goed voor wie graag rood vlees eet!

[MeDieViL]

No Beef Behind Red-Meat Cancer Scare
Friday, January 14, 2005
By Steven Milloy

Eating a hamburger a day can increase your risk of colon cancer (search), according to a new study. Is it time to switch to chicken, fish or tofu ? Or is time to ask your congressman to check into whether the National Cancer Institute is spending its budget wisely?

Researchers from the National Cancer Institute and the American Cancer Society concluded in this week’s Journal of the American Medical Association (Jan. 12) that “prolonged high consumption of red and processed meat may increase the risk of cancer in the distal portion of the large intestine.”

Their “conclusion” is based on a study of 148,610 adults aged 50 to 74 years who provided information on meat consumption in 1982 and again in 1992/1993 as part of their enrollment in the Cancer Prevention Study II (search). Through Aug. 31, 2001, a total of 1,667 cases of colorectal cancers were reported among the study subjects.

I suspect that the researchers actually had no conclusion worth reporting after they did an initial analysis of their data. They reported, in fact, no association between red meat consumption and overall colon cancer risk after considering the study subjects’ exposures to other colon cancer risk factors.

They parsed the results as follows, “High intake of red meat reported in 1992/1993 was associated with higher risk of colon cancer after adjusting for age and energy intake but not after further adjustment for body mass index, cigarette smoking and other [risk factors],” they stated in the study. Facing the prospect of no result, I think the researchers then engaged in some slicing-and-dicing of their data in hopes of discovering some statistical correlation they could point to as a “risk.”

Since there was no correlation between red meat consumption and overall cancer risk, the researchers examined their data looking to see whether there was an association between red meat consumption and cancer of the proximal colon (search), distal colon (search) and of the rectosigmoid (search) and rectum. The more analyses performed, after all, the greater the likelihood that some newsworthy result will be found, albeit, due to chance perhaps.

These subsequent analyses produced three correlations on which the scary headlines are based: a 50 percent increase in distal cancer risk among high consumers of processed meats; a 53 percent increase in distal cancer risk among those with the highest ratio of meat to chicken and fish consumption; and a 71 percent increase in rectal cancer risk among high consumers of red meat.

With respect to the claims concerning distal cancer risk, both results are of unimpressive size — risks smaller than 100 percent don’t have much credibility. They are of borderline statistical significance — meaning that there is a good possibility that the results are due to chance. This statistical weakness is in large part due to the fact that they are based on analyses involving only 79 and 92 cases of distal cancer, respectively. For these analyses to start to be taken seriously, they should involve hundreds, not dozens, of cancer cases.

As to the reported 71 percent increase in rectal cancer risk among red meat eaters, I can only conclude that this result was cherry-picked for sensationalistic purposes. The 71-percent claim is based on an analysis involving only the 1992/1993 data. When the analysis includes the 1982 data, the result drops to 43 percent and becomes statistically insignificant.

These weak statistics are just the surface of the problem. Likely nullifying the entire study is the unreliability of the researchers’ data.

The data for the study was initially collected by 77,000 untrained volunteers who interviewed family and friends about their lifestyle habits. None of this lifestyle data was verified or validated.

Exactly what and how much the study subjects ate, smoked, drank, and how much they exercised is really anybody’s guess. And forget about reliable information on genetic predisposition to colon cancer, which is thought to be a major risk factor. The researchers acknowledged in their write-up that they didn’t even have any information on family history of colon cancer for the analysis of 1992/1993 data.

The results of previous studies on meat consumption and colon cancer have produced similar inconsistent, contradictory, weak and even nonsensical results. There really is no persuasive evidence that meat consumption is in any way related to colon cancer risk.

So what’s up with this study?

Aside from the usual hijinks of researchers looking for media attention and their next grant, I noticed that one of this study’s authors has somewhat of a track record trying to link meat consumption with cancer.

The National Cancer Institute’s Rashmi Sinha (search) has a long history of trying to use weak statistics to convict meat of causing cancer. I first brought her antics to the attention of my FoxNews.com readers in a November 2000 column amid her crusade to link well-done meat with cancer.

