The reporter from Men’s Health asked me: “You finish dinner, even a satisfying low-carb dinner,” — he is a low-carb person himself — “you are sure you ate enough but you are still hungry. What do you do?” I gave him good advice. “Think of a perfectly broiled steak or steamed lobster with butter, some high protein, relatively high fat meal that you usually like. If that doesn’t sound good, you are not hungry. You may want to keep eating. You may want something sweet. You may want to feel something rolling around in your mouth, but you are not hungry. Find something else to do — push-ups are good. If the steak does sound good, you may want to eat. Practically speaking, it’s a good idea to keep hard-boiled eggs, cans of tuna fish around (and, of course, not keep cookies in the house).” I think this is good practical advice. It comes from the satiating effects of protein food sources, or perhaps the non-satiating, or reinforcing effect of carbohydrate. But the more general question is: What is hunger? (more…)
Archive for the ‘Protein’ Category
I Told George Bray How to do it Right.
Posted: January 19, 2012 in energy metabolism, low-carbohydrate diet, Protein, The Nutrition StoryTags: dietary guidelines, Good Calories Bad Calories, low carbohydrate, nutritional studies
“Despite the claims of various diet gurus, excess calorie consumption alone and not the amount of protein in an individual’s diet contributes to the accumulation of unwanted fat….” That’s the tendentious and pretty much inaccurate first line of the press release from JAMA on George Bray’s over-feeding study “Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating.” “Amount of protein?” What’s going here? It hasn’t really been about protein. Most of us “diet gurus” have claimed that carbohydrate, not protein, in the diet was the key macronutrient in regulating metabolism, consistent with the basic biochemistry of the glucose-insulin axis, or as Dr. Bray described Gary Taubes’s position in a review of Good Calories, Bad Calories:
“The problem is the carbohydrates in the diet, their effect on insulin secretion, and thus the hormonal regulation of homeostasis – the entire harmonic ensemble of the human body.”
Reduction in dietary carbohydrate puts increased demands on protein for gluconeogenesis and other processes but the controlling variable is the carbohydrate. The controversy in nutrition has been largely about fat vs carbohydrate. Should we be on a low-carbohydrate diet or a low-fat diet?
The quotation in the press release says accurately that “Earlier studies in human beings suggested that diets containing either high or low [levels of] protein are less ‘metabolically efficient’ than diets with normal protein levels.” Accurate, but written as if metabolic efficiency had always been recognized for its importance in weight loss, as if there had not been a dispute over whether the costs of processing protein were important in energy balance, indeed, written as if Bray and coworkers had not maintained that only calories count in weight gain or loss. The idea of metabolic advantage, that one diet could be more efficient — more weight gained/calorie — has been largely resisted by the nutritional establishment. Is this slouching toward Metabolic Advantage? (“Who knows not [the Duke] is dead? Who knows he is?”)
The debate is also about calories. Should you cut calories or just cut out carbs? Is it really “excess calorie consumption” and not the effect of excess carbohydrates ? “A calorie is a calorie” or not. Many of the gurus have gone beyond “claiming” to demonstrating that when carbohydrates are low, weight loss is greater than when carbohydrate is high and that the weight loss on a low-carbohydrate diet is primarily in fat stores rather than lean mass. In head-to-head comparisons, for however long they are compared, low-carbohydrate diets generally out-perform low-fat diets on other parameters as well, glycemic control, the features of atherogenic dyslipidemia. This has been the major challenge to traditional nutrition and the general approach has been to simply ignore this data and dismiss the researchers with innuendo as above.
In some sense, Bray, et al. answered a question that we weren’t asking, but protein is important if more complicated than carbohydrate and fat. So what did the study find? Bray and coworkers compared three diets of 5 %, 15 % and 25 % protein at an excess of calories, that was nominally the same in each group. The study was a random controlled study and was carried out in a metabolic ward so the results are more accurate than the usual diet study that relies on dietary records. There is something odd about this study, though, in that if you want to say that only calories are the independent variable, you can’t keep calories constant. What was actually done was to determine the energy requirements for weight maintenance over a run-in period of 2-3 weeks on a maintenance and then an additional 40 % of calories was added. So although the calories are constant relative to initial energy expenditure, they are not absolutely the same and this is a study of the effect of varying calories while keeping calories constant. The figure below, re-drawn from Figure 6 of the paper comparing intake of absolute energy to protein intake makes you stop and think.
