Meat and meat products consumption and cancer

Meat and meat products consumption
and cancer
Dr. Karl O. Honikel
Chairman of Nutrition and Health Working Group
CLITRAVI
Preface
During the meeting of the Nutrition and Health Working Group at the
annual meeting of CLITRAVI in Toulouse on 13 May 2009 the idea arose to
compile and evaluate the most recent data on meat/meat products and
cancer.
As the chairman I have collected and read in the last few months quite a
number of papers and reports. The result is quite promising. Contrary to the
decades before when positive papers on meat were only published by meat
oriented people, now scientists well recognized as toxicologists, nutritionists
or medical doctors report that meat is good for you and should be a part of a
balanced diet. I assume that the rather aggressive statements (some call it
“nannying” the consumer) of the 2nd World Cancer Research Fund report
(WCRF II) published in a joint effort with the American Institute for Cancer
Research (AICR) in November 2007 and the way it was made public triggered
some recent publications and statements.
Even the International Agency for Research on Cancer (IARC) in Lyon which
published in the years before (see the paper of Norat et al in the table) and
by the E. Riboli a former scientists in the IARC sounds nowadays much more
careful. In http://www.iarc.fr IARC states in a report of December 2008:
“The high expectations we had that epidemiological studies would discover
that the dietary habits are associated with increased or decreased cancer
were not realized”. They continue later on: “In particular intakes of fat, fruit,
vegetables and of meat either not associated or only slightly associated with
colorectal, breast or prostate cancer occurrence”. Other critical remarks on
the WCRF II have been published elsewhere. Now the WCRF/AIRC rows
backwards in a new report (WCRF 2009), see table for details.
Despite this promising outlook we should take this worldwide read and
accepted report WCRF II serious and I will evaluate the points on meat in the
following.
Points to observe in the WCRF reports
The report II of the World Cancer Research Fund (WCRF II) was published
(see table, paper 5) with 2 parallel press conferences in Washington, DC and
London in November 2007. We still have a short statement about it in the
CLITRAVI homepage. WCRF published it in a joint venture with the
American Institute for Cancer Research (AICR) and it was supported by
leading scientists worldwide in its evaluations of about 7000 publications
and conclusions on food and cancer and opinions drawn finally by a panel of
toxicologists. The studies evaluated on meat and cancer are much smaller
with 12 and 5 studies (see table). The opinions have caused in some
countries and with several governments the concern that besides other
causes the eating of red meat and processed meat may promote colorectal
cancer.
The WCRF panel states that there is a relationship of colorectal cancer
and intake of red meat / processed meat with “Convincing Evidence”
This “convincing evidence” is met in the foods area only by alcohol and
aflatoxin contaminated foods. However, a BMI >30, no or low physical
activity and other none food attributed behaviours like smoking are even
worse with convincing evidence for 7 different kinds of cancer.
The report received criticism from many sides mainly by opposing its
“nannying” recommendations. In a new report of WCRF in 2009 called” The
Policy and Action for Cancer Prevention Food, Nutrition and Physical
Activity: a Global Perspective” (WCRF 2009), see table for details, they step
back slightly and state that is was by no means their intentions to tell the
people what to eat. In the Appendix A of this report on page 150 they try on
the example of red meat to improve their statements by stating that eating
red meat between 10 and 80g/day has a relative risk (RR) of 1.03 and a
Population Attributable Fraction (PAF)of cancer incidence of 5% for colorectal
cancer calculated for UK. A RR of 1.03 is regarded in such statistical
evaluations as not significant at all, (actually up to RR 1.1 values are
regarded as insignificant) and a 5% PAF lets one wonder where the
“Convincing Evidence” remains. But as it is common this second statement
only a few people will read and take up in their judgements. Thus I will take
a look at the arguments of the November 2007 report.
1. The panel recommends with regard to meat
a.) to eat as an individual <500g cooked red meat including the part of
red meat in the processed products per week. This is equivalent to 71g
red meat/day.
