Drink at your own perceived risk

2 05 2012

by Helen Shen

How dangerous is unpasteurized milk? Many health-conscious consumers want to know. The answer depends on how you look at the numbers.

In March, CDC scientists published a study in the journal Emerging Infectious Diseases that tried to quantify this risk by analyzing milk-related disease outbreaks from 1993 to 2006.

The research was widely covered in the mainstream news media, including in a story I wrote for the San Jose Mercury News. The study also attracted a fair amount of online outrage from many raw milk enthusiasts, who treated it as a piece of biased government propaganda.

The CDC media press release, several news stories, and the research paper itself highlighted two main points: first, that 75 percent of raw milk outbreaks occurred in states where raw milk was legal at the time (in an interview with me, first author Adam Langer called this “the most important result of the study”); and second, that raw milk is 150 times more dangerous than pasteurized milk.

Plenty of aspects of the raw milk debate are unscientific. Food choices are personal, cultural, and political. Twelve states allow retail sales of raw milk. Twenty states ban raw milk sales outright. The remaining states allow only limited raw milk sales, such as on-farm transactions.

Unfortunately, emphasizing those particular research findings may have hindered a truly scientific discussion about raw milk risks.

Photo credit: cyclonebill, Wikimedia Commons

Proving the obvious

Let’s think about the first conclusion. Between 1993 and 2006, raw milk caused more outbreaks in states where the unpasteurized product was legal. Is that like saying car accidents happen more often on roads that permit cars?

Langer told me, “It is not necessarily surprising. We do occasionally have to do scientific studies in order to prove what one would think would be obvious. But it is important evidence to show that laws that restrict the sale of unpasteurized dairy products are very important public health tools to reduce the number of outbreaks that are caused by these products.”

Basically, the study suggests that in states that ban raw milk sales, few people consume and get sick from black market raw milk, says Michele Jay-Russell, a food safety expert at UC Davis and a former scientist with the California Department of Public Health.

Hm. That’s probably good news, but it doesn’t offer any real information about how risky raw milk actually might be. That’s where the second point could help.

Outbreaks versus individuals

The authors concluded that raw milk carries 150 times greater risk than pasteurized milk of causing disease outbreaks. (A disease outbreak is a cluster of illnesses thought to originate from the same source. It could involve 2, 200, or 2,000 people.)

Here’s some of the math: Only about 1 percent of the population is thought to consume raw milk. Assuming they consume milk in roughly the same quantities as other milk drinkers, and assuming the two types of milk were equally safe, you’d expect about 1 percent of outbreaks to be related to raw milk. Instead, the CDC found 60 percent of outbreaks—150 times more than expected—were linked to raw milk.But what happens if, instead of using outbreaks, you look at those individuals involved in milk-related outbreaks? Those numbers tell a slightly different story.

In total, raw milk outbreaks sickened 1571 people. Pasteurized milk sickened 2842. So, while raw milk was implicated in 60 percent of outbreaks, it accounted for only 35 percent of all outbreak-sickened individuals. Thirty-five percent is still 55 times more than you’d expect to see from the small fraction of milk drinkers who consume unpasteurized dairy. That’s cause for concern, but it’s a much smaller effect than if you measure risk by outbreaks.

The average reader doesn’t think in terms of disease clusters, but is interested in individual risk. Health agencies, on the other hand, get concerned and become involved when outbreaks occur, says Jay-Russell.

“If you’re part of an outbreak, or if you’re the only one that got sick, it’s all the same ‘badness’ for you personally. From a public health resource standpoint, having these dozens of outbreaks, every one of those requires stopping work on other public health issues,” she said.

Milking a goat
Photo credit: Teunie from nl, Wikimedia Commons

The authors didn’t communicate the reasons for their choice—non-intuitive for the general public—for calculating outbreak statistics in their paper. Nor did they include the relative risk statistics for individuals. Doing so could have helped their case.

But because the omitted statistics would have produced a weaker result, the authors invited criticisms of manipulating the numbers to their advantage.

In a press release entitled “CDC Cherry Picks Data to Make Case Against Raw Milk,” the pro-milk non-profit Weston A. Price Foundation said, “Perhaps most troubling is the authors’ decision to focus on outbreaks rather than illnesses… In addressing the risk posed for individuals who consume a food, the logical data to examine is the number of illnesses, not the number of outbreaks.”

Distracting from the data

Jay-Russell says she’s more concerned that young people and children are disproportionately sickened by raw milk—a finding that received relatively less attention. The CDC study found that 60 percent of individuals sickened by raw milk outbreaks were younger than 20. That number contrasts with 23 percent for pasteurized milk outbreaks.

