What You’d Expect
I know that many of you are suspicious of nutrition research. Many are convinced that the dairy, egg, beef, corn, or [fill in the blank] industries have bought off the researchers, journals, government, and the media in an effort to cover up the truth about their products–suppressing negative research and fixing studies to produce findings favorable to their products. There are certainly times when research is misconducted, misinterpreted, and/or misreported. That’s why all research (and reporting!) needs to be viewed with a critical eye–and all potential interests need to be disclosed.
Related content: Can we trust industry funded research?
The White Hat Bias
But biases don’t always run in favor of commercial interests. Researchers writing in the International Journal of Obesity have documented what they’re calling a “white-hat bias,” which influences researchers to reach conclusions that support their preconceived notions about nutritional “bad guys.”
As evidence, they present two widely-cited studies on the link between sweetened beverage consumption and obesity. Both studies found that the link between the two was statistically insignificant. Yet these studies are regularly misrepresented by the press and cited by other researchers as evidence that sweetened beverages are positively linked to obesity.
They also show that studies which do find a link between sweetened beverages and obesity are much more likely to be accepted for publication than studies that fail to find a link–a so-called publication bias. In other words, scientists have become so convinced that soda is a “bad guy” in the war on obesity that they overlook or misinterpret evidence to the contrary.
I’m not saying that sweetened beverages aren’t a problem. But ignoring evidence that doesn’t conform to what we’ve decided is “true” isn’t going to improve our understanding. And for those who believe that all nutritional research has been bought and paid for by Big Industry, it’s worth noting that an entrenched “thought bias” can be just as influential (and just as counter-productive) as commercial interests.
Purslane as a source of omega-3: a reality check
Purslane has gained a reputation as being a good source of omega-3 fatty acids. An oft-cited 1992 analysis, published in the Journal of the American College of Nutrition, found that 100 grams of purslane contained 300-400 mg of omega-3 fats.
But if you search the scientific literature, you’ll see that the amount of omega-3 fats in purslane varies a LOT, depending on the variety, the age of the plant, the part of the plant you analyze (leaves, stems, seeds), and the time of harvest. The purslane analyzed in the 1992 study was clearly at the high end of the range.
Is purslane a valuable source of omega-3 or not?
It’s true that, compared to other green vegetables, purslane is rich in omega-3 fatty acids. About half the fat in purslane is omega-3. But green vegetables are very low in fat, so that doesn’t add up to much.
Let me put this in perspective for you: Even if you were lucky enough to got some high octane purslane like the stuff analyzed by Simopoulos in 1992, you’d need to eat 4 pounds of it to get the amount of ALA found in one tablespoon of flaxseed oil. Hope you’re hungry!
Can yogurt protect you from the flu?
Q. I recently read about a study showing that probiotics protected kids from getting the flu. It seemed like a pretty powerful study in favor of the health benefits of yogurt, at least in kids. Do you have any recommendations for a reasonable “dose” of yogurt would be for an adult?
A. Yes, I noted that study with interest as well. The kids (about 300 of them, aged 3 to 5) were taking probiotic supplements or placebo pills twice a day. The kids getting the probiotics had about half as many fevers, coughs, and runny noses, took fewer prescriptions and missed fewer days of school.
We should note that the study was funded by a company that makes probiotic products. That said, the results were published in a peer-reviewed journal (Pediatrics) so the study design apparently passed muster.
See also: Can we Trust Industry Funded Research?
There’s no RDA for probiotics for kids or adults so it’s hard to say what a good”dose” might be. Most probiotic supplements contain 10 to 20 billion active cultures per dose at the time of manufacture. Yogurt that carries the “Live and Active Cultures” seal is certified to contain at least 100 million cultures per gram at the time of manufacture, which translates into about 22 billion live cultures in an eight ounce cup of yogurt.
So, I’m thinking that a single serving of yogurt every day would be a reasonable start for kids and adults. But the amount of sugar (often high fructose corn syrup) in sweetened yogurts is shocking. I’d advise you to steer clear of sweetened (and artificially-sweetened) yogurts and go for the plain yogurt. Sweeten (if you must) with fruit or a drizzle of honey.
Can yogurt protect you (or your kids) from getting the flu this season? Might help and can’t hurt (unless you’re lactose intolerant).
Are Saturated Fats from Vegetables Better?
I’ve been getting a lot of questions about coconut oil–a vegetable source of saturated fat. It’s alleged health benefits are being heavily promoted but there’s not much solid evidence to back up the claims.
It’s hard to say whether saturated fats from vegetables are better than saturated fats from animals–in part because the evidence that saturated fats cause heart disease looks increasingly shaky. Maybe the truth is that the vegetable saturated fats aren’t better than animal saturated fats but that the animal fats weren’t that bad in the first place?
How can people who try so hard to get it right get it wrong so often?
Why is it so hard for us to get it right? As Marion Nestle’s argues in the introduction to her recent book, What to Eat, part of the problem is embedded in the very nature of scientific research. In an effort to reduce the variables, nutritional research focuses too much on the details and not enough on the big picture.
“The range of healthful nutrient intake is broad, and foods from the earth, tree, or animal can be combined in a seemingly infinite number of ways to create diets that meet health goals,” she writes. “The attention paid to single nutrients, to individual foods, and to particular diseases distracts from the basic principles of diet and health…But you are better off paying attention to your overall dietary pattern than worrying about whether any one single food is better for you than another.”
I suspect that the kind of reductionist thinking that Nestle is deploring is exactly what got us into this mess about saturated fat. We were looking for a culprit for heart disease. We found one in saturated fat…but I suspect we overlooked the critical importance of the context in which that saturated fat was being consumed.