Monthly Archives: June 2014

Embracing Confirmation Bias

Confirmation bias is one of the great enemies of good science. Wikipedia (I know, I know) defines the phenomenon as “the tendency of people to favor information that confirms their beliefs or hypotheses.” Most of the confirmation bias that exists in science is perpetrated unconsciously. What makes it so insidious is that our brains are hardwired to reinforce existing beliefs. Unbiased thinking does not come naturally to humans. Scientific methodology is fundamentally nothing more than a set of procedures designed to overcome confirmation bias in the search for truth.

Outside of science, confirmation bias is generally ignored and often even embraced as “faith.” In the late 19th century, for example, some Christian theologians explained away the discovery of dinosaur bones by suggesting that God had planted them in the earth to test the faith of those who believed in the literal truth of the Bible’s take on history.

Rarely are scientists ever so shameless in their efforts to preserve their existing beliefs in the face of contrary evidence. Most scientists make honest attempts to account for and overcome their biases in their research. But there are exceptions, and for some reason (actually, I know the reason, which is explained here) these exceptions often involve scientists who hold strong beliefs about what people should eat.

Whether it concerns diet or anything else, confirmation bias is classically expressed through a double standard for evidence. A nutrition scientist who is in the grip of confirmation bias has very high standards for evidence that supports ways of eating that defy his preferred diet and much lower standards for evidence that validates his preferred diet. Put another way, the same kind of evidence that is judged weak when it contradicts a biased scientist’s favored dietary prescription is considered strong when it supports the doctrine of his chosen “diet cult.”

I’ll give you an example. On June 11 of this year, James Allan Davis, a runner from Cape Town, South Africa, tweeted out a link to a BBC News story about a new Harvard study indicating a link between red meat consumption and breast cancer. The next day, Tim Noakes, an exercise scientist at the University of Cape Town and a staunch advocate of a high-fat/low-carbohydrate diet, tweeted this reply: “All evidence against meat and pro veg is based on associational studies which cannot prove causation. Need better evidence.” Minutes later Noakes tweeted a second reply that included the remark, “Associational studies prove zero.”

What Noakes said is true: Every scientist learns on day one of Statistics 101 that “correlation does not equal causation.” But as a practical matter, when a strong statistical correlation exists between two phenomena, it is very often precisely because they have a causal relationship. As the saying goes, where there’s smoke, there’s fire, and evidence from associational studies frequently turns out to be the first smoky clue pointing toward a fire of causality.

In the last century, for example, scientists representing the cigarette industry continually reminded the government and the public that “associational studies prove zero” in reference to evidence of a link between tobacco smoking and lung cancer. While these bought-and-paid-for PhD’s acknowledged that tobacco smokers were much more likely than nonsmokers to develop lung cancer, they argued—fairly—that cigarettes themselves might not be to blame. It was possible, they contended, that for some reason individuals with a predisposition to develop lung cancer were attracted to smoking. Better evidence was needed, they said, knowing full well that no scientist was ever going to turn a bunch of volunteer nonsmokers into smokers and track lung cancer diagnoses within the cohort for 20 years in order to get definitive proof of causality.

Today it is universally acknowledged that cigarette smoking causes lung cancer, but not because such interventional studies were ever done. Rather, it is because the associational evidence is extremely strong, and because there is a highly plausible mechanism to explain causality—tobacco smoke goes into the lungs, after all—and because whistleblowers exposed documents revealing that tobacco industry executives themselves privately believed that tobacco smoking caused cancer despite publicly denying it.

The associations between high vegetable intake and positive health outcomes and between high red meat intake and negative health outcomes are not quite as strong as those between tobacco smoking and lung cancer, but they are significant and consistent and, what’s more, there are plausible causal mechanisms for them. For example, high intakes of red meat are associated with elevated risk of colon cancer. Research has shown that increased red meat consumption results in an almost immediate spike in DNA damage to colon cells, and DNA damage is where cancerous tumors get started. The dots are pretty well connected.

Suppose that ten reasonable people who remembered what they had learned on day one of Statistics 101 but who somehow had no preexisting beliefs about healthy eating were presented with a summary of everything science currently knows about the health outcomes associated with high levels of vegetable consumption and red meat consumption and were then asked to adopt either a high-vegetable/low-meat diet or the opposite. Probably nine of these intelligent, unbiased persons would consider the former a safer bet, if not quite a sure thing; the tenth would be Tim Noakes (i.e. not unbiased after all).

