Category Archives: Diet

Consuming Peanuts in Infancy Can Help Prevent Peanut Allergies

Photo: Wikimedia / public domain
Photo: Wikimedia / public domain

Food allergies are commonly misunderstood, so please bear with me while I first explain what food allergies are and are not. Various foods can cause all sorts of unpleasant effects. Most of these are not allergies. Allergies are only reactions caused by a specific antibody (called IgE) that results in hives, trouble breathing, or a life-threatening condition called anaphylaxis. So, if yogurt gives you diarrhea, that’s not an allergy. It might be lactose intolerance. If coffee gives you palpitations, you’re not allergic to coffee; you’re having a side-effect from the caffeine. Ditto chocolate worsening your heartburn; not an allergy.

Of all foods that cause allergic reactions, peanut allergies are the leading cause of anaphylaxis and death, and the prevalence of peanut allergies in the US has grown fivefold in the last 13 years, from 0.4% in 1997 to more than 2% in 2010. This increasing prevalence of a potentially life-threatening allergy has caused some schools to ban peanut products and has caused some airlines to stop offering peanuts in their snacks.

Believing that repeated exposure in infancy of allergy-causing foods leads to allergies, health officials in the UK in 1998 and in the US in 2000 published guidelines recommending the exclusion of foods likely to cause allergies from the diets of infants at high risk of developing allergies. But subsequent studies failed to show that elimination prevented the development of allergies, so the recommendations were withdrawn in 2008. Since then, pediatricians have had no solid evidence on which to base recommendations, until now.

A study in the UK published this week in the New England Journal of Medicine (NEJM) enrolled 640 infants between the ages of 4 and 11 months who were considered to be at high risk for peanut allergy because they had severe eczema or egg allergies, or both. They were all given a skin-prick test to check for peanut sensitivity. The infants that had a severe reaction to the skin-prick test were excluded from the study. Infants who had no reaction or a mild reaction were enrolled and were randomized to two groups.

The parents of children in one group were told that their children should avoid peanut products. The parents of children in the second group were instructed to give their children at least two grams of peanut protein three times a week. (Their first exposure to peanut protein was done under medical supervision.)

The peanut source given to the infants in the study was Bamba, an extremely popular Israeli children’s snack made from puffed corn and peanut butter. If you’ve spent any time in Israel around kids you’ve seen Bamba. Hilariously, the authors admit that “it was not possible to administer a placebo for Bamba because of financial and logistic constraints.” I can imagine the researchers desperately trying to figure out how to make something that looked and tasted like Bamba but without peanuts, and then giving up when they realized that that this would be more expensive and take longer than the rest of the study. The authors tell us that smooth peanut butter was supplied for those infants who didn’t like Bamba, but intensive psychiatric testing would have been more appropriate, because Bamba is delicious.

The children were followed until they were five years old and then given a supervised oral challenge of peanut protein to test them for allergies.

The results were quite dramatic. Among the children who initially had no reaction to the peanut sensitivity skin-prick test, 13.7% (about 1 in 7) of the children who avoided peanuts became allergic, compared to 1.9% (about 1 in 50) of children who consumed peanuts. That means that for every 8 children who consumed peanuts one fewer child developed a peanut allergy.

The results in children who initially had a mild reaction to the skin-prick test were even more impressive. These children were at much higher risk of becoming allergic since their mild skin test result suggests that their immune system had already been partially sensitized to peanut protein. 35.3% (about 1 in 3) of the children who avoided peanuts became allergic, compared to 10.6% (about 1 in 10) of the children who consumed peanuts. That means that for every 4 children with a mildly positive skin test who consumed peanuts, one fewer child became allergic.

Recommendations will likely be updated to account for these findings. First, infants with no eczema or family history of peanut allergies are at low risk of developing allergies and should start eating peanut products as soon as they start eating solid foods. (Don’t feed whole peanuts to infants. They’re a choking hazard. Anyway, Bamba tastes better and now might be one of the most evidence-based snacks.) Infants who are at high risk for peanut allergy because of eczema, an egg allergy, or a family history of peanut allergy should have a skin test to check for sensitivity to peanut. Those who have a negative test can proceed with Bambafication. Those who have a positive test should have their first exposure to peanut product under the supervision of an allergist.

