The most common explanation given for the recent wave of obesity is that “We don’t work as hard as we used to and we overeat.” This is what evolutionary biologist Stephen Jay Gould calls a “just-so story”, an untestable narrative explanation for a cultural practice, a biological trait, or behavior of humans or other animals. This idea comes out of the puritanical nature of American thought. If a person is obese they must be gluutonous and slothful. But if this is right, why was the New York City banker, who took the subway to work, the elevator to his office and sat at a desk all day, lean in 1960 and fat in 2020?
My belief is that the wave of modern obesity is caused by biochemical changes due to the recent addition of large amounts of polyunsaturated fat to our diet, which ultimately led to our regulatory feedback systems becoming deranged as exemplified by the increase in out desaturase index that happened sometime between 1962 and 1991.
The desaturase index (DI) is simply the amount of oleic acid (the monounsaturated fat also known as 18:1) divided by the amount of stearic acid (the saturated fat known as 18:0) in any given tissue. It varies a lot between tissues, so that a blood test measuring red blood cell phospholipids gives you a much different range of DI values than does a fat tissue biopsy, but a high DI within any given tissue is strongly associated with obesity and is a sign that a master regulatory enzyme – SCD1, whose only job is to convert saturated fats to monounsaturated fats – has become dysregulated.
If we look at obese newborn babies, we can eliminate the idea that they got that way by sloth or gluttony. Babyfat is cute, but some have more than others.
This paper1 examined the question of whether or not the maternal desaturase index (DI) is associated with obesity in newborns. These are the conclusions of the authors:
So the maternal post-obese phenotype can seemingly be transferred straight to the next generation. Isn’t that lovely?
This paper relies on some pretty heavy statistical methods. I’m not a statistician so I’m relying on the study authors to have gotten this right. If any statisticians read this I’d love to see your comments on this.
My understanding is that the numbers in bold are the ones that were statistically significant after adjusting for the “False Discovery Rate(FDR)”, which corrected for things such as maternal BMI, maternal blood sugar and maternal insulin levels. Even after the corrections for these confounding variables, there is a strong correlation between late pregnancy maternal blood DI and newborn BMI, birth weight and weight-for-length. The DI of blood from the umbilical cord was strongly correlated to the birth waist-to-length. The correlations remained significant at two years of age, suggesting that the maternal DI helped set the newborns up for a lifelong battle of the bulge.
But sloth and gluttony didn’t play a role in it.
- 1.Marchioro L, Hellmuth C, Uhl O, et al. Associations of maternal and fetal SCD-1 markers with infant anthropometry and maternal diet: Findings from the ROLO study. Clinical Nutrition. Published online July 2020:2129-2136. doi:10.1016/j.clnu.2019.08.030