In any case, my point is that Noakes has very high standards for evidence supporting a high-vegetable/low-meat diet, which is a de facto high-carb/low-fat diet. Does he have equally high standards for evidence that appears to support a high-fat/low-carb diet? Alas, he does not.

Exactly one week after Noakes claimed via Twitter that “associational studies prove zero,” a gentleman named David Gillespie tweeted out a graph that showed changes in per capita daily sugar consumption in the United States between 1822 and 2004 alongside changes in the percentage of the U.S. population that was obese between 1882 and 2004. Both trend lines were generally upward sloping. Although everyone agrees that correlation does not equal causation, Gillespie captioned the graph with these words: “The cause of obesity in 1 simple chart” (emphasis added). And what did Tim Noakes do when he saw this tweet? He retweeted it without additional comment.

What’s funny is that the correlation between the two trends is not particularly strong. Most of the growth in per capita sugar consumption in the U.S. occurred before 1930, whereas most of the growth in the rate of obesity occurred after 1978. It is apparent that neither Gillespie nor Noakes studied the graph very closely. When you believe what you want to believe, you see what you want to see.

Never Try Anything New

This post consists of three observations that may or may not be related to one another.


The Paleo diet is built on the premise that all animal species, humans included, are rigidly dependent on the foods that have been in their diet for the greatest amount of time. The genome of each species is like a lock that only one key will open, and that key is the specific food or set of foods that the species has evolved to depend on. Any other foods are like non-fitting keys that not only lack the ability to open the lock but destroy the lock when one tries to jam them in anyway.

In other words, animals are not very adaptable dietetically.

It was on the basis of this belief that Loren Cordain asserted in his book The Paleo Diet that the “333 generations [that] have come and gone” since the dawn of the agricultural revolution have offered “scant evolutionary experience” for the human body to adapt to “new” foods such as cow’s milk, and therefore these foods must be killing us.


The quino checkerspot is a species of butterfly that is native to Mexico and California. Since time immemorial it has eaten only one food, the dwarf plantain. Unfortunately, global warming has created climatic conditions in its native habitat that are too warm and dry for the plant to survive in. In the 1990s, biologists began to warn that when the dwarf plantain went extinct, the butterfly that was completely dependent upon it would disappear with it.

But then a funny thing happened. The two surviving colonies of checkerspots spontaneously migrated from their natural, sea-level habitat to a new habit at higher elevation. When biologists discovered this relocation they also discovered that the checkerspot had chosen a completely new food source—a flowering plant that has little in common with the dwarf plantain. Far from ruining the health of the species, this sudden and total transformation of the species’ diet has caused its population numbers to rebound dramatically.


Last year, Lawrence David and colleagues at Duke University conducted an experiment that was designed to study the effects of radical changes in diet on the microbiome in human subjects. The term “microbiome” refers to the large and diverse populations of bacteria that live in the human gut, and without which we would be incapable of properly digesting food.

The Duke researchers recruited 10 healthy volunteers (six men and four women between the ages of 21 and 32) and placed them sequentially on two different diets for five consecutive days. One diet consisted entirely of plant foods (grains, legumes, fruits, and vegetables), while the other diet consisted entirely of animal foods (meat, cheese, and eggs). As you would expect, the nutritional compositions of the two diets were divergent in the extreme. For example, on the carnivorous diet, subjects got 70 percent of their daily calories from fat and consumed zero fiber, whereas on the herbivorous diet, subjects got only 22 percent of their calories from fat and fiber intake increased nearly threefold from baseline levels.

After just three days on each diet, significant changes were seen in the composition and functioning of the microbiome in all subjects. On the carnivorous diet, subjects exhibited a marked increase in the presence and activity of bacteria that thrive in a bile-rich environment, which makes sense, because the gut produces more bile when digesting animal foods. In contrast, on the herbivorous diet, the subjects exhibited a large increase in the presence and activity of bacteria that metabolize polysaccharides from plants.

