Is meat killing us

The Journal of the American Osteopathic Association May 2016 | Vol 116 | No. 5296
CLINICAL REVIEW
respectively). Unprocessed red meat consumption
increased all-cause mortality in the US cohorts
(RR, 1.23 [95% CI, 1.17-1.30]) but not in the
European cohorts (RR, 0.90 [95% CI, 0.59-1.38]).
In addition, the steepest increase in mortality was
found at the smallest increases of intake from the
reference ranges of 0.6 g/d (0.02 oz/d) of processed
meat and 13.9 g/d (0.49 oz/d) of total red meat, in-
dicating that even a small amount of meat may have
an impact on mortality risk.
Another 2014 meta-analysis, by Abete et al,2
en-
compassed 6 of the same cohort studies included by
Larsson and Orsini,1
along with 7 other studies, for a
total of 13 studies and more than 1.5 million people.
The analysis not only looked at all-cause mortality
but also examined associations with mortality from
cardiovascular disease (CVD) and ischemic heart
disease (IHD). Abete et al2
included white meat
(poultry or rabbit) in addition to processed and red
meats. In comparing highest vs lowest consumption
of meats, only processed meat significantly increased
risk for all-cause mortality (RR, 1.22 [95% CI,
1.16-1.29]).2
Both processed meat and red meat were
positively associated with CVD mortality (RR,
1.18 [95% CI, 1.05-1.32] and RR, 1.16 [95% CI,
1.03-1.32], respectively). However, total meat (white
meat, processed meat, and unprocessed red meat)
(RR, 1.08 [95% CI, 0.85-1.36]) and white meat
Is Meat Killing Us?
Heather Fields, MD; Denise Millstine, MD; Neera Agrwal, MD; and Lisa Marks, MLS, AHIP
From Mayo Clinic
Arizona in Scottsdale.
Financial Disclosures:
None reported.
Support: None reported.
Address correspondence to
Heather Fields, MD,
Mayo Clinic,
Division of Community
Internal Medicine,
13400 E Shea Blvd,
Scottsdale, AZ
85259-5452.
E-mail:
fields.heather@mayo.edu
Submitted
November 20, 2014;
revision received
April 8, 2015;
accepted
June 18, 2015.
P
atients commonly ask physicians about
the diet’s role in health, including pre-
venting disease and decreasing mortality.
Primary care physicians must navigate nutrition
evidence to answer these questions, but the sci-
ence is commonly flawed in study design or bias.
Currently, low-carbohydrate/high animal protein
diets are popular, and many people in the United
States consider “meat and potatoes” to be culinary
staples. Yet, concern exists that meat consumption
is harmful. How should physicians apply the evi-
dence to offer advice about inclusion and quantity
of meat in a diet when patients ask about their
food choices?
In this brief review, we identified 6 articles that
evaluated the effects of meat and vegetarian diets on
mortality (Table 1). We discuss some of the perti-
nent available evidence regarding whether primary
care physicians should discourage some or all con-
sumption of meat.
The Evidence
Table 2 summarizes the effects of meat consump-
tion on mortality, and Table 3 summarizes the effect
of the vegetarian diet on mortality.
Does Meat Consumption
Increase Mortality?
In a 2014 meta-analysis and systematic review,
Larsson and Orsini1
reviewed 9 prospective cohort
studies conducted in the United States, Europe, and
China. They evaluated the association of processed
meat (eg, bacon, sausage, salami, hot dogs, ham),
unprocessed red meat (eg, uncured, unsalted beef;
pork; lamb; game), and total red meat with all-cause
mortality in more than 1 million people over
follow-up periods ranging from 5.5 to 28 years.1
All-cause mortality for the highest vs lowest cate-
gory of processed meat and total red meat intake
was statistically significant (RR, 1.23 [95% CI,
1.17-1.28] and RR, 1.29 [95% CI, 1.21-1.35],
Clinical Question:
Does meat consumption affect mortality?
Evidence: All-cause mortality is higher for
increased daily consumption of red meat,
especially processed meat. However,
the compiled evidence does not link other
meat products to all-cause mortality.
Recommendation: Physicians should
encourage patients to limit animal products
when possible, and substitute red meat and
processed red meat with plant-based foods.
Patients may supplement a plant-based
diet with moderate amounts of fish, poultry,
eggs, and dairy if desired.
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The Journal of the American Osteopathic Association May 2016 | Vol 116 | No. 5 297
These findings were confirmed by Huang et al5
in a
2012 meta-analysis and systematic review of vegetari-
anism and associated cancer incidence and CVD mor-
tality. This review5
included 7 observational studies
with a total of 124,706 participants (including a longer
follow-up of the aforementioned investigation). Results
showed that vegetarians had a significant decrease in
IHD mortality (RR, 0.71 [95% CI, 0.56-0.87]) and re-
duction in cancer incidence (RR, 0.82 [95% CI, 0.67-
0.97]), but the study did not reveal a statistically
significant reduction in all-cause mortality (pooled RR,
0.91 [95% CI, 0.66-1.16]).5
In 2014, Le and Sabaté6
published a review of 3 large
prospective cohort studies of Adventists in North
America.6
Adventists who were vegetarians had a 10% to
20% decrease in all-cause mortality compared with
nonvegetarian-matched Adventist cohorts, and a 26% to
68% decreased risk of mortality from IHD, CVD, and
cerebrovascular disease.6
Vegetarians also had an 8%
risk reduction for overall cancer.
The study defined a nonvegetarian diet as containing
red meat or poultry and allowed the vegetarian diet to
contain fish, milk, and eggs. Yet, in this review,6
the
vegan diet (void of fish, milk, eggs, and all animal prod-
ucts) extended further protection for obesity, hyperten-
(RR, 1.01 [95% CI, 0.96-1.07]) were not associated with
CVD mortality. Neither processed meat, total meat, nor
white meat were associated with IHD mortality (RR, 1.52
[95% CI, 0.50-4.66]; RR, 1.52 [95% CI, 0.68-3.40]; and
RR, 1.00 [95% CI, 0.82-1.21], respectively); however, CIs
were broad for processed meat and total meat. Of note,
both of these analyses demonstrated statistically signifi-
cant heterogeneity.
These recent large meta-analyses are consistent with
a 2003 review by Singh et al3
of 6 cohort studies. Singh
et al3
found a decreased risk (25% to nearly 50%) of all-
cause mortality for very low meat intake compared with
higher meat intake in 5 of the studies. They also found a
3.6-year increase in life expectancy when comparing
long-term (≥17 years) vs short-term vegetarians.3
Does a Vegetarian Diet
Decrease Mortality?
Should patients, then, avoid all meat and eat a strictly
vegetarian diet? In a 1998 collaborative investigation4
of 5 prospective cohort studies comprising more than
76,000 people, vegetarians had a 24% RR reduction in
mortality from ischemic cardiac disease. However, no
significant differences between vegetarians and non-
vegetarians were found in other causes of mortality.
Table 1.
Studies Evaluating the Effects of Meat and Vegetarian Diets on Mortality
No. of No. of
Source Year Study Design Location Studies Participants
Meat
Larsson and Orsini1
2014 Meta-analysis US, China, EU 9 1,330,352
Abete et al2
2014 Meta-analysis US, WA, EU, Asia 13 1,674,272
Singh et al3
2003 Review US, EU 6 >50,000a
Vegetarian
Key et al4
1998 Prospective collaborative analysis US, EU 5 76,172
Huang et al5
2012 Meta-analysis/systematic review US, EU, Japan 7 124,706
Le and Sabaté6
2014 Review US 3 96,000b
a
Singh et al3
did not report exact total No. of participants.
b
Some participants were included in multiple cohorts.
Abbreviations: EU, Europe; US, United States; WA, West Australia.

