Category Archives: Weight Loss

A Comparison of Low Carb and Low Fat Diets

Image credit: Wikimedia commons, public domainThe joys of September! Parents gleefully shove their reluctant children onto school buses, the palm trees in Los Angeles don’t change color, and everyone realizes that they gained 20 pounds during their summer vacation. It’s time to get serious again about losing weight.

But how should you eat to best help you shed the extra pounds? Many people are passionate about their favorite diet, but there is very little data comparing different diets to each other. Some swear by low carbohydrate diets (like Atkins), while others insist that low fat diets (like Weight Watchers and others) yield more weight loss and achieve healthier cholesterol numbers.

This week, a study published in Annals of Internal Medicine attempted to shed some light on this question. The study enrolled 148 men and women who were obese (BMI 30 to 45) but didn’t have diabetes or cardiovascular disease. The participants were randomized into two groups. One group was counseled to eat a low carbohydrate diet, with less than 40 grams of carbohydrates per day. The second group was counseled to eat a low fat diet, with less than 30% of total calories from fat, and less than 7% from saturated fat. Neither group was counseled about limiting total calories or about exercise. Both groups received ongoing periodic dietary counseling throughout the study.

The subjects were followed for a year and had periodic assessments of their weight, diet, cholesterol, blood pressure, and other blood tests measuring cardiovascular risks.

At the end of the study the group eating a low fat diet lost an average of 4 lbs. while the group eating a low carbohydrate diet lost an average of 12 lbs. Even more impressive was that the low-fat group lost lean body mass (muscle weight) and gained fat weight, while the low-carbohydrate group lost fat weight and gained muscle. This is especially surprising since average caloric intake and physical activity was similar between groups. One frequent criticism of low carbohydrate diets – that it results in an increase of LDL (bad cholesterol) – was dispelled. Total cholesterol and LDL levels remained similar between groups, but the low-carbohydrate group had bigger increases of HDL (good cholesterol).

This all suggests that a low carbohydrate diet leads to more weight loss than a low fat diet while improving body fat composition and some cholesterol measures. For those who are losing weight on a low carbohydrate diet but were worried that the excess fat intake was increasing their cardiovascular risk, this is good news.

Though the results were trumpeted as a major vindication for low carbohydrate diets, I interpret the results differently. Sure, the low carbohydrate group fared better than the low fat group, but what I find striking is how disappointingly modest the results in both groups were. The participants had a BMI of 30 to 45 which means that at minimum they were 35 lbs. overweight, some much more. An average weight loss of 12 lbs. is a laudable step in the right direction but is a small fraction of the weight that should be lost. Considering the fact that this weight loss took 12 months and that all longer term studies suggest that some of this lost weight will be regained, the results seem quite discouraging.

So I conclude from this study that any diet that helps you eat less and that you can maintain indefinitely will help you lose weight but that for meaningful weight loss you have to make a more radical change in your diet than the groups in this week’s study. If you feel full and not deprived on a low carbohydrate diet, then do it and stick to it. But you should probably have even less carbohydrates than 40 gm per day until you reach your target weight. This study at least reassures you that your cholesterol and body fat composition won’t get worse. If you do best with a low fat diet, consider a diet that is radically low in fat, like a plant-based vegan diet without processed foods. My patients who have stuck with either strategy have done well. This study is also a reminder that without exercise, changing what you eat will only achieve modest results. Frequent exercise can accelerate weight loss while maintaining muscle mass.

And for people who are over 100 lbs. overweight, especially those with diabetes, studies increasingly suggest that weight loss surgery has healthier outcomes than diet and exercise alone.

So let’s all make a plan and get started. Thanksgiving is just around the corner.