In the report (WCRF II) on several pages and especially in the printed
summary of the report it is said that the 500g are calculated from 700 to
750g raw red meat. It means that on processing and preparation one looses
29 to 33% of the raw weight. It is, however, a long experience in the meat
business and catering that preparing fresh meat result in a loss of 15 to
25%. Let us take a mean value of 20 %.
The apparently intended figure for intake of red meat by the WCRF panel is
based on 700 to 750g raw meat. Nutritionists who refer to the WCRF report
state indeed 100g raw red meat/ day. This is equivalent to 80 g prepared
meat /day. This figure is the value in the new report with 10 to 80g/day
(WCRF 2009) and an RR of 1.03.
What about the processing?
In the 80g/day also the processed red meat is included. Do we loose weight
during processing? I calculated it taking into account the cooked and nonheat treated meat products. By adding water, salt and additives to the meat
in heated product and the loss of weight in the non-heat treated dried
products one ends up at about 97 to 103 g per 100g raw meat, depending on
the percentage of the meat product groups which varies between the
countries. Thus we can state that there is no weight loss in processed meat
in comparison to the raw meat used. In order to avoid too much complexity I
recommend that we take 80g/day prepared and processed red meat also
used by the WCRF in the new 2009 report as the figure for further
calculations keeping in mind that this is a conservative value.
According to our calculations in the list of last year for meat and meat
products intake and composition (see annex 1 to NUT/08/057) compiled vs
the unsatisfying list of EFSA for nutritional profiles and thresholds we stated
that the average European consumer has 150g of raw meat available/day of
which 2/3 = 100g/day is red meat.
Thus we can state that the European consumer eats the amount what
the WCRF panel recommends for an individual as the maximum value.
We assume further on that of the total meat 40% is processed. That means
40% of 150g is 60g/day are used for processed meat resulting in 48g
processed meat products (80%) of which we can assume that 75% are made
from red meat which is equal to 36g/day.
Taking then the white meat remaining it means that 50g/day are available
as raw material resulting in 40g prepared white meat (80% of raw).
b.) The panel states that all processed meats should be avoided.
In Europe it means according to the calculations above that 36g
processed red meat and about 12g of processed white meat, total
48g/day of processed meat, are produced. They should be avoided.
2.
Causes for red meat/processed meat and cancer
The expressions and explanations of the WCRF II report about the causes for
red meat and cancer are not very clear. The panel gives only hints what
could be the cause for the convincing evidence which they state. In the text
they indicate some possible causes:
i.) the nitrite in the food itself forming nitrosamines in the food and the
body. In other parts of the report, however, they clearly say that 70 to 90% of
the nitrite comes by reduction in the body and saliva from plant nitrate.
Furthermore studies since 3 decades show very clearly that meat products
themselves contain very low concentrations of nitrite and nitrosamines for
various reasons.
ii.) free iron as a transition metal can easily take up various states of
oxidation. Fe2+, Fe3+ and Fe4+ are common in food. In raw meat without
any question the Fe is bound. In cooked meat some iron is free. Also it is a
known fact that the iron in meat is absorbed in the intestines about 4 times
higher than plant iron (ca. 20 vs 5%). Absorbance means it must have been
at least free iron for some time to be absorbed. By the change of oxidation
status Fe ions promote radical formation. Myoglobin with its iron containing
porphyrin moiety is believed to be involved in the radical forming process.
The presence or addition of antioxidants like ascorbate will prevent the
formation of radicals.
