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A return of the Grumbleweed Blog - and from now on it will be entirely science-based. YAY!
It is a weird title for a blog post I know, but it is based on a couple of reports I have heard recently in which it is claimed that salt is no longer deemed bad for your health and that fish oil has a link to prostate cancer (see also this)….
So, the new normal is salt=good and fish oil=bad?
Aaaargh! Don’t these scientists know what they are doing? Isn’t salt supposed to cause high blood pressure and isn’t fish oil supposed to protect us from heart disease and cancer? I don’t really want to die of heart disease, but do I have to lose my prostate? Dudes, what is going on?
Let’s start with what I still believe to be an absolute – based on decades of scientific research.
Salt DEFINITELY causes high blood pressure (along with a bunch of other problems such as fluid retention, weight gain etc….we’ll get to the details in part 2). And the omega-3 fatty acids found in fish oil DEFINITELY DO protect against cardiovascular disease and cancer. NOTHING HAS CHANGED.
What has happened is that science is moving forward and bringing us the very latest data. This is what science – and scientists – do. Scientists make observations about the world and report on those observations. In turn, these observations add to the wealth of information we have so that the population as a whole can make informed decisions and/or take actions. However, sometimes the information about the observations the scientists have made is presented to the public badly. Sometimes this is the fault of scientists who are notoriously bad at being communicators. They have advanced degrees in 'nerdery' - not in media or communication - and their use of scientific jargon can often make their message confusing or downright incomprehensible. Sometimes, the information is presented to the public by poor journalists who don’t have a good grasp of science and miss out some very important details. And sometimes (actually, far too often), the information is deliberately misrepresented by people with some vested interest in making the science look confusing or lacking in consensus.
There is another important detail about science that should be stressed here. Sometimes, scientists get it wrong.
Yes, I’ll say that again. Sometimes, scientists get it wrong.
This is why we have a system called peer-review. Before a scientist (or group of scientists) can publish anything and put it into the public domain, their work is looked at by a small group of other, independent scientists who make sure that some detail hasn’t been missed out, or some data misinterpreted, or some daft mistake made. If these other scientists - peer-reviewers - approve of the work, it can be published. However, the process of peer-review continues even after the science is published and placed in the public domain. Now it is out in the open, where even more scientists can look at the data, perhaps even try to duplicate the experiments, or identify flaws and mistakes or misinterpretations that the initial panel of peer-reviewers might have missed. This is how science is ‘self-correcting’. The reputation of a flawed piece of scientific work simply doesn’t survive in this system and, more importantly, if a huge body of scientific work has survived this system well and thus moves into the category of 'scientific consensus', then a single study that comes along and challenges that consensus will undoubtedly be investigated very thoroughly. Any such challenge to the scientific consensus needs to be extremely robust in order to survive and change that consensus. Such challenges have happened, but they are quite rare.
So, what of the latest information on salt and fish oil? Has what we know changed? Were the new scientific papers robust enough to shift the scientific consensus?
In a word, “No”. In a bigger, more emboldened, more italicized word, "NO".
In this two part post, I will explain a little.
The fish oil story is easiest to deal with, because it is a simple example of someone attempting to challenge the consensus – and actually doing very well as far as media hype is concerned, but pretty badly scientifically speaking. So let’s start there.
The controversy begins with a scientific article published by a group of scientists headed by Dr. Theodore M. Brasky in the Journal of the Natural Cancer Institute, titled “Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial”. In this paper the scientists conclude that there is an “increased prostate cancer risk among men with high blood concentrations of LCω-3PUFA (long-chain omega-3 polyunsaturated fatty acid)”. They say that their findings “suggests that these fatty acids are involved in prostate tumorigenesis” and that people who have been given “recommendations to increase LCω-3PUFA intake should consider its potential risks”
Without delving too far into the details (though I can't resist a little delving), this study has some fundamental flaws that have already been highlighted by dozens (maybe hundreds) of scientists.
In the first place, the study was a retrospective (looking back) analysis of data collected for a different study performed between 2001 and 2008. That study, known as the SELECT study (Selenium and Vitamin E Cancer Prevention Trial), had been designed to determine if there is a link between dietary intake of selenium and/or vitamin E and prostate cancer. In that PROSPECTIVE (planning ahead) study, men were split into four groups and given either selenium + vitamin E; vitamin E + placebo (a sugar pill); selenium + placebo; or placebo + placebo. At the end of the study, the scientists were able to determine if a higher incidence of prostate cancer was observed in any of the four groups.
