Israeli and Korean studies show women more vulnerable to ill effects of “omega-imbalanced” diets
by Craig Weatherby
Today’s American-style diets contain very high proportions of omega-6 fatty acids—and low proportions of omega-3s— compared with the diets consumed by prehistoric and modern hunter-gatherers.
In America and most of the developed world, people’s omega-6/omega-3 intake ratio averages 30/1. But for a million years or more, humans and their evolutionary ancestors evolved in response to diets that provided an omega-6/omega-3 intake ratio closer to 2/1.
We’ve reported extensively on the growing evidence tying today’s “omega-imbalance” to increased rates of cancer and heart disease (See “Overview of the omega-imbalance”, below).
And new studies from Israel and Korea add to fears that Americans’ vegetable oil habit is undermining their health.
Israelis may be serving as unwitting canaries in a dietary coal mine
A dozen years ago, researchers at Israel’s Weizmann Institute of Science noted that Israeli Jews consumed more omega-6 polyunsaturated fats than any other country in the world.
- Israeli and Korean studies affirm the ill effects of “omega-imbalanced” diets, those extremely high in omega-6 fats and low in omega-3s.
- Rates of cancer and heart disease appear to rise along with people’s intake of omega-6 fats relative to omega-3 fats.
- The modern “omega-imbalance” dates to the 1960s, when doctors began urging people to shun saturated animal fats in favor of vegetable oils high in omega-6 fats.
At the time, Israelis averaged an omega-6 intake that was about eight percent higher than Americans’ and about 11 percent higher than in most European countries.
And as the researchers wrote, "Israeli Jews may be regarded as a population-based dietary experiment of the effect of a high omega-6 diet, a diet that until recently was widely recommended.”
The Weizmann Institute team noted that compared with people in other developed countries, Israeli Jews suffer high rates of cancer, cardiovascular diseases, hypertension, diabetes and obesity... and the risk factors for these diseases, which include high insulin levels (hyperinsulinemia), insulin resistance, and metabolic syndrome.
And to them, these correlations suggested an obvious hypothesis that has since gained a great deal of evidentiary support:
“…rather than being beneficial, high omega-6 PUFA diets may have some long-term [adverse] side effects...”
Overview of the omega-imbalance
Today’s omega imbalance began in the mid-1800s, but the dietary dominance of omega-6-rich vegetable oils accelerated greatly in the 1960’s in response to the (now-discredited) hypothesis that blamed cholesterol and saturated fats for heart disease.
The shift can be attributed in part to Americans’ increasing consumption of grain-fed meats since the end of World War II.
But it stems much more from copious consumption of vegetable oils high in omega-6s and low in omega-3s.
Nearly 50 years ago, doctors and public health authorities began pushing manufacturers and consumers to shun animal fats in favor of vegetable oils high in polyunsaturated (i.e., omega-6) fats: corn, safflower, sunflower, soy, and cottonseed oils. The only major exception is “hi-oleic” sunflower oil, which is very low in omega-6s.
Canola oil is also pretty high in omega-6s, but it at least offers a substantial portion of omega-3s and monounsaturated omega-9 oleic acid. At about 11 percent, the omega-3 content of canola oil far exceeds that of all other common cooking oils except soybean oil, which contains about 8 percent omega-3s.
(Note: The omega-3 fat found in all plants and seed oils is ALA, and the body converts only about five percent of dietary ALA into the long-chain omega-3s it actually needs to survive and thrive (EPA and DHA). The only food sources of EPA and DHA are fish and algae.)
These are some of the articles we’ve written concerning the apparent ill effects of the overload of omega-6 fatty acids in Western-style diets… an imbalance increasingly seen in developing countries as well.
Last fall, Niva Shapira, Ph.D., R.D., of Tel Aviv University analyzed diet patterns and health statistics among Israel’s Jewish and Arab citizens (Shapira N 2007).
Her findings confirm the risks of omega-imbalanced diets and detected signs that women may be much more vulnerable to the negative health effects of such diets.
Dr. Shapira noted that Israeli Arabs consume a more traditional Mediterranean diet, with more monounsaturated fatty acids (mostly olive oil), and less omega-6 fatty acids. Their cancer rates are lower than those of Israeli Jews, but are increasing as their diets shift to a more “Israeli” mode with increased intake of omega-6 fats.
Compared with Israeli-Jewish men, she found that Israeli-Jewish women die from cancer at much higher rates, and have much higher cancer rates than Israeli-Arab women.Dr. Shapira stressed that the diets of Jewish and Arab Israeli women were similar... except that Jewish women consumed much great amounts of omega-6 fatty acids (from various vegetable oils other than olive oil) and much less monounsaturated fat (e.g., from olive oil).
Her paper included these key points:
- Population studies of Israeli Jews and Arabs support a link between diets high in omega-6 fats and an increased cancer risk, especially among women.
- Gender and sex hormones may influence how women’s bodies metabolize omega-6 fats, in ways that promote cancer.
And more recent findings from Korea add to concerns that the omega-imbalance is unhealthful… especially for females.
Korean findings affirm Israeli indications
Earlier this year, Korean scientists conducted research among 120 pre-menopausal and post-menopausal women (Rhee Y et al. 2008).
About half of each group had diabetes or heart disease, and the Korean team analyzed blood from all of the women to see if there were differences between the healthy women and their fellow volunteers, in terms of fatty acid profiles.
(Blood tests offer a more accurate way to gauge people’s dietary intakes of fatty acids, compared with diet questionnaires.)
The results showed that the healthy post-menopausal women had higher blood levels of omega-3s and lower omega-6/omega-3 ratios, compared with the women diagnosed with heart disease and/or diabetes.
As the Koreans wrote, “There was a significant relationship between omega-3 and omega-6 profiles and risk for coronary heart disease in women.”
On average, the healthy pre-menopausal women had higher omega-3/omega-6 ratios, compared with the post-menopausal women.
Given the post-menopausal shift in levels of sex hormones such as estrogen, this finding seems to support Dr. Shapira’s hypothesis that they influence how women’s bodies metabolize omega-3 and omega-6 fatty acids.]
- Rhee Y, Paik MJ, Kim KR, Ko YG, Kang ES, Cha BS, Lee HC, Lim SK. Plasma free fatty acid level patterns according to cardiovascular risk status in postmenopausal women. Clin Chim Acta. 2008 Feb 16; [Epub ahead of print]
- Shapira N. Israeli 'cancer shift' over heart disease mortality may be led by greater risk in women with high intake of n-6 fatty acids. Eur J Cancer Prev. 2007 Oct;16(5):486-94.
- Yam D, Eliraz A, Berry EM. Diet and disease--the Israeli paradox: possible dangers of a high omega-6 polyunsaturated fatty acid diet. Isr J Med Sci. 1996 Nov;32(11):1134-43. Review.