Learn more:

Exposing infants to peanuts causes big reduction in peanut allergy, study shows (The Washington Post)
Feeding Infants Peanut Products Could Prevent Allergies, Study Suggests (Well, New York Times health blog)
About-Face on Preventing Peanut Allergies (Wall Street Journal)
The LEAP Trial (NEJM Quick Take video)
Randomized Trial of Peanut Consumption in Infants at Risk for Peanut Allergy (NEJM article)
Preventing Peanut Allergy through Early Consumption — Ready for Prime Time? (NEJM editorial)

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Thank You Very Much

Image credit: Jim/Wikimedia, Creative Commons license
Image credit: Jim/Wikimedia, Creative Commons license

Tomorrow I expect to sit with my extended family at my sister’s house and consume copious quantities of yummy food. After that, my and her kids will destroy her house in cute ways that will delight the grandparents. Good times.

That in itself is a reason for gratitude. Given the fact that most humans who have ever lived spent every winter nearly starving to death, the abundance of food and material comfort at our disposal is nothing short of miraculous. And the fact that we’re all healthy enough to get together to celebrate is a true blessing.

But I would be remiss if I headed off to celebrate without thanking you.

To my readers: I’m grateful for all your feedback, for pointing me to interesting stories, and for forwarding my posts on social media. It’s largely because of you that my posts have appeared on KevinMD, American College of Physicians Internist blog, The Jewish Journal, and other publications. I know my blogging has been very intermittent this year. Patient care will always come first, but I promise to keep trying to inform you.

To my patients: I’m so thankful to you for the trust you place in me. Some of you have had serious illnesses this year and it’s been an honor and a privilege to guide you through such trying times. It’s a blessing to simply make a living, but I have the double blessing of getting paid to do what I love. I owe that to all of you. And because so many of you mentioned me to your colleagues and loved ones, this year is my best so far. Thank you very much. I promise to do my best to keep you healthy.

As is my tradition, I hereby lift my patients’ dietary restrictions for one day. Of course, I can’t suspend the laws of biology. If you take your dietary indiscretion too far, I’ll probably hear about it from your local emergency department. I hope you are able to gather with loved ones and energetically attempt to enumerate your countless blessings.

Happy Thanksgiving!

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Eating Breakfast Neither Helps nor Hinders Weight Loss

Breakfast, entirely optional for weight loss Photo credit: Alisdair McDiarmid via Flickr, Creative Commons license
Breakfast, entirely optional for weight loss
Photo credit: Alisdair McDiarmid via Flickr, Creative Commons license

It’s nearly impossible for us not to believe that what we eat has a profound effect on our health. But what we know about the link between food and health is much less than what we believe. A study published this week provides a perfect example.

An overweight person trying to lose weight is likely to hear advice about the importance of eating breakfast. We have some reasons to guess that skipping breakfast might hamper weight loss efforts. Skipping breakfast should increase hunger which might cause overeating at lunch. Hunger can also trigger hormonal changes that make weight loss more difficult. There have even been some observational studies showing that people who eat breakfast are thinner than those who don’t. (See here for a quick primer on the difference between an observational study and a randomized study and why observational studies should be largely ignored.)

Of course in the past we had very good reasons to guess that heavier objects fall faster than lighter objects, that light travels faster going west than north, and that estrogen prevents heart attacks. These guesses were all proven false as soon as someone actually tested them.

In the study published this week, investigators enrolled about 300 overweight and obese adults and randomized them to three groups. One group in addition to receiving general weight loss advice was instructed to eat breakfast every day. The second group was instructed to skip breakfast every day. The third group received general nutrition advice that didn’t mention any advice about breakfast.

The groups were quite compliant with following their instructions. The group that was supposed to skip breakfast almost always did so, and the group that was supposed to eat breakfast almost always did so. The three groups lost equal amounts of weight. The senior investigator of the study, David Allison, summed it up well. “The field of obesity and weight loss is full of commonly held beliefs that have not been subjected to rigorous testing.”

There’s nothing wrong with educated guesses. They’re the seeds of discovery. But without testing we shouldn’t forget that they are not knowledge. We mistakenly keep guesses around for decades, grow comfortable with them, and forget that they’re untested. It seems that the field of nutrition is especially littered with these long-held assumptions. (The myth of the harms of saturated fats is another recent example.) I’m delighted that Dr. Allison is committed to either confirming or discarding them. I hope he gets some help.