It appears that Dr. Sinha remains bent on using her position at the National Cancer Institute to scare us away from eating meat. She’s been at it since at least 1994, but with little to show except a stack of scary, but unsupported headlines — which in itself is somewhat revealing.

If after all the time and effort Sinha has put into trying to link meat consumption with cancer, she still can’t do it, isn’t it time that the NCI reassign her to more productive work?

Steven Milloy publishes JunkScience.com and CSRwatch.com, is adjunct scholar at the Cato Institute, and is the author of Junk Science Judo: Self-defense Against Health Scares and Scams (Cato Institute, 2001).

http://www.foxnews.com/story/0,2933,144326,00.html

[Big'r]

Eens kijken hoe mijnheer Milloy zich hier uitlult.
De systematic review/meta analyses zijn eenduidig over een negatieve invloed van rood vlees op colorectal cancer:

Systematic review of epidemiological studies on meat, dairy products and egg consumption and risk of colorectal adenomas.
In view of the direct contact between food residues and metabolites and the large bowel mucosa, it might be expected that food consumption patterns would affect the risk of colorectal carcinogenesis. Many lines of evidence support the adenoma-carcinoma sequence as the major mechanism of colorectal carcinogenesis. The present study aimed to investigate the role of foods of animal origin such as meat, dairy products and eggs in the early stages of colorectal carcinogenesis. Eleven case-control and two cohort studies on colorectal polyps and meat, dairy products and eggs were identified. A quantitative review of these studies and a meta-analysis were carried out. The combined odds ratios suggest a positive association between the risk of colorectal polyps and beef consumption and a negative association with fish or combined poultry/fish consumption. An increase in the ratio of the consumption of red meat to consumption of fish/chicken was associated with an increase in the colorectal polyp risk. Neither dairy product nor egg consumption had a substantial effect on the development of colorectal polyps. These results suggest that dietary factors associated with polyp development may be not the same as those associated with cancer.

Mediterranean diet and cancer.
OBJECTIVE: To analyse the role of various aspects of the Mediterranean diet in several common epithelial cancers, including digestive and selected non-digestive tract neoplasms. DESIGN: Systematic analysis of data from a series of case-control studies. SETTING: Northern Italy, between 1983 and 1998. SUBJECTS: Over 12,000 cases of 20 cancer sites and 10,000 controls. RESULTS: For most epithelial cancers, the risk decreased with increasing vegetable and fruit consumption, with relative risk (RR) between 0.3 and 0.7 for the highest versus the lowest tertile. For digestive tract cancers, population-attributable risks for low intake of vegetables and fruit ranged between 15 and 40%. A protective effect was observed also for breast, female genital tract, urinary tract and a few other epithelial neoplasms. A number of antioxidants and other micronutrients showed an inverse relationship with cancer risk, but the main components responsible for the favourable effect of a diet rich in vegetables and fruit remain undefined. Fish tended to be another favourable diet indicator. In contrast, subjects reporting frequent red meat intake showed RRs above unity for several common neoplasms. Intake of whole-grain foods was related to a reduced risk of several types of cancer, particularly of the upper digestive tract. This may be due to a favourable role of fibre, but the issue is still open to discussion. In contrast, refined grain intake and, consequently, glycaemic load and glycaemic index were associated with increased risk of different types of cancer including, among others, breast and colorectal. CONCLUSIONS: A low-risk diet for cancer in the Mediterranean would imply increasing the consumption of fruit and vegetables, as well as avoiding increasing the intakes of meat and refined carbohydrates. Further, olive oil and other unsaturated fats, which are also typical aspects of the Mediterranean diet, should be preferred to saturated ones.