This indication by the panel cannot be put aside. It is the most serious
one. We should consider doing something about it.
iii.) Heterocyclic aromatic amines (HAA) or polycyclic aromatics
hydrocarbons (PAH) are definitely no serious problem in products. The HAA
and PAH may occur in frying and grilling of meat and to a lower extent in
meat products. Actually much more HAA precursors are present in the white
poultry meat which is supposed to be less “dangerous”. Heavy metals are
very low in European meat cuts and products. PCB, Dioxins and related
compounds are present in meat but in much smaller amounts than in dairy
products which show no such incidence of cancer.
iv.) The panel also mentions the fatty acid composition of meat and
cholesterol as a cause for cancer. It is more than astonishing actually
irritating that these people who dare to make recommendations about cancer
evidence do not know the basic facts of textbooks on nutrition that meat and
meat fat is not rich in saturated fatty acids and cholesterol. In their
ignorance they point to the statements of saturated fatty acids in dairy
products in which indeed the saturated fatty acids are higher with about
65%.
3.
The panel recognizes also that in the studies used for evaluation
the definitions of meat and meat products vary considerably.
I myself read through several of the original papers. In some the expression
of meat is defined as all meat in cuts including cooked and raw ham but
interestingly in one paper not bacon. They define as meat products every
processed meat which is minced or comminuted including even minced meat
itself which has in Hamburgers quite a share of 5-10%. Others call
processed meat everything with a cured red colour. Taking such a variation
into account how can the conclusions be compared? Nevertheless the panel
does so. Sometimes in white meat also fish is included.
4.
Red meat is defined meat from bovines, porcines, goat, sheep,
and wild animals.
White meat is then in consequence the meat of all birds. Even accepting that
ducks and geese together with wild birds are of minor importance, the fact
that some turkey muscle contain at least the same or more myoglobin then
some porcine muscles has not been taken into account. Chicken and turkey
carcasses do not contain light breast muscles only.
5.
Statistical approach in the studies evaluated.
In nearly all of the studies used by the WCRF for the evaluation of meat and
cancer incidents meat is the only food, sometimes also fish, at which the
authors look. Besides food the age, gender, race, physical activity, BMI and
smoking are evaluated for cancer. That means that other foods are neglected
and not statistically evaluated which is even often stated in the introduction
of the papers.
It is also a common approach and applied also in the WCRF report that the
highest vs the lowest intake is compared and the high RR is taken for
evaluation and reported.
As an example the most recent paper of Sinha et al. (see table for details)
compares the eating of about 200g red meat/day with the low intake of
97g/day and states the high RR as the relevant figure for the cancer
incidence. The RR for the 97g/day is set at 1.00.
Furthermore very interesting in this paper is the fact that the amount of
meat and products and of what species and cut (fat/energy content) eaten in
the last 12 months was asked retrospective twice in 10 years of follow-up.
Everybody can do the testing himself: what did you eat in September 2008
as meat, products, which cut which species and what other foods did you eat
and in which quantity?
Sinha et al. came to the statistical conclusion that the RR of highest
200g/day vs. lowest 97g/day was 1.44. Using the Sinha figures in its
quintiles and applying it to European conditions, then the RR is 1.07.
This is as said above of no statistical significance.
Conclusions
Reading the reported facts and figures and investigating in detail the figures
I wonder how the panel comes to such conclusions. But due to the
importance and worldwide acceptance of the WCRF which is a joint venture
with the powerful AICR we must take their statements seriously and we
should investigate the questions involved.
Demeyer, De Smet and I have made last year in the Meat Science paper
some recommendations for research. Little reaction has been reported to me.
In the list below I compiled some publications of recent years which are often
cited or used pro and contra meat and meat products. Even if the opinions
are no longer unisono against meat we should be aware that it will take a
full generation or its professional period to change the opinions.
Finally I recommend reading the cited paper of Jarvis 2007 for arguments.
References
1. Sandhu M.S.and White I.R.(2001). “Systematic review of the prospective cohort
studies on meat consumption and colorectal cancer risk: a meta-analytical approach”.
Cancer Epidemiol Biomarkers Prev 10: 439-446
2. Norat, T., Lukanova, A., Ferrari, P., Riboli, E. et al. (2002). “Meat consumption and
colorectal cancer risk: dose-response meta-analysis of epidemiological studies”.