Learn more:

Skipping Breakfast May Not Be Bad For Weight Loss After All (Forbes)
Eating breakfast may not matter for weight loss (CNN Health blog)
Passing on Breakfast OK for Weight Loss (Medpage Today)
The effectiveness of breakfast recommendations on weight loss: a randomized controlled trial (The American Journal of Clinical Nutrition)

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What We Don’t Know About Eating Fat

A hamburger patty is loaded with saturated fats and is delicious. Image credit: Jeff’s Gourmet Sausage Factory, from their Facebook page
A hamburger patty is loaded with saturated fats and is delicious.
Image credit: Jeff’s Gourmet Sausage Factory, from their Facebook page

Most humans have spent most of human history nearly starving to death. So it’s no surprise that we spend a lot of time thinking about food. And it’s no surprise that food has acquired cultural, social, and religious significance in almost every society. Because food is so important, and because it’s nearly impossible for us not to ascribe powerful effects to anything important to us, every society imbues special health properties to various foods.

From believing that some foods are aphrodisiacs to believing that some foods improve sleep or fertility or athleticism, superstitions about the effects of food on health are ubiquitous. But we are modern, rational creatures that would never subscribe to such claptrap. Right? Wrong. We also cling to our own mythology about the health effects of food but we dress up our ignorance in scientific words. We (correctly) sneer at anyone who asserts that ingesting powdered rhinoceros horn improves erectile function. After all, there’s no scientific reason to even believe such a thing, and the connection between a rhinoceros horn and erectile dysfunction is purely visual. That’s like eating a giraffe because you want to be taller.

But take the assertion that eating saturated fat increases the risk of heart disease. We all believe that. After all, saturated fat is a molecule. Molecules are very scientific, which means there are men in white lab coats somewhere with blinky machines proving that saturated fats are very very bad to eat. In fact, current cardiovascular guidelines from respected groups like the American Heart Association suggest low consumption of saturated fats and high consumption of polyunsaturated fats. And the American Heart Association would never recommend rhinoceros horn.

This week’s study is an important reminder that we know much less than we believe, but before we dive into it, allow me a paragraph to make sure we know what we’re talking about.

There are three families of energy containing molecules in food – fats, carbohydrates, and proteins. Fats are further subdivided into saturated fats and unsaturated fats. Saturated fats are typically found in dairy products and fatty meats and are typically solid at room temperature (like butter, lard, and beef fat). Unsaturated fats are found in vegetable oils and fish oils and are typically liquid at room temperature (like olive oil).

For decades we have been hearing and repeating to our patients that saturated fats are unhealthy for hearts and unsaturated fats are healthy. A meta-analysis (study of studies) published in the current issue of Annals of Internal Medicine attempted to review all the studies that have ever examined the link between saturated and unsaturated fats and cardiovascular health. What they found was underwhelming. There were 45 observational studies, the kind that I routinely criticize in my posts and urge readers to ignore. There were 27 randomized studies that looked at the effects of fatty acid supplementation on heart disease. All of them tested whether supplements of unsaturated fatty acids (like fish oil) helped prevent stroke and heart attacks. None of them tested whether supplements of saturated fatty acids (lard capsules!) increased cardiovascular risks.

The results were meh. The data as a whole showed no significant increase in risk from saturated fats, nor decrease in risk from unsaturated fats. The authors conclude

“[T]his analysis did not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats.”

Not surprisingly none of the experts quoted in the media coverage said the simple truth, which is that we have no idea if dietary fats affect health apart from the calories they contain. It would be nice to hear an expert declare “We have no clue about whether some fats are healthy or unhealthy” since that statement would be solidly supported by the evidence.

How did saturated fat’s bad reputation ever get started? I’m not sure. It’s conceivable some observational study that should have been ignored suggested that saturated fat was unhealthy. It’s also possible that saturated fat’s ignominy began because lard and butter look so much like the fat in a cholesterol plaque that blocks an artery. Olive oil is liquid. How could that block an artery? Maybe the whole idea was as simple-minded and as visual as the rhinoceros horn remedy.

Learn more:

Saturated Fat Is Back! (NPR)
Saturated fat ‘ISN’T bad for your heart’: Major study questions decades of dietary advice (Daily Mail Online)
Review questions effects of saturated fats on heart disease (Fox News)
Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis (Annals of Internal Medicine)
Even More Studies You Should Ignore (my last post about fish oil)

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The Blood Type Diet Remains on the Fiction Bookshelf

Photo credit: Wikimedia commonsIn 1996 a naturopath published “Eat Right 4 Your Type”, a diet book purporting that people with different blood types would benefit from different diets. There are a lot more people who want to lose weight than who want to exercise skepticism, so the book became a multi-million dollar success.