Learn more:

A Call for a Low-Carb Diet That Embraces Fat (New York Times)
Cutting Back On Carbs, Not Fat, May Lead To More Weight Loss (NPR)
Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial (Annals of Internal Medicine)

Some of my past posts on diet and weight loss:

Why Losing Weight Is So Hard
Startling Scientific Finding: Dieting Leads to Weight Loss
Scientifically Proven Weight Loss Method: Eat Less

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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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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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ACP Potpourri

Image credit: ACP

Greetings from San Francisco, where I am attending the American College of Physicians 2013 Scientific Program, their annual conference covering the latest progress in internal medicine. Though the conference is obviously geared for physicians, I’ve compiled below a half dozen points from the various lectures that I think might be of interest to patients. Feel free to skim, and if you want to learn more about any point, follow the links.

  • Ezekiel Emanuel, MD, PhD, gave the keynote address. Those unfamiliar with his biography and his work on healthcare reform can learn more by following the link. His speech highlighted the many changes anticipated in healthcare in the next few years and was intended to reassure us that physicians will be leaders in the transformation of American medicine. The specifics he discussed, however, were largely centrally planned policy directives over which physicians will have little influence. This makes me suspect that physicians will be passengers, not drivers, in the coming revolution.
  • More than one lecture mentioned the very important study a year ago that demonstrated that patients with sinus infections treated with antibiotics don’t improve any faster than on placebo. A very large fraction of all antibiotic prescriptions are for sinus infection, and as my regular readers know antibiotic use increases the risk of bacterial resistance and of Clostridium difficile infection. The latest recommendations for acute sinusitis is to use only nasal decongestants and pain relievers for 10 days after symptom onset. The vast majority of patients improve with only symptomatic treatment, either because they had a viral infection (for which antibiotics are ineffective) or because the nasal decongestants allowed drainage of the sinuses, allowing the patients’ immune system to kill the few remaining bacteria. Only patients who have not improved in 10 days should be prescribed antibiotics. This may be a difficult change both for patients and physicians. I know that despite my best efforts I am occasionally pressured by (well-meaning) patients to prescribe unnecessary antibiotics. I hope I can educate patients about this in a way that does not frustrate them.
  • The new medications for obesity were discussed by several speakers. Belviq (lorcaserin) and Qsymia (phentermine/topiramate) will be available by prescription soon for treatment of obesity. The difference in attitudes towards these medications of the different speakers was fascinating. The professor who was a general internist was hesitant to recommend them based on the absence of long-term safety data and the terrible safety track-records of prior obesity medications that were withdrawn from the market. The obesity specialist, on the other hand, seemed quite enthusiastic to prescribe these medications given how empty our armamentarium is for this serious problem. (I side with the general internist.)
  • An important study last year showed that in patients with blood clots in their legs who are treated with a blood thinner (warfarin, Coumadin) for 6 to 18 months should continue taking aspirin thereafter to prevent a recurrent clot.
  • Women with normal bone density or mild osteopenia can wait 10 to 15 years before next rechecking their bone density, with very little risk of missing their transition to osteoporosis. I really should be recommending bone density testing less frequently in these women.
  • More than one lecturer on various different topics mentioned Choosing Wisely, the partnership between the American Board of Internal Medicine and various physician specialty organizations dedicated to educating physicians and patients about tests and treatments that have no benefits. Speakers about topics from ranging from preoperative chest X rays to CT scans for acute sinusitis showed us the studies proving that the tests are worthless and mentioned that Choosing Wisely is trying to get physicians to stop ordering such tests. I remain supportive of the program’s goals but pessimistic about its effectiveness. This may be effective if enough patients become well-informed, but hoping that thousands of physicians will behave against their interests by ceasing to order high-price low-benefit services is unrealistic. This may be another reason for patients to choose physicians who have no incentive (or disincentive) to recommend any specific test or treatment.

Finally, I was pleasantly surprised to find that many of the studies that were highlighted by the professors were ones I wrote about over the year. Reviewing the literature has helped me understand the studies, and composing the posts in non-technical language has helped me remember the key points. There is no better way to learn than to teach. Thank you for reading.

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Are You Obese?

