Do Omega-3 Fatty Acids Cause Prostate Cancer?

Written by Steve Chaney on . Posted in Food and Health, Issues

Fish, Fish Oils And Prostate Cancer

Author: Dr. Stephen Chaney

Pure Fish OilMy phone has been ringing off the hook. My email in-box is full. It seems that everyone wants to know if the headlines about omega-3 fatty acids and prostate cancer are true.

In case you have just gotten back from a vacation on some deserted island with no newspapers and no internet, let me bring you up to date. The headlines are saying things like “Fish Oils May Increase Your Risk of Prostate Cancer” and “Latest Study Links Fish Oils to Prostate Cancer”.

Once again, it seems like just when you’ve figured out which foods that are good for you, someone tells you they could actually kill you. It’s no wonder so many of you have been asking me to cut through the hype and put this latest study in perspective.

What the study actually says:

As usual, let me start with the study itself (Brasky et al., Journal of the National Cancer Institute, doi: 10.1093/jnci/djt174). On the surface, it appears to be a reasonably well designed study, and the conclusions were dramatic. They reported that subjects with high levels of omega-3 fatty acids in their blood were 43% more likely to develop prostate cancer, 44% more likely to develop low grade prostate cancer, and 71% more likely to develop high grade prostate cancer compared to those with low levels of omega-3 fatty acids in their blood.

The flaws in the study:

Case closed you might be tempted to say. However, once you dig a little deeper, the study does have two important weaknesses.

1)     It used data from another study that was designed for a totally different purpose. They went back and analyzed blood samples from a previous study that was actually designed to measure the association between vitamin E and selenium intake and prostate cancer. That’s a scientific no-no.  Let me explain why.

If they had designed a study to investigate the association between omega-3 fatty acids and prostate cancer, they probably would have selected participants with a wide range of omega-3 fatty acids in their blood at the beginning of the study. The subjects in this study actually had a very narrow range of omega-3 fatty acids in their bloodstream.

They also would probably have done a diet analysis and found out whether the subject’s omega-3 fatty acids were coming from fish or fish oil supplements. They might have even asked whether the omega-3 fatty acids were from farm-raised fish or inexpensive fish oil supplements known to be contaminated with PCBs. This study collected none of these data.

2)     This is a single study, and individual studies often provide misleading results. For example, if you examine their data closely, it looks like heavy drinkers and smokers might have a decreased risk of prostate cancer. I think that’s unlikely, but weird associations like that often pop up in individual studies.

What do you find when you look at other studies?

Expert scientists aren’t swayed by individual studies. We prefer to look at the “big picture” that emerges when you combine the results of many studies. For example, a meta-analysis of 24 studies with 461,402 subjects (Symanski et al, American Journal of Clinical Nutrition, 92: 1223-1233, 2010) found no association between fish consumption and prostate cancer risk.

Individual studies ranged from a 61% decrease in risk to a 77% increase in risk, but the overall effect was zero! Even more importantly, fish consumption decreased prostate cancer deaths by 63%.

The Bottom Line:

1)     Don’t panic. Don’t change what you are doing based on the latest sensational headlines. This study has been way overblown. We have come to expect sensational headlines and hype from journalists and bloggers because that’s how they get people to read what they write.

However, I find the comment from the senior author that “We’ve shown once again that use of nutritional supplements may be harmful” to be very irresponsible, especially since they have no data showing that anyone in their study actually used fish oil supplements.

2)     The benefits of assuring optimal omega-3 fatty acid intake clearly overshadow the risks. Omega-3 fatty acids have been shown to lower triglycerides and blood pressure, reduce inflammation and depression, and may even help prevent dementia.

3)     This study does raise a caution flag, but I would not recommend reducing your omega-3 fatty acid intake on the basis of these data alone – especially since most published studies show no increased risk of prostate cancer. There are much better designed studies underway that should clearly show an increase in prostate cancer risk if it is a real effect. I will monitor those studies closely and keep you abreast of any new developments.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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Comments (2)

  • Linda Walls

    |

    I have been hearing that there is a study saying that fish oil causes inflamation, what do you know?
    Thanks
    Linda

    Reply

    • Steve Chaney

      |

      Dear Linda,
      I will comment more fully on that in a future issue, but this comes under what I call “The Headline of the Day”. In fact, there are dozens of studies showing that omega-3 fatty acids have an anti-inflammatory effect, so the preponderance of evidence is in favor of the anti-inflammatory effects of omega-3 fatty acids.
      Dr. Chaney

      Reply

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Latest Article

Can Plant-based Diets Be Unhealthy?

Posted September 10, 2019 by Dr. Steve Chaney

Do Plant-Based Diets Reduce Heart Disease Deaths?

Author: Dr. Stephen Chaney

 

plant-based diets vegetablesPlant-based diets have become the “Golden Boys” of the diet world. They are the diets most often recommended by knowledgeable health and nutrition professionals. I’m not talking about all the “Dr. Strangeloves” who pitch weird diets in books and the internet. I am talking legitimate experts who have spent their life studying the impact of nutrition on our health.

Certainly, there is an overwhelming body of evidence supporting the claim that plant-based diets are healthy. Going on a plant-based diet can help you lower blood pressure, inflammation, cholesterol and triglycerides. People who consume a plant-based diet for a lifetime weigh less and have decreased risk of heart disease, diabetes, and cancer.

