While there is a general move to have us lose some of our collective weight, regular readers may have noticed that I’m a less exercised regarding this than most health professionals. Just last week, one of my posts included several links to articles which appear to show that individuals in the ‘overweight’ category have health status at least as good, if not better, than those in the supposedly ‘healthy’ category.
Now this week, the subject of body weight was raised in no small way again as a result of a review on the link between lifestyle factors and cancer. The report, a joint effort by the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR), makes a number of recommendations designed to ward off cancer. The most prominent of these, is the need to keep our weight within the ‘healthy’ body mass index range of 21-23.
The WCRF/AICR recommendations and other recommendations are the distillate of a 5-year trawl through more than 7000 studies. Big numbers that, it seems, deserve big claims. For instance, I read that Philip James, a member of the report’s panel of experts, says that they are convinced that excess body fat increases risks for cancer of the colon, kidney, pancreas, esophagus and uterus, as well as breast cancer in post-menopausal women. This week’s New Scientist which landed on my doormat yesterday pronounces that: ‘Obesity causes cancer’.
What is striking to me is the apparent certainty with which such statements are made. But does the science support such sureness?
After all, these recommendations come from what are known a epidemiological studies, which look for associations betweens things. Clearly, the panel has found a stack of evidence that links, say, excess weight with cancer. However, this link does not mean that one is causing the other.
Let’s for a moment imagine that a study finds that owning a television is associated with obesity. The question is, does owning a TV cause heart disease? Imagine you bought a TV but left it in its box and stored it in the attic. Would you be at increased risk of heart disease? Probably not. However, watching the TV endlessly for hours might be a problem. However, it’s not really owning a TV, but watching it and therefore being more sedentary that is the likely true cause of an enhanced risk of heart disease. It doesn’t matter whether we have 1 or a hundred such studies ” they still cannot be used to impugn TV ownership, because we just don’t know that it is this or something associated with TV ownership (such as being more sedentary) that is the true cause of heart disease.
The same argument can be made for any association found in epidemiological studies, including those found between body weight and cancer.
Scientists can, however, get closer to the truth by accounting for factors that may also affect the association. So, for instance, in the case of the TV, researchers could look at the relationship between TV ownership and heart disease, but this time they could take into account, say, the activity levels of those who own a TV. Now, if the link between heart disease and TV ownership appeared to remain having taking into account activity levels, then that would strengthen the notion that owning a TV actually causes heart disease. This technique, known as ‘controlling for confounding factors’ is not easy to do with any real accuracy, partly because health and disease tend to be highly ‘multifactorial’, which means potentially important influences may not be accounted for.
And even when such ‘controlling’ is done quite brilliantly, we’re still left with that pesky epidemiological data, which can never prove causality. In certain epidemiological studies, such associations can be tracked over time, which is better than just assessing them on a single occasion. But, still, causality cannot be assumed, however ‘strong’ the evidence.
So, when scientists say they’re ‘convinced’ that excess body weight or body fat increases risk of cancer, what they are offering is an opinion, not scientific certainty. And it’s simply not accurate to say that ‘obesity causes cancer’.
Another major deficiency of the WCRF/AICR report is that it focuses on cancer. I don’t deny for one moment that this is an important condition: t currently affects about 1 in 3 of us in the Western world and kills about 1 in 4. However, when data is available, it’s sometimes better to pan out and examine the influence of a factor not on a defined condition such as cancer, but something with broader implications such as overall risk of death (what scientists call ‘total mortality’). With regard to this, one study published in the Journal of the American Medical Association in 2005 found that individuals in the ‘overweight’ category (BMI of 25-29.9) were actually at a reduced risk of dying compared to those in the ‘healthy’ category .
Awareness of this sort of statistic leads me to be somewhat doubtful about the broad value of encouraging individuals to conform to a BMI of 21-23.
Another prominent recommendation made in the WCRF/AICR report is the need to limit red meat and avoid processed meats such as bacon and salami. Again, this advice is based on epidemiological data which is although is not to be dismissed out of hand, provides no certainty either.
And again, the focus is on cancer. When we broaden the debate and focus on overall mortality rates, we find that these are not any higher in meat-eaters than vegetarians. . In light of this, meat somehow doesn’t look quite so ‘deadly’.