Americans are getting heavier and have been doing so for decades. One in three adults in the US is obese. Overweight and obese people are more likely to develop diabetes, high blood pressure, heart disease, and other serious health problems. What can be done?

Last month the US Preventive Services Task Force (USPSTF) released a new recommendation that all primary care doctors screen their patients for obesity. To do that, a doctor measures the patient’s weight and height and uses it to calculate the patient’s body mass index (BMI). Do you know your BMI? If not, use this handy BMI calculator to figure it out.

The BMI is a somewhat imprecise measure of healthy weight since it doesn’t take into account body fat percentage, but it’s easy to determine and therefore widely used. Normal weight for adults is from a BMI of about 20 to about 25. A BMI over 25 is considered overweight. Over 30 is obese.

The USPSTF recommends referring everyone with a BMI greater than 30 to an intensive behavioral intervention program that focuses on increasing exercise, controlling food portions, and self-monitoring progress towards weight-loss goals. Of course, eating better and exercising is notoriously difficult, and on average the long term weight-loss is only modest. But in obese people a loss of even 5% of weight is likely to lead to some health benefits. In any case, increasing physical activity and eating better is likely to lead to health benefits even if weight loss is not achieved, or if the weight is regained later.

The medications currently available for weight loss are only minimally effective and have some side effects, so the USPSTF did not recommend medication use. The current recommendations also did not evaluate surgery for weight loss, which has been gaining supporting evidence in the last few years.

So know your BMI. If it’s too high, that’s a good sign you should be eating less and moving more.

Learn more:

Obesity screenings for all American adults? Not so fast, some say (Booster Shots, the Los Angeles Times health blog)
Doctors Hesitant To Deal With Patients’ Weight Problems (Shots, NPR’s health blog)
BMI calculator (Centers for Disease Control and Prevention)
About BMI for Adults (Centers for Disease Control and Prevention)
Screening for and Management of Obesity in Adults: U.S. Preventive Services Task Force Recommendation Statement (Annals of Internal Medicine)

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A New Weight Loss Drug is Closer to FDA Approval

The current range of options for medications for weight loss is not encouraging. The only medication approved by the FDA for long-term use for weight loss is orlistat, available over the counter by the brand name Alli, or Xenical by prescription. It is only modestly effective and its most common side effect, diarrhea and greasy stool, is somewhat icky. The rest of the medications used for weight loss are only effective for a few weeks and have the potential for addiction. Even these riskier medications don’t provide significant sustained weight loss.

And that’s just the weight loss drugs that are still available. Others, like Meridia and fenfluramine, have been withdrawn from the market because of serious side effects.

Two years ago I wrote about a new weight loss medication, lorcaserin, which was at that time meandering through the FDA approval process. So far, it seems much safer than other weight loss medicines. This week, lorcaserin cleared a major hurdle for FDA approval, gaining a recommendation from a committee that advises the FDA on this class of drugs. If approved by the FDA in June, lorcaserin would be the first new weight loss drug available to patients in over a decade.

Before we get too excited, we should realize that the weight loss achieved in the trials was not spectacular. On the medication 38% of patients were able to lose 5% or more of their weight over a year, compared with 16% of patients taking a placebo. The average weight loss on the medication over a year was 3%. That’s pretty tiny, but still better than those on placebo, which should remind us how tough it is to lose weight.

Until June, the best advice I have for most people trying to lose weight is to get plenty of sleep, eat a little less, and exercise a little more. Weight loss surgery is probably the most effective choice for those who are extremely overweight, especially if their weight has resulted in health consequences such as diabetes.

Learn more:

FDA Panel Favors Arena Obesity Drug (Wall Street Journal)
FDA Advisers Recommend Approving Weight Loss Drug (NPR via Associated Press)

My previous posts about lorcaserin:

Meridia Withdrawn from US Market
A New Medication for Weight Loss (about the initial studies of lorcaserin)

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Weight-Loss Surgery More Effective for Diabetes than Medication

About 20 million Americans currently have type 2 diabetes, three times more than in 1980. Diabetes is a major risk factor for stroke and heart attack, is the leading cause of new cases of blindness, and is the largest cause of the need for dialysis. Diabetes is also usually progressive, meaning that on the same medications and on the same diet and exercise regimen, the blood sugar of a patient with diabetes will slowly increase, necessitating constantly increasing amounts of medications.