When you have a small number of subjects, a single outlier can bias the results. If you remove the single highest point (circled in red), the correlation is likely to get much weaker and the normals and low begin to separate. In other words, the individual variation (the relative efficiency) is sufficient to make it hard to see the effect of variable energy or, perhaps, as the authors themselves set it up, it is energy normalized for baseline that is the key variable. Then the authors are right (at least by inspection) that the protein intake does not effect the change in body fat but you have only a single value for the energy. In this case, you cannot say “calories alone account for the increase in fat” (Conclusion in Abstract) because you have only a single point. If you keep constant the variable (carbohydrate) that is most likely to bring out differences, you shouldn’t be surprised in there are no big differences.
Even taking the conclusions at face value, the authors found, as other diet comparison studies have, that weight loss or, in this over-feeding study, weight gain, was not dependent on calories alone: “a calorie is a calorie” not. It is likely that this was what the study was originally trying to disprove and the results must have been a disappointment. The way out was that, in this particular case, the differential weight loss showed up in difference in lean mass, rather than in fat mass as has been found in other studies showing variable efficiency. Since 5 % is very low protein it is probably not surprising that the diet could not provide enough protein for an increase in lean mass this group.
So what are the other diet studies that have found variable efficiency. The reduction in weight found in studies comparing low-carbohydrate diets and low-fat diets not only shows a difference favoring carbohydrate restriction but the improved weight loss is preferentially fat over lean mass. For example, Volek, et al. compared a low fat with a VLCK and the results are as shown below. In their study, subjects were randomized to one of two hypocaloric diets, a very low-carbohydrate ketogenic (VLCK) diet (carbohydrate <10% of energy) or a low fat (LF) diet and after 8 weeks switched to the other diet. Reported energy was slightly higher during the VLCK but the VLCK group lost more weight and as shown below predominantly in fat, total fat loss, and trunk fat loss for men (despite significantly greater energy intake). The majority of women also responded more favorably to the VLCK diet, especially in terms of trunk fat loss the ratio of trunk fat/total fat was also significantly reduced during the VLCK diet in men and women. These studies depend on diet recall so are less accurate than the JAMA study but because of the better experimental design, the changes are bigger and with appropriate correction make a less ambiguous case than the JAMA study. The more accurate measurements in the metabolic chamber suggest that individual variation is real and not just due to random error.
So what do we know from Bray, et al.? As described above, there is some ambiguity in what constant energy means. Still, nobody questions that under many conditions, a “calorie is a calorie,” but they actually found that weight gain was different so when metabolic advantage is “claimed” it cannot be dismissed out of hand. This is different than widely cited studies in the literature that claim macronutrients do not effect weight loss, since if weight gain depends on macronutrient, it is reasonable that weight loss does too. Similarly, if tissue distribution affects lean mass in this case, then studies where the tissue distribution shows preferential loss of fat can’t be dismissed — again, it is certainly not surprising that a low protein diet will lead to less storage of protein; generally, while it is just as bad a generalization as “a calorie is a calorie,” there is some truth in “you are what you eat.” Also, in the JAMA study, protein was exchanged for fat so a reduction in fat did not have an effect on fat which may or may not be a surprise to many people. Tom Naughton raised a few other questions about Bray, et al. but in the end, the paper reminds me of the joke about the Polish Mafia: they make you an offer you can’t understand.
How to do it.
But I told George how to do it. A couple of years ago, he and I had a brief correspondence. I made the following proposal. I suggested we could apply for a joint grant and publication to get the answer. The following is from my email to him in 2008 (I have added some highlights):
“A modest proposal
Proponents of carbohydrate-restricted diets (CRD) and critics of such diets cooperate to design a long-term comparison of CRD and low-fat diets. The groups agree on methods of procedure, make-up of the diets, how compliance will be effected, and what parameters will be measured.