The real test of any recommendations or treatment is to apply it to a group of individuals and compare the results with a ‘control’ group who were not subjected to the intervention being tested. Next week, I’ll report in some detail on the results of a recent, large study which assessed the ‘benefits’ of ‘healthy’ eating (broadly similar to those recommended by the WCRF/AICR) with regard to a variety of conditions including cancer. As you’ll learn, the findings of this study were less than impressive.
My aim here is not to pour cold water on the whole of the WCRF/AICR report, but to put it in context. The certainty with which some of its findings have been reported are just not justified by the science. And, taking a broader look at health, it seems that being heavier than is traditionally advised and eating meat just ain’t that bad.
1. Flegal KM, et al. Excess deaths associated with underweight, overweight, and obesity. JAMA. 2005;20;293(15):1861-7.
2. Key TJ, et al. Mortality in British vegetarians review and preliminary results from EPIC-Oxford. Am J Clin Nutr 2003;78(suppl):533S-8S
Even though I work in cancer research my reaction to this report was that it’s too narrow – cut your risk of cancer but what about your chances of getting something else? Isn’t a small amount of alcohol suppose to be associated with improved survival? A bit of body fat can be beneficial in relation to osteoporosis.
I am so convinced that Big Pharma is behind these studies, the idea is to terrify people and then once scared enough, saturate the market with new weight reduction drugs, the huge pharmeceutical companies are constantly inventing “disease” such as social shyness, restless leg etc. for which we can ask our doctors to write prescriptions. Once you begin to experience “side effects’ from your new miracle drug, you can take another drug to help with “side effects’ which in fact are direct effects of these drugs. I predict a tidal wave of “obesity” drugs are about to hit our TV screens shortly. Big Pharma’s profits must be expanded at any cost, only by constantly creating new markets can they continue to acquire profit at the expense of us who mindlessly insist on believing better living is possible through chemistry alone.
I would like to know what the death rate of cancer are in other european countries where a lot of processed meats are eaten. Do they get the same nutritional advise?
You are right to refer to overall mortality in your comments, as it’s actually dying which is important. We need no research to establish that death affects us all. These epidemiological studies seem often to be an opportunity to postulate extraordinary claims that contradict earlier claims about nearly everything. Drinking red wine is a classic example.
I think that it’s fair to conclude mankind has been eating red meat for quite a while and some groups of people – notably the Masai – have a very odd diet that the WCRF would probably see as outrageous.
There’s rather more to the inexorable growth in cancer deaths than what you or I eat.
Thin people get cancer too! And lots of fat people don’t get cancer, so more needs to be understood about what makes certain fatties “cancer resistant”.
Another thing to consider – the overall tone of the report was rather nannyish – exercise, don’t get overweight, don’t eat bacon and so on. Now there are people who never have a problem with their weight, like “healthy” food, love exercise, go to bed early and never go out in the cold without their mittens on.
But most of us aren’t that knowledgable or diligent or motivated. Knowing what we should do doesn’t tell us how to do it. Of course to the mitten-wearers it’s obvious, but to the rest of us doing the right thing may be difficult or a complete mystery. So advising us to change without giving us the motivational tools to do it seems a bit pointless.
My mum (82) thinks eating lots of steak and drinking far too much sounds a wonderful way to die!
Can I suggest everybody also reads Sandy Szwarc’s column on this ‘report’ ??
She debunks bad science in a readable yet comprehensive way, and this report gets a good going over
Thanks for the link Neil.
Great post Doc.
What types of Cancer? This didn’t seem clear. There seems to such an emphasis on changing individual behaviour and not as much on corporations and organisations that contribute to toxic living and working environments, which can be carcinogenic.
“mortality rates, we find that these are not any higher in meat-eaters than vegetarians”
One of the conclusions, in the study John has as reference for this statement, goes on to say:
“The mortality of both the vegetarians and the nonvegetarians in these studies is low compared with national rates”
Were the nonvegetarians in the study eating less red/ processed meat than the national average we wonder?
No one will come out & say it but the reason people are getting so ill & fat is all the sugar, sugar like foods & chemicals in our diets. It would seems us meat eaters are fatter & decidedly more ill than our skinny vegetarian or vegan friends. I don’t think so!