So despite new families of medications for diabetes, and despite the fact that most patients require more than one medication, many patients never achieve good control of their blood sugar.

Two studies published this week in the New England Journal of Medicine offer tantalizing hope for overweight patients with diabetes. Both studies attempted to discover whether overweight patients with diabetes would achieve better control of their diabetes through weight loss surgery or through standard medical care.

One study, conducted in Italy, randomized 60 patients to three groups. One group was treated with medication. Another underwent gastric bypass surgery. The third group underwent biliopancreatic diversion surgery. (See the helpful graphic in the NY Times article for an explanation of the different surgeries. I thought biliopancreatic diversion was the name of a gastroenterology theme park.) The endpoint of this study was very ambitious – remission of diabetes, defined as normal sugars without medication for over a year.

None of the patients receiving medical therapy achieved remission, compared with 75% of the patients who underwent gastric bypass, and 95% of the patients undergoing biliopancreatic diversion.

The second study, from the Cleveland Clinic, randomized 150 overweight diabetic patients to gastric bypass, sleeve gastrectomy, or medical therapy. The patients in the surgical groups had much better control of their diabetes than the medical therapy group, and many in the surgical group were able to stop their diabetes medications.

Those are very impressive results, but some questions remain unanswered. Does the remission of diabetes mean that the patient is cured? We don’t know. Since the studies followed patients for at most two years, it is entirely possible that years from now their diabetes will recur. Will the excellent control of diabetes translate to fewer diabetic complications, like strokes, heart attacks, and kidney disease? Do diabetics who are less overweight than those in these studies still benefit from surgery? Larger long-term studies will be needed to find out.

But for now it is clear that for overweight patients with diabetes, surgery should no longer be thought of as a last resort. Surgery is increasingly a proven therapy with much greater effectiveness than other alternatives.

Learn more:

Weight-loss surgery effective against diabetes, studies show (LA Times article)
Surgery for Diabetes May Be Better Than Standard Treatment (NY Times article)
Bariatric Surgery (NY Times, instructional diagrams explaining the anatomy of various weight loss surgeries)
Bariatric Surgery versus Conventional Medical Therapy for Type 2 Diabetes (New England Journal of Medicine article)
Bariatric Surgery versus Intensive Medical Therapy in Obese Patients with Diabetes (New England Journal of Medicine article)
Surgery or Medical Therapy for Obese Patients with Type 2 Diabetes? (New England Journal of Medicine editorial)
Evidence Mounts in favor of Weight Loss Surgery (My last post about weight loss surgery in 2011, with links to my previous posts about this topic)

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Why Losing Weight Is So Hard

I’ve written many times that losing weight is the second hardest thing I ask my patients to do. (Breaking an addiction like smoking or alcoholism is the hardest.) The frustrating thing is how little we know about how to lose weight successfully. But we are learning more all the time about why losing weight is so difficult.

Much about dieting and weight loss is poorly understood, but let’s first lay out some facts that are well established.

Weight loss and weight gain are caused by an imbalance between calories ingested and calories burned. That’s not controversial. If you eat fewer calories than you use in exercising, you will lose weight. If you eat more, you will gain. How many calories it takes to simply maintain one’s weight varies between individuals and the mechanisms behind that variation are still being explored, but for every person there is a number of ingested calories below which weight loss will happen. That means that if someone else is in control of what you eat (for example in a prison in a totalitarian country) and doesn’t provide you enough food, you will lose weight.

That makes it sound fairly simple, right? If you eat less, you lose weight. Since eating is a volitional behavior, overweight people should simply choose to eat less, and their failure to do so simply reflects poor judgment or weak willpower.