The researchers even noted changes in gene expression within certain strains of bacteria in response to the disparate diets. So not only had the human subjects rapidly adapted to changes in diet through their gut flora, but the flora themselves had adapted epigenetically.

In three days.

Don’t Blame the Dentist for Your Cavities

Among the more absurd ideas being peddled by certain diet cults these days is the idea that mainstream guidelines for healthy eating are directly responsible for the ongoing American epidemic of metabolic syndrome. If you know a hardcore Paleo dieter or a high-fat/low-carb eater, then you probably know someone who believes this astoundingly ridiculous notion, having learned it from Denise Minger’s book Death by Food Pyramid or from Paleo guru Robb Wolf’s blog ravings or from some other mouthpiece of Paleo or HFLC dietary doctrine.

The logic of the argument is well summarized in the promotional copy for Minger’s opus. Here’s a sample: “Shoddy science, sketchy politics and shady special interests have shaped American dietary recommendations—and destroyed our nation’s health—over recent decades. The phrase Death by Food Pyramid isn’t shock-value sensationalism [no, of course not], but the tragic consequence of simply doing what we have been told to do by our own government—and giant food profiteers—in pursuit of health.”

If your IQ is higher than 85, you don’t need me to tell you that this line of reasoning depends on one very big and very false assumption: namely, that most Americans actually obey mainstream dietary recommendations. In fact, the diet of the average American is very nearly the opposite of what is recommended in official resources such as the U.S. government’s Dietary Guidelines for Americans.

Among these guidelines is the familiar recommendation to consume at least five servings of fruits and vegetables daily. Only 11 percent of Americans meet this requirement. The American Heart Association recommends that adults consume no more than six teaspoons of added sugar each day. The average American consumes 22 teaspoons of added sugar each day. The USDA’s MyPlate program advises people to get at least half of their grains in the form of whole grains. Forty percent of Americans never eat whole grains. The American Heart Association recommends that fish be eaten at least twice a week. Only one-third of Americans eat fish even once a week. And so on.

Not only do most Americans fail to follow mainstream dietary recommendations, but they also don’t even know what these recommendations are—or that they exist at all. According to a large scientific survey conducted a few years ago, fewer than half of American adults have ever heard of the Dietary Guidelines for Americans and less than 40 percent are aware that these guidelines include the recommendation to eat five or more servings of fruits and vegetables daily.

Blaming mainstream dietary recommendations for the high rates of obesity, heart disease, and type 2 diabetes in America is logically equivalent to blaming dentists for the high rate of tooth decay among our citizens. The American Dental Association recommends that people brush their teeth at least twice a day and floss at least once a day. Only 53 percent of Americans follow the first of these recommendations and even fewer of us follow the second. Ninety-two percent of American adults have decayed teeth, despite almost universal exposure to the ADA’s recommendations for dental hygiene. So do we blame the dentists? That wouldn’t make much sense, because the incidence of tooth decay is much lower among those who actually do follow ADA guidelines. Similarly, only a fraction of Americans follow mainstream dietary recommendations, but those who do are much healthier than those who don’t.

Proof that following mainstream nutritional guidelines results in much better health than does eating like the average American is piling up rapidly. Some of the best recent evidence comes from a study associated with the ambitious Dietary Patterns Methods Project. This project is investigating the health effects of various eating patterns that are consistent with mainstream dietary guidelines. The first study to issue from the project measured the degree to which the diets of 424,000 older men and women conformed to each of four indexes of healthy eating—the Healthy Eating Index 2010, the alternative Healthy Eating Index 2010, the alternative Mediterranean Diet, and the DASH diet—and correlated this data with death risk over a 15-year period.

The mortality rate for those whose eating patterns conformed most closely to each of these indexes was significantly lower than it was for those whose eating patterns conformed least closely. Since the subjects were American, it is safe to assume that the men and women who had the lowest scores on these indexes tended to eat the typical American diet. According to this study, the people whose eating habits fell furthest outside official recommendations were up to 28 percent more likely to die of cancer or heart disease between the ages of 62 and 77 than were those who ate according to mainstream dietary guidelines.

Despite such evidence, Paleo and HFLC diet advocates continue to conflate mainstream dietary recommendations with the typical American diet. They do this most insidiously with their use of the term “standard American diet” (or SAD—get it?) to refer to both the way the average American eats and the way mainstream nutrition scientists advise people to eat.

