Why Simply Adding Fish Oil Doesn’t Work

Diets high in omega-6 fatty acids can limit the conversion of omega-3 to EPA/DHA. Therefore, if we don’t decrease our omega-6, we may not get the anti-inflammatory benefits.

In my last article, I began to dissect the American dietary guidelines. We uncovered the importance of eating nutrient-dense foods. In this installment, we will take a closer look at the myth that fats are unhealthy. This fear of saturated fat is what led to the high carbohydrate-low fat diet recommendation here in the United States.

Saturated fat has been vilified in our society as being an unhealthy option and we have been encouraged to get 70% of our fat from polyunsaturated fatty acids while keeping our total fat intake to 20-35% of our overall calories. But does the science support this?

The Relationship Between Unsaturated and Saturated Fats

The USDA does not actually distinguish between different polyunsaturated fats. We learned from my last article that the ratio of omega-3 polyunsaturated fats to omega-6 polyunsaturated fats plays a critical role in overall health. Our Paleolithic ancestors consumed these fats in a ratio of approximately 1:1. Today we consume up to thirty times more of the pro-inflammatory omega-6 fats.

Traditional cultures consumed much less polyunsaturated fats than we do in the typical American diet. The Kitavans, a modern-day hunter-gatherer group, consume approximately 2% of their calories from polyunsaturated fats, compared to 7% in the American diet. The Kitavans are also free from the diseases of modern society, including heart disease, even though the majority of them smoke.1 How can this be if polyunsaturated fats are heart healthy? This can be explained by two key studies that looked at polyunsaturated fats versus saturated fats and rates of disease.

The Minnesota Coronary Study

The first one is the Minnesota Coronary Survey. This study was published in 1989 and placed hospital patients on a higher vegetable oil (polyunsaturated fat) diet for a year, and then compared the results with those on a higher saturated fat diet. There was no difference in cardiovascular disease rates. In fact, the saturated fat group lived longer, but it was not deemed statistically significant.2

The LA Veterans Study

The second key study was the LA Veterans Administration Hospital study, which looked at more long-term effects of substituting polyunsaturated fats for saturated fats. The Minnesota Coronary Survey only looked at the data for a year. The LA Veterans study lasted for eight years.

In the beginning of the LA Veterans study, it looked promising for polyunsaturated fats. The polyunsaturated fat group had lower rates of heart disease. However, they had higher rates of all other causes of mortality, and the long-term effects of eating polyunsaturated fats got much worse over time. Cancer rates began to climb in the polyunsaturated group after two years and then rates increased again after five.3 Heart disease rates climbed significantly after seven years in the polyunsaturated group as well.4 What would have happened if this study had gone on for longer?

And yet, we are encouraged to eat 70% of our fat calories from these polyunsaturated fats throughout our lifetime. Industrial seed oils, which are polyunsaturated fats high in omega-6 fats, are a major component of the American diet. Could this be a major culprit in modern disease? I would say yes.

Why Simply Adding Fish Oil Doesn’t Work

But can’t we just eat more omega-3-rch fish and fish oil to balance out the ratio of omega-3 to omega-6 fats? I wish it were only that easy. Polyunsaturated fats are highly unstable and easily oxidized. Oxidative stress is an underlying cause of aging and modern disease. When we consume high amounts of polyunsaturated fats, then we get an increase in oxidative stress markers.5 To turn the fat intake around in the American diet we need to decrease our intake of high omega-6 foods and increase our intake of omega-3 fats, especially long-chain omega-3 fats such as EPA and DHA. DHA is important for cognitive development in infants and cognitive maintenance in adults. Deficiencies are associated with delayed learning. One study also showed that when patients with heart disease or type 2 diabetes were told to eat a low-fat diet, that it could lead to lead to deficiencies in DHA as well as unfavorable bloodwork.6

fats, polyunsaturated fats, saturated fats, omega 3, omega 6

Pharmaceutical companies are aware of the inflammatory effects of omega-6 fatty acids. In fact, NSAIDs such as aspirin work by disabling the inflammatory compounds formed by omega-6 fatty acids. We can get this same effect by balancing our ratio of polyunsaturated fats, but it’s not as simple as just adding more fish oil. Omega-3 and omega-6 fats fight with each other to enter cells, and research shows that diets high in omega-6 fatty acids can limit the conversion of omega-3 fats to EPA/DHA by up to 40%.7 Therefore, if we just increase our intake of omega-3 without decreasing our intake of omega-6, we may not get the beneficial effects of the anti-inflammatory fats. Instead, we may actually be setting the stage for more inflammation by adding more easily oxidized fats into the blood.

What to Eat and What to Avoid

Foods high in omega-6 fats include industrial seed oils, nuts, and seeds. Fatty cold-water fish such as salmon, herring, and sardines are high in omega-3 fats. Meat from pasture-raised animals has a more balanced ratio of polyunsaturated fats when compared to grain-fed animals. To optimize polyunsaturated fat intake, I advise clients to avoid industrial seed oils and use nuts and seeds sparingly, while consuming about one pound of fatty fish per week and eating the meat of grass-fed animals. 

fats, polyunsaturated fats, saturated fats, omega 3, omega 6

But wait, I know – you may still be thinking, “But what about the saturated fat?” In upcoming articles we will discuss the importance of animal fats in the diet. We will dissect other studies that claimed meat led to inflammation and look at the bioavailability of nutrients as well as anti-nutrients found in alternative sources of protein. So stay tuned for a continued education on the science behind your nutrition.


1. Lindeberg, S, et. Al., “Age relations of cardiovascular risk factors in a traditional Melanesian society: the Kitava Study.” American Journal of Clinical Nutrition (1997). Retrieved on February 2, 2014.

2. Frantz, I, et. Al., “Test of effect of lipid lowering by diet on cardiovascular risk. The Minnesota Coronary Survey.Arteriosclerosis (1989). Retrieved on February 2, 2014.

3. Pearce, M and Dayton, S., “Incidence of cancer in men on a diet high in polyunsaturated fat.” Lancet (1971). Retrieved on February 2, 2014.

4. Dayton, S and ML Pearce., “Diet high in unsaturated fat. A controlled clinical trial.” Minnesota Medicine (1969). Retrieved on February 2, 2014.

5. Jenkinson, E, et. Al., “Dietary intakes of polyunsaturated fatty acids and indices of oxidative stress in human volunteers.” European Journal of Clinical Nutrition (1999). Retrieved on February 2, 2014.

6. Horrocks, LA and YK Yeo. “Health benefits of docosahexaenoic acid (DHA).” Pharmacological Research (1999). Retrieved on February 2, 2014.

7. Kris-Etherton, PM, et. Al., “Polyunsaturated fatty acids in the food chain in the United States.The American Journal of Clinical Nutrition (2000). Retrieved on February 2, 2014.

Photos courtesy of Shutterstock.

Leave a Comment

Do Not Sell My Personal Information