We write the paper first, leaving room for the data, that is, we agree in advance on what the possible outcomes are and what conclusions could be drawn from them. The final MS can only be edited for language usage. There are no disclaimers, no Monday-morning-quarterbacking, no excuses.
The paper could be submitted while the grant application is being written and would have to be accepted because any objections could be incorporated in the plan. The grant itself would surely be funded since it incorporates everybody’s specific aims.”
George hasn’t answered and he obviously has a different approach to the problem but my offer still stands.
In the end, that is what it will take to solve the problem. Unless we agree on what the question is, how it can be tested and work together to do the experiment, the lipophobes will ignore the low-carbohydrate studies and we will criticize their studies. The real losers, of course, will be the people suffering from obesity and diabetes. The question everybody always asks me, is why can’t there be a meeting of the minds? In the current case, why was the JAMA study done?
Why was this study done?
“Dr Bray discussed the results with news@JAMA via e-mail.
news@JAMA: What are the practical implications of these findings for patients trying to lose weight or for the physicians trying to counsel them?
Dr Bray: The first practical implication is an old one: calories count. We showed very clearly that the increase in body fat was due to the increased intake of calories and that the amount of protein in the diet did not change it.
To avoid that slow weight gain that many adults experience in their middle years, people need to watch their weight and increase activity, decrease food intake, or both; changing the diet alone will not do it.”
This sounds like the the same recommendations we’ve had for years. Writing this, I suddenly realized that, as they say in German: that’s where the dog is buried. It is about recommendations. This research is following the recommendations. It used to be (should be? assume it must be?) that recommendations follow from the research. Now, it’s the other way around. Committees make recommendations and then research (sometimes by members of the committee) tries to support the recommendations. Something about this bothers me.
Intro to Fatty Acids and Triglycerides
Posted: October 20, 2011 in lipid metabolism, low-carbohydrate diet, Protein, triglyceridesTags: biochemistry, carbohydrate, diet, insulin, low carbohydrate, triglycerides
The following question was posted on Facebook:
I had thought that free fatty acids were triglycerides. But I am reading a study that measured both. Can someone enlighten me on free fatty acids? … please.
I think I can help. The good news is that, contrary to the college myth, organic chemistry is easy — it is freshman chemistry that is hard because it has more physics and mathematics. Now, jumping into lipid metabolism is a little bit of starting in the middle of things but the reason organic chemistry is easy is that it has only a few assumptions and basic principles and the basic theory, at least, is logical and you can get pretty far deducing things from simple principles, so with a few basic ideas we may have a shot. I have two YouTube videos that are short, relatively easy and might be a background. The take home message from the videos, the one big idea in organic, is that organic compounds have two parts: A hydrocarbon backbone and a non-hydrocarbon part that contains the chemically reactive part of the molecule, the functional groups. The assumption is that all compounds with the same functional group have similar chemistry. So, for example, all carboxylic acids have the carboxyl (-COOH) functional group. In many ways, even a simple acid like acetic acid has chemical properties that are similar to a complicated acid, like the fatty acids. You may need the YouTube to appreciate this: chemistry is about structure, that is, it is visual.
Bottom line on fatty acids and Triglycerides
All dietary and body fats and oils are triglycerides (TG) or, more correctly, triacylglycerols (TAG). The term “acyl” (pr. A-sill) is the adjective form of acid (i.e. There are three acids).
Fats have a roughly E-shaped structure. The arms of the E are the fatty acids and there are three of them. The fatty acids provide the real fuel in fats. The three fatty acids are attached to the compound glycerol which is the vertical stroke of the E. The chemical bond that attaches the fatty acid to the glycerol is called an ester bond. You only need to know the term ester because when the fatty acids are found alone, especially in blood, they are referred to either as free fatty acids (FFA) or, because they are no longer attached to the glycerol by the ester bonds, as non-esterified fatty acids (NEFA): FFA and NEFA are the same thing.
Metabolism: the fatty acid-TAG cycle.