As an aside, the proliferation of myriad different diets on the market should make us suspect that none of them are very effective. For example, there were countless ineffective but widely used remedies for pneumonia before the discovery of penicillin. Afterwards, there was only one treatment.

I wrote in 2011 that the blood type diet had two very important flaws. The first is that it makes absolutely no sense physiologically. That is, there is absolutely no reason to suppose that blood types, which are proteins on the surfaces of our red blood cells, have anything to do with the way we burn calories or use micronutrients. This is not a fatal flaw. Just because something doesn’t mesh with our current understanding doesn’t mean it’s false. The effectiveness of this diet would be easy to show in a rigorous randomized trial, and if proven effective this would trump the first objection. That is the second flaw – that this diet was completely unproven. There was absolutely no evidence that people eating their blood-type-specified diet did any better than those eating a diet for some other blood type.

Now just because something is unproven doesn’t mean it’s not true, but that should be our assumption. Most things have nothing to do with most other things. Given any pair of things – the position of the planets and your romantic fate on Valentine’s Day, the last four digits of your social security number and the winning lottery ticket, your blood type and what you should eat –a scientist would (in the absence of evidence) assume the null hypothesis, that thing A is totally unrelated to thing B.

So it’s pretty safe to assume that something unproven is ineffective. And when that unproven thing would be easy to test and is a big money maker, we should be very suspicious that the people making the money would prefer to keep it untested.

So why is “Eat Right 4 Your Type” such a big success? As I suggested in my prior post, each of the diets it recommends for each blood type is quite sensible. Any diet that results in the consumption of fewer calories will result in weight loss. You could pick one of the four diets randomly and do pretty well.

The new chapter in this story is that last month investigators at the University of Toronto published a study in PLOS ONE testing the blood-type diet. I’ll spare you the details of the study, but it showed that people who followed most of the diets lost weight independently of whether they were following the diet suggested for their blood type or for some other blood type.

The study wasn’t randomized. It just looked at the diets that people were already eating. My regular readers know that I don’t give observational studies much weight. I would never recommend a new medication or surgery based on a non-randomized study (because I would cling to the null hypothesis). But given a diet that already had a lot going against it and no evidence for it, this is another suggestion that you should choose what you eat based on your belt size not your blood type.

Learn more:

Blood type diet not based in science, new study says (Today Health)
Blood Type Diet – Disproved (Neurologica Blog)
ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors (PLOS ONE article)
Eat Right for Your Belt Size, Not Your Blood Type (my post from 2011)

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The Last Nail in the Coffin for Multivitamins

pillsHow much money would the US auto industry be making if every car they sold never started? How much could video game console makers charge if their products didn’t play any games? Well, in 2010 the US dietary supplement industry sold $28 billion dollars in vitamins, minerals and other supplements that, as far as we can tell, benefited virtually no one.

The current issue of Annals of Internal Medicine published three studies examining the effects of multivitamins. This is not the first investigation of a mysterious unexplored field. Lots of studies have already shown that in well-nourished people living in the Western Hemisphere, multivitamins are not helpful. Think of this more as sweeping away any traces of doubt.

One study explored the effects of a high-dose vitamin and mineral supplement on heart disease. About 1,700 patients who had a heart attack in the past were randomized to the supplement or a placebo. They were followed for four years to measure their rates of recurrent cardiovascular events. There was no difference in the occurrence of these events between the group receiving the supplement and the group receiving placebo.

Another study examined the effects of a multivitamin on cognitive decline. About 6,000 male physicians aged 65 and older were randomized to a multivitamin or placebo and given a battery of five tests of cognition and memory over 12 years of follow up. The two groups did the same.

The third study was a review of prior studies of vitamin and mineral supplements for the prevention of cancer or cardiovascular disease. The study conclusion was negative. There is no reason to take vitamins or minerals for cancer or cardiovascular disease prevention. And the review highlighted the harms of some vitamins. β-carotene and vitamin A increase lung cancer risk in smokers, and vitamin E increases the risk of prostate cancer.

An editorial in the same journal issue crystalized our current knowledge.

In conclusion, β-carotene, vitamin E, and possibly high doses of vitamin A supplements are harmful. Other antioxidants, folic acid and B vitamins, and multivitamin and mineral supplements are ineffective for preventing mortality or morbidity due to major chronic diseases.

Their conclusion:

The message is simple: Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided.