Diet, nutrition and the prevention of cancer.
OBJECTIVE: To assess the epidemiological evidence on diet and cancer and make public health recommendations. DESIGN: Review of published studies, concentrating on recent systematic reviews, meta-analyses and large prospective studies. CONCLUSIONS AND RECOMMENDATIONS: Overweight/obesity increases the risk for cancers of the oesophagus (adenocarcinoma), colorectum, breast (postmenopausal), endometrium and kidney; body weight should be maintained in the body mass index range of 18.5-25 kg/m(2), and weight gain in adulthood avoided. Alcohol causes cancers of the oral cavity, pharynx, oesophagus and liver, and a small increase in the risk for breast cancer; if consumed, alcohol intake should not exceed 2 units/d. Aflatoxin in foods causes liver cancer, although its importance in the absence of hepatitis virus infections is not clear; exposure to aflatoxin in foods should be minimised. Chinese-style salted fish increases the risk for nasopharyngeal cancer, particularly if eaten during childhood, and should be eaten only in moderation. Fruits and vegetables probably reduce the risk for cancers of the oral cavity, oesophagus, stomach and colorectum, and diets should include at least 400 g/d of total fruits and vegetables. Preserved meat and red meat probably increase the risk for colorectal cancer; if eaten, consumption of these foods should be moderate. Salt preserved foods and high salt intake probably increase the risk for stomach cancer; overall consumption of salt preserved foods and salt should be moderate. Very hot drinks and foods probably increase the risk for cancers of the oral cavity, pharynx and oesophagus; drinks and foods should not be consumed when they are scalding hot. Physical activity, the main determinant of energy expenditure, reduces the risk for colorectal cancer and probably reduces the risk for breast cancer; regular physical activity should be taken.

Meat consumption and colorectal cancer risk: dose-response meta-analysis of epidemiological studies.
The hypothesis that consumption of red and processed meat increases colorectal cancer risk is reassessed in a meta-analysis of articles published during 1973-99. The mean relative risk (RR) for the highest quantile of intake vs. the lowest was calculated and the RR per gram of intake was computed through log-linear models. Attributable fractions and preventable fractions for hypothetical reductions in red meat consumption in different geographical areas were derived using the RR log-linear estimates and prevalence of red meat consumption from FAO data and national dietary surveys. High intake of red meat, and particularly of processed meat, was associated with a moderate but significant increase in colorectal cancer risk. Average RRs and 95% confidence intervals (CI) for the highest quantile of consumption of red meat were 1.35 (CI: 1.21-1.51) and of processed meat, 1.31 (CI: 1.13-1.51). The RRs estimated by log-linear dose-response analysis were 1.24 (CI: 1.08-1.41) for an increase of 120 g/day of red meat and 1.36 (CI: 1.15-1.61) for 30 g/day of processed meat. Total meat consumption was not significantly associated with colorectal cancer risk. The risk fraction attributable to current levels of red meat intake was in the range of 10-25% in regions where red meat intake is high. If average red meat intake is reduced to 70 g/week in these regions, colorectal cancer risk would hypothetically decrease by 7-24%. Copyright 2001 Wiley-Liss, Inc.

Systematic review of the prospective cohort studies on meat consumption and colorectal cancer risk: a meta-analytical approach.
The relation between meat consumption and colorectal cancer risk remains controversial. In this report, we quantitatively reviewed the prospective observational studies that have analyzed the relation between meat consumption and colorectal cancer. We conducted electronic searches of MEDLINE, EMBASE, and CANCERLIT databases through to the end of June 1999 and manual searches of references from retrieved articles. We used both fixed and random-effects meta-analytical techniques to estimate the overall association and to investigate possible sources of heterogeneity among studies. Thirteen studies were eligible for inclusion in the meta-analysis. Pooled results indicate that a daily increase of 100 g of all meat or red meat is associated with a significant 12-17% increased risk of colorectal cancer. The marginally significant between-study heterogeneity for all meat and red meat was explained by a number of study-level covariates. A significant 49% increased risk was found for a daily increase of 25 g of processed meat. The individual study estimates for processed meat showed no detectable heterogeneity. On the basis of this quantitative review of prospective studies, the overall association between meat consumption and risk of colorectal cancer appears to be positive, with marginal heterogeneity between studies. The finding for processed meat and data from experimental studies suggests that it may also be an important predictor of colorectal cancer risk. However, because only a few of the studies reviewed here attempted to examine the independent effect of meat intake on colorectal cancer risk, the possibility that the overall association may be confounded or modified by other factors cannot be excluded.

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