However, even that study had some potential flaws, because the men in the clinical trial were studied at more than 400 sites in 3 different countries and there were no specified or standardized protocols for important things such as how often patients had a prostate-specific antigen (PSA) test, how that PSA test was managed, whether they had a prostate biopsy, or how the prostate biopsy was done. What this means is that the “control group” – those determined NOT to have prostate cancer – may actually have had individuals whose low grade cancer had not been spotted. This would surely have an impact on the end result and possible conclusions of that trial. And, clearly, the SELECT study was NOT designed to assess a link between omega-3 fatty acids and prostate cancer.
The identification of omega-3 fatty acids was made by looking - again, retrospectively - at the results of a single blood draw that had been taken very early from a sub-group of men in this SELECT study. It was taken at the time when these men were enrolled in the trial and then a test was performed on the blood plasma. Such a a test would have been more informative had it been performed on red blood cells, because the blood plasma merely provides an indication about what these individuals had eaten over the previous few hours, rather than any indication of long term dietary intake. The levels of these fatty acids in the plasma will rise and stay high for between 4 and 12 hours after someone consumes a fish oil supplement or a meal containing fish, but will ‘wash out’ completely in about 48 hours. But no questions were asked about whether these men had eaten fish or if they had ever taken a fish oil supplement, so we have no idea about the origin of the omega-3 fatty acids found in their plasma – maybe up to 7 years before the trial was terminated – or whether the levels of those fatty acids would have been different by testing just a few hours before or after!
Then, when all is said and done, the difference between the average levels of omega-3 fatty acids in the plasma of those individuals diagnosed with prostate cancer and those without was 4.66% versus 4.48% - that’s a difference of less than 0.2% - again, based on a blood draw taken years before cancer diagnosis. Not impressive!
At best, this study shows a minor (and very tenuous) correlation between omega-3 fatty acids in the plasma and prostate cancer, but it absolutely does NOT show cause and effect.
So how does this study compare with that scientific consensus I mentioned earlier?
We know that experimental studies suggest that omega-3 fatty acids have an anti-cancer effect on prostate tumor vells in vitro. And although many compounds can be shown to have anti-cancer effects on tumor cells in a Petri dish, we also know that populations or ethnicities with a high consumption of fish have a lower incidence rate of prostate cancer that populations with Western food habits, where fish intake is generally lower. In Japan, for example, where consumption of fish is high, the incidence of prostate cancer is 1/10th of that in the USA. Similar low rates are seen among Eskimos in Alaska and in folks who live in the Mediterranean. Surely, if there was a causative link between fish oils and prostate cancer, the opposite phenomena would occur in these populations and men would be dropping like flies. But perhaps this is a whole heap of anecdotal evidence, which can be appealing, but scientifically tenuous. So what about hard science?
Well, here are a few examples of hard science:
In New Zealand, in a well-designed PROSPECTIVE study involving 797 men, those with the highest levels of omega-3 fatty acids – measured in red blood cells – had an almost 40% decreased prostate cancer incidence
Several studies in Japan have found either fish in the diet or omega-3 fatty acid blood levels correlate to a reduction in the incidence of prostate cancer
In another PROSPECTIVE study that looked at 6272 Swedish men over 30 years, the men who didn't eat any fish had a 2-fold to 3-fold higher rate of prostate cancer (200% - 300%) versus those who consumed moderate or large amounts of dietary fish.
A 2010 analysis of numerous studies involving more than 15,000 patients looking specifically at the link between fish consumption and prostate cancer showed that men who ate more fish had a 63% reduction in deaths from prostate cancer. The study did not show a specific decrease in the rates of diagnosis of prostate cancer, but it did show that men who had the cancer faired better, suggesting that the presence of the fish oil in the diet may actually allow the body to keep the cancer manageable.
In 2003, when the Departments of Nutrition and Epidemiology at the Harvard School for Public Health followed almost 48,000 people for 12 years they found that high dietary fish intake (more than 3 times a week) correlated with both a reduction of prostate cancer, and its ability to spread (metastasize) when compared to low intake (less than twice a month). Similarly, in a 2008 follow-up, prostate cancer survivability was increased by 48% in men consuming fish more than 5 times a week compared to those eating fish less than once weekly.
I could go on, but the message is that the science still tells us that the omega 3 fatty acids found in fish oil are protective against prostate cancer. AND they also seem to exert a protective effect on other cancers and diseases, too. For example (here’s one for the ladies), a 2013 paper in the British Medical Journal that summarizes the results of 21 studies that included almost one million participants shows that consumption of fish oil and its omega 3 fatty acids produces a significant reduction in the incidence of breast cancer.
In summary, one poorly designed study doesn’t upset the scientific consensus and it would be a terrible shame if such a study led to people changing their dietary habits out of fear of increased risk, only to find that they had increased their risk BECAUSE of that fear.
Omega 3 fatty acids are good for you. Keep taking those fish oil supplements folks!