Consider these sentences from “Paleo Runner” Aaron Olsen’s review of my book, Diet Cults: “Considering the fact 2/3 of Americans are either overweight or obese, I fail to see how mainstream recommendations such as the SAD should be used as a template for an optimal eating strategy. The reason diet fads are so popular in the first place is because the SAD has failed us so miserably.”

Here we have an egregious misrepresentation of the “agnostic healthy eating” guidelines I present in the book, which are based on mainstream nutrition science, not on what the average American eats. But is this misrepresentation deliberate or merely a consequence of the reviewer’s own prior brainwashing? I won’t hazard a guess, but it is evident that some high priests of the Paleo and high-fat/low-carb diets choose to conflate mainstream dietary guidelines with the standard American diet despite knowing full well that the two are worlds apart. In so doing they betray not only a startling lack of intellectual integrity but also a troubling assumption about the intelligence of the eating public.

Here, in essence, is what these folks expect you to believe: that if a typical American eater, who spends $1,200 annually on fast food, were to hire a registered dietitian to help him get healthier, the R.D. would make no changes to her client’s diet.

For the record, I don’t think you’re that stupid.

How the Pros Eat: Gabriele Grunewald


Gabriele Grunewald, 27, is a top American middle-distance runner and the reigning U.S. indoor 3000m champion. Her many other accomplishments include a fourth-place finish in the 2012 U.S. Olympic trials 1500m and a third-place finish at the USA 1 Mile Road Championships. A native of Minnesota and a graduate of the University of Minnesota, Gabe now represents Team USA Minnesota and Brooks. She is a two-time cancer survivor. Follow her on Twitter at @gg_runs.

What is your racing weight?


What are your personal dietary “rules”?

I don’t necessarily have “rules” — but I try to make a fruit or vegetable a part of every meal. I also try to eat whole grain options instead of refined whenever possible, and I try to cut out fried foods almost completely when I’m in the peak of my season.

What’s a typical breakfast for you?

Usually I’ll have some form of a hot cereal or oatmeal topped with berries and nuts. And a cup of coffee (or two, or espresso).

A typical lunch?

Turkey or tuna sandwich on whole wheat, accompanied by a cup of vegetable soup or a salad. Some combination of those, or sometimes I’ll eat leftovers from last night’s dinner. As a snack at some point throughout the day, I’ll have a yogurt, banana or a Generation UCAN shake.

A typical dinner?

Grilled barbecue chicken is a favorite — with something like sweet potatoes and black beans. Tonight I’m baking salmon and having brown rice and green beans. Spinach/kale side salads usually make an appearance at dinner too.

What’s the biggest change you’ve made to your diet since college?

I’m just a lot more consistent with my diet throughout the day. In college I was always on the go, sometimes not eating enough before or right after practice. I would have a huge dinner to compensate for not eating throughout the day. Now, I’m always able to fuel properly. Having a Generation UCAN before workouts and their protein version post-workout has taken the guesswork out of what I should be fueling with before a workout. Also, I have more time to cook so I can experiment more with new foods and have more variety in my diet. I’m also a bit more conscientious of my diet during the peak of my season when I’m tapering my training.

Bacon, potato chips, or ice cream?

Chips! Kettle chips or tortilla chips for me.

How to Outsmart Diet Cult Spin

Imagine that a juicy new diet controversy has piqued your curiosity. People on one side of the debate are claiming that a certain category of food or type of nutrient is bad, while people on the other side are claiming the opposite. You want to know who’s right. Where can you go for an unbiased answer? The best place to look is PubMed, a U.S. Library of Medicine-funded online database that contains more than 23 million citations for biomedical literature. This is where nutrition scientists themselves go when they need a question answered.

For the sake of illustration, let’s suppose that the particular diet controversy that has captured your interest is the one surrounding grains. One on side of this debate are low-carb and Paleo diet advocates claiming that all grains are unhealthy. On the other side are vegetarians, “clean eaters,” and others claiming that whole grains are healthy. Who’s right? A quick visit to PubMed will answer this question in a jiffy.

