Butter versus Margarine

This month I am piloting a new elective in nutrition for senior medical students. Every day they read a combination of historical and contemporary literature on food and diet, and we meet for 2 hours for a lecture and/or discussion. Each week has a different theme: "adult" nutrition, including the food groups and common "dietary diseases" such as diabetes and hypertension; pediatric nutrition, including infant feeding and eating disorders; obesity, including both medical/surgical solutions for weight loss as well as the anti-diet movement; and surgical nutrition, including perioperative management of fluids and "artificial" nourishment via TPN or tube feeds. I started with a brief history of some themes in the science of nutrition; here is the YouTube recording of my lecture.

For the day on fats and cardiovascular disease, I assigned Todd Olszewski's article "The Causal Conundrum: The Diet-Heart Debates and the Management of Uncertainty in American Medicine" (JHMAS, 2014); Edgar R. Miller III, Thomas P. Erlinger, and Lawrence J. Appel's summation, "The Effects of Macronutrients on Blood Pressure and Lipids: An Overview of the DASH and OmniHeart Trials" (Current Atherosclerosis Reports, 2006); and the latest version(s) of the American Heart Association and American College of Cardiology nutritional recommendations, Lichtenstein, et alia (Circulation, 2021) and/or Van Horn, et alia (Circulation, 2016).

Olszewski writes about the sometimes furious professional debates in the mid-twentieth century over "the diet-heart hypothesis," or the idea that increased dietary fat correlates with increased serum lipid levels, which are associated with higher rates of heart attacks and strokes. Some experts were persuaded by the circumstantial evidence, while others pointed out these are correlations of risk factors based mostly on epidemiological studies, not causations proven through strict feeding studies with histological proof of clinical disease. Meanwhile, the American public largely accepted the argument and changed their dietary practices (consider the substitution of cereal or a bagel for a breakfast of eggs and bacon), despite the lack of scientific agreement, probably due to fear of suffering ill health.

Images from Jeff Nobs

I broke the students into four groups in Zoom breakout rooms and asked them to research and defend a position for or against butter or margarine. 20-30 minutes later, they were ready to present. I asked the first group why I should put butter on my toast. Their spokesman acknowledged that there was an association between saturated fats and cardiovascular disease BUT, based on the label from the butter in someone's fridge, 1 serving was only 1 tablespoon with 11 total grams of fat and 63 kcal, with 7 grams of that being saturated. However, they argued that the most common butter fats are palmitic acid (29%), maristic acid, stearic acid, and laric acid. They had found two epidemiological studies that proposed those last two reduce the HDL/TGL ratio decreased CVD risk. Furthermore, the national Dietary Guidelines allow up to 5% of calories to come from saturated fat for the production of hormones, cell membranes, etc., and that amounts to 100kcal in a 2000kcal/day diet.

The pro-margarine group pointed out that their product had been designed to reduce the amount of saturated fat in the diet, with only 0.67 grams per serving of tub margarine versus 7 grams from stick butter. They acknowledged that the original margarine had contained more trans fats (as well as a color packet to make it yellow instead of white), whereas newer margarines are healthier because they contain more unsaturated, non-trans fats. I pointed out that it is important to remember food history when weighing evidence of nutritional claims, because food products have changed over time. They even found a study from the Journal of Epidemiology (2018) that showed lower rates of myocardial infarction (but not other outcomes) among individuals who consumed margarine rather than butter. This is an impressive example of a nutritional study with a clinical outcome rather than one based on risk factors like measuring serum lipids or blood pressure. They concluded with the statistic that margarine production releases 3.5x less carbon dioxide than butter, making it the better choice for the environment.

Images from Jeff Nobs

When I asked the third group why I shouldn't put butter on my toast, their spokespeople warned us about high saturated fat content (especially any product with >60% fat), salted butters as a double health-whammy, too many calories, and not enough micronutrients. Plus, many people are lactose intolerant [however, the lactose content is very low, so this actually isn't a problem]. The anti-butter students urged us to "free the dairy cows!" and choose one of the many, many non-butter options for our toast...like avocados. They used the webpages from HealthLine, Harvard Health, and Mayo Clinic.

Finally, the anti-margarine group argued hyperbolically yet persuasively against the butter substitute. Their very entertaining spokesman railed against polyunsaturated fats being associated with obesity and heart disease, and that margarine couldn't be classified as a "health product" given its association with asthma, eczema, and other inflammatory disease processes. He then graphically described the "disgusting process" of manufacturing margarine with chemicals and metals as compared to "just churning butter" [as if that were not also a highly industrialized process these days]. It was a command performance that left us in stitches, and I was sorry we weren't in a room together to share the laughter. The students joked in the chat that the anti-margarine spokesman had roasted margarine so well its fats had turned rancid. Interestingly this "anti" group had also used patient-facing sources such as from the Cleveland Clinic.

When I asked what evidence they had found most persuasive, the students discussed individual health concerns, butter as part of a balanced diet ("a little dab'll do 'ya"), and environmental worries such as how much water has to be diverted into California for agricultural production of non-butter options. It was an engaging lesson that let the students think about the nature of evidence, how a message can be shaped by its presentation, and the applicability of general nutritional advice for individual patients. Me? I reverted from the margarine of my childhood--when it was a health product--to butter in college, based on the strength of my roommate's argument, "If it was good enough for my grandmother, it's good enough for me!" How's that for an emotional argument? But then, we don't just eat for nutrition, so it makes a certain kind of sense.