Monday, November 12, 2007

Flabby claims about food and cancer

A widely publicised report says that having a 'spare tyre' and consuming anything from bacon to milkshakes could increase your risk of cancer. Fat chance. Professor Patrick Basham and Dr John Luik, authors of "Diet Nation: Exposing the Obesity Crusade", pick apart two deliberately misleading reports on food and cancer that hit the headlines around the world last week. They reinforce what has already been said on this blog about the reports concerned

Scientists find link between body fat and cancer risk', declared the UK Independent. `Cancer study sparks bacon sandwich backlash', said the Melbourne Herald Sun. `To avoid the Big C, stay small', warned The Economist. Publications around the world summarised the findings of the latest report on cancer to tell us that bad diets and expanding waistlines are a public health disaster.

But before committing ourselves to a dietary life of little red meat or alcohol, and few fizzy drinks, milk shakes, crisps or other such `bad' foods, let's look behind the scary headlines and ask whether the scientific evidence really supports these cancer truths. The catalyst for these stories was the World Cancer Research Fund's new report, "Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective". The report proclaims three truths about cancer, fat and food. First, being fat increases our risk for cancer; second, eating certain foods gives us cancer; and third, cancer is `mostly preventable'.

The report's authors tell us they looked at over half a million studies, and then concentrated on the 7,000 that were most relevant. That is not quite true, for they actually reference slightly fewer than 2,500 studies on diet and disease. More importantly, they conveniently omit many major studies that don't support their three truths theory.

Crucially, they almost exclusively reference epidemiological studies
, which inherently cannot establish that being fat or that eating red meat gives you cancer, as that's not what this type of study does. Instead, such studies look for associations between various factors and the risk of disease. For example, this report was interested in whether the variation in people's weights or their diets were correlated with the development of cancer. But the very nature of epidemiological studies means that the margin of error arising from the nature of the data almost invariably exceeds the supposed relationships that the study has found. Only in a very few cases - like the link between active smoking and lung cancer - is the association between a lifestyle factor and disease strong enough for us to be reasonably sure that one causes the other.

What about the headline-grabbing claim that being fat gives you cancer? The report actually claims that being overweight or obese increases your risk for six cancers - cancers of the oesophagus, pancreas, colon/rectum, breast, endometrium (the inner lining of the womb), and kidney. However, when you look at the report's support for this conclusion, the evidence is extremely thin.

Take pancreatic cancer, for example. The report cites 20 case control studies. (These are studies where groups who already have a disease are compared to reasonably matched people who do not, in order to look for possibly significant differences. Case control studies have a greater risk of bias than cohort studies.) Only three of these studies show a statistically significant association between obesity and pancreatic cancer. Similarly, of 42 cohort studies (where you start with a group of healthy people and see who develops the disease) on colorectal cancer, only 13 show a link with obesity.

Of the 16 studies that the report documents on the relationship between breast cancer and obesity, only three are statistically significant, while eight actually show a decreased risk between breast cancer and obesity. Even for oesophageal cancer, the increased risk was largely confined to the morbidly, as opposed to the moderately, obese. With endometrial and kidney cancers, the relative risks were below two. According to the US National Cancer Institute, such risks are so small that they may be due to `chance, statistical bias or the effects of confounding factors'. Such results should be treated with extreme caution.

The just-published Million Women Study from the UK, which examined the evidence for a link between 17 of the most common cancers and Body Mass Index (BMI), the conventional yardstick for measuring overweight and obesity, found a similar pattern of results. In this study, 10 of the cancers do not show a statistically significant association with either higher levels of overweight or obesity. Of the remaining seven cancers, the association between overweight and the cancer is non-significant in four, and where the results are significant, the risks (except for endometrial and oesophagal cancer) are never stronger than two, except among the obese. [See the comments about weak statistical relationships in the above study made here on 8th]

A new study from the National Cancer Institute and the US Centers for Disease Control also contradicts the obesity-cancer link. This study found that being overweight was not associated with those cancers previously considered obesity-related. The study found `little or no association of excess all-cancer mortality with any of the BMI categories'. Indeed, the study suggests that overweight might in fact be protective against cancer.

Is the second truth in the World Cancer Research Fund's report - that eating certain foods increases our risk for cancer - really true? Of the 17 cancers discussed in the report, virtually all have statistically non-significant associations with every type of food, which means that they provide no evidence of a link between a particular food and a particular cancer. For example, of the 17 studies cited which assessed the link between colon cancer and processed meat, 13 are not statistically significant. Despite those scary headlines about red meat, the report concludes that `there is limited evidence.suggesting that red meat is a cause of oesophageal cancer'. Again, `there is limited, inconsistent evidence.that grilled.or barbecued animal foods are causes of stomach cancer'. And `there is limited evidence suggesting that processed meat is a cause of stomach cancer'. Given the limited nature of this evidence, it is difficult to see how the report authors justified the advice to avoid red and processed meat.

Are these anomalous findings? On the contrary. Consider, for example, the American Cancer Society's 2001 study of diet and stomach cancer, which looked at 436,000 men and women and found no increased risk of stomach cancer associated with eating processed meats. What that study did find, however, was an increased risk of stomach cancer with women who consumed more vegetables!

What of the report's claim that cancer is `mostly preventable'? This is perhaps the most curious claim since there is massive evidence of the best kind that suggests that it is simply not true. The Women's Health Initiative Dietary Modification Trial is the most recent, and one of the largest and most expensive, randomised controlled studies of the effect of diet and weight on breast cancer, colon cancer, heart disease and stroke. It studied 49,000 American women over an eight-year period. The women in the intervention group ate diets that were low fat and high fibre with six servings of grains and five servings of vegetables and fruits per day.