There are specific patient populations who are especially vulnerable to vitamin malabsorption, such as those who have had intestinal surgery and patients on long-term acid suppressing medications. They may be recommended specific vitamin supplements. Women in their child-bearing years should take folic acid. And it’s possible that vitamin D in the elderly prevents falls. But apart from those narrow groups, well-nourished people don’t benefit from supplements. (I don’t take any vitamins or minerals.)

Perhaps the latest studies and the barrage of resulting media coverage will make a difference. Then maybe we could save some of that $28 billion and spend it to buy some skepticism.

Learn more:

Multivitamins Found to Have Little Benefit (Wall Street Journal)
How do Americans waste $28 billion a year? On vitamins, doctors say (Los Angeles Times)
The Case Against Multivitamins Grows Stronger (Shots, NPR’s health news)
Oral High-Dose Multivitamins and Minerals After Myocardial Infarction: A Randomized Trial (Annals of Internal Medicine article. Abstract available without subscription)
Long-Term Multivitamin Supplementation and Cognitive Function in Men: A Randomized Trial (Annals of Internal Medicine article. Abstract available without subscription)
Vitamin and Mineral Supplements in the Primary Prevention of Cardiovascular Disease and Cancer: An Updated Systematic Evidence Review for the U.S. Preventive Services Task Force (Annals of Internal Medicine. Available without subscription.)
Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements (Annals of Internal Medicine editorial. Subscription required.)
A Reminder to Dump Your Multivitamin (my post from 2011 reviewing the known effects of various vitamin supplements)

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Even More Studies You Should Ignore

Fish oil capsules. Image credit: Wikimedia Commons.
Fish oil capsules. Image credit: Wikimedia Commons.

Back when I was a medical student (in the Cretaceous Period) we were taught that someone once did a study comparing folic acid levels in the blood of cancer patients compared to the blood of healthy patients. The cancer patients had, on average, significantly lower folic acid levels. And the ones with the largest, fastest growing tumors tended to have the lowest folic acid levels. “Aha,” they thought. “Something about folic acid deficiency predisposes them to cancer. We should give folic acid to cancer patients.” Bad idea. A randomized trial showed that cancer patients given folic acid died sooner than those given placebo.

What happened? Low folic acid levels are a consequence, not a cause, of cancer. Folic acid is needed to synthesize DNA, and DNA synthesis is necessary for one cell to divide into two cells. So folic acid gets used up by rapidly dividing cells – like cancer cells. Giving cancer patient folic acid just gives their tumor a helping hand. (This roundabout insight led to medications that block folic acid metabolism which are used as chemotherapy to this day.)

The main lesson here is that correlation tells us almost nothing about causation. That means if A and B occur together, we say that they are correlated, but we have to be very careful not to assume that one causes the other. A might cause B, or B might cause A, or they may both be caused by some other factor that we’re not paying attention to. This is the cognitive error that the farmer makes when he notices that the daily number of deaths of his livestock correlates with sales of ice cream in the town’s ice cream parlor. He figures that some waste from the ice cream is contaminating his feed or water. He lobbies the legislature to ban ice cream sales around his farm. He doesn’t realize that the rise in ice cream sales and his livestock deaths are both caused by very hot days.

This week a study was published that encourages just such a mistake. It should be universally ignored, but a handful of patients have already emailed me about it, and it’s receiving a fair amount of confused media attention.

Before we look at the study, we need to learn a little about omega-3 polyunsaturated fatty acids. Omega-3 fatty acids are the predominant molecules in fish oil. They have been proven to lower triglycerides. They have gained popularity in the last few years, though the most recent trials (reviewed last year by The Medical Letter) have failed to show that they prevent stroke or heart attacks. There is certainly no convincing reason for the general population to be taking fish oil.

This week’s study, published in the Journal of the National Cancer Institute, compared blood levels of omega-3 fatty acids in patients with prostate cancer to those levels in healthy adults. Prostate cancer patients had higher levels of omega-3 fatty acids. Note that the study had nothing to do with fish oil supplements or diet. None of the study subjects were asked about supplements or how frequently they ate fish. The only comparison was blood levels of omega-3 fatty acids of people with prostate cancer to healthy people.

This should remind you of the ancient folic acid study.

The study authors conclude that this should make us worry about the risks of increasing omega-3 fatty acids in our diet, and some of the media coverage warns that fish oil supplements may increase the risk of prostate cancer, but the study proves no such thing. Other possibilities are that prostate cancer patients produce elevated levels of omega-3 fatty acids, or that some unknown metabolic defect both increases prostate cancer risk and elevates omega-3 fatty acid blood levels.