Even though a small fraction of the population drinks raw milk, the majority of those sickened in raw milk outbreaks are young. This effect is partly explained by the fact that raw milk is touted by its fans as a health food—not just acceptable for children, but especially beneficial to their growth and well-being.

In my next blog post, I’ll examine some of these health claims.

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Making Room for Thanksgiving Stuffing

21 11 2011

Helen Shen

by Helen Shen

I didn’t grow up eating Thanksgiving dinner, but over the years I’ve learned how to do the traditional American turkey-day right. There’s the carving of large birds, the mashing of potatoes, and of course, the skipping of lunch.

Most people I know skip lunch on Thanksgiving. We may call it “saving room for dinner,” but aren’t we really just buying caloric credits for the inevitable metabolic assault? This year, I wanted to explore the scientific evidence that either supports or debunks this holiday eating strategy.

Unfortunately, PubMed has exactly zero hits for the search term “Thanksgiving lunch.” Researchers I contacted directly or through news officers at Stanford University and UC San Francisco did not feel up to speaking on the subject of how meal timing (or skipping Thanksgiving lunch) affects metabolism.

Lunch — the other Thanksgiving meal. (Photo by Helen Shen)

I can imagine why some scientists might not want to touch this question with a ten-foot pole. With the Centers for Disease Control and Prevention reporting that 33.8% of American adults are obese, everyone just wants to know the simple bottom line on what we should eat, how much, and when. But biologically speaking, the human body may not lend itself to a straightforward answer.

Here’s an example. You may have heard some reports that eating breakfast could help you lose weight, while skipping breakfast could lead to weight gain.*

But consider this paper, published in The American Journal of Clinical Nutrition, in which 52 obese women, some of whom were habitual breakfast eaters and others breakfast skippers, were randomly assigned to eat or skip breakfast every day for 12 weeks. The two groups (eat versus skip breakfast) were given different sample menus to follow for the rest of the day that were matched in total calories and nutritional factors.

The confusing result: baseline breakfast eaters lost weight when they skipped breakfast every day, while baseline breakfast skippers lost weight when they ate breakfast regularly.**

What???

Obviously, it’s complicated. And as a scientist, getting large numbers of people of similar genetic makeup, with similar exercising, sleeping, and smoking habits to eat exactly what and when you tell them is also… complicated.

But getting back to skipping Thanksgiving lunch… The most interesting research paper I found, and the one most relevant to my original question, comes from the niche field of studying Muslims fasting for Ramadan.

In a study published online Nov. 13 in the Journal of Public Health, British researchers studied weight change in observant Muslims during and after the month-long Ramadan fasting period. Between Aug. 11 and Sept. 9, 2010, the 202 study subjects did not eat or drink between sunrise and sunset.

The participants, primarily male worshipers at the East London Mosque, were weighed at the beginning and end of Ramadan, as well as one month later. In all, 62 percent of participants lost at least 0.5 kg (1.1 lbs), 17 percent gained at least 0.5 kg, and 21 percent did not change their weight appreciably.

I like this study for a few different reasons. First, like the above breakfast-skipping paper, the study employs a per-person, intervention-style design, looking at the very same people before and after a change in daily meal schedule (and controlling for some of the genetic and environmental differences that plague many population-level studies in this field).

But, importantly, unlike the breakfast-skipping study, participants were not selected for being obese. Thus, the Ramadan fasters were less likely than the obese breakfast-skippers to be trying other, non-study-related strategies to lose weight during the observation period (which fall into the category of terribly uncontrolled factors***).

Lastly, as the authors point out, because the Ramadan fasters were not skipping meals to lose weight, they might be more likely to indulge in a large meal at the end of each day’s fast. So, this paper may be the closest we can come to studying what happens when we skip Thanksgiving lunch to feast at dinnertime.

I’m inclined to believe that if the Ramadan fasters skipped breakfast and lunch for a whole month, potentially binged on late dinners, and did not gain massive amounts of weight (and even lost weight in many cases), we’re probably all OK skipping lunch just on Thursday. Any conclusions beyond that are just gravy.

References:

Schlundt DG, Hill JO, Sbrocco T, Pope-Cordle J, Sharp T. The role of breakfast in the treatment of obesity: a randomized clinical trial. Am J Clin Nutr. 1992 Mar;55(3):645-51.

Hajek P, Myers K, Dhanji AR, West O, McRobbie H. Weight change during and after Ramadan fasting. J Public Health (Oxf). 2011 Nov 13. [Epub ahead of print]

* WebMD cites this paper, which finds children who regularly eat breakfast tend to have higher metabolisms. (Research funded partly by the Florida Department of Citrus.)