But, can a plant-based diet be unhealthy? Some people consider a plant-based diet to simply be the absence of meat and other animal foods. Is just replacing animal foods with plant-based foods enough to make a diet healthy?

Maybe not. After all, sugar and white flour are plant-based food ingredients. Fake meats of all kinds abound in our grocery stores. Some are very wholesome, but others are little more than vegetarian junk food. If you replace animal foods with plant-based sweets, desserts, and junk food, is your diet really healthier?

While the answer to that question seems obvious, very few studies have asked that question. Most studies on the benefits of plant-based diets have compared population groups that eat a strictly plant-based diet (Seventh-Day Adventists, vegans, or vegetarians) with the general public. They have not looked at variations in plant food consumption within the general public. Nor have they compared people who consume healthy and unhealthy plant foods.

This study (H Kim et al, Journal of the American Heart Association, 8:e012865, 2019) was designed to fill that void.

 

How Was The Study Done?

plant-based diets studyThis study used data collected from 12,168 middle aged adults in the ARIC (Atherosclerosis Risk in Communities) study between 1987 and 2016.

The participant’s usual intake of foods and beverages was assessed by trained interviewers using a food frequency questionnaire at the time of entry into the study and again 6 years later.

Participants were asked to indicate the frequency with which they consumed 66 foods and beverages of a defined serving size in the previous year. Visual guides were provided to help participants estimate portion sizes.

The participant’s adherence to a plant-based diet was assessed using four different well-established plant-based diet scores. For the sake of simplicity, I will include 3 of them in this review.

  • The PDI (Plant-Based Diet Index) categorizes foods as either plant foods or animal foods. A high PDI score means that the participant’s diet contains more plant foods than animal foods. A low PDI score means the participant’s diet contains more animal foods than plant foods.
  • The hPDI (healthy plant-based diet index) is based on the PDI but emphasizes “healthy” plant foods. A high hPDI score means that the participant’s diet is high in healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) and low in animal foods.
  • The uPDI (unhealthy plant-based diet index) is based on the PDI but emphasizes “unhealthy” plant foods. A high uPDI score means that the participant’s diet is high in unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) and low in animal foods.

For statistical analysis the scores from the various plant-based diet indices were divided into 5 equal groups. In each case, the group with the highest score consumed the most plant foods and least animal foods. The group with the lowest score consumed the least plant foods and the most animal foods.

The health outcomes measured in this study were heart disease events, heart disease deaths, and all-cause deaths. Again, for the sake of simplicity, I will only include 2 of these outcomes (heart disease deaths and all-cause deaths) in this review. The data on deaths were obtained from state death records and the National Death Index. (Yes, your personal information is available on the web even after you die.)

 

Do Plant-Based Diets Reduce Heart Disease Deaths?

plant-based diets reduce heart deathsThe participants in this study were followed for an average of 25 years.

The investigators looked at heart disease deaths over the 25 years and compared people with the highest intake of plant foods to people with the highest intake of red meat and other animal foods. The results were:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

What Else Did The Study Show?

The investigators made a couple of other interesting observations:

  • The association of the overall diet with heart disease and all-cause deaths was stronger than the association of individual food components. This underscores the importance of looking at the effect of the whole diet on health outcomes rather than the “magic” foods you hear about on Dr. Strangelove’s Health Blog.
  • Diets with the highest amount of healthy plant foods were associated with higher intake of carbohydrates, plant protein, fiber, and micronutrients, including potassium, magnesium, iron, vitamin A, vitamin C, folate, and lower intake of saturated fat and cholesterol.
  • Diets with the highest amount of unhealthy plant foods were associated with higher intake of calories and carbohydrates and lower intake of fiber and micronutrients.

The last two observations may help explain some of the health benefits of plant-based diets.

 

Can Plant-Based Diets Be Unhealthy?

plant-based diets unhealthy cookiesNow, let’s return to the question I asked at the beginning of this article: “Can plant-based diets be unhealthy?” Although some previous studies have suggested that unhealthy plant-based diets might increase the risk of heart disease, this study did not show that.

What this study did show was that an unhealthy plant-based diet was no better for you than a diet containing lots of red meat and other animal foods.

If this were the only conclusion from this study, it might be considered a neutral result. However, this result clearly contrasts with the data from this study and many others showing that both plant-based diets in general and healthy plant-based diets reduce the risk of heart disease deaths and all-cause deaths compared to animal-based diets.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

There is one other subtle message from this study. This study did not compare vegans with the general public. Everyone in the study was the general public. Nobody in the study was consuming a 100% plant-based diet.

For example:

  • The group with the highest intake of plant foods consumed 9 servings per day of plant foods and 3.6 servings per day of animal foods.
  • The group with the lowest intake of plant foods consumed 5.4 servings per day of plant foods and 5.6 servings per day of animal foods.

In other words, you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet.

 

The Bottom Line

A recent study analyzed the effect of consuming plant foods on heart disease deaths and all-cause deaths over a 25-year period.

When the investigators looked at heart disease deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

A more subtle message from the study is that you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet. The people in this study were not following some special diet. The only difference was that some of the people in this study ate more plant foods and others more animal foods.

For more details on the study, read the article above.

 

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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