The only way to know for sure is to randomize lots of people to fish oil capsules or to placebo, follow them, and count the resultant prostate cancer. That study hasn’t been done, but that study would deserve our attention.

So am I saying that fish oil is safe and everyone should resume taking it? No. It has no proven benefits (except possibly for elevated triglycerides). That the connection to prostate cancer is unproven isn’t a reason to take it.

Who knows? Maybe after a randomized trial is done and the biological connection is meticulously worked out this might lead to a new prostate cancer test or treatment. Then medical students not yet born will learn about it as an example of the importance of not confusing correlation with causation.

Learn more:

Hold The Salmon: Omega-3 Fatty Acids Linked to Higher Risk of Cancer (Time)
Too Much Fish Oil Might Boost Prostate Cancer Risk, Study Says (US News)
Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial (Journal of the National Cancer Institute article, abstract available without subscription)
Fish Oil Supplements (The Medical Letter, by subscription only)

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Weight Loss Doesn’t Decrease Strokes and Heart Attacks in Overweight Diabetics

Photo credit: Wikimedia commonsDoctors spend a lot of time recommending diet and exercise for weight loss. If you’re my patient, unless you’re quite fit, you’ve probably heard me ask you to exercise more and eat less. There is good reason for this. Many short term studies have convinced us of multiple benefits of weight loss – better sugar control in diabetics, lower blood pressure, improved mood, higher quality of life.

Nevertheless, there is little data about the long term benefits of weight loss. If you were to design a trial looking to measure the cardiovascular benefits of weight loss you would want to focus on a group of people who would benefit most, a group at high risk for strokes and heart attacks. Overweight diabetics would be a great choice.

Last week the New England Journal of Medicine (NEJM) published the results of a long term trial testing whether intensive lifestyle modification aimed at weight loss would prevent strokes and heart attacks in overweight patients with type 2 diabetes.

Over 5,100 middle aged and elderly patients with type 2 diabetes were enrolled. They were all overweight or obese (BMI 25 or over). They were randomized to two groups. One group was counseled about diet and exercise. They were educated to exercise for about 3 hours per week and consume 1,200 to 1,800 calories daily with less than 30% of the calories from fat. The control group was not given specific targets for calories or exercise. Both groups had their diabetes and other medical problems managed by their own physicians, and their medications were not controlled by the study.

Both groups were followed for an average of 9.6 years to see if one group had fewer strokes, heart attacks, or death due to cardiovascular causes.

Not surprisingly, the lifestyle intervention group lost more weight than the control group. After one year the intervention group lost on average 8.6% of body weight, compared to 0.7% in the control group. After the first year, the intervention group regained some weight, a common occurrence in weight-loss studies (and in the personal experience of dieters). Still, by the end of the study the intervention group lost 6% of their initial body weight, compared to 3.5% in the control group. The intervention group had lower glucose levels (i.e. better diabetes control), was on less medication, and had less serious kidney disease, depression, and sleep apnea.

That’s not bad, right? If I had diabetes I would exercise regularly and eat less for those benefits.

So you would think that with all those benefits including the pretty impressive weight loss, the intervention group would have had fewer strokes and heart attacks. They didn’t. The numbers of strokes, heart attacks, and deaths in the two groups were not significantly different.

Across the scientific land there was wailing and gnashing of teeth. What happened? Surely, we can’t throw in the towel on diet and exercise.

An editorial in the same NEJM issue suggests possible explanations. Perhaps the weight loss achieved in the study was simply too small to decrease cardiovascular risk. That would be a very depressing explanation since the weight loss achieved in the study is greater than most people are able to maintain. Hoping that a larger weight loss is needed for cardiovascular benefits would not be very realistic for real patients. Another possibility is that the cardiovascular benefits only accrue after a longer delay, and that following the patients for longer than 10 years is needed to measure this benefit.

The explanation I find most plausible has to do with the medications the patients were taking. Again, the medications taken by the patients were not controlled by the study; they were left up to each patient’s physician. As it turned out, blood pressure medicines, statins (a family of cholesterol-medicines), and insulin were used more frequently in the control group than in the intervention group. One result of this is that LDL (the most important cholesterol molecule) was lower in the control group.