Start by typing “whole grain” (or “whole grains”) in the search box. As you punch the keys, an auto-complete function will generate a dropdown menu with suggestions for specific searches that contain your key words. Examples are “whole grain cardiovascular,” “whole grain diabetes,” and “whole grain inflammation.” Choose a search string from among these options, then browse through the list of studies that are called up until you find one that interests you. Click on the title and you will be taken to a one-paragraph abstract that summarizes the study. Now look at some of the related studies whose titles appear on the right of your screen. When you’re satisfied that you’ve come up to speed on the current scientific understanding of the effect of whole grain consumption on cardiovascular disease risk (or whatever), back up and choose another whole grain-related search string.

If you actually do this, you will quickly discover that whole grains are in fact exceedingly beneficial to human health. For starters, they promote a healthy body weight. A 2011 study conducted by researchers at the Harvard School of Public Health and published in the New England Journal of Medicine found that adults who increased their consumption of whole grains gained 11 percent less weight over a 20-year period compared to the average person.

Whole grains are also good for cardiovascular health. A 2003 study published in the Journal of the American Medical Association found that elderly men and women who consumed lots of whole grains had a 21 percent lower incidence of cardiovascular disease.

The effect of whole grains on type 2 diabetes is even more striking. In 2002, researchers at Simmons College published the results of an experiment in which they tracked whole grain consumption and diabetes risk in a population of nearly 43,000 men for 12 years. Those who ate the most whole grains were found to be almost 50 percent less likely to develop type 2 diabetes compared to those who ate the least whole grains.

The beneficial effects of whole grains on the risk for chronic diseases such as cardiovascular disease and type 2 diabetes appears to be mediated in part by the food’s effect on systemic inflammation, which is an underlying factor in many chronic diseases. Numerous studies have shown that consumption of whole grains reduces systemic inflammation. For example, a 2008 study published in the American Journal of Clinical Nutrition found that 12 weeks of substituting refined grains with whole grains reduced levels of C-reactive protein, a major marker of systemic inflammation, by 38 percent in a group of overweight adults.

There is so much good news about whole grains in the PubMed database that, after looking through it, you might be left wondering why whole grains are condemned as unhealthy by the low-carb and Paleo crowds. The reason is that the creators of the low-carb and Paleo diets made up their minds about whole grains without reference to the published research. In the case of the low-carb philosophy, the notion that carbohydrate is bad serves as a first principle. Since whole grains are rich in carbohydrate, they must be unhealthy, regardless of what the research says. In the case of the Paleo diet, the first principle is that humans living today should not eat foods that were not eaten by our ancestors a million years ago. Since cultivated grains were not eaten a million years ago, they must be unhealthy, regardless of what the research says.

The fact that science overwhelmingly supports the healthfulness of whole grains presents a problem for low-carb and Paleo diet proponents with respect to their efforts to win new converts. How do these diet cults convince people to stop eating whole grains when science says they keep us from getting fat and developing chronic diseases? With trickery, that’s how! There are two tricks in particular that the low-carb and Paleo diet cults use to create the illusion that science does not support the healthfulness of whole grains.

The first trick is a special form of nitpicking that entails focusing on microscopic mechanisms instead of big-picture final outcomes. The anti-grain faction delights in pointing out that many grains contain a tiny compound called phytic acid that is known to limit the absorption of some vitamins and minerals. It sounds bad, but reduced absorption of some vitamins and minerals is not itself a disease. It is merely an intermediate effect of digestion that could conceivably be linked to long-term health consequences. But we’ve already seen that the long-term health outcomes associated with eating lots of whole grains are all positive. What’s more, big eaters of whole grains are actually less likely than others to be deficient in essential vitamins and minerals. So phytic acid is a problem without a consequence—which means it’s not really a problem.

Where health is concerned, the ultimate big picture is longevity. If eating a given food type increases lifespan, the details of how it is digested and metabolized really don’t matter. A 2008 study from the Harvard School of Public Health found that a diet including large amounts of whole grains reduced the risk of death by 21 percent in a population of 72,000 women over a period of 18 years. In short, people who eat lots of whole grains live longer. Who the hell cares if the phytic acid in whole grains slightly reduces the amount of iron in the body if whole grains as a whole add years to a person’s life?

