Currently browsing posts about: Research

May 24 2012

POM fights back with out-of-context ads

POM Wonderful has a full-page ad in today’s New York Times (how much do these things cost?) titled “FTC v. POM: You be the judge.”  The ad includes selected quotes from the judge’s decision (see yesterday’s post) and refers readers to its wonderfully named website, pomtruth.com, where you can see the quotes and the ads for yourself.

I couldn’t help doing some checking.

The POM ad quotes from Chief Administrative Law Judge’s decision:

Competent and reliable scientific evidence supports the conclusion that the consumption of pomegranate juice and pomegranate extract supports prostate health, including by prolonging PSA doubling time in men with rising PSA after primary treatment for prostate cancer (page 282).

I turned immediately to page 282.  The sentence before the one quoted would seem to support it:

The basic research, the Pantuck Study, and the Carducci Study, relied on by Respondents [POM Wonderful], support the conclusion that pomegranate juice has a beneficial effect on prostate health.

But what follows the quotation makes it clear that although the research claims to support the effect, it really doesn’t.  Here’s what immediately follows the quotation in the same paragraph:

However, the greater weight of the persuasive expert testimony shows that the evidence relied upon by Respondents is not adequate to substantiate claims that the POM Products treat, prevent, or reduce the risk of prostate cancer or that they are clinically proven to do do so.  Indeed, the authors of the Pantuck Study and the Carducci study each testified that their study did not conclude that POM juice treats, prevents, or reduces the risk of prostate cancer.  And, as Respondents’ expert conceded, no clinical studies, research and/or trials show definitely that the POM Products treat, prevent, or reduce the risk of prostate cancer.

I will just do one more of the quotes.  The ad says:

Competent and reliable scientific evidence shows that pomegranate juice provides a benefit to promoting erectile health and erectile function (page 198).

This is indeed on page 198 but is followed immediately by:

There is insufficient competent and reliable scientific evidence to show that pomegranate juice prevents or reduces the risk of erectile dysfunction or has been clinically proven to do so…There is insufficient competent and reliable scientific evidence to show that pomegranate juice treats erectile dysfunction in a clinical sense or has been clinically proven to do so.

Because these statements are attributed to the same expert witnesses, this must mean that while some studies show benefits, the experts do not believe that these studies (many of them sponsored by POM) are scientifically credible.

Pomegranate juice is a juice.  Fruit juices are healthy and especially delicious when fresh.  I happen to like the taste of pomegranate juice.

But does it have any special health benefits as compared to orange, grapefruit, grape, or any other fruit juice?

Would any fruit juice be likely to prevent heart disease or prostate problems on its own?

Despite POM’s out-of-context advertisement, the Administrative Law Judge did not think so, and neither do I.

Addition: I’m indebted to FoodNavigator.com for noticing some of the other ads.

The caption reads: “Natural Fruit Product with Health Promoting Characteristics–FTC Judge.”

May 23 2012

The FTC vs. POM Wonderful: the latest round

I’ve been following the legal battles between the Federal Trade Commission (FTC) and the makers of POM juice and other pomegranate juice products with avid interest, mainly because they deal with the credibility of sponsored scientific research.

This week, an administrative law judge ruled that POM violated federal law when it deceptively advertised  its products as able to “treat, prevent, or reduce the risk of heart disease, prostate cancer, and erectile dysfunction.”

The judge ruled that reasonable consumers would interpret the ads as making such claims but that the company had not produced convincing evidence to support them.

The judge’s decision makes entertaining reading for someone like me who enjoys debates about whether sponsorship of scientific studies influences results and interpretation—as evidence shows they most definitely do.

POM has invested more than $35 million in research to prove that pomegranate juice has health benefits.  It has sponsored about 100 studies at 44 different institutions.  At least 70 of these studies were published in peer-reviewed journals.

It is not difficult to design research studies to give sponsors the answers they want and to make sure they are conducted well.  POM is getting the best research that money can buy.

One such study, of the effects of drinking pomegranate juice on myocardial perfusion (MP, blood flow to the heart), was conducted by Dr. Dean Ornish, who runs a preventive medicine institute in California (the quotes come from pages 268-269 of the decision).