The digestion of fat in the intestine involves the progressive removal of the fatty acids from the first and last position of the glycerol. The process is called lipolysis and the enzyme that catalyzes the reaction is called a lipase. What remains is called 2-monoacylglycerol, or 2-MAG (fatty acid still attached at the center carbon of glycerol) and 2-MAG and the free fatty acids from digestion are absorbed into the intestinal cells. Within these cells they are re-formed into TAG which is exported together with cholesterol and other components in particles called chylomicrons. Chylomicrons, in turn, represent one type of complex structure known as lipoproteins. The lipoproteins transport lipids and some of these are familiar, e.g., LDL (low density lipoprotein), HDL. Triglycerides in the blood are carried in these particles. So this is probably the triglycerides you read about.
These are the transporters of lipids. TAG, in particular is brought into cells by another lipase (lipoprotein lipase or LPL) on the cell surface that removes the fatty acids. In other words, to be absorbed the TAG is broken down into fatty acids again. Once absorbed, the fatty acids can be oxidized for fuel or, once again can be re-synthesized, step-wise: → MAG → diacylglycerol (DAG) → TAG. Here’s the summary figure:
Bottom line:
Fat (TAG) is continually broken down and re-synthesized. The breakdown process is called lipolysis and the lipolysis-synthesis cycle goes on in different places in the body but notably in fat cells. An interesting thing about fat cells is the way they carry out the cycle. Lipolysis is a simple process but synthesis is complicated. Speaking in energy terms, it is easy to break down nutrients. It requires energy to put them back together. To make TAG, either the glycerol or the fatty acid has to be “activated”: so the actual reactive form is a molecule called fatty acyl-coenzyme A or fatty acyl-CoA (pr. Co-A).
Biochemical reactions almost never run by themselves even if energetically favorable but are rather controlled by catalysts, that is, enzymes. The enzyme that catalyzes the first step in the reaction, a transferase, will not work with glycerol itself. The enzyme requires a particular form of glycerol, glycerol-phosphate. The special characteristic of the fat cell is that the required glycerol-phosphate cannot be made directly from glycerol as it can, for example, in the liver which also has an active fatty acid-TAG cycle. In order to make glycerol phosphate, fat cells require glucose. In the absence of glucose, as in starvation or a low carbohydrate diet, fat synthesis is repressed. At the same time the enzyme that catalyzes breakdown, hormone-sensitive lipase, is enhanced because it is turned on by glucagon and turned offby insulin (these are the hormones in the term “hormone-sensitive lipase”). This was the original rationalization for the apparent advantage in a low-carbohydrate diet: without carbohydrate the adipocyte would not be able to supply glycerol-phosphate and the fatty acid-TAG cycle would go largely in one direction: breakdown to produce fatty acids and this is undoubtedly one of the major effects.
It turns out, however, that the fat cells protect stores of energy in fat by other methods. We now understand that cells run a process called glyceroneogenesis which is a truncated form of gluconeogenesis, the process whereby glucose is synthesized from other nutrients, mostly protein, that is, the process supplies an intermediate in the synthesis of glucose and this can be converted to glycerol-phosphate. Generally, especially if the diet is hypocaloric, the net effect is to break down fat and supply fatty acids as a fuel for other cells. Fatty acids circulate in the blood bound to a protein called albumin. Under conditions where there is higher carbohydrate, however, and the fatty acids are not being used for fuel, they can stimulate insulin resistance. So, fatty acids in the blood are a good thing if you are breaking down fat to supply energy. They are not so good if you are over-consuming energy or carbohydrates because, in the presence of insulin, they can lead to insulin resistance.
Summary: triglycerides are made of three fatty acids. There is a continual fatty acid-TAG cycle that goes on all the time in different cells. Triglycerides in the blood are carried in lipoprotein particles, chylomicrons, LDL, HDL. Fatty acids in the blood are carried by the protein albumin.
MedicineBall*: Harvard School of Public Health steps up to the Plate.
