Linoleic acid is an omega-6 polyunsaturated fatty acid (PUFA) that makes up a large proportion of seed oils. It's a very bioactive molecule, in part because it's the precursor of two classes of signaling molecules (eicosanoids and endocannabinoids), some of which influence the development of fat tissue and regulate appetite.
Dr. Ailhaud and his colleagues pointed out that not only are people eating far more linoleic acid than ever before; that very same linoleic acid is accumulating in our fat tissue and showing up in breast milk. Here are a few graphs to illustrate the point. The first graph is of PUFA consumption in the US over the last century, primarily reflecting seed oil intake (based on USDA food disappearance records):
Here's a graph of added fat intake based on USDA data. Added animal fats such as butter and lard have remained stable since 1970 (although total animal fat intake has declined), while seed oil consumption has gone from high to higher:
The following graph shows linoleic acid accumulation in human body fat over the last few decades in Western nations (mostly the US). I put this together based on two references (2, 3). I didn't find any data from the US past 1986. Linoleic acid, unlike most other fatty acids, accumulates disproportionately in body fat (4):
In 2009, Dr. Ingeborg Hanbauer published a paper showing that when mice are fed a diet with a poor omega-6:3 balance (77:1), after three generations they develop adult obesity (5). Mice fed the same diet with a better omega-6:3 balance (9.5:1) did not develop obesity, and remained smaller overall. This shows that PUFA imbalance can cause multi-generational effects resulting in obesity and excessive tissue growth. Cmdr. Joseph Hibbeln, a collaborator of Dr. Bill Lands, was an author. The thing I don't like about this paper is they didn't quantify the obesity by measuring fat mass, so we have to take the authors' word that they had more fat.
This week, Dr. Florence Massiera and collaborators published a similar paper titled “A Western-like fat diet is sufficient to induce a gradual enhancement in fat mass over generations” (6). Drs. Ailhaud and Guesnet were both on this paper. They showed that a 35% fat diet with an omega-6:3 ratio of 28 caused obesity that progressively increased over four generations of mice. Although this study was more detailed than the study by Dr. Hanbauer and colleagues, it lacked a comparison group with a more favorable omega-6:3 balance to show that the obesity was specifically the result of omega-6:3 imbalance, rather than the fact that the diet was higher in fat overall or some other aspect of its composition.
If this is true in humans, it would be a straightforward explanation for the obesity epidemic that has plagued the Western world in recent decades. It would explain why the epidemic began in children around 1970, but didn’t show up in adults until about 1980. It would explain why the epidemic is less severe in Europe, and even less so in Asia. And of course, it correlates well with trends in seed oil consumption. This graph is based on US NHANES survey data:
We already know that a number of prenatal factors can have an effect on adult body fat levels in rodents, and observational studies have suggested that the same may apply to humans. If a mother’s body fat is full of linoleic acid, she will pass it on to the fetus as it grows, and after birth in breast milk, influencing its development.
As long-time followers of Whole Health Source know, I suspect industrial seed oils contribute to many of our modern ills. I can’t say for sure that seed oils are responsible for the current obesity epidemic, but the evidence certainly gives me pause. In any case, seed oils are an unnatural part of the human diet and it won’t hurt anyone to avoid them. The half-life of linoleic acid in fat tissue is about two years, so reducing it is a long-term prospect.