The Ornish MP study was originally designed to last 12 months, with measurements at baseline, 3 months, and 12 months.  [The FTC] charges that the study was cut short when the three-month data came in favorably and Dr. Ornish faced cost overruns.

Dr. [Frank] Sacks [expert witness for the FTC] opined that the shortened study period and failure to report the planned duration are inconsistent with widely accepted standards for conduct of clinical trials and undermine any confidence in the findings.

Dr. Ornish testified that the Ornish MP Study was terminated after three months only because the Resnicks did not provide the funding that they had previously committed to this study….[he said the study]constitutes credible and reliable science showing that pomegranate juice lessens the risk of cardiovascular problems.

The judge found evidence on this study and many others conflicting.  He ruled that this level of disagreement about the quality of the research means that the scientific evidence is not good enough to substantiate the claims.

I was interviewed for a story in Business Week about this decision.

This makes it clear why everyone should be suspicious of the results of sponsored studies…POM-sponsored studies produce results favorable to POM.

POM’s owners have their own spin on the decision.

It says the ALJ’s ruling affirms the scientific validity behind the general health benefits of pomegranates and “completely exonerates” POM regarding its claims in broadcast or print interviews.

Let’s be clear what’s at stake here.  According to the decision document, the owners of POM control 18,000 acres of pomegranate orchards.

From September 2002 through November 2010, sales of POM juice alone totaled nearly $248 million (the supplements and other products add more).

The owners must believe that nobody will buy pomegranate juice and supplements for any reason other than health benefits.

Health claims are about marketing, not health.

Let’s hope the FTC can make the decision stick.

Nov 11 2011

Oh no! USDA cutting back on research.

A couple of days ago, William Neuman wrote about an announcement by the USDA’s statistical research unit that under pressures to cut budget, it would eliminate or cut back on its ongoing research reports.

This is alarming.

As USDA explained:

The decision to eliminate or reduce these reports was not made lightly, but it was nevertheless necessary, given the funding situation. Because of the timing of the agency’s survey work during the coming year, these decisions are necessary now.

The affected reports include these, among others:

  • Annual Reports on Farm Numbers, Land in Farms and Livestock Operations – Eliminate
  • Catfish and Trout Reports – Eliminate all
  • Annual Floriculture Report – Eliminate
  • Chemical Use Reports – Reduce frequency of commodity coverage
  • Annual Bee and Honey Report – Eliminate
  • Fruit and Vegetable in-season forecast and estimates– Reduce from monthly and quarterly to annual report
  • Nursery Report – Eliminate

This decision, Neuman reports, “reflects a cold-blooded assessment of the economic usefulness”—translation: lack of political clout in the affected industry—of the 500 or so reports issued by the National Agriculture Statistics Service each year.  The reports will still be issued on the big commodities: corn, soybeans, cattle, and pigs, for example.

Why do I find this alarming?  If these reports can be eliminated, so can the ones that I personally care about and depend on for my research.

I am particularly worried about the invaluable data produced by USDA’s Economic Research Service on the composition of foods, their availability (production less exports plus imports), and per capita nutrient availability in the American diet.

I have plenty of reason to be worried.

For decades, USDA has converted information about food availability to nutrient availability in a continuous series dating back to 1909.  This is the data set I use to explain how calories in the food supply have increased to today’s 3,900 per person per day from 3200 in 1980—an increase of 700 calories per day exactly in parallel with rising rates of obesity.

USDA stopped this series in 2006.

I wrote USDA to ask whether more recent data were available.  Here is the response in its entirety:

Because of other project priorities the Food Supply project has been curtailed.  There are programming issues to which we haven’t been able to devote available resources.

Neuman quoted a former USDA official who argues that pressures to continue the statistical reports are an example of

how hard it was to eliminate a government program, no matter how small the constituency….These congressmen up on the Hill say, “$50,000 is not much, let’s give it to them.”   [The reports apparently cost about $50,000 to produce]

I have a different reaction.  Isn’t it a responsibility of government to produce research that nobody else has the resources to produce?   This argument reminds me of similar ones I hear that if a book hasn’t been taken out of a library in ten years, the library ought to dump it.

