I've been writing about nutrition for 30-some years. As I listen to people, I often hear less science and more of what could best be described as a variety of belief systems.
There are the vegetarian, vegan, and macrobiotic sects. There's the church of low-fat eating. And there's the pervasive belief that everything boils down to calories in and calories out, with exercise being the penance for overeating.
But the fact is, there's very little science to support many common nutrition beliefs. They're just beliefs. And having millions of adherents or thousands of experts repeat the same mantras doesn't make these beliefs truer.
I know this sounds like heresy to many of you. And I'm not trying to offend anyone's nutritional or religious sensibilities. But the only food we definitely know we were meant to consume is breast milk, in infancy.
In anthropology, the term "belief system" is usually used to describe a religion. And when it comes to nutrition, many scientists and consumers are so wedded to their beliefs that they're not interested in adjusting their beliefs in response to new scientific findings.
I'll give you three examples.
Saturated Fat. Millions of people believe that low-saturated fat diets will prevent heart disease. But the research now shows the opposite to be true. Saturated fat is either neutral or protective, according to an impressive body of research. It's the refined carbs and sugars and the trans fats that seem to be the real problem in cardiovascular risk.
Why do so many people still believe that saturated fat is bad? It's a matter of belief - shaped by studies that failed to factor in the effects of carbs, sugars, and trans fats, as well as publication bias favoring the sat-fat-is-bad belief.
Calories. Nearly everyone believes that, to lose weight, you have to either eat less or exercise more. But different types of calories prompt different biological responses. Nutrients that trigger insulin - think carbs and sugars - are more likely to result in weight gain, compared with protein. Protein has little effect on insulin.
The calorie idea was based on energy transfer in steam engines and the 1st Law of Thermodynamics. Biological systems - you are a biological system - are far less efficient and are governed by the 2nd Law of Thermodynamics.
Vegetarian Diets. If you look at the history of human cultures, as anthropologists and other scientists have done, you'll realize that there have been no completely vegetarian cultures. People simply didn't have the luxury to be so picky about food until relatively recently. Yes, veggies are good for health, but so is unadulterated animal protein. Biologically, we're designed as omnivores.
Vegetarianisms and its many forms are a belief system. Understand that I have no issue with any sensible vegetarian. However, I've met many vegetarians who don't eat vegetables and prefer sugary soft drinks, bagels, and muffins. Should any of us be surprised that they are often overweight and have a lot of health problems?
Again, I'm not trying to offend anyone or their beliefs. Rather, I'd like to encourage people to gain a better understanding of what shapes their nutritional beliefs and to remain open to where the scientific evidence leads.
Siri-Tarino PW, Sun Q, H FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. American Journal of Clinical Nutrition, 2010;91:535-545.
Siri-Tarino PW, Sun Q, H FB, Krauss RM. Saturated fat, carbohydrate, and cardiovascular disease. American Journal of Clinical Nutrition, 2010;91:502-509.
Feinman RD, Fine EJ. "A calorie is a calorie" violates the second law of thermodynamics. Nutrition Journal 2004;3:9-13.
Feinman RD, Fine EJ. Nonequilibrium thermodynamics and energy efficiency in weight loss diets. Theoretical Biology and Medical Modelling, 2007;4:27 doi:10.1186/1742-4682-4-27.
Eaton SB, Eaton SB III, Konner MJ, et al. An evolutionary perspective enhances understanding of human nutritional requirements. Journal of Nutrition, June 1996;126:1732-40.
O'Keefe JH Jr, Cordain L. Cardiovascular disease resulting from a diet and lifestyle at odds with our Paleolithic genome: how to become a 21st-century hunter-gatherer. Mayo Clinic Proceedings, 2004;79:101-108.