Bad omega-3/omega-6 balance, corn syrup, and sedentary lives contribute… but DNA can’t be dismissed
by Craig Weatherby
Two years ago we reported on the intriguing preliminary findings of an Australian study, which indicated that exercise and fish oil brought independent benefits to overweight people with risk factors for cardiovascular disease.
The results suggested the shortage of omega-3 fatty acids and overload of omega-6 fatty acids in the American diet make for fatter people.
The Aussie scientists found that overweight people who took omega-3-rich fish oil, exercised modestly, or did both had better weight-loss, body composition, and cardiovascular outcomes than study subjects who instead took capsules containing omega-6-heavy sunflower oil (See “Exercise + Omega-3s = Perfect Weight Loss Pair”).
The results supported the hypothesis—supported by other research (see “Israeli diet reveals ill effects” below)—that diets higher in omega-3s and lower in omega-6s than usual in America promote fat-burning and reduce body fat.
(For more on this topic, see “Omega-3s Boost Weight Loss Benefits of Low-Cal Diets,” “Wild Salmon Excels for Sports and Fitness,” and “Eat Fish, Lose Weight, Feel Better.”)
The innovative Aussie clinical trial was finally published formally last month, and this event coincided with announcement of a new weight-related book by veteran New York Times medical correspondent Gina Kolata, titled Rethinking Thin: The New Science of Weight Loss—and the Myths and Realities of Dieting.
Let’s review the Aussie study again before moving on to the ”revisionist” views presented in the excerpt from Ms. Kolata’s new book, the conclusions of a British obesity panel, and the dismaying example of Israel’s omega-6-heavy national diet.
New York Times writer pins obesity on genes
The May 8 edition of The New York Times included an excerpt from Ms. Kolata’s new book in which she addressed the woefully ignored findings of several body-weight studies conducted from the late 1950’s through the 1990’s.
The overlooked studies produced three major findings:
1. The fat stay fat (more or less): When people who’ve always been fairly fat lose large amounts of weight their metabolisms slow to match the rate of people who are starving:
- When a calorie-restriction diet study begins, the metabolisms of “fat” subjects’—that is, the number of calories burned per square meter of body surface—is the same as in naturally thin people.
- But when they lose weight, they start burning about one-quarter fewer calories per square meter of body-surface, compared with people who are naturally thin.
- This happens because their bodies are genetically programmed to innately, unconsciously “crave” a specific calorie intake range. While their fat cells will shrink in size due to dieting, it doesn’t affect their genetically programmed calorie-requirement parameters much at all.
2. The thin stay thin: Naturally thin people who volunteer to gain weight have little difficulty losing it later and keeping it off.
3. Twins prove the dominant influence of genetics:
- Identical twins—who by definition have identical genes—have nearly identical BMIs, whether they’ve been reared apart by different sets of parents or raised together with their biological parents.
- Fraternal twins—who by definition have genes as different as those of regular siblings—have BMIs just as different as regular, non-twin siblings’.
The results of the studies cited by Ms. Kolata suggest that genes account for about 70 percent of the likelihood of having one BMI or another, with diet and exercise responsible for about 30 percent of a person’s normal BMI.
It seems that people only feel comfortable within 10 or 20 pounds of their genetically programmed BMI. Going any lower induces cravings that are near impossible to resist over the long term.
So if the results of these repeated, scientifically sound studies seem to scream “it’s the genes, stupid,” why does American society keep obsessing over the causes and remedies for being overweight or obese? And why does government keep funding research into obesity causes and remedies?
For one thing, rates of overweight and obesity have definitely risen over the past 60 years, with serious health consequences. (Being overweight is a risk factor for diabetes and heart disease, although it’s not nearly as risky as being genuinely obese.)
And there are many billions of dollars spent every year to persuade people of the efficacy of various diet books, foods, supplements, and programs.
Meanwhile, hopes of a “cure” also fuel billions in federal and pharmaceutical funding of research into potential obesity remedies.