This is short-sighted.

Yes, $50,000 seems like a lot of money to you and me, but it is peanuts in comparison to the billions the USDA spends every year on support payments to people who aren’t even farmers.

Hence: alarming.

Oct 13 2011

Alas, vitamin supplements

Two studies released this week provide additional evidence that vitamin supplements are potentially harmful and, at the very least, do no good.

This depressing news comes from the Iowa Women’s Health Study.  Older women in the study who took supplements ranging from multivitamins to high doses of single nutrients had a greater risk of dying than those who did not.

Equally depressing are the results of a trial of high-dose vitamin E and selenium versus prostate cancer.  It found higher rates of the cancer among men taking vitamin E (selenium was somewhat protective).   In this trial, it was so obvious that the supplements did not protect against prostate cancer that the investigators ended it before its scheduled date of completion.

USA Today interviewed me and Dr. Jeffrey Blumberg (Tufts University) about our interpretations of these trials.

I think that the main conclusion to be drawn from this research is that supplements do not make healthy people healthier.   They may not cause harm at high doses, but they appear not to do good.

I don’t take them and I don’t recommend them—except to people who have diagnosed nutrient deficiencies or other problems handling nutrients.

Dr. Blumberg, in contrast, thinks multivitamins constitute a useful nutrition insurance policy and everybody should be taking them.

Supplements are a good example of how scientists can interpret research in different ways, depending on point of view.  I illustrate this point in Food Politics in a table in which I compare what I call “belief-based” (for lack of a better term) and “science-based” approaches to deciding whether supplements are needed, effective, or safe (see table 29, page 232).

For example, on the need for supplements, a belief-based approach rests on:

  • Diets do not always follow dietary recommendations.
  • Foods grown on depleted soils lack essential nutrients.
  • Pollution and stressful living conditions increase nutrient requirements.
  • Cooking destroys essential nutrients.
  • Nutrient-related physiological functions decline with age.

A science-based approach considers:

  • Food is sufficient to meet nutrient needs.
  • Foods provide nutrients and other valuable substances not present in supplements.
  • People who take supplements are better educated and wealthier: they are healthier whether or not they take supplements.

The statements in both approaches are true.

This is why point of view is such an important consideration in interpretation of nutrition research.

Aug 23 2011

New study: healthy diets produce health benefits

The latest issue of JAMA has a paper on a “portfolio” of dietary means to reduce blood cholesterol levels.

The paper is likely to get lots of press because it concludes that consuming the “portfolio”—a combination of plant sterols, soy protein, viscous fibers, and nuts—does a better job of lowering LDL-cholesterol (the “bad” kind) than does dietary advice to reduce saturated fat.

The paper is unusually difficult to read  (see the Abstract, for example).  But besides that, I interpret the study in part as a drug trial.

One look at the Abstract and I immediately suspected that this study must have been sponsored by a maker of plant sterol margarines.

Bingo!

Plant sterols are well established to reduce blood cholesterol levels.  Unilever, which makes Take Control margarines, is one of the sponsors.

As I interpret it, the study shows:

  • Advising people who weigh an average of 76 kg (167 pounds) to consume a healthy diet doesn’t work.  Study subjects did not change their diets by much during the six months of the trial.  No news here.
  • Advising people to add things to their diets has a better chance of succeeding than advising taking things away (like saturated fat).
  • All of the portfolio items have been established to lower blood cholesterol in clinical trials, although the evidence for soy protein seems a bit iffy these days.
  • The study does not distinguish between the relative effects of soy protein, fiber, or cholesterol lowering margarines. If soy is eliminated, that leaves fiber and margarines. I’m guessing the margarines were the critical factor. Hence: a partial drug trial.

And because my book on calories is coming out next March, I must point out that the study groups reported losing  losing small amounts of weight, which means they must also have reduced their calorie intake.  Weight loss alone should help with blood cholesterol.

The take-home message: if you really do substitute nuts, sources of fiber, and healthy foods for whatever less healthful foods you used to eat, you ought to get some health benefit, with or without plant sterol margarines.

QED: Healthy diets produce health benefits.

It’s always nice to see that confirmed.