The trick of turning public attention away from final health outcomes (which matter) and toward intermediate digestive and metabolic mechanisms (which don’t), which low-carb and Paleo diet advocates use to disparage whole grains, is used by other diet cults to disparage other food types. No food type is immune to such scrutiny. If you look closely enough at nuts, fish, or even vegetables, you will find something microscopic inside that the body has a little trouble dealing with. Big deal! No food is perfect. The anti-grain faction wants to use one small imperfection in grains to distract you from their big-picture benefits and convince you that wheat, rice, and so forth are “killing you slowly” (as one “wellness” blogger put it). It’s amazing to me that anyone is fooled by this kind of chicanery, but at least you won’t be fooled by it ever again.

The second trick that certain diet cults use to create the appearance that science does not support the healthfulness of whole grains is to discredit the relevant research. Because this trick is so desperate and outlandish, members of the anti-grain faction typically resort to it only when the first one fails, but when backed into a corner they will not hesitate to insinuate or even claim outright that the hundreds of studies proving the healthfulness of whole grains represent a giant conspiracy funded by, and serving the interests of, the grain industry.

It is true that industry money has some influence on nutrition science. One of the studies I described above, the one concerning systemic inflammation, was paid for by General Mills. An anti-grain zealot will look at such corporate backing and reflexively assert that the results cannot be trusted. That’s a bit over the top. While industry dollars do sometimes determine which studies are conducted in the first place, and corporate influence may at times be used to ensure that unfavorable results are not published, nutrition scientists by and large do not risk their reputations and careers by going so far as to manipulate data to please breakfast cereal makers. To suspect this is to take cynicism to the brink of slander.

People become scientists because they love and respect truth. Some are corruptible, but most are not. The typical nutrition scientist is like David Katz, a professor at Yale University, who said in a recent article on, “I don’t have a dog in the fight. I don’t care which diet is best. I care about the truth.”

Even if a rogue researcher were tempted to fudge data to make whole grains look better, it would be hard for him to get away with it. Science has many layers of checks and balances—including peer reviews, the requirement to disclose funding sources, and the practice of duplicating results independently in multiple labs—to minimize the impact of unethical scientists.

In any case, the majority of studies linking positive health outcomes with whole-grain consumption are not underwritten by the grain industry. For example, a recent study by Korean researchers that found favorable effects of whole grains on fasting glucose and triglyceride levels was funded by the National Research Foundation of Korea and the Ministry of Science, ICT & Future Planning. (Here’s where the most bug-eyed anti-grain crusaders try to argue that these organizations have an interest in boosting the Korean grain industry. The problem here is that there essentially is no Korean grain industry.)

Conspiracies do exist, but they can only get so big and last so long before they are exposed and brought down. For example, the cigarette industry maintained a conspiracy to hide scientific evidence that cigarettes create health risks. But this conspiracy was exposed by whistleblowers including Merrell Williams, Jr., who leaked documents proving that the cigarette makers acknowledged the risks internally. No whistleblower has come forward with evidence showing that the vast ocean of science supporting the healthfulness of whole grains is tainted by fraud. And none will ever come forward, because there is no conspiracy.

You can’t reason with people who want to believe what they believe, but if I were to try, I would make one last point. The soft drink and confectionary industries are huge and powerful and rich beyond imagining. They have poured a lot of money into efforts to counter scientific evidence that consuming lots of refined sugar is not healthy. Those efforts have failed miserably. If you go to PubMed and type in search phrases such as “high fructose corn syrup diabetes” or “soft drinks obesity” you will find all kinds of bad news about excess refined sugar consumption and not much good news.

If nutrition science were corruptible on a large scale, every college nutrition textbook would teach students that soda pop is healthy. But they don’t, so when science says that whole grains are healthy, you can trust it. What you cannot trust is any diet cult advocate who resorts to the conspiracy argument. The use of this tactic should instantly disqualify its user from further debate, the same way throwing up in a beer mile invalidates a competitor’s finishing time (unless he completes a penalty lap).

Like the first trick I discussed—that of distracting public attention from meaningful final health outcomes and turning it towards meaningless digestive and metabolic mechanisms—this second trick of sweepingly discrediting research that produces “inconvenient truths” is used by many diet cults, not just those that have a beef with grains (so to speak). Look for both of these tricks in your future dealings with diet cult advocates of all varieties, and don’t fall for them!