Posted: October 3, 2011 in Dietary Fiber, Evidence Based Medicine, Lipophobes, low-carbohydrate diet, Observational Studies, Protein, The Nutrition Story, Uncategorized, USDA Dietary GuidelinesFirst published in October of 2011, this post announced a Q&A on line with Harvard’s Eric Rimm to answer question about the School of Public Health’s new “Healthy Eating Plate,” its own version of nutritional recommendations to compete with the USDA’s MyPlate. A rather limited window of one hour was allotted for the entire country to phone in our questions. Unfortunately HSPH was not as good at telecommunications as it is at epidemiology and the connection did not start working for a while. The questions that I wanted to ask, however, still stand and this post is a duplicate of the original with the notice about the Q&A removed. Harvard has been invited to participate in a panel discussion at the Ancestral Health Symposium, and we will see how these questions can be answered.
— adopted from Pops (at Louder and Smarter), the anonymous brilliant artist and admitted ne’er do well.
One of the questions surrounding USDA Nutrition Guidelines for Americans was whether so-called “sunshine laws,” like the Freedom of Information Act, were adhered to. Whereas hearings were recorded, and input from the public was solicited, there is the sense that if the letter of the law was followed, the spirit was weak. When I and colleagues testified at the USDA hearings, there was little evidence that their representatives were listening; there was no discussion. We said our piece and then were heard no more. In fact, at the break, when I tried to speak to one of the panel, somebody came out from backstage, I believe unarmed, to tell me that I could not discuss anything with the committee.
Harvard School of Public Health, home of “odds ratio = 1.22,” last month published their own implementation of the one size-fits-all approach to public nutrition, the”Healthy Eating Plate.” Their advice is full of “healthy,” “packed with” and other self-praise that makes this mostly an infomercial for HSPH’s point of view. Supposedly a correction of the errors in MyPlate from the USDA, it seems to be more similar than different. The major similarity is the disdain for the intelligence of the American public. Comparing the two plates (below), they have exchanged the positions of fruits and vegetables. “Grains” on MyPlate is now called “Whole Grains,” and “Protein” has been brilliantly changed to “Healthy Proteins.” How many NIH grants were required to think of this is unknown. Harvard will, of course, tell you what “healthy” is:, no red meat and, of course watch out for the Seventh Egg.
So here are the questions that I wanted to ask:
- Dr. Rimm, you are recommending a diet for all Americans but even within the pattern of general recommendations, I don’t know of any experimental trial that has tested it. Aren’t you just recommending another grand experiment like the original USDA recommendations which you are supposedly improving on?
- Dr. Rimm, given that half the population is overweight or obese shouldn’t there be at least two plates?
- Dr. Rimm, I think the American public expects a scientific document. Don’t you think continued use of the words “healthy,” “packed with nutrients,” makes the Plate more of an informercial for your point of view?
- Dr. Rimm, the Plate site says “The contents of this Web site are not intended to offer personal medical advice,” but it seems that is exactly what it is doing. If you say that you are recommending a diet that will “Lower blood pressure; reduced risk of heart disease, stroke, and probably some cancers; lower risk of eye and digestive problems,” how is that not medical advice? Are you disowning responsibility for the outcome in advance?
- Dr. Rimm, more generally, how will you judge if these recommendations are successful? Is there a null hypothesis? The USDA recommendations continue from year to year without any considerations of past successes or failures.
- Dr. Rimm, “healthy” implies general consensus but there are many scientists and physicians with good credentials and experience who hold to different opinions. Have you considered these opinions in formulating the plate? Is there any room for dissent or alternatives?
- Dr. Rimm, the major alternative point of view is that low-carbohydrate diets offer benefits for weight loss and maintenance and, obviously, for diabetes and metabolic syndrome. Although your recommendations continually refer to regulation of blood sugar, it is not incorporated in the Plate.
- Dr. Rimm, nutritionally, fruits have more sugar, more calories, less potassium, fewer antioxidants than vegetables. Why are they lumped together? And how can you equate beans, nuts and meat as a source of protein?
- Dr. Rimm, looking at the comparison of MyPlate and your Plate, it seems that all that is changed is that “healthy” has been added to proteins and “whole” has been added to grains. If people know what “healthy” is, why is there an obesity epidemic? Or are you blaming the patient?
- Dr. Rimm, you are famous for disagreeing on lipids with the DGAC committee yet your name is on their report as well as on this document is supposed to be an alternative. Do we know where you stand?