 

 

Aug 8 2011

It’s time for some Q and A’s

I’ve just turned in the copy-edited manuscript of Why Calories Count: From Science to Politics (pub date March 2012) and now have time to catch up on some questions:

Q. I was recently given to read a book titled “The China Study” which is based on research conducted in 1970′s in China by Dr. Colin Campbell. His main conclusion is that eating dairy and meat causes cancer. His resolution is that a plant-based diet (i.e. vegan) is the (only?) healthy diet for humans. This book has made strong enough of a point to convince several of my friends to “convert” to a vegan diet in order to save their health. Could you share some comments on the validity of the research and conclusions this book presents with regards to detrimental effects of dairy and meat on human health?

A. Campbell makes a forceful argument based on his interpretation of the research and on case studies of people whose diseases resolved when they became vegans. And yes I’ve seen Dr. Campbell’s new movie, Forks over Knives. The first half is a terrific introduction to how the current food environment promotes unhealthy eating.  The second half promotes Dr. Campbell’s ideas about the hazards of meat and dairy foods.

Whether you agree with these ideas or not, the film is well done and worth a look.

Some scientists, however, interpret the research as demonstrating that people are healthier when they eat dairy foods.  For example, the enormous consensus report on diet and cancer risk from the American Institute for Cancer Research and the World Cancer Research Fund concluded in 2007 that eating lots of red meat and processed meat is convincingly associated with an increased risk of colorectal cancer (but no others).

On the other hand, they found dairy foods to be associated with a decrease in the risk of colorectal cancer.  They found limited and less convincing evidence that dairy foods might decrease the risk of bladder cancer but increase the risk of prostate cancer.

How to make sense of this?  These are two food groups in the diets of people who consume many kinds of foods and who do many things that might increase or decrease cancer risk.  Given this complexity, one food or food group seems unlikely to have that much influence on cancer when considered in the context of everything else people eat and do.

Nutrition research, as I am fond of saying, is difficult to do and requires interpretation. Intelligent people can interpret the studies differently depending on their point of view.

The new Dietary Guidelines say to cut down on saturated fats. Those are most plentiful in meat and dairy foods (plant foods have them, but in smaller amounts). Pretty much everyone agrees that plant-based diets promote health/  But whether they have to be 100% plant-based is highly debatable.

The new USDA MyPlate food guide suggests piling plant foods—fruit, vegetables, and grains—on 75% of your plate so the argument is really about what goes on the remaining 25%, what USDA calls the  “Protein” section. You can put beans in that quarter if you don’t want to eat red meat, poultry, or fish.

Q. I’d love to hear your take on the recent walnut flap [accusations that the FDA now considers walnuts to be drugs].  I suspect walnuts got caught with such offenders as Pom, Froot Loops, and Juicy-Juice, but I’d love to find out what the FDA actually said about this. For some odd reason I don’t believe the article is presenting the whole truth.

A. This is a health claims issue. The FDA is not saying walnuts are drugs. It is saying that Diamond Walnut is claiming walnuts as drugs on package labels. How so?

The labels say the omega-3 fatty acids in walnuts may help lower cholesterol; protect against heart disease, stroke and some cancers (e.g. breast cancer); inhibit tumor growth; ease arthritis and other inflammatory diseases; and even fight depression and other mental illnesses. These are disease claims for which the FDA requires scientific substantiation.

The company’s petition did not provide that substantiation so the FDA issued a warning letter. In general, you should be skeptical any time you see a nutritional factor advertised for its ability to prevent or treat such a broad range of problems.

Q. A question about sugar and how it is counted: My books say: 4 g = 1 teaspoon = 15 calories. My Illy Caffe says 10 g of sugar, but 50 calories. Ingredients: coffee, sugar, potassium bicarbonate, potassium citrate. If the drink is 50 calories, shouldn’t it say 12 g or more for the sugar listing?

A. Sugar should be the only ingredient that has calories in this coffee but I’ve seen calorie lists that say 5 calories per gram for sugars. Food companies have some leeway in the way they compute calories. Illy may be using a method that gives 5 rather than 4. But the difference between 40 and 50 is hardly measurable and I wouldn’t worry about amounts this small, annoying as imprecise figures may seem.