It’s easy to see how this might have happened. Imagine two overweight diabetics with elevated cholesterol. One is in the control group. He’s not making much progress losing weight, so his doctor starts him on a statin. Statins have solid evidence that they prevent strokes and heart attacks. The other patient is in the intervention group. He’s making good progress losing weight with diet and exercise, so the doctor delays starting the statin, choosing instead to recheck his cholesterol in a few months. Maybe his cholesterol eventually drops or maybe it doesn’t but the proven statin therapy is delayed despite the high cholesterol because of the optimism generated by the impressive weight loss. The delayed statin use negates whatever benefit the weight loss would have caused, and the two groups end up with equal numbers of strokes and heart attacks.

To put it another way, I think current medical treatment for high blood pressure, diabetes, and high cholesterol is so effective in preventing strokes and heart attacks that it is very difficult to find an intervention that will decrease cardiovascular risk even further. Perhaps the most positive thing that can be said about the weight-loss group is that it had the same cardiovascular outcomes as the control group which was taking more medications.

So my lesson is that overweight diabetics should diet and exercise, but medications to aggressively lower their blood pressure, sugar and cholesterol should not be delayed due to optimism about their weight loss. Lose some weight, but take your statin.

Learn more:

Disappointing Results for Weight Loss and Diabetes (Wall Street Journal)
Weight loss, exercise didn’t affect heart outcomes in Look AHEAD (Internal Medicine News)
Weight loss does not lower heart disease risk from type 2 diabetes (National Institutes of Health)
Cardiovascular Effects of Intensive Lifestyle Intervention in Type 2 Diabetes (NEJM article)
Do Lifestyle Changes Reduce Serious Outcomes in Diabetes? (NEJM editorial)

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Hepatitis A Outbreak Linked to Frozen Berry and Pomegranate Mix

Product label of Townsend Farms Organic Anti-Oxidant Blend frozen berry and pomegranate mix
Click for larger image. Image credit: CDC

Hepatitis A is an illness which affects the liver and is caused by a virus. (You’ll be shocked to learn it’s called the hepatitis A virus.) It is usually transmitted through food and water contaminated by human feces, even in microscopic amounts. In the US outbreaks have frequently been linked to food workers who have hepatitis A and contaminate food with their hands. The disease typically causes fatigue, abdominal pain, jaundice (yellowing of the skin and eyes), and dark urine. Patients typically recover completely without lasting damage to the liver. Unlike other forms of viral hepatitis, hepatitis A does not cause chronic infection. After the patient has recovered, the virus is cleared from the body and the patient is no longer infectious. Recovery is followed by lifelong immunity.

An outbreak caused by a negligent restaurant worker is bad enough, but we live in an interconnected international food marketplace. Contamination of the food supply can happen anywhere from the farm to the consumer’s hands; the farther upstream the contamination, the more people may be affected.

The most recent food-borne hepatitis A outbreak has been sickening people since March. This week the Centers for Disease Control and Prevention (CDC) updated their findings from their ongoing investigation. The outbreak has been linked to Townsend Farms Organic Anti-Oxidant Blend frozen berry and pomegranate mix. As of Wednesday 97 people have become ill in eight states including California. About half of those affected have been hospitalized. There have been no deaths. The berry and pomegranate mix is sold at both Costco and Harris Teeter, though all the affected people who recall eating the berry mix bought it at Costco.

The product has obviously been removed from store shelves. If you have any, discard it immediately. If you have eaten this product in the past two weeks and have never been vaccinated against hepatitis A, contact your doctor immediately. Vaccination may lower your chance of becoming ill.

I’ve written previously about food-borne illness, about the lack of evidence that anti-oxidants have health benefits, and about the lack of evidence that organic food is healthier than food grown with industrial fertilizer and pesticides. This is an unfortunate story in which these topics intersect. The recent media coverage of the outbreak included an interview with the wife of one of the people sickened with hepatitis A. She expressed surprise that organic food could become contaminated. But there has never been any suggestion that organic food is less likely to bear infectious diseases than food grown with pesticides. Even organic food producers have never made such a claim. If anything, the withholding of industrial fertilizers may increase the likelihood of food contamination if animal waste is used instead and if it is not cleaned off the food.

So please wash all uncooked fruits and vegetables before eating them, even frozen produce. Please wash your hands after using the bathroom. And please feel free to buy organic food because you think it tastes better, or because you’d like to spend more money on food, or because you know it will impress the intriguing hipster checking out your shopping cart. But don’t do it for health benefits.