International Journal of Cancer 98: 241-256
3. Chang-Claude, J., Hermann, S., Eilber, U., and Steindorf, K. (2005), Life-style
Determinants and Mortality in German Vegetarians and Health-conscious Persons.
Results of a 21 Year Follow-up, Cancer, Epidemiol. Biomarkers Prev.14(4) 963-968
4. Larsson, S.C., Wolk, A., (2006). “Meat consumption and risk of colorectal
cancer: A meta-analysis of prospective studies”. International Journal of Cancer,
119: 2657-2664
5. The World Cancer Research Fund/American Institute for Cancer Research
(2007). “Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global
Perspectiv”. Washington, DC, AICR,
6. Policy and Action for Cancer Prevention, Food, Nutrition and Physical Activity: a
Global Perspective WCRF and AICR, Washington , DC (2009)
7. Sinha, R., Cross, A., Graubard, B.I., Leitzmann, M.F, Schatzkin, A., (2009). “Meat
Intake and Mortality“, Arch. Intern. Med, 169, 6, 562-571
8. Key, T., J., Appleby, P., N., Spencer, E., A., Travis, R., C., Roddam, A., W., Allen,
N., E., (2009), Cancer Incidence in Vegetarians: Results from a European
Prospective Investigation into Cancer and Nutrition (Epic –Oxford) Am. J. Clin.
Nutr. 89, supplement 1S-7S
9. Alexander, D., D., Cushing, C. A., Lowe, K.A., Sceurman, B., and Roberts, M.A.
(2009) Metaanalysis of Animal Fat and Animal Protein Intake and Colorectal
Cancer, Am. J. Clin. Nutr. 89, 1-8
Other reports either general or on specific cancer types:
EPIC-Studie 2009. http://epic.iarc.fr/ [online 8. Juni 2009]
Gonzalez et al. (2006). “Meat Intake and Risk of Stomach and Esophageal
Adenocarcinoma within the European Prospective Investigation Into Cancer and
Nutrition (EPIC)”; Journal of the National Cancer Institute, Vol. 98, No. 5, March 1,
345-354
MF Faramawi, E Johnson, MW Fry, M Sall and Z Yi (2006). “Consumption of different
types of meat and the risk of renal cancer: meta-analysis of case-control studies.”
Cancer Causes and Control 18: 125-133
Jarvis, W.T., (2007), The Role of Meat in the Diet, Misinformation and Misbelief,
Proc. 60th Reciprocal Meat Conference, Brookings S:D. AMSA Chicago Ill. USA 1-11
Table: Meta-analyses and publications on red meat and cancer
year
type of analysis
area
2001 13 prospect.
studies
USA, NL,
JP,SF
2002 9 prospect.
studies
worldwide
1973-99
2005 1 prosp.study
D veget.
2006 15 prosp. st.
on red meat
(N=7400 p)
14prosp.st.
meat products
(N=7900)
2007 12
prosp.studies.
red meat
5 prosp.studies
proc. meat
worldwide
2009 addition to
WCRF
2007report
2009 1 prosp. study
2009 1 prosp.study
2009 6 prosp. study
worldwide
1975-2005
USA
UK, EPIC
Oxford
worldwide
animal fat
animal
protein
cancer
type
result
and
rel.risk
(RR)
colorectal 100g/d
totalmeat
1.15
25g/d products
1.49
colorectal low vs high
red meat 1.35
proc.meat 1.31
cancer
veget vs
meateater
meteater -17%
colorectal low vs high
red meat 1.28
meatproducts
1.20
colorectal >100g
rawmeat/d
1.43
>50g proc.meat
1.21
reference
1
2
3
4
5 WCRF
colorectal red meat 1080g/d
1.07
6 WCRF
page 150
cancer
7
low vs. high
high ca.200g/d
1.44
colorectal nonveget.
vs.veget. 0.84
colorectal low vs. high
1.02-1.04
1.05
8
9