Maybe if processed meats were a little less chemically enhanced, sugar & soy infused then they would not be so bad to eat. Anyway how did “processed meats” suddenly become red meat by the end of the article? Probably this article was sponsored by the grain industry – now there is a truly unhealthy product & totally unnecessary in our diets – only food eats grains!
yes, definitely all the sugar and chemicals etc. I hate the lumping of meat with processed meat!
Is the (one) study you refer to that demontrates that that fat people live longer, the one in which they falied to control for the fact that people often lose weight when ill (specially with cancer), and so are thinner when they die?
I worry a little about your tendency to seep away many studies that show one result, and offer one that disagrees. Reproducibilty of results is evidence for the strength of the effect, is it not ?
“I worry a little about your tendency to seep away many studies that show one result, and offer one that disagrees.”
Actually, I have provided several studies which appear to show that individuals traditionally regarded as ‘overweight’ (according to the BMI) have a health status at least as good, if not better, than, those regarded as of a ‘healthy’ weight.
I am happy to review my stance on this in the light of good evidence to the contrary. Can you please let me have the ‘many studies’ you refer to?
I agree with Helen and Sue.
Why are those people over weight? Perhaps they have a diet high in sugar and grains, which could stimulate surges in insulin resulting in fat gain.
Elevated levels of Insulin-Like Growth Factor (IGF-1) are assoiciated with an increased cancer risk. Insulin-Like Growth Factor Binding Protein 3 (IGFBP-3) works to balance IGF-1. In Loren Cordain’s book “The Dietary Cure For Acne” he says spikes in blood sugar and surges of insulin unbalance these subtances. Maybe then if cancer is present this could make conditions favourable to its proliferation. And perhaps if these substances are balanced the growth of cancer might be inhibited, prevented or even allow the body to destroy it.
I think maintaining an even, balanced blood sugar level could be very important.
Included in the Cancer reports key recommendations
3 Limit consumption of energy dense foods. Avoid sugary drinks
4 Eat mostly foods of plant origin. States this should be “non-starchy” vegetables, goes on to say ‘Limit refined starchy foods’
So the report is not saying eat sugary or “sugar like foods” quite the opposite. By the way the report makes it clear it is not recommending a totally vegetarian diet (though some might think it was the logical conclusion). I know it is shocking for some people to hear that a vegetarian diet can be healthy. Certainly not what you were brought up to believe.
I would recommend reading the report anyway to make up your own mind
Richard said, “the growth of cancer might be inhibited, prevented or even allow the body to destroy it.” I am not YET willing to say that I have “destroyed” my Prostate Cancer, but my PSA has been below 3.2 for five years now.So at worse, I have gotten it to a reduced state of growth.
My case parameters; PSA went from 2.7 to 5.0 in a year – done during my yearly physicals. A recheck two weeks later got a reading of 5.6. DRE was negative and an earlier ultrasound, done for base line, showed a slight and repoducable irregualrity on one side with some slight indication of vascularity. Biopsy done seven months later (because of a whole bunch of missteps) was 7% positive in one of six cores, Gleason 3+3. A check of the PSA four weeks later found it to be 5.2, and a month from that 3.7, then 3.2, 3.0 and 2.5 six months from biopsy. Since then it got a low of 1.9 and just last test was 3.2. Most tests, taken every three months (about), were in the 2.2 to 2.7 range. DREs all have been negative each time I have a physical.
My “treatement” was ONLY a change in diet that I started just before the physical that had the high PSA. I started a low-carb (hi fat) diet after the one described by the Drs. Eades in their Protein Power books (PP and PPLifeplan – pub. in 2000) to which I added supplements that the research literature indicated some anti-cancer properties.
I for one am convinced that diet is ALL important in the cancer fight. It is both amazing and also infurating (I lost my dad when I was 20 to Prostate Cancet) how the whole American cancer research effort has ignored Dr. Otto Warburgs work on cancer metabolism. Looking on the web will find a lot of other people that have found that “Cancer Loves Sugar” since that is the principal source of energy for a cancer cell – defective mitochondria cannot use fat for energy or the end product of glycolsis (first steps in “burning” glucose for ATP production (the energy “currency” used in the cells).