Jul 15 2011

Interview with Scientific American on the complexities of salt science

I complained to Scientific American about one of its blog posts about salt, which I viewed as rather one-sided.  The result was a conversation with Michael Moyer that ended up in the form of a Q and A.  I did not have a chance to review it before it was posted, so please see addendum at the end). 

The Salt Wars Rage On: A Chat with Nutrition Professor Marion Nestle

A researcher explains why there may never be a good study on whether excess dietary salt causes hypertension and heart disease

By Michael Moyer | Thursday, July 14, 2011

 Is salt bad for us? In just the past few months researchers have published seemingly contradictory studies showing that excess sodium in the diet leads to heart disease, reduces your blood pressure, or has no effect at all. We called Scientific American advisory board member Marion Nestle, a professor of Nutrition, Food Studies, and Public Health at New York University and the author of Food Politics, to help parse the latest thinking regarding salt and heart health.leads to heart disease, reduces your blood pressure, or has no effect at all. We called Scientific American advisory board member Marion Nestle, a professor of Nutrition, Food Studies, and Public Health at New York University and the author of Food Politics, to help parse the latest thinking regarding salt and heart health.

[An edited transcript of the interview follows.]

I understand this area is controversial.

Hugely.

Could you take us through some of the controversy?

If you talk to any kidney specialist or anybody working on hypertension they will tell you that the first thing they do is try to lower the amount of salt their patients are eating because it helps with blood pressure control. But if you do a clinical trial where you try to put large amounts of people on a low-salt diet, you just don’t see much difference between the people who say they eat a lot of salt and the people who say they don’t eat a lot of salt. In clinical trials the relationship doesn’t show up.

Why not?

Two reasons: One that it’s impossible to put a population of people on a low-salt diet. Roughly 80 percent of the salt in the American food supply is in foods before people eat them—either in processed food or in restaurant food. Because so much salt is added to the food supply and because so many people eat out, it’s impossible to find a population of people who are eating a low-salt diet. They basically don’t exist.

In the one comparative epidemiological study they did some years ago—the Intersalt study—they managed to find two populations of people in remote areas of the jungle someplace who weren’t eating a lot of processed foods and who weren’t eating in restaurants. They were on a low-salt diet, and they never developed hypertension.

So in that trial did they put one group on a high-salt diet and put one on a low-salt diet?

No, no, no. It wasn’t a comparative trial. They just looked at the amount of salt that populations were eating and the amount of hypertension that they had. Only in these two populations were there very low rates of hypertension. With everybody else the salt intake was so high that they couldn’t see any difference between high and higher.

So except for people living in the jungle somewhere, there aren’t any populations on Earth that are eating a low amount of salt?

Not anymore. Maybe we used to be, but not anymore. We have a global food supply, so it’s impossible to do a really careful study.

What’s the other issue?

Not everybody responds to a low-salt diet. There’s a proportion of people in the population who are sensitive to salt—if you lower their intake of salt, then their blood pressure goes down. There’s another (probably larger) percentage of the population who doesn’t respond. They are people who can eat as much salt as they want and still their blood pressure is low.

So you have this curious anomaly where whenever you do a clinical trial you get these complicated, difficult-to-interpret results that don’t show much of an effect. But everybody who works with patients who have hypertension think they do better [on a low-salt diet]. And every committee, body, and group that has ever in my lifetime considered whether salt has anything to do with hypertension says, “yes,” and has recommended salt reduction as a public health measure. That’s the curious situation that we are in.

There’s one other wrinkle and has to do with people’s taste for salt. Campbell’s soup, for example, just announced yesterday that can’t sell low-sodium soups and so they’re adding salt back. And part of the reason they can’t sell it is that if you’re on a high-salt diet, food that isn’t salty tastes terrible to you. And if you’re on a low-salt diet it takes three to six weeks to get accustomed to being on a low-salt diet and then everything you eat tastes salty. And so the more salt in the food supply the more salt people need to bring the flavor you associate with salt. That complicates things, too.