Permit me a brief digression about control systems. I think about them a lot because of my engineering background. Our body has many mechanisms that very tightly regulate certain biological parameters, like the sodium concentration in our blood, or the amount of light that is shining on our retinas. Many of these mechanisms are entirely out of our conscious control. For example, if we walk into a brighter environment our pupils automatically constrict, letting less light hit our retinas. That happens without our attention or knowledge.

The control of our breathing is a very interesting example. Our breathing is usually not under our conscious control. Our brain monitors the amount of carbon dioxide (CO2) in our blood from moment to moment. When the level of CO2 increases we take a breath, lowering the CO2 level. The cycle repeats continuously even in our sleep. Without our attention or intention the CO2 level in our blood is kept within a fairly narrow range. But anyone who plays a wind instrument or sings can tell you that breathing is also volitional. You can take a breath purposefully between sentences and blow through a horn exactly when you want to. So which is it? Is breathing voluntary or not?

The answer depends on the time scale. From second to second you can control your breathing. You can hold your breath for a few seconds or you can hyperventilate for a few seconds. But over minutes you will not be able to override the drive to keep your CO2 at a certain level. That is, if you try to hold your breath or slow down your breathing over minutes, your CO2 will slowly climb and your urge to breathe faster will eventually prove to be irresistible. Similarly if you try to hyperventilate over minutes, your CO2 will fall and your urge to slow your breathing will eventually overwhelm your conscious control. So breathing is voluntary over seconds but entirely involuntary over minutes or longer.

Are you getting a sense of how this may relate to control of weight?

Long ago researchers began suspecting that there were control mechanisms responsible for maintaining weight within some range. Just as there is an internal set point for our blood sodium concentration that the kidneys maintain, and a set point for our CO2 concentration maintained by our breathing, researchers argued that there must be an internal set point for our weight. A set point simply means a normal level of some measure that a control mechanism tries to achieve – the temperature that the thermostat is set to, for example.

I first discovered the idea of a possible weight set point in a fascinating paper by Seth Roberts, a psychologist. He cites much evidence that weight must be controlled by an internal set point. For instance, many people occasionally fast for a day. This results in a small weight loss. Without an internal set point for weight, that weight loss would be permanent or would fade very slowly. But weight loss after a fast usually disappears within a few days, suggesting that hunger is increased for the subsequent few days until the weight renormalizes.

The general idea is that the quantity of fat stores in our body is monitored by our brain (perhaps using hormones released by fat cells) and compared to some set point. Whenever our weight (or fat stores) falls below this set point various hormonal mechanisms increase hunger and decrease physical activity. Research is currently attempting to unfold the details of these mechanisms. The current understanding and consequences of this theory is explained in a illuminating article in the New York Times Magazine – The Fat Trap. If you’re trying to lose weight, I urge you to read it.

The article cites several studies including a study published in The New England Journal of Medicine in October. The study enrolled 50 overweight or obese adults and for 10 weeks put them on a very low calorie diet. They lost an average of 30 lb. Before the study and periodically for a year after, the levels of hormones thought to mediate hunger and satiety were measured. The subjects were also asked for their subjective levels of hunger and appetite.

The results showed that the hormones that cause hunger and weight gain increased after the weight loss and remained increased a full year later, even after most subjects had partially regained their lost weight. More sobering is the fact that the subjects’ self-reported sense of hunger rose after the weight loss and didn’t return to baseline levels throughout the one year study.

The authors state that the result

“supports the view that there is an elevated body-weight set point in obese persons and that efforts to reduce weight below this point are vigorously resisted… suggesting that the high rate of relapse among obese people who have lost weight has a strong physiological basis and is not simply the result of the voluntary resumption of old habits.”