Aussies find exercise and fish oil bring independent and synergistic benefits
Two studies published before the preliminary Australian findings appeared in 2005 showed benefits from replacing other fats with omega-3s (Couet C et al 1997, Groh-Wargo S et al 2005).
But two others detected no omega-3-induced reductions in body weight or fat mass beyond those that would be expected from calorie restriction alone (Fontani G et al 2005, Krebs JD et al 2006).
However, the negative studies either did not include control groups or they used the crude, imprecise skinfold-thickness method to estimate changes in body composition.
Let’s recap the results of the well-designed 2005 Aussie study (Hill AM et al 2007) and take a closer look at it using the newly available peer-reviewed version.
Scientists at the University of South Australia in Adelaide set out to examine the effects of fish oil and exercise, alone and together, on the body compositions (relative and total amounts of fat and lean mass) and cardiovascular health factors of 75 overweight adults aged range 25-65.
All of the participants had at least one cardiovascular risk factor: mild hypertension, elevated blood triglyceride levels, and/or high total cholesterol levels.
They were randomly assigned to one of four groups:
- Fish oil supplements only.
- Sunflower oil supplements only.
- Fish oil capsules + exercise.
- Sunflower oil capsules + exercise.
The exercise consisted of walking for 45 minutes twice a week, and the fish oil capsules contained 260 mg of omega-3 DHA plus 60 mg of omega-3 EPA.
Group #1 enjoyed a desirable 14 percent decrease in blood triglyceride levels and a desirable 10 percent rise in levels of “good” HDL cholesterol.
The placebo (sunflower oil) group (#2) suffered weight gain and showed smaller drops in blood triglyceride levels (average five percent) and rise in HDL cholesterol levels (average three percent).
Group #3’s fish oil + exercise combination reduced their body weight by an average of 3.5 pounds (mostly fat).
Group #4—sunflower oil + exercise—had only about half the weight loss (about 1.7 pounds) of the fish oil + exercise group.
There were no significant weight changes in the fish oil/no exercise Group #1. None of the groups saw significant changes in lean body mass.
As the researchers said, “We… showed that both fish oil supplementation and regular moderate exercise reduced body fat in overweight or obese subjects who were at risk of CVD [cardiovascular disease].”
It seems very likely that the difference between the fish oil and placebo sunflower oil groups was that sunflower oil is high in the pro-inflammatory omega-6 fatty acids deemed overabundant in Western (and Australian) diets.
Omega-6 fatty acids are known to promote fat storage, while omega-3s are proven to alter metabolism in ways that discourage fat storage and promote fat-burning.
UK panel blames microwaves, prepared foods, and lack of physical labor
Earlier this month, Britain’s Cheltenham Science Festival hosted a panel discussion on the causes of the rise in rates of obesity in the UK: a phenomenon that parallels the increase in America:
- In 1980, only eight percent of British women and six percent of men were classified as obese.
- By 2004, the UK’s obesity rates had risen to encompass 24 percent of men and women alike.
- Likewise, rates of childhood obesity in the UK rose from 10-12 percent in 1995 to 16 percent in 2003.
Professor Jane Wardle of University College London noted that obesity rates started to rise between 1984 and 1987, just as microwave ovens and takeout meals became widely popular.
In addition to microwave ovens and prepared meals, all of the panelists pointed to reduced levels of physical activity associated with the sharp increase in auto and television ownership and sedentary jobs that followed the end of World War II.
Pre-WW II generations may actually have consumed more calories, but they were much more active and most worked on farms or at other physically demanding jobs.
And, according to Dr. Wardle, cheaper food prices, prepared and takeout meals and microwave ovens have facilitated overeating.
(For more on these topics, see “Slow Eating May Prevent Weight Gain” and “Portion Control for Weight Control: Size Perceptions Called Key.”)
Professor Ken Fox, professor of exercise and health science at the University of Bristol agreed, telling the BBC, “We're the only generation where there's never been a shortage of food...”
It seems likely that all of these factors combined to cause the sharp rise obesity rates, with no single one primarily responsible.