Learn more:

Multistate outbreak of Hepatitis A infections potentially associated with “Townsend Farms Organic Antioxidant Blend” frozen berry and pomegranate mix (CDC)
Advice to Consumers (CDC)
CDC: 87 Now Sickened in Hepatitis A Outbreak (WebMD)
Hepatitis A victim shocked organic berries almost led to liver transplant (CBS News)
Hepatitis A (review article by the Mayo Clinic)

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Little Evidence that Low-Salt Diet Prevents Heart Disease

salt shakers
Photo credit: Jorge Royan/Wikimedia

We know that people with high cholesterol have a higher risk for strokes and heart attacks than people with low cholesterol. So if a medicine lowers cholesterol it should also lower the frequency of strokes and heart attacks too. Right? Not necessarily. Estrogen lowers cholesterol and doesn’t lower stroke or heart attack risk. We also know that people with high blood pressure have a higher risk for strokes and heart attacks. Does that mean that a food that elevates blood pressure increases stroke and heart attack risk? Again, not necessarily.

The confusion here is a misunderstanding of the difference between clinical outcomes and intermediate outcomes. A clinical outcome is something that a patient notices herself and that impacts her life directly – like a stroke, a heart attack, or a bone fracture. An intermediate outcome is something that is measured by the doctor and that doesn’t cause symptoms directly – for example, elevated blood pressure, elevated cholesterol, or low bone density. Intermediate outcomes can be risk factors for clinical outcomes but shouldn’t be confused with them.

What does this have to do with salt?

Lots of evidence shows that eating more salt raises blood pressure, so doctors have always made the assumption that eating more salt also increases the risk of strokes and heart attacks. But as we’ve seen with estrogen and many other examples, guessing the effects on clinical outcomes from intermediate outcomes is frequently incorrect. In 2005 the USDA and Department of Health and Human Services wanted to revise their dietary recommendations for salt intake. Given the very little scientific evidence they had, what they did was both simple and presumptuous. They knew that 1,500 mg of sodium intake daily was the minimum needed for adequate nutrition. They also knew that at daily intake levels above 2,300 mg of sodium (which is about a teaspoon of salt) blood pressure begins to increase. So the US recommendations since 2005 have been that everyone should eat no more than 2,300 mg of sodium daily, and that people at very high risk of stroke and heart attack should ingest no more than 1,500 mg.

How are we doing? Well, on average Americans ingest 3,400 mg of sodium daily, well above the recommendations. A host of policy initiatives has been spawned by the recommendations in an effort to educate consumers, clarify food labels, and coerce restaurants to lower sodium.

But did anyone test the effects on the clinical endpoints?

The institute of Medicine (IOM) was commissioned to review all the studies relating to the health effects of sodium intake. Their report (which is over 150 pages) was released last week. A major conclusion of the IOM paper is that the quality of the current evidence linking salt to health outcomes is very poor. There are virtually no randomized studies and the rest of the studies suffer from important methodological flaws (like imprecisely measuring salt intake or using self-reported food diaries to estimate salt intake). The surprising and worrisome finding was that some of the randomized trials actually found worse outcomes with very low salt intakes. This isn’t as preposterous as it may sound. We have no solid understanding on salt’s effect on the body beyond that on blood pressure, so there could be many mechanisms that could explain worse cardiovascular outcomes with a very low salt diet.

The IOM endorsed the current belief that there is very likely a quantity of daily salt intake above which the risk of cardiovascular disease increases. The current evidence is simply insufficient to figure out what that limit is.

I’m always impressed when science comes up with the answer “We have no idea” because that’s very likely to be honest. Those who are more committed to enacting policy than to figuring out the truth are less likely to confess ignorance and to wait for better studies before making up their minds. The American Heart Association issued a press report criticizing the IOM paper and arguing essentially “But salt increases blood pressure!” which no one disputes.

So for now add me to the list of salt agnostics. I frequently ask patients to cut down on salt in the short term to avoid fluid retention, for example when traveling. But we should have the honesty to admit that in terms of long term outcomes we don’t know how much salt is too much.

And if you’re not going to eat that pickle, can I have it?

Learn more:

No Benefit Seen in Sharp Limits on Salt in Diet (New York Times)
Low-Salt Benefits Questioned (Wall Street Journal)
Is Eating Too Little Salt Risky? New Report Raises Questions (NPR)
Sodium Intake in Populations: Assessment of Evidence (Institute of Medicine)
Shaking the Salt Habit (American Heart Association)
New IOM report an incomplete review of sodium’s impact, says American Heart Association (American Heart Association Media Alert)

Merck Knows More about Zetia than They’re Telling Us (my post in 2007 explaining the difference between clinical outcomes and intermediate outcomes)

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