For now, this isn’t a particularly helpful discovery, but it helps explain a lot. It explains, for example, why the myriad diets on the market all have approximately the same lousy long-term success rates. It also explains that eating, like breathing, and like refraining from scratching that patch of eczema, is a voluntary behavior only on short time scales. I can choose whether to have a snack now or not, but I can’t choose to fast for three days or to eat much less than my caloric needs for a month.

Overweight people have a “weight thermostat” that is turned up too high. We need researchers to to find a medical solution to reset this set point or to break one of the mechanisms that mediate hunger.

The best we have to offer overweight patients at this point is the advice to diet and exercise, though in the long term this seems to be effective only for a small minority of patients. For the morbidly obese, surgery for weight loss is an increasingly evidence-based option.

Perhaps the best advice we can learn from this is to at least encourage patients not to gain more weight. We now know that losing it will be much more difficult and that maintaining the current weight after weight gain and loss will be harder than never gaining in the first place.

Learn more:

The Fat Trap (New York Times Magazine)
Long-Term Persistence of Hormonal Adaptations to Weight Loss (New England Journal of Medicine article)
What Makes Food Fattening? A Pavlovian Theory of Weight Control (Seth Roberts, unpublished paper)
My previous posts on weight loss

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Sitting Won’t Kill You, Except on Train Tracks

In the last couple of weeks the media has published stories making it sound like your Ikea chair is a death trap waiting to assist your suicide through the dangerous activity of sitting down. Stories with sensational titles like “Is Sitting a Lethal Activity?” (see link below) make you think that you’re better off walking outside for a smoke. Let’s spend a few minutes sifting the solid science from the wacky conjecture. You might as well sit down for this.

The media interest in the idea that sitting might kill you started with the publication last month of a paper entitled “Sedentary Behaviors Increase Risk of Cardiovascular Disease Mortality in Men” in the journal Medicine and Science in Sports and Exercise. (The link to the paper is below, but I’ve read it so you don’t have to.) The study followed thousands of men who in the 1980s were surveyed about their activity levels. They were asked how many hours per week they spent riding in a car and watching TV. They were also asked about how physically active they were. The study then followed these men for over twenty years and counted those who died of cardiovascular disease. The men who spent the most time watching TV and riding a car were at highest risk of dying of cardiovascular disease. So the authors conclude that time spent sedentary, regardless of how much exercise is done the rest of the day, is dangerous.

My regular readers will know that this doesn’t mean that sedentary activity causes cardiovascular disease, because the study isn’t randomized. This conclusion is just as wrong as guessing that there’s something specifically about televisions or cars that cause cardiovascular disease. The only way to sort out whether sedentary time in itself causes cardiovascular disease is to force one group to spend a lot of time sitting and to force another group not to sit (which I think is an enhanced interrogation technique). We can assume that sitting is perfectly safe and still imagine lots of factors that would lead men who sit a lot to die sooner. Sick people, for example, may feel too poorly to be active. They will therefore sit a lot more and die sooner than their healthier counterparts. The authors took some precautions to avoid such confounding factors, but these factors can’t be eliminated entirely without randomization.

The NY Times article about this issue (link below) is an interesting jumble of good science and unfounded conclusions. The article cites a study by James Levine in which subjects were instructed not to exercise and were carefully fed a diet containing 1,000 more calories than needed to maintain their weight. Some subjects gained weight and others didn’t. The ones who didn’t gain weight subconsciously increased their activity level when their caloric intake increased. They fidgeted, paced, stood, stretched and generally moved enough to burn the excess calories. That’s a fascinating discovery which teaches us that even small repeated movements can burn a lot of calories. But this has nothing to do with the article’s main claim which is that being sedentary poses a hazard that is not compensated by exercise – that sitting for 8 hours is dangerous even if you’re going to jog for 30 minutes later that day. The article supports that claim only by a lot of non-randomized epidemiology and metabolic studies, nothing persuasive.