- Dr. Rimm, the Healthy Plate “differences” page says “The Healthy Eating Plate is based exclusively on the best available science and was not subjected to political and commercial pressures from food industry lobbyists.” This implies that the USDA recommendations are subject to such pressures. What is the evidence for this? You were a member of the USDA panel. What pressures were brought to bear on you and how did you deal with them
- Dr. Rimm, the Healthy Plate still limits saturated fat even though a study from your department showed that there was, in fact, no effect of dietary saturated fat on cardiovascular disease. That study, moreover, was an analysis of numerous previous trials, the great majority of which individually showed no risk from saturated fat. What was wrong with that study that allows you to ignore it?
*Medicineball, (colloq) a game that derives from Moneyball, in which an “unscientific culture responds, or fails to respond, to the scientific method ” in order to stay funded.
Red Meat and the New Puritans
Posted: April 7, 2011 in Association and Causality, Protein, The Nutrition StoryTags: Barry Popkin, beef, Dr. R Sinha, hazard ratio, Meat Intake and Mortality, mortality, red meat,, statistics
“Dost thou think, because thou art virtuous, there shall be no more cakes and ale?”
— William Shakespeare, Twelfth Night.
Experts on nutrition are like experts on sexuality. No matter how professional they are in general, in some way they are always trying to justify their own lifestyle. They share a tendency to think that their own lifestyle is the one that everybody else should follow and they are always eager to save us from our own sins, sexual or dietary. The new puritans want to save us from red meat. It is unknown whether Michael Pollan’s In Defense of Food was reporting the news or making the news but it’s coupling of not eating too much and not eating meat is common. More magazine’s take on saturated fat was very sympathetic to my own point of view and I probably shouldn’t complain that tacked on at the end was the conclusion that “most physicians will probably wait for more research before giving you carte blanche to order juicy porterhouse steaks.” I’m not sure that my physician knows about the research that already exists or that I am waiting for his permission on a zaftig steak.
“Daily Red Meat Raises Chances Of Dying Early” was the headline in the Washington Post last year. This scary story was accompanied by the photo below. The gloved hand slicing roast beef with a scalpel-like instrument was probably intended to evoke CSI autopsy scenes, although, to me, the beef still looked pretty good if slightly over-cooked. I don’t know the reporter, Rob Stein, but I can’t help feeling that we’re not talking Woodward and Bernstein here. For those too young to remember Watergate, the reporters from the Post were encouraged to “follow the money” by Deep Throat, their anonymous whistle-blower. A similar character, claiming to be an insider and identifying himself or herself as “Fat Throat,” has been sending intermittent emails to bloggers, suggesting that they “follow the data.”
The Post story was based on a research report “Meat Intake and Mortality” published in the medical journal, Archives of Internal Medicine by Sinha and coauthors. It got a lot of press and had some influence and recently re-surfaced in the Harvard Men’s Health Watch in a two part article called, incredibly enough, “Meat or beans: What will you have?” (The Health Watch does admit that “red meat is a good source of iron and protein and…beans can trigger intestinal gas” and that they are “very different foods”) but somehow it is assumed that we can substitute one for the other.
Let me focus on Dr. Sinha’s article and try to explain what it really says. My conclusion will be that there is no reason to think that any danger of red meat has been demonstrated and I will try to point out some general ways in which one can deal with these kinds of reports of scientific information.
A few points to remember first. During the forty years that we describe as the obesity and diabetes epidemic, protein intake has been relatively constant; almost all of the increase in calories has been due to an increase in carbohydrates; fat, if anything, went down. During this period, consumption of almost everything increased. Wheat and corn, of course went up. So did fruits and vegetables and beans. The two things whose consumption went down were red meat and eggs. In other words there is some a priori reason to think that red meat is not a health risk and that the burden of proof should be on demonstrating harm. Looking ahead, the paper, like analysis of the population data, will rely entirely on associations.