To these major pro-obesity factors we would add two more:
- The increasing share of total caloric intake contributed by non-satiating, insulin-desensitizing liquid calories from corn syrup (see “High-Fructose Corn Syrup Takes another Hit” and “The Calories We Quaff”).
- The sharp rise in consumption of vegetable oils high in omega-6 fatty acids, excesses of which appear to promote weight gain.
Indeed, as an Israeli team concluded in 1996, excessive omega-6 intake may be a major but overlooked obesity factor.
Israeli diet reveals ill effects of omega-6 overload
Israelis consume eight percent more omega-6s than Americans do. This is quite a feat, given the extreme excess in American diets, and may be due in part to heavy use of omega-6-rich sesame seeds, sesame butter (tahini), and sesame oil in Israeli cuisine.
In fact, as the scientists wrote, “Israeli Jews may be regarded as a population-based dietary experiment of the effect of a high omega-6 diet…”
In fact, Israelis suffer unusually high rates of obesity, cardiovascular disease, hypertension, and diabetes, which led the researchers to the obvious conclusion: “…rather than being beneficial, high omega-6 PUFA diets may have some long-term side effects…” (Yam D et al 1996).
Genes, diet, and exercise all count… just not equally
The seeming contradictions between two bodies of evidence—the overlooked gene-blaming research cited by Ms. Kolata and the rise in Americans’ and Brit's BMIs over the past several decades—aren’t really contradictory.
Instead, these seemingly divergent indications highlight the generally fattening effect of strong, nearly society-wide dietary shifts on people possessing all but the fastest metabolisms (hence the leanest body compositions and lowest BMIs).
The landmark studies cited by Ms. Kolata should not be ignored. But they do not disprove the ability of diet to produce seemingly small—but actually very meaningful, health-enhancing—changes in people’s tissue and body compositions.
Even if everyone is born to gravitate toward a “pre-set” BMI, diet and exercise can improve the health and well-being of overweight or obese people with risk factors for heart disease and diabetes, as the Israeli investigation and the newly peer-reviewed Aussie study suggest.
- Hill AM, Buckley JD, Murphy KJ, Howe PR. Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors. Am J Clin Nutr. 2007 May;85(5):1267-1274.
- Couet C, Delarue J, Ritz P, Antoine JM, Lamisse F. Effect of dietary fish oil on body fat mass and basal fat oxidation in healthy adults. Int J Obes Relat Metab Disord. 1997 Aug;21(8):637-43.
- Groh-Wargo S, Jacobs J, Auestad N, O’Connor DL, Moore JJ, Lerner E. Body composition in preterm infants who are fed long-chain polyunsaturated fatty acids: a prospective, randomized, controlled trial. Pediatr Res 2005;57:712– 8.
- Fontani G, Corradeschi F, Felici A, et al. Blood profiles, body fat and mood state in healthy subjects on different diets supplemented with omega-3 polyunsaturated fatty acids. Eur J Clin Invest 2005;35:499–507.
- Krebs JD, Browning LM, McLean NK, et al. Additive benefits of long-chain N-3 polyunsaturated fatty acids and weight-loss in the management of cardiovascular disease risk in overweight hyperinsulinaemic women. Int J Obes (Lond) 2006;30:1535– 44.
- Kolata G. Genes Take Charge, and Diets Fall by the Wayside. Accessed online June 18, 2007 at http://www.nytimes.com.
- Massiera F, Guesnet P, Ailhaud G. The crucial role of dietary n-6 polyunsaturated fatty acids in excessive adipose tissue development: relationship to childhood obesity. Nestle Nutr Workshop Ser Pediatr Program. 2006;(57):235-42; discussion 243-5. Review.
- Ailhaud G, Massiera F, Weill P, Legrand P, Alessandri JM, Guesnet P. Temporal changes in dietary fats: role of n-6 polyunsaturated fatty acids in excessive adipose tissue development and relationship to obesity. Prog Lipid Res. 2006 May;45(3):203-36. Epub 2006 Feb 10. Review.
- 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.