Red-hued carotenoid in wild salmon aids weight control by promoting fat-burning
Wild and farmed salmon alike owe their red-orange color to a carotenoid-class antioxidant pigment called astaxanthin … as do lobsters, crab, shrimp, and other shellfish with reddish parts.
Salmon and shellfish get astaxanthin from eating plankton (or creatures that food on plankton), which get astaxanthin from feeding on micro-algae that produce the carotenoid in the first place.
The results of a study from Japan may offer extra help to those of us who want or need to control our weight and love salmon.
Astaxanthin in wild vs. farmed salmon
Farmed salmon get astaxanthin as a feed additive, both because consumers will not buy white- or grey-fleshed salmon, and because astaxanthin is essential for salmon's growth and overall health.
(The astaxanthin in some farmed salmon chow is a synthetic isomer with different health effects, while some salmon chow contains the natural form, derived from cultivated algae.)
But wild salmon is far richer in astaxanthin, compared with farmed fish.
Tissue levels in the flesh of Atlantic salmon range from about four to 10 mg per kilogram (2.2. pounds).
But astaxanthin levels in wild Pacific salmon can be much higher, with an FDA study reporting an average of about 14 mg per kg in silver (coho) salmon and about 40 mg per kg in sockeye salmon (Turujman et al 1997).
A six-ounce portion of farmed Atlantic salmon averages 0.75 to 1.65 mg of astaxanthin, while wild sockeye salmon offers 6.75 mg of astaxanthin per six-ounce serving, or four to nine times as much.
Astaxanthin is proven to support eye health, and is an unusually potent antioxidant, with a free-radical-fighting capacity 500 times greater than vitamin E's.
Study marks astaxanthin a serious weight control contender
Researchers at the Tokyo University of Marine Science and Technology fed female mice a high-fat diet supplemented with astaxanthin (Ikeuchi M et al 2007).
The added astaxanthin reduced weight gain in the mice, decreased build-up of fatty tissue, and improved the fatty acid profiles of the animals' blood.
According to lead author Mayuni Ikeuchi, “These results indicate that astaxanthin might be of value in preventing obesity and the metabolic syndrome in affluent societies.”
The researchers assigned month-old female mice to one of five groups, and fed them different diets for 60 days:
- Normal mouse chow diet (control group)
- High-fat diet supplemented with olive oil (placebo)
- High-fat diet plus 1.2 mg astaxanthin per kilogram (kg) of body weight
- High-fat diet plus 6 mg astaxanthin per kg of body weight
- High-fat diet plus 30 mg astaxanthin per kg of body weight
The olive oil group showed significant weight gain, compared to the control group.
But, as the Japanese team reported, “…feeding a high-fat diet plus astaxanthin at levels of 6 mg/kg or 30 mg/kg significantly reduced the body weight gain induced by the high-fat diet” (Ikeuchi M et al 2007).
The two higher-dose astaxanthin groups (6 mg per kg and 30 mg per kg) also had less adipose (under-skin fat) tissue, while the lower dose astaxanthin groups did not have significantly lower adipose tissue weight than the olive oil group. (Excess adipose tissue is a risk factor for metabolic syndrome, diabetes, and heart disease.)
In addition, blood triglyceride levels were higher in the olive oil group than for the control group, while triglyceride levels in the two highest-dose astaxanthin groups were about 50 percent lower than in the olive oil group.
Based on the known properties of similar polyphenol antioxidants—including those in tea—the researchers hypothesized that astaxanthin stimulates burning of fatty acids rather than blood sugar (glucose) for energy, but more research is needed to confirm this.
Note: In order to match the lowest effective dose level in this study (6 mg per kg), a 130-pound person would need to ingest 354 mg of astaxanthin per day, which is the amount in 52 servings of Sockeye Salmon.
Researchers typically start with very high doses of promising food factors, so that any good effects manifest quickly, thereby giving fast indications of which substances to test at lower doses over longer periods.
Don't expect the astaxanthin in it to make a big impact by itself, even if you dine on wild Sockeye salmon everyday. The idea is to enjoy a variety of antioxidant-rich foods—and drink tea—to help optimize your metabolic patterns.
Astaxanthin: other health effects
The available animal studies and preliminary human trials indicate that astaxanthin may help protect against cataracts and sunray damage to the skin, support immunity, and help prevent or ameliorate the effects of cancer, diabetes, hypertension, stroke, and vascular dementia (Hussein G et al 2006).
Astaxanthin is produced by algae, probably to protect against the effects of UV radiation.
And this is partly why it supports eye health. Like lutein and zeaxanthin, from green vegetables astaxanthin is a carotenoid compounds belongs to the carotenoid subgroup called xanthophylls (zan-thuh-fills): But astaxanthin is an even stronger antioxidant than its close chemical cousins.
Like lutein and zeaxanthin, astaxanthin may help protect against cataracts and age-related macular degeneration (AMD).
Astaxanthin neutralizes free radicals, thereby preventing oxidative stress on cells in the eyes and the body's unintentionally damaging inflammatory response.
When researchers administered astaxanthin to rats intravenously, it reduced inflammation—a key contributing factor in the development of AMD and cataracts—in rodents' eyes (Suzuki Y 2005). It remains to be seen whether dietary astaxanthin exerts a similar beneficial effect in people's eyes, although that seems very likely.
These preliminary findings suggest that wild salmon could be a potent ally in the battle to decelerate the aging process in our eyes.
And wild salmon may be more helpful than white fish. Higher intake of white fish is associated strongly with reduced risk of macular degeneration and cataracts.
This effect of fish is attributed to marine omega-3s, which occur at higher levels in wild salmon and other fatty fish like sablefish and tuna (Seddon JM et al 2006 and Chua B et al 2006).
Studies indicate that astaxanthin is safe for humans… a scientific finding supported by centuries of copious wild salmon consumption among Native Americans, Scots, and Scandinavians.
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