So from a public health standpoint, if you want to deal with the percentage of the population that seems to be extremely responsive to a low-salt diet what you want to do is get the sodium level in the food supply as low as you can. And that makes the people who sell salty food go nuts. And it makes the people who like salty foods go nuts. They think the food tastes bland. And so there are different stakeholders in this system who have very different views and that accounts for the level of passion, I think, in a situation where the science is murky.

Couldn’t you just make the case that people should eat fewer processed foods?

Well what about restaurants? I’m a food professional. I eat out professionally.

Well chefs need to make their food taste good—otherwise people won’t go to their restaurant.

No, they need to make the food taste good by their standard. And chefs, because they’re dealing with a great deal of salt in their food, tend to raise the sodium level. It just goes up and up and up and up. As they get more used to a certain level of salt taste it no longer tastes salty to them and they have to raise it. So the pressure is to raise the salt in the food supply. And reducing it is very difficult.

So you advocate regulation to limit the amount of salt in restaurants?

Yeah, I do. Certainly for processed food. I think everybody would be healthier if they ate less salt. You can always add salt if you don’t think it’s salty enough, whereas I can’t take it away if it’s presented to me. And that’s the dilemma. And the ferocity of the arguments gets into the whole question of personal responsibility and “nanny state” and all of these other enormous debates that really don’t get at the public health question. And the public health question is hard to resolve because the science is really difficult to do.

Couldn’t you imagine a study where you look at sodium levels in urine, which is a direct measure of salt intake, and correlate that with hypertension?

Yeah they’ve done that, and they don’t see any difference in hypertension rates. The reason is that the baseline [level of salt intake] is so high that it doesn’t make any difference. To suggest that people get down to 1,500 mg a day—the recommended level—would be really really hard, and that level may be too high. And it’s unclear that that’s the right level because you can’t do a really decent dose response, and because people vary so much.

Will there ever be a good study?

I don’t know!

Is it possible that this represents the limits of science? It’s black hole event horizons and salt intake?

It may be. It very well may be. Or the science that we have is completely adequate and we already have the answer. I was once at a sodium meeting at which there were a bunch of statisticians. And I left with the statisticians and they said that “anyone who thinks that salt has anything to do with hypertension is delusional.” And that was on the basis on the clinical trials that show so little. And yet every single committee that has dealt with this question says, “We really need to lower the sodium in the food supply.” Now either every single committee that has ever dealt with this issue is delusional, which I find hard to believe—I mean they can’t all be making this up—there must be a clinical or rational basis for the unanimity of these decisions.

But that’s the thing—these committees should be able to point to the evidence that supports their recommendations. But they seem to rely so much on anecdote and individual experience.

Or on some clinical trials that everybody argues about. Everybody argues about every clinical trial no matter what the conclusion. So I find the whole thing completely fascinating. I don’t think anybody can underestimate the difficulty of doing nutritional research. Because people aren’t eating just sodium. They’re eating sodium in food. And it may be that high-sodium diets are a marker for some other things in the food supply or it may be that the physiological differences are so profound that you just don’t get clean results. That human variation is so great. I don’t know the answer to that. I just know it works for me. That’s anecdotal. With an “n” of one.

Addendum

If I had been given the opportunity to review this before it was posted, I would have edited it carefully.  Yes, this is the way I talk but I don’t think what I said reads clearly in print.  In reading over this piece, I think it may give the wrong impression of my views on how expert committees decide on salt recommendations.  The piece may give the impression that committees make dietary recommendations basied on anecdotal evidence, not science.  That’s not true.  They base their recommendations on their interpretation of the experimental and clinical evidence, including that from clinical trials.

For example, the Advisory Committee for the 2010 Dietary Guidelines concluded that “a strong body of evidence has documented that in adults, as sodium intake decreases, so does blood pressure.”  Was this committee delusional in viewing the evidence as strong?  I don’t think so.

Mar 6 2011

The perils of food and nutrition research

I write a monthly (first Sunday) Food Matters column for the San Francisco Chronicle.  Today’s is about the difficulties of doing nutrition research.  The Chronicle headline writer titled it, “Be skeptical of food studies.”  Oops.

I’m not skeptical about Food Studies—the capitalized field of study—at all.  My NYU department started undergraduate, master’s, and doctoral programs in Food Studies in 1996 and they have flourished ever since.