The conclusion of the study was that “Red and processed meat intakes were associated with modest increases in total mortality, cancer mortality, and cardiovascular disease mortality.” Now, modest increase in mortality is a fairly big step down from “Dying Early,” and surely a step-down from the editorial quoted in the Washington Post. Written by Barry Popkin, professor of global nutrition at the University of North Carolina it said: “This is a slam-dunk to say that, ‘Yes, indeed, if people want to be healthy and live longer, consume less red and processed meat.'” Now, I thought that the phrase “slam-dunk” was pretty much out after George Tenet, then head of the CIA, told President Bush that the Weapons of Mass Destruction in Iraq was a slam-dunk. (I found an interview with Tenet after his resignation quite disturbing; when the director of the CIA can’t lie convincingly, we are in big trouble). And quoting Barry Popkin is like getting a second opinion from a member of the “administration.” It’s definitely different from investigative reporting like, you know, reading the article.
So what does the research article really say? As I mentioned in my blog on eggs, when I read a scientific paper, I look for the pictures. The figures in a scientific paper usually make clear to the reader what is going on — that is the goal of scientific communication. But there are no figures. With no figures, Dr. Sinha’s research paper has to be analyzed for what it does have: a lot of statistics. Many scientists share Mark Twain’s suspicion of statistics, so it is important to understand how it is applied. A good statistics book will have an introduction that says something like “what we do in statistics, is try to put a number on our intuition.” In other words, it is not really, by itself, science. It is, or should be, a tool for the experimenter’s use. The problem is that many authors of papers in the medical literature allow statistics to become their master rather than their servant: numbers are plugged into a statistical program and the results are interpreted in a cut-and-dried fashion with no intervention of insight or common sense. On the other hand, many medical researchers see this as an impartial approach. So let it be with Sinha.
What were the outcomes? The study population of 322, 263 men and 223, 390 women was broken up into five groups (quintiles) according to meat consumption, the highest taking in about 7 times as much as the lower group (big differences). The Harvard News Letter says that the men who ate the most red meat had a 31 % higher death rate than the men who ate the least meat. This sounds serious but does it tell you what you want to know? In the media, scientific results are almost universally reported this way but it is entirely misleading. (Bob has 30 % more money than Alice but they may both be on welfare). To be fair, the Abstract of the paper itself reported this as a hazard ratio of 1.31 which, while still misleading, is less prejudicial. Hazard ratio is a little bit complicated but, in the end, it is similar to odds ratio or risk ratio which is pretty much what you think: an odds ratio of 2 means you’re twice as likely to win with one strategy as compared to the other. A moment’s thought tells you that this is not good information because you can get an odds ratio of 2, that is, you can double your chances of winning the lottery, by buying two tickets instead of one. You need to know the actual odds of each strategy. Taking the ratio hides information. Do reporters not know this? Some have told me they do but that their editors are trying to gain market share and don’t care. Let me explain it in detail. If you already understand, you can skip the next paragraph.
A trip to Las Vegas
Taking the hazard ratio as more or less the same as odds ratio or risk ratio, let’s consider applying odds (in the current case, they are very similar). So, we are in Las Vegas and it turns out that there are two black-jack tables and, for some reason (different number of decks or something), the odds are different at the two tables (odds are ways of winning divided by ways of not winning). Table 1 pays out on average once every 100 hands. Table 2 pays out once in 67 hands. The odds are 1/99 or close to one in a hundred at the first table and 1/66 at the second. The odds ratio is, obviously the ratio of the two odds or 1/66 divided by 1/99 or about 1.55. (The odds ratio would be 1 if there were no difference between the two tables).
Right off, something is wrong: if you were just given the odds ratio you would have lost some important information. The odds ratio tells you that one gambling table is definitely better than the other but you need additional information to find out that the odds aren’t particularly good at either table: technically, information about the absolute risk was lost.
So knowing the odds ratio by itself is not much help. But since we know the absolute risk of each table, does that help you decide which table to play? Well, it depends who you are. For the guy who is at the blackjack table when you go up to your hotel room to go to sleep and who is still sitting there when you come down for the breakfast buffet, things are going to be much better off at the second table. He will play hundreds of hands and the better odds ratio of 1.5 will pay off in the long run. Suppose, however, that you are somebody who will take the advice of my cousin the statistician who says to just go and play one hand for the fun of it, just to see if the universe really loves you (that’s what gamblers are really trying to find out). You’re going to play the hand and then, win or lose, you are going to go do something else. Does it matter which table you play at? Obviously it doesn’t. The odds ratio doesn’t tell you anything useful because you know that your chances of winning are pretty slim either way.