** Interestingly, the authors conclude by recommending that people who normally skip breakfast and are hoping to lose weight should be encouraged to start eating it regularly. In contrast, they balk at recommending that regular breakfast eaters who lost weight by skipping breakfast should keep up the new habit (“Although subjects who initially ate breakfast lost more weight in the no-breakfast group, we do not believe that these individuals should be advised to stop eating breakfast…”)

*** Could it be that all the obese subjects wanted to lose weight, and those who implemented one lifestyle change (switching their breakfast habits, whether eating or skipping), were more inspired to make other changes to lose weight?





Gargantuan Gourds

27 10 2011

Helen Shen

by Helen Shen

Wake up, Linus, the Great Pumpkin is finally coming!

On Oct. 10, Leonardo Ureña of Napa won the Half Moon Bay giant pumpkin weigh-off with a 1704-pound behemoth — a new California record. Ureña is part of a blooming subculture of competitive pumpkin growers that are smashing pumpkin records left and right. The world record, set this year at 1818.5 pounds, has been beaten each year for three straight years.

The sport dates back to 1900, when Canadian grower William Warnock grew a 400-pound specimen, declared a world record at the Paris World’s Fair. Since then, record-breaking pumpkins have more than quadrupled in weight. The pumpkin enthusiast website Pumpkinnook.com’s once-exclusive “Club 1000” for pumpkins exceeding 1,000 pounds was updated in 2004 to become the “1100 Club.”

Giant pumpkins on display at the Stanford Shopping Center in Palo Alto. Can you spot the kid? (Photo by Helen Shen)

Jim Borchard Sr. of Borchard Farms in Salinas believes that much of this explosive growth can be traced to genetics. He’s been growing giant pumpkins for over 30 years and even won the Half Moon Bay contest several times “before the pumpkins started getting really big.”

According to Borchard, about 15 years ago, many growers started making super-giant varieties by cross-pollinating pumpkin plants by hand—using a cotton swab to transfer pollen from the male flower of one giant pumpkin to the female flower of another giant pumpkin.

Normally, each pumpkin plant grows several fruits on the same vine. Most modern competitive growers pinch off all the stems but one so that the nutrients from the roots are funneled to a single pumpkin. That one pumpkin could yield anywhere from a few hundred to a thousand seeds. Borchard belongs to the close-knit community of giant pumpkin growers who connect over the internet and swap their best seeds at seed meetings.

If all these pumpkin growers are tapping the same gene pool, I had to wonder whether winning one of these contests comes down to sheer luck. Borchard says luck certainly plays a part. Pumpkin splitting, which happens in normal pumpkins, too, occurs at devastatingly high rates in the giants. Depending on weather and geography, growers need to feed each plant about 500 gallons of water per week. “In August, these guys are taking on sometimes 40 pounds in one day,” he said, and the skin doesn’t always keep pace with the expansion.

Joel Holland holds the Washington state record with this pumpkin from 2009. (Photo by Mari Lou Holland)

Weather is another unpredictable factor. Joel Holland, a giant pumpkin grower from Sumner, Wash., says pumpkins typically fare better at northerly latitudes, but in the last 10 years, he’s seen the epicenter of winning pumpkins shift farther south. He’s noticed a general cooling trend that has helped produce ideal growing conditions in California, while making his own state a little too cold.

Bad weather and pumpkin explosions aside, serious growers can and do try to control other factors. Holland runs a thriving business that sells supplies, fertilizers, and instructional DVDs to fellow giant pumpkin growers.

One of his most popular products is a mycorrhizal soil treatment, which infects the pumpkin root system with a sort of helper fungus. The fungus lives inside the root and puts out “hyphae,” which are tiny rootlets that scout out valuable phosphorus in the soil and bring it back to the mothership. In exchange, the fungus feeds off sugars in the roots.

The contests are decided by weight, not size — although the two are usually correlated. When Holland trucked his own world record-breaking pumpkin from Washington to the Half Moon Bay festival in 1992, he took precautions to keep the fruit from losing water weight through its surface (a process called transpiration). Soaking the stem in water and filling his pickup truck bed with ice helped keep the pumpkin cool and hydrated on the three-day road trip. That pumpkin kept its weight and took first place at 827 pounds.

Is the sky the limit?

So what does one do with a pumpkin the size of a refrigerator? “You’re probably not going to want to make pie out of it,” said Borchard. Most contest pumpkins are not grown for tastiness, and some can have rinds up to 8 to 10 inches thick. Instead, Borchard saves some seeds for trading and planting, and uses the remaining pumpkin bits to feed his cattle and sheep through the winter. Many giant pumpkins are also purchased by businesses for holiday displays.

If there’s any limit to the size these pumpkins can reach, recent data suggests we may still be a ways off. My own data crunching revealed an approximately linear increase in world record pumpkin weights over the past three decades.

“People used to talk like we wouldn’t ever break 1,000,” said Holland. “I’m sure there will be a 1-ton pumpkin within the next 10 years.”