CLINICAL REVIEW
cohol; and a reduction in sodium intake.7,9,11
One study
included moderate aerobic exercise, stress management
training, tobacco cessation, and group support in its in-
tervention group.11
However, another study,12
which
included 60,903 Adventists, compared different types of
vegetarian diets and their associations with type 2 dia-
betes mellitus and elevated BMI. Vegan and lacto-ovo-
vegetarian diets decreased the risk for type 2 diabetes
mellitus by half compared with an omnivorous diet.
Pesco-vegetarian and semi-vegetarian (meat consump-
tion less than once per week but more than once per
month) diets also decreased this risk by one-fourth to
one-third.12
The study12
found that only the vegan diet
was associated with a BMI in the optimal range. In addi-
tion to mortality effects, the topic of plant-based diets in
chronic disease has been reviewed and found to be po-
tentially beneficial in weight management, CVD, and
metabolic disorders.13
The aforementioned studies1-13
suggest that perhaps
complete avoidance of meat could be best for improved
health. However, several of the cohorts in these reviews
examined the effects of white meat separately and re-
vealed opposing results. In a 2009 cohort study,14
those
who consumed the highest quintile of white meat had a
statistically significant decrease in all-cause mortality
(hazard ratio [HR], 0.92 [95% CI, 0.88-0.96]) and cancer
mortality (HR, 0.89 [95% CI, 0.83-0.95]) compared with
the cohort of the lowest quintile of white meat. Another
cohort showed no significant effect on all-cause mor-
tality with daily poultry consumption and noted a J curve
in which the lowest HR for all-cause mortality was in
people with low to moderate red meat consumption
(10.0-19.9 g/d) with an HR of 1.00 (set at reference)
rather than no red meat (0-9.9 g/d) at an HR of 1.07 (95%
CI, 1.01-1.13).15
In a review16
of 2 US cohort studies, a
substitution analysis estimated the effect of replacing
1 serving of red meat with 1 serving of either fish, poultry,
nuts, legumes, low-fat dairy products, or whole grains.
It showed a statistically significant lower risk of all-cause
mortality with every type of substitution.16
In the 2014
meta-analysis, when stratified by sex, white meat was as-
sociated with a lower risk of all-cause mortality in women
sion, type 2 diabetes mellitus, and CVD mortality in
comparison with the lacto-ovo-vegetarian diet. Seventh
Day Adventists participate in additional aspects of
healthy lifestyles, such as abstinence from tobacco and
alcohol, and thus may have other independent factors
lending to overall decreased CVD. However, these
studies used nonvegetarian Adventists as controls, thus
mitigating this potential confounding effect.
Additional Evidence
Past clinical trials have shown substantial benefits of a
vegetarian or vegan diet in reduced body mass index
(BMI), reversal of CVD, and improved hypertension and
type 2 diabetes mellitus.7-10
Limitations of these studies
include a small number of participants and a short dura-
tion. In addition, many studies included confounding
dietary variables in the intervention group, such as the
elimination of added oils, avocado, nuts, dairy, processed
foods, and sugary foods; avoidance of caffeine and al-
Table 2.
Statistically Significant Increase in Mortality
With Increased Meat Intake
Meat Category
Increased Mortality Red Processed White Totala