Now going over to the Red Meat article the hazard ratio (again, roughly the odds ratio) between high and low red meat intakes for all-cause mortality for men, for example, is 1.31 or, as they like to report in the media 31 % higher risk of dying which sounds pretty scary. But what is the absolute risk? To find that we have to find the actual number of people who died in the high red meat quintile and the low end quintile. This is easy for the low end: 6,437 people died from the group of 64,452, so the probability (probability is ways of winning divided by total possibilities) of dying are 6,437/64,452 or just about 0.10 or 10 %. It’s a little trickier for the high red meat consumers. There, 13,350 died. Again, dividing that by the number in that group, we find an absolute risk of 0.21 or 21 % which seems pretty high and the absolute difference in risk is an increase of 10 % which still seems pretty significant. Or is it? In these kinds of studies, you have to ask about confounders, variables that might bias the results. Well, here, it is not hard to find. Table 1 reveals that the high red meat group had 3 times the number of smokers. (Not 31 % more but 3 times more). So the authors corrected the data for this and other effects (education, family history of cancer, BMI, etc.) which is how the final a value of 1.31 was obtained. Since we know the absolute value of risk in the lowest red meat group, 0.1 we can calculate the risk in the highest red meat group which will be 0.131. The absolute increase in risk from eating red meat, a lot more red meat, is then 0.131 – 0.10 = 0.031 or 3.1 % which is quite a bit less than we thought.
Now, we can see that the odds ratio of 1.31 is not telling us much — and remember this is for big changes, like 6 or 7 times as much meat; doubling red meat intake (quintiles 1 and 2) leads to a hazard ratio of 1.07. What is a meaningful odds ratio? For comparison, the odds ratio for smoking vs not smoking for incidence of lung disease is about 22.
Well, 3.1 % is not much but it’s something. Are we sure? Remember that this is a statistical outcome and that means that some people in the high red meat group had lower risk, not higher risk. In other words, this is what is called statistically two-tailed, that is, the statistics reflect changes that go both ways. What is the danger in reducing meat intake. The data don’t really tell you that. Unlike cigarettes, where there is little reason to believe that anybody’s lungs really benefit from cigarette smoke (and the statistics are due to random variation), we know that there are many benefits to protein especially if it replaces carbohydrate in the diet, that is, the variation may be telling us something real. With odds ratios around 1.31 — again, a value of 1 means that there is no difference — you are almost as likely to benefit from adding red meat as you are reducing it. The odds still favor things getting worse but it really is a risk in both directions. You are at the gaming tables. You don’t get your chips back. If reducing red meat does not reduce your risk, it may increase it. So much for the slam dunk.
What about public health? Many people would say that for a single person, red meat might not make a difference but if the population reduced meat by half, we would save thousands of lives. The authors do want to do this. At this point, before you and your family take part in a big experiment to save health statistics in the country, you have to ask how strong the relations are. To understand the quality of the data, you must look for things that would not be expected to have a correlation. “There was an increased risk associated with death from injuries and sudden death with higher consumption of red meat in men but not in women.” The authors dismiss this because the numbers were smaller (343 deaths) but the whole study is about small differences and it sounds like we are dealing with a good deal of randomness. Finally, the authors set out from the start to investigate red meat. To be fair, they also studied white meat which was slightly beneficial. But what are we to compare the meat results to? Why red meat? What about potatoes? Cupcakes? Breakfast cereal? Are these completely neutral? If we ran these through the same computer, what would we see? And finally there is the elephant in the room: carbohydrate. Basic biochemistry suggests that a roast beef sandwich may have a different effect than roast beef in a lettuce wrap.
So I’ve given you the perspective of a biochemistry professor. This was a single paper and surely not the worst, but I think it’s not really about science. It’s about sin.
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Nutrition & Metabolism Society
Richard David Feinman 