Friday, April 30, 2010

Fish Oil, Colitis, And Cancer

Remember this study that showed both omega-3 fatty acids (in the form of fish oil) and omega-6 fatty acids (in the form of safflower oil) promoted colon cancer in rats? (Fish oil was worse.)
"At 3 weeks after tumor transplantation, the fish oil diet and the safflower oil diet had induced, respectively, 10- and 4-fold more metastases (number) and over 1000- and 500-fold more metastases (size) than were found in the livers of rats on the low-fat diet."
- Dietary Omega-3 Polyunsaturated Fatty Acids Promote Colon Carcinoma Metastasis in Rat Liver, Cancer Research 1998
Here's a later one that cited it and added to it:

Dietary Fatty Acids Modulate Chronic Colitis, Colitis-Associated Colon Neoplasia And COX-2 Expression In IL-10 Knockout Mice, Nutrition, 2006

Mice were fed chow supplemented with:
  • Corn oil (control)
  • Olive oil
  • Fish oil
Findings:
  • "The average colitis score was higher in the Fish Oil than in the Corn Oil group."
  • "The incidence of severe colitis (score ≥ 3) was significantly higher in the Fish Oil group than in the Corn Oil and Olive Oil groups (50% versus 7.7% and 3.7%)."
  • "Aberrant crypt foci and crypt index were significantly higher in the Fish Oil Group than in the Corn Oil group."
  • "Dysplasia [abnormal, precancerous] was more frequent in the Fish Oil group and less frequent in the Olive Oil than in the Corn Oil group (47% and 4% versus 15%)."
Conclusion:
"[In mice], fish oil exacerbates chronic colitis and colitis-associated premalignant changes."
They used corn oil for the control group. But the corn oil group actually performed worse than the olive oil group. Perhaps it was a function of type of fat? - Both corn oil and fish oil are high in polyunsaturated fat, olive oil is higher in monounsaturated fat.

The trend I see in these and other studies is that dietary fat has some association with cancer, that the type of fat matters (e.g. in colon cancer, polyunsaturated fat seems more problematic), and that certain individuals, especially those with a genetic predisposition, are at increased risk for cancer when they consume certain fats. A low-fat diet, which is by default a high-carbohydrate diet, tends to be protective.

I have a human study I'll post shortly.
________
Photo of fish oil extracted from seafood waste from: Angling For Fortune With Omega-3 Fish Waste Venture.
Fish oil has become a profitable business, not only because of increased consumer demand, but because it can be produced from exploitation of waste products from other industries - input costs are low.

9 comments:

Matthew said...

They are interesting studies though it is hard to tell how relevant the first is to human nutrition.

The first study used a diet of 70% fish oils, equivalent to a human eating about 150 grams of fish oil a day! It would be interested to see if they could show any similar effect from a more realistic long-term consumption of say 0.5-1% fish oil. I expect if you fed rats 70% of their calories as pure fructose, the effect on their livers would probably be unpleasant. This does not mean the equivalent to an apple a day has the same effect.

The second I think illustrates the complexity of the immune system. As omega 3 fatty acids are used to derive signalling molecules to alter immune function it is not surprising that their function can change in complex ways depending on the state of immune response. "Omega 3 = anti-inflammatory", while often accurate, simplifies a large amount of rather confusing complexity in the system.

However in this recent study http://www.ncbi.nlm.nih.gov/pubmed/20363597 fish oil balanced with omega 6 fats reduced inflammation in experimental colitis by increasing the IL-10, the very cytokine that was knocked-out of the experimental mice in the previous study.

It is quite a confusing picture and hard to read a clear meaning into these kinds of studies in isolation other than that almost nothing has only positive or negative effects.

Tschäff said...

Love the blog, even when it freaks me out. Also... I ordered from nutsonline for the first time, and love them too. Keep it up.

Tschäff said...

Love the blog, even when it freaks me out. Also... I ordered from nutsonline for the first time, and love them too. Keep it up.

Charles R. said...

I guess I would suggest a high-fat, low carb diet would be the least inflammatory, as long as the fat was primarily saturated...

Bix said...

People who can eat diets high in fat without negative health effects are fortunate.

One drawback for those with a genetic predisposition to cancer is ...

The amount of fat we eat controls how much bile our liver makes. Bile is good in that it helps break up fats so we can absorb them. Bile can be harmful because it irritates the lining of the colon. The more fat some people eat, the more bile acids irritate their colon, the greater their risk for colon cancer.

Bix said...

Matt, good points. The omega-3 studies are so back and forth it's hard to discern much.

One thing ... The omega-3 in fish oil supplements comes from processing. I've been investigating those forms of processing. Heat is often employed to render the fat from the fish tissue. (The fish may not be fresh to begin with.) The unsaturated bonds in omega-3 fatty acids are vulnerable to oxidation during heat processing. (The omega-3 in flax is also vulnerable to heat processing.)

Maybe it's the quality of the omega-3 used in studies that impacts outcome. Low quality fish oil is oxidized and smells fishy.

I think it would be better to eat the fish directly.

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Bix said...

Every morning when I sign in I have to rummage through all the anonymous comments promoting Russian escorts, erectile dysfunction drugs, online casino games, and the occasional bit of software. I decided to let through this spammer for a fish oil manufacturer because I think it demonstrates what businesses will do to make a buck.

Fish oil is just another poor quality, overly-processed, food-like "nutraceutical" that is not a necessary component of a human diet. I could argue it's even harmful.

The best way to improve your omega-3:omega-6 ratio is to cut down on omega-6 ... or eat some fish outright.

Anonymous said...

What about pharmaceutical grade fish oil such as Lovaza?