All Cause
Larsson and Orsini1
Yes Yes NA NA
Abete et al2
No Yes No No
Singh et al3
Yes Yes No NA
Cardiovascular Disease
Abete et al2
Yes Yes No No
Singh et al3
Yes Yes Yesb
NA
Ischemic Heart Disease
Abete et al2
No No No No
Cancer
Singh et al3
Yes Yes No NA
a
Only the article by Abete et al2
evaluated the effects of total meat defined as
white processed and unprocessed red meat. The other studies combined red and
processed meat at times, but these combinations are not reflected in this table.
b
Singh et al3
reported a statistically significant increase in cardiovascular
disease mortality among men but not among women.
Abbreviation: NA, not applicable.

CLINICAL REVIEW
The Journal of the American Osteopathic Association May 2016 | Vol 116 | No. 5 299
(RR, 0.95 [95% CI, 0.91-0.99]).2
A pooled analysis of
Asian cohorts revealed an inverse association with poultry
intake for all-cause mortality in men and women (P=.02
and .03, respectively) and cancer mortality in women
(P.01).17
In addition, all-cause and CVD mortality in
women were inversely associated with seafood intake
(P=.05 and .04, respectively).The associations of different
types of vegetarian diets with all-cause mortality in a co-
hort from the previously described review6
found the most
benefit in the pesco-vegetarian diet (HR, 0.81 [95% CI,
0.69-0.94]).18
Conclusion
Despite variability in the data, the evidence is consistent
that increased intake of red meat, especially processed
red meat, is associated with increased all-cause mortality.
Red meat also increases CVD and cancer mortality in
Western cohorts.Avegan diet has been shown to improve
several parameters of health, including reversal of CVD,
decreased BMI, decreased risk of diabetes, and decreased
blood pressure in smaller studies. Data regarding inclu-
sion of some fish and white meat are conflicted—
although fish and white meat consumption are not clearly
associated with increased mortality, they do decrease
mortality when they replace red meat in the diet.
Even though limitations exist in these studies (eg,
lack of large, long-term randomized controlled trials;
large amount of heterogeneity), avoidance of red and
processed meats and a diet rich in plant-based whole
foods including fruits, vegetables, whole grains, nuts,
and legumes is a sound, evidence-based recommenda-
tion. If such a recommendation represents a difficult
change for a patient, physicians should encourage
limited animal products when possible and substi-
tuting red meat with plant-based proteins, fish, or
poultry. (doi:10.7556/jaoa.2016.059)
References
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consumption and all-cause mortality: a meta-analysis.
Am J Epidemiol. 2014;179(3):282-289.
doi:10.1093/aje/kwt261.
2. Abete I, Romaguera D, Vieira AR, Lopez de Munain A,
Norat T. Association between total, processed, red
and white meat consumption and all-cause, CVD and IHD
mortality: a meta-analysis of cohort studies. Br J Nutr.
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3. Singh PN, Sabaté J, Fraser GE. Does low meat
consumption increase life expectancy in humans [review]?
Am J Clin Nutr. 2003;78(3 suppl):526S-532S.
4. Key TJ, Fraser GE, Thorogood M, et al. Mortality in vegetarians
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6. Le LT, Sabaté J. Beyond meatless, the health effects
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2014;6(6):2131-2147. doi:10.3390/nu6062131.
Table 3.
Statistically Significant Decrease in Mortality With Vegetarian Diet
Decreased Mortality
Cardiovascular Ischemic
Source All Cause Disease Heart Disease Cancer
Key et al4
No NA Yes Sometimesa
Huang et al5
Yes No Yes Yes
Le and Sabaté6
Yes Yes Yes Yes
a
The study by Key et al4
was a collaborative analysis of 5 large cohorts. It separated cancer into categories of cancer
of the stomach, colon, lung, female breast, and prostate without combining these results. The results were fairly
heterogenous, so none of the cancers had a consistent statistically significant decrease in mortality in all 5 cohorts.
Abbreviation: NA, not applicable.

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© 2016 American Osteopathic Association
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Is meat killing us