The NPR story and The Dish graphic (links below) also commit the very common error of arguing from design. Arguing from design happens whenever someone asserts what our bodies are “built for” or “meant to do”. The stories state that “we just aren’t really structured to be sitting for such long periods of time” and “a hundred years ago, when we were all out toiling in the fields and factories, obesity was basically nonexistent.” Yes, and a hundred years ago life expectancy was much shorter. We are more sedentary now and living longer than ever. The problem with arguing from what nature “meant” us to do is that for most of human history most humans lived on the edge of starvation, fleeing from predators, and dying young. All of human progress, from wearing glasses to modern medicines, has been marked by rebellion against what nature intended for us. What we were “built” to do can’t help us figure out what we should do. Only a randomized study can.

The articles do have some good common-sense suggestions. If you’re overweight, or have poorly controlled diabetes, high blood pressure or high cholesterol, then more physical activity would certainly help you. You can get that activity by spending more time exercising or less time sitting. There’s certainly no harm in getting up from your chair periodically to stretch or pace around the office, and every calorie burned is a good thing. But if your weight, blood pressure, cholesterol and blood sugar are normal and you exercise regularly, there is nothing in these articles that should convince us that sitting in a chair is bad for you. But you should probably take your feet off the desk before your boss walks in.

Learn more:

NY Times article: Is Sitting a Lethal Activity?

NPR story: Sitting All Day: Worse For You Than You Might Think

The Dish graphic: Sitting Is Deadly?

Medicine & Science in Sports & Exercise article: Sedentary Behaviors Increase Risk of Cardiovascular Disease Mortality in Men

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Eat Right for Your Belt Size, Not Your Blood Type

Every couple of months I get asked this same question.

“Doc, what’s my blood type?”

I load my “why you don’t need to know your blood type” speech from my cerebrum and press replay, trying to add a little spontaneous variation for authenticity.

“Actually, I’ve never checked it.”

“I thought you check everything.”

“Nobody checks everything. There are thousands of different available blood tests. Most of them would be completely useless to you.”

“Well doc, could you check my blood type?”

“I’m happy to, but unless a surgeon asked you to have it checked in anticipation of a surgery, it’s really not a handy thing to know.”

“Really? What if I get hit by a truck and need a transfusion?”

“If you ever need a transfusion and tell them your blood type, they won’t believe you. They’ll check it again.”

“But I need to know it because I heard about this great diet…”

Oh, no! Another trusting soul nearly lost in the sticky swamp of quackery. In 1996 a naturopathic doctor published “Eat Right 4 Your Type” a book claiming that your blood type determines your ideal diet. If you want the physiologic details of why this connection between diet and blood type is complete nonsense, check out the links below, especially the detailed and scathing book review from Quackwatch. (By the way, Quackwatch is a terrific resource for sorting the scams from the truth in medicine.)

But forget the physiology. This link between optimal diet and blood type would be very easy to prove without knowing any physiology. You would just take a large group of overweight adults, check their blood types and randomize them into two groups. Group 1 would be assigned the diet appropriate for their blood type according to the book. Group 2 would be assigned a diet suggested by the book for some other blood type. If group 1 lost significantly more weight than group 2 you would have convincing proof that the book isn’t a pile of rubbish. That trial has never been done, though the book has been republished several times. So it makes claims that make no physiologic sense and are unproven.

So why do people fall for it? Because the diets suggested for each blood type are fairly reasonable. Any one of the four diets is fairly healthy and could lead to weight loss, but you can pick one of the four at random; they have nothing to do with blood type. So (just like with bogus cold remedies) people try it, get good results, and spread the word.

“Well, thanks, doc! Sounds like I should just eat less and maybe crank up the exercise a couple of notches.”

“You’re very welcome. By the way, there is a beautiful way to find out your blood type and save a life – donate blood.”

Thus, quackery is foiled again, and there is much rejoicing!

Learn more:

Quackwatch book review: Eat Right 4 Your Type

Wikipedia article: Blood type diet

WebMD article: The Eat Right for Your Blood Type Diet

The Cedars-Sinai blood donor facility

Public Service Announcement: Starve a Vampire, Donate Blood

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