Diets high in omega-6 fatty acids are associated with greater body weight and fat compared with diets having less omega-6 fat and more omega-3 fat.
Several studies presented at the recent ISSFAL conferfence seem to support prior research results.
Mouse study finds omega-6 fats promote weight gain
At the ISSFAL conference, researchers reported that mice fed 50 percent less omega-6 fat than the control group for the first 6 weeks of life and then switched to a western-style diet (high in omega-6 fat) for eight weeks had 27 percent less fat compared with the controls.
The rodents also had fewer fat cells, lower blood triglyceride (fat) levels, improved glucose (blood sugar) tolerance, and greater insulin sensitivity… all of which are associated with reduced risk for diabetes and heart disease (Oosting A et al., 2010).
American babies' bellies grew along with increasing omega-6 intake
The type of dietary fat a person eats affects the development of metabolic syndrome (MetS).
Population studies suggest that diets high in saturated fats increase the chance of developing MetS, while high polyunsaturated fat lower the risk.
Whether diets high in omega-6 fat promote weight gain and fat accumulation and contribute to MetS is hotly debated.
Adiposity—the medical term for excess belly fat—in six to 11-month old infants in the U.S. increased nearly two-fold from 1976 to 1994.
This sharp rise occurred during the same time span when the omega-6 fat content of infant foods, including breast milk and infant formula, also increased (Alvheim A, 2010).
In contrast, infants' intake of omega-3s declined during this period.
Associations like these do not establish cause-effect relationships, but they raise questions.
Infant mice show similar reaction to diets high in omega-6 fats
French researchers have reported that a western-like diet is sufficient to induce greater fat mass over generations (Massiera F, et al. 2010)... and a study in mice presented at ISSFAL also addressed this issue.
Mice consumed diets containing either one or eight percent omega-6 fat from weaning (Alvheim A, 2010).
Those on the eight percent omega-6 fat diet exhibited significantly greater appetite, feed efficiency and fat tissue compared with those on the one percent omega-6 fat diet.
Adding one percent of energy from long-chain omega-3 fish fats (EPA and DHA) to the eight percent omega-6 fat diet was accompanied by reduced fat accumulation and lower feed efficiency, which means that fewer of the animals' calories were absorbed.
The French team noted that even diets that were extremely high in fat (60 percent of calories)—but in which omega-6 fat contributed only one percent of total calories—did not produce obesity.
Omega-3s may lower risk factors for cardiovascular disease and diabetes
In one invited ISSFAL presentation, the speaker noted that lifestyle modifications, such as the inclusion of long-chain omega-3 fats from fish (EPA and DHA) can help deter development of obesity, liver-fat accumulation, abnormal blood fat profiles and impaired glucose tolerance (Kopecky J, 2010).
But once diabetes has developed, these fatty acids are much less effective and drugs are necessary to reverse obesity, abnormal lipids and insulin resistance.
The potential for preventing MetS and ultimately diabetes by increasing long-chain omega-3 fatty acid intake—in conjunction with reducing omega-6 fat consumption—deserves much more investigation and attention.
“Mono” fats appear to bear little blame for weight gain
We've had relatively little evidence on how diets rich in monounsaturated fats—chiefly, the oleic acid in olive, macadamia nut, canola and “high-oleic” sunflower oil—affect the risk of metabolic syndrome (MetS), though there is as yet no evidence that mono-unsaturated fats raise it.
At the conference, investigators from Spain reported that MetS patients with the highest proportion of monounsaturated oleic acid in their blood had less abdominal obesity and were more likely to have higher (more desirable) HDL levels.
These observations suggest that in addition to protecting heart health, diets rich in olive oil may help to deter weight gain (Sala-Vila A et al., 2010).