There were no statistically significant differences between the intervention group and the control group in the incidence of breast cancer, colon cancer, strokes or heart attacks. Ironically, the women following the `healthy' diet designed to reduce cancer and heart disease didn't even weigh less than they did at the beginning of the study, or less than the women in the control group who continued to eat as they always had. Unlike the epidemiological studies cited in the World Cancer Research Fund report, this gold standard, randomised, controlled intervention found no evidence to support the claim that there is a connection between eating certain foods and being a certain weight and preventing cancer.

This study is not unique. A newer one, published in the Journal of the National Cancer Institute analysed data from 14 studies involving 756,000 men and women who were followed from six to 20 years. The study found that fruit and vegetable intake was not associated with a reduced colon cancer risk. Some cancer prevention! Contrary to recent media headlines, the World Cancer Research Fund report does not prove there is a causal connection between cancer and being fat, or cancer and eating certain foods, or diet and cancer prevention. Rather, the report merely demonstrates that, as epidemiologist Petr Shrabanek observed, `people who eat, die'.


Curvy women are cleverer too

This I believe. It is just natural selection. Cleverer men get more attractive wives so the offspring tend to be both clever and attractive. It's got sod-all to do with the sacred Omega3s

It was already known that men find curvy women more attractive and that they live longer. Now research suggests that women with an hourglass figure are brighter and have cleverer children, too. The study found that women with large hips and small waists are more intelligent than those with either “apple-shaped” or linear bodies. The paper, to be published in the journal Evolution and Human Behaviour this week, suggests that such women give birth to more intelligent children - possibly a result of higher levels of omega3 fatty acids on the hips.

The researchers believe that the results offer a new explanation for why many men find curvy women more alluring. Nigella Lawson, the cookery presenter and Oxford University graduate, has one of Britain’s most famous hourglass figures, while Rachel Weisz, the curvy actress who won an Oscar for her role in The Constant Gardener, completed an English degree at Cambridge University while embarking on the first stages of her acting career.

In the research, scientists at the Universities of Pittsburgh and California, Santa Barbara, used data from a study of 16,000 women and girls, which collected details of their body measurements and their scores in cognitive tests. They found that those women with a greater difference between the waist and hips scored significantly higher on the tests, as did their children. Such women are not necessarily skinny. What is important is that their waist should be smaller than their hips, with the ideal ratio being between 0.6 and 0.7.

The researchers suggest that the fat around fuller hips and thighs holds higher levels of omega3 fatty acids which are essential for the growth of the brain during pregnancy. Fat around the waist may have higher levels of omega6 fatty acids, which are less suited to brain growth. Waist fat can also be a contributory factor in diabetes and heart disease. Thinner or linear-shaped women would simply lack enough of either type of fat.

Although these theories await confirmation, Paula Hall, a sexual and relationship psychologist with Relate, said: “Having research that proves you can be sexy and intelligent is really positive. It shows that curvy women may be better at things other than raising children and doing cooking and housework.” The research may also explain why children born to teenage mothers do worse in cognitive tests: their mothers may have had insufficient stores of the best fatty acids. “The cognitive development of their children is reduced, and their own cognitive development is impaired compared with those mothers with a later first birth,” say the researchers. What utter Bollocks! Teen mothers tend to be dumber and their children inherit that] The study noted, however, that children born to teenage girls with traditional hourglass figures seemed to be protected from this phenomenon and did better in tests.

A number of scientific studies have shown that men are “hard-wired” to find women with a greater waist-hip differential the most attractive. No one has yet been able to explain this, although theories include enhanced fertility, better childbearing abilities and longer life expectancy.

Dr Harry Witchel, a senior lecturer in physiology at the Brighton and Sussex Medical School and a body language expert on the television programme Big Brother, said: “Until this point the only thing we have accepted is that they [curvy women] are at an advantage in contemporary western society. What these people are saying is that they also have an advantage biologically.”



Just some problems with the "Obesity" war:

1). It tries to impose behavior change on everybody -- when most of those targeted are not obese and hence have no reason to change their behaviour. It is a form of punishing the innocent and the guilty alike. (It is also typical of Leftist thinking: Scorning the individual and capable of dealing with large groups only).

2). The longevity research all leads to the conclusion that it is people of MIDDLING weight who live longest -- not slim people. So the "epidemic" of obesity is in fact largely an "epidemic" of living longer.

3). It is total calorie intake that makes you fat -- not where you get your calories. Policies that attack only the source of the calories (e.g. "junk food") without addressing total calorie intake are hence pissing into the wind. People involuntarily deprived of their preferred calorie intake from one source are highly likely to seek and find their calories elsewhere.

4). So-called junk food is perfectly nutritious. A big Mac meal comprises meat, bread, salad and potatoes -- which is a mainstream Western diet. If that is bad then we are all in big trouble.

5). Food warriors demonize salt and fat. But we need a daily salt intake to counter salt-loss through perspiration and the research shows that people on salt-restricted diets die SOONER. And Eskimos eat huge amounts of fat with no apparent ill-effects. And the average home-cooked roast dinner has LOTS of fat. Will we ban roast dinners?

6). The foods restricted are often no more calorific than those permitted -- such as milk and fruit-juice drinks.

7). Tendency to weight is mostly genetic and is therefore not readily susceptible to voluntary behaviour change.

8). And when are we going to ban cheese? Cheese is a concentrated calorie bomb and has lots of that wicked animal fat in it too. Wouldn't we all be better off without it? And what about butter and margarine? They are just about pure fat. Surely they should be treated as contraband in kids' lunchboxes! [/sarcasm].

And will "this generation of Western children be the first in history to lead shorter lives than their parents did"? This idea emanates from a much-cited editorial in a prominent medical journal that said so. Yet this editorial offered no statistical basis for its opinion -- an opinion that flies directly in the face of the available evidence.


No comments: