HOME
Animal Fats Don't Cause Breast Cancer
Did you notice how low-carb diets have hit the news in 2003? Wheat farmers
in the USA were finding they can't sell their crop as people were giving up
eating bread. Potato farmers faced a similar crisis in Britain. And I heard a spokeswoman from the Vegetarian Society admit that 600,000 people had given up on vegetarianism.
The next thing
to happen may well be all the people who have taken the 'healthy' advice and
put weight on or developed diabetes as a consquence may decide to sue those
nutritionists who gave them that bad advice.
During the third week of July, 2003, two studies were published which purported
to show that an increasing intake of animal fat increased the risk of breast
cancer. It looks like the conventional 'fat is bad for you' nutritionists are
stepping up their rearguard action in a vain attempt to prevent this inevitable
backlash.
The first was an American study published on 16 July in the
Journal of the National Cancer Institute
; the second out on 18 July in the British medical journal,
Lancet
. Below I have included abstracts from them. Look carefully at them and you will see what the real truth is. I must confess,
when I read them both, I was decidedly underwhelmed by the arguments. As the
media — and the researchers — tend to hype up their results for
maximum impact, I have added comments to each to explain what the figures mean
in real terms.
The first study was reported in the American press thus:
Now let's look at what the study really revealed:
Animal Fats Linked to Increased Breast Cancer Risk, Study Finds
July 15 (Bloomberg) — Eating high-fat red meats and dairy products such as cream may increase the risk of breast cancer in pre-menopausal women, according to a study published in tomorrow's issue of the Journal of the National Cancer Institute.
A diet high in animal fat raised the risk by as much as 54 percent, said lead author Eunyoung Cho, a nutrition researcher at Boston's Harvard Medical School and Brigham and Women's Hospital. The eight-year study enrolled 90,000 women aged 26 to 46.
The findings suggest that the Atkins diet and other regimens that encourage people to eat meat to lose weight may harm younger women, Cho said. Her study found no link between breast cancer, which kills about 40,000 people a year in the U.S., and high levels of vegetable fat or animal fat from chicken, turkey or fish, she said in an interview.
"I would not recommend that diet for pre-menopausal women, unless they replace red meat with poultry and fish," Cho said.
Women at the high end of animal fat consumption got 23 percent of all their calories from meats and dairy products, almost twice as much as those who ate the least animal fat. Some researchers believe that a high-fat diet may increase the risk of breast cancer by spurring the body to make estrogen, which can contribute to tumor growth, Cho said.
|
Eunyoung Cho, Donna Spiegelman, David J. Hunter, Wendy Y. Chen, Meir J.
Stampfer, Graham A. Colditz, Walter C. Willett Premenopausal Fat Intake and
Risk of Breast Cancer.
J Natl Cancer Inst
2003;95:1079-85
Background: International comparisons and case-control studies have suggested a positive relation between dietary fat intake and breast cancer risk, but prospective studies, most of them involving postmenopausal women, have not supported this association. We conducted a prospective analysis of the relation between dietary fat intake and breast cancer risk among premenopausal women enrolled in the Nurses' Health Study II. Methods: Dietary fat intake and breast cancer risk were assessed among 90 655 premenopausal women aged 26 to 46 years in 1991. Fat intake was assessed with a food-frequency questionnaire at baseline in 1991 and again in 1995. Breast cancers were self-reported and confirmed by review of pathology reports. Multivariable relative risks (RRs) and 95% confidence intervals (CIs) were calculated. All statistical tests were two-sided. Results: During 8 years of follow-up, 714 women developed incident invasive breast cancer. Relative to women in the lowest quintile of fat intake, women in the highest quintile of intake had a slight increased risk of breast cancer (RR = 1.25, 95% CI = 0.98 to 1.59; Ptrend = .06). The increase was associated with intake of animal fat but not vegetable fat; RRs for the increasing quintiles of animal fat intake were 1.00 (referent), 1.28, 1.37, 1.54, and 1.33 (95% CI = 1.02 to 1.73; Ptrend = .002). Intakes of both saturated and monounsaturated fat were related to modestly elevated breast cancer risk. Among food groups contributing to animal fat, red meat and high-fat dairy foods were each associated with an increased risk of breast cancer. Conclusions: Intake of animal fat, mainly from red meat and high-fat dairy foods, during premenopausal years is associated with an increased risk of breast cancer. COMMENT: Now let's look at their figures for animal fats.