The column is about small-letter food studies, meaning nutrition and food research studies:

Q: You were quoted saying that you didn’t believe newspaper reports linking diet sodas to an increased risk of stroke and heart disease. How do you decide whether research is good or bad?

A: This one was easy. I didn’t think it made sense. Mind you, I’m no fan of diet sodas. They violate my rule never to eat anything artificial. And I don’t like the taste of artificial sweeteners.

Whenever a study comes out claiming harm – or benefits – from eating a single food or ingredient, I get skeptical. That’s why I also questioned these recent study results: high-fructose corn syrup (HFCS) makes rats gain weight faster than sucrose (table sugar); zinc supplements prevent symptoms of the common cold; and pomegranate juice has greater health benefits than any other kind of fruit.

When I read about single-factor studies, I want to know three things: Is the result biologically plausible? Did the study control for other dietary, behavioral or lifestyle factors that could have influenced the result? And who sponsored it?

Plausibility: The diet soda study used a self-reported questionnaire to find out how often people reported drinking diet sodas. Nine years later, people who reported habitually drinking diet sodas had a 60 percent higher rate of stroke and heart attacks. The rate was somewhat lower when controlled for age, sex, race, smoking, exercise, alcohol, daily calories and metabolic syndrome.

Leaving aside the unreliability of self-reported dietary intake, the study raises a more important question. Was it designed to investigate the link between diet sodas and stroke or was this just an accidental finding? The questionnaire undoubtedly asked hundreds of questions about diet and other matters. Just by chance, some of them could be giving results that look meaningful. And the increase in stroke risk seems surprisingly high for something not previously known to be a stroke risk factor.

Mostly, I can’t think of a biological reason why diet sodas might lead to cardiovascular disease unless they are an indicator for some other stroke risk factor such as obesity, high blood pressure or binge drinking. It would take a study designed to test this idea specifically – and a good biological explanation – to convince me that diet sodas cause strokes.

The plausibility issue also rises in the HFCS study. Again, I’m not a fan of HFCS – we would all be healthier if we ate less sugar – but from a biochemical standpoint, HFCS and table sugar are pretty much the same. They have similar amounts of glucose and fructose, are digested as quickly and are metabolized the same way. Even the average amounts consumed are about the same. That soda companies are replacing HFCS with sucrose is strictly about marketing, not health.

Controls: The zinc-and-colds study was a comprehensive review (a “meta-analysis”) of previous studies done since the first one in 1984. Eleven studies have showed some benefit; seven have not. All of them were placebo controlled, double-blind. This meant that half the participants were given a dummy pill, and neither participants nor investigators were supposed to know who was taking what.

But in some studies, the zinc takers complained about the taste of the pills, hinting that they knew what they were.

I’ve heard this before. In the early 1970s, National Institutes of Health investigators did a study of vitamin C and the common cold. They got about 300 NIH employees to take either vitamin C or a placebo, double-blind. The tantalizing result: People taking vitamin C reported fewer colds and milder symptoms than people taking placebos.

Alas, many participants withdrew from the study before it ended. When asked why, they admitted tasting the pills. The investigators reanalyzed the results. Bingo! No matter what pill the participants actually took, those who thought they were taking vitamin C reported fewer colds and milder symptoms.

If the studies were not really blinded, the zinc results are questionable. I have no doubt that many people feel better when they take zinc supplements, but I’m not sure whether that’s because of something zinc really does or just its placebo effect.

Sponsorship: Vested interests influence the design and interpretation of studies. The best-designed studies control for factors that might influence results. Even so, their results require interpretation. Interpretation requires interpreters. Interpreters bring their own biases into the interpretation.

I mention pomegranate juice because one of its major producers sponsors studies to hype its benefits. Yes, pomegranates are delicious, but antioxidant powerhouses? So are most fruits. Pomegranates may have high antioxidant activity, but compared with what? Its maker does not say. Sponsored research is also about marketing, not health.

Nutrition research is hard to do, which makes study design and interpretation particularly challenging. Nutrition is a thinking person’s field, requiring careful analysis at every step. When you hear a result that sounds too good to be true, it usually is.