Over the past century or more, America’s fat intake has slowly but steady drifted toward a pattern that, in evolutionary terms, is both extremely recent and grossly imbalanced.
Diets typical of modern America—ones high in omega-6 fatty acids and low in omega-3s—are linked to higher risk of cancer, diabetes, and immunity disorders.
Lab studies indicate that these associations reflect real influences that various patterns of omega-3 and omega-6 fat intake exert over the risks of major chronic diseases.
Both of these essential fats are indeed essential to health, with each playing different but critical roles in inflammation, metabolism, and vascular health.
The effects of America’s “omega-imbalanced” diets on cardiovascular disease remain unclear—while low omega-3 intake is clearly undesirable, high omega-6 intake isn’t necessarily bad.
But while moderate intake of omega-6s clearly aids cardiovascular health, there’s growing evidence that human arteries—and people's bodies as a whole—would be better off without the very high levels of omega-6s typical of today's diets (Wijendran V et al. 2004; Ghosh S et al. 2007).
Omega-6 fatty acids abound in common vegetable oils (corn, safflower, sunflower, cottonseed, soy) and the many packaged and prepared foods high in these oils, as well as in standard, grain-fed meats, poultry, and farmed fish.
To learn more about the effects of the current, widespread omega-imbalance, see “Women’s’ Excess Omega-6 Intake Raises Health Risks”, “Prostate/Colon Health Linked to Omega-6/Omega-3 Ratio”, and “Omega-6/Omega-3 Imbalance Pushes Heart/Diabetes Perils”, and see the Omega-3 / Omega-6 Balance section of our news archive.
And this extreme omega-imbalance may also blunt development of human brains, as we reported previously (See “Omega-3s Boost Infant Brains; Omega-6 and Trans Fats Hinder Them”).
Today’s news concerns an experiment in pigs that highlights possible developmental detriments from America’s omega-imbalanced diets.
Developmental downside seen from omega-6 overload
Pediatric researchers at the University of British Columbia fed one of four milk formulas to groups of infant pigs, to simulate the effects of different maternal intakes of omega-3 and omega-6 fats (Novak EM et al. 2008).
In all cases, the piglets’ formulas contain only short-chain omega-3s (ALA) and omega-6s (LA).
The body must first convert these short-chain forms to long-chain omega-3s (DHA and EPA) and omega-6s (AA) before they can be used to build brain cells (neurons) and promote connections between brain cells (dendrites).
Fish fat and oil are the only significant food sources of the long-chain omega-3s (DHA and EPA) essential to human health.
Most of omega-3 fat in most Americans’ diets is the short-chain, plant-source omega-3 called ALA, small amounts of which occur in leafy greens, flaxseed/oil, walnuts, grass-fed meats and poultry, and canola oil.
The Canadian researchers gave piglets short-chain omega-3s and omega-6s instead of long-chain fats, for two reasons:
- They wanted to simulate modern human diets, and most modern mothers consume few long-chain omega-3s.
- They wanted to see whether diets high in omega-6s would reduce conversion of short-chain omega-3 ALA to the useful long-chain forms (DHA and EPA)… especially the conversion of ALA to DHA, which is critical to brain growth and function.
These were the four experimental diets:
- Evolutionary Diet—roughly equal amounts of omega-3s and omega-6s: that is, the ratio found in the diets of hunter-gatherer societies that resemble those of our distant human and pre-human past
- Deficient Diet—Very low in omega-3s
- Contemporary Diet—Very high in omega-6s and heavily imbalanced in favor of omega-6s
- DHA-Supplemented Diet—Contemporary diet plus supplemental omega-3 DHA
The results were disturbing, with respect to the effects of today’s omega-imbalanced diets on child development.
Results support developmental benefits of balanced omega fat intake
The results affirmed the indications of prior research, showing that the imbalanced Contemporary diet, which was very high in omega-6 ALA, reduced brain levels of omega-3 DHA and yielded high levels of long-chain omega-6s in the brain.
In contrast, the Evolutionary diet, with a rough balance between omega-6 and omega-3 fats, produced high brain levels of DHA.
The DHA-supplemented” contemporary diet increased DHA brain levels, compared with the omega-6-heavy, omega-3-light “Contemporary” diet.
And, they found that the short-chain omega-6 LA fat was efficiently converted to the useful long-chain form (AA) absorbed, compared to the conversion of short-chain omega-3 ALA to omega-3 DHA.
However, as they noted, it was omega-3 DHA, not long-chain omega-6 AA that promoted growth of brain-cell connections networks (secondary neurites).
As they wrote, “Our results suggest the need to consider whether current high dietary omega-6 fatty acid intakes compromise brain DHA accretion [buildup] and contribute to poor neuro [brain] development” (Novak EM et al. 2008).
The solution is for expectant and nursing mothers to cut back on omega-6-rich vegetable oils (corn, safflower, sunflower, cottonseed, soy) in favor of olive oil, avoid packaged and prepared foods, reduce intake of standard, grain-fed meats, poultry, and farmed fish, and eat plenty of fatty fish and/or fish oil.
In terms of fatty, omega-3-rich fish, the purest choices include canned sardines or mackerel, wild Alaskan salmon and sablefish, and small, troll-caught tuna.
- Bouwstra H, Dijck-Brouwer DJ, Decsi T, Boehm G, Boersma ER, Muskiet FA, Hadders-Algra M. Relationship between umbilical cord essential fatty acid content and the quality of general movements of healthy term infants at 3 months. Pediatr Res. 2006 May;59(5):717-22.
- Bouwstra H, Dijck-Brouwer J, Decsi T, Boehm G, Boersma ER, Muskiet FA, Hadders-Algra M. Neurologic condition of healthy term infants at 18 months: positive association with venous umbilical DHA status and negative association with umbilical trans-fatty acids. Pediatr Res. 2006 Sep;60(3):334-9. Epub 2006 Jul 20.
- Ghosh S, Novak EM, Innis SM. Cardiac proinflammatory pathways are altered with different dietary n-6 linoleic to n-3 alpha-linolenic acid ratios in normal, fat-fed pigs. Am J Physiol Heart Circ Physiol. 2007 Nov;293(5):H2919-27. Epub 2007 Aug 24.
- Novak EM, Dyer RA, Innis SM. High dietary omega-6 fatty acids contribute to reduced docosahexaenoic acid in the developing brain and inhibit secondary neurite growth. Brain Res. 2008 Oct 27;1237:136-45. Epub 2008 Aug 5.
- Wijendran V, Hayes KC. Dietary n-6 and n-3 fatty acid balance and cardiovascular health. Annu Rev Nutr. 2004;24:597-615. Review.