COMMENT:If eating animal fat increased the risk of breast cancer, one would expect
that the more animal fat is eaten, the more breast cancer there will be. That
is clearly not the case. Those eating the most animal fat (5th quintile) have
less
breast cancer than those eating less (3rd and 4th quintiles). That is the first
sign that something is not quite what it should be.
Holmes MD, Colditz GA, Hunter DJ, Hankinson SE, Rosner B, Speizer FE, Willett WC. Meat, fish and egg intake and risk of breast cancer. Int J Cancer. 2003 Mar 20;104(2):221-7. |
The second study was published in
Lancet.
Again it was hyped up by the media as 'conclusive proof that a high animal fat
diet causes breast cancer' but, again, it is nothing like conclusive! Using similar
methodology to that which I have applied above, you will see a similar pattern
here:
|
Are imprecise methods obscuring a relation between fat and breast cancer?
Sheila A Bingham, Robert Luben, Ailsa Welch, Nicholas Wareham, Kay-Tee Khaw, Nicholas Day Lancet 2003; 362: 212-14 Abstract Pooled analyses of cohort studies show no relation between fat intake and breast-cancer risk. However, food-frequency questionnaire (FFQ) methods used in these studies are prone to measurement error. We assessed diet with an FFQ and a detailed 7-day food diary in 13 070 women between 1993 and 1997. We compared 168 breast-cancer cases incident by 2000 with four matched controls. Risk of breast cancer was associated with saturated-fat intake measured with the food diary (hazard ratio 1·22 [95% CI 1·06-1·40], p=0·005, per quintile increase in energy-adjusted fat intake), but not with saturated fat measured with the FFQ (1·10 [0·94-1·29], p=0·23). Dietary measurement error might explain the absence of a significant association between dietary fat and breast-cancer risk in cohort studies. COMMENT:As its title suggests, this study is really looking at the way data are
gathered. What it is really saying is "We 'know' that saturated animal fat
causes breast cancer, but we can't prove it in trials." (This is, of course,
because all trials published so far — and there have been a lot —
have found that animal fats do NOT cause breast cancer, only vegetable fats do
— but that finding isn't politically correct). So now, this team looked
at the way data are gathered to see if they could spin their findings to show
what they want to see.
|
Here is an example of a Data Dredge from Number Watch , an extremely interesting website if you want to know how scientists use figures to mislead us lesser mortals. It is based on an Italian study that found that if women lived a more 'healthy' life, they would live longer.
Number Watch decided to perform its own study, but not having generous donors to fund a jaunt to Italy, it has to rely on the random number generator in Mathcad. It was easy enough to use the same Trojan numbers, but necessary to make a guess at the number of lifestyle habits and the proportion of women adopting each one. The numbers chosen were fifty habits and a one in ten adoption of each. A set of 50 binomial random numbers was generated (for the cognoscenti by rbinom(50,2800,0.1) ) and another set for the 4000 controls with exactly the same number of habits and probability. The percentage difference was then recorded and ranked, the five at each extreme being used to form the table. The habits were named from the standard SIF hit list. The results were as follows.
| Habit | % change in risk |
| Tomatoes | -11.355 |
| Jogging | -11.354 |
| Green vegetables | -10.891 |
| Aubergines | -10.223 |
| Olive oil | -8.807 |
| Insecticides | +8.753 |
| Passive smoking | +10.883 |
| Saturated fats | +12.128 |
| Alcohol | +16.305 |
| Smoking | +16.456 |
Not bad, when you consider that there is no difference in the probabilities in the two populations! Combining the last three observations, we can now announce to the women of the world that by giving up smoking, alcohol and saturated fats they can cut their risk of breast cancer by one third — a similar result to the good professor's at a tiny fraction of the cost.
As you can see, although the parameters were exactly the same for both the 'treatment group' and the 'control group', merely the fact that there were not exactly the same number of people in each group, skewed the figures. And that may be exactly what happened in the two studies above.
Last updated 15 July 2008
Related Articles
