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The impacts of lean red meat consumption on human health: a reviewF. B. Lucianoa

a Faculty of Agriculture and Food Sciences, Department of Food Science, University of Manitoba,

Winnipeg, MB, Canada

Online publication date: 27 October 2010

To cite this Article Luciano, F. B.(2009) 'The impacts of lean red meat consumption on human health: a review', CyTA - Journal of Food, 7: 2, 143 — 151

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REVIEW ARTICLES

The impacts of lean red meat consumption on human health: a review

Impactos del consumo de carne roja magra en la salud humana: una revisio ´ n

F.B. Luciano*

Faculty of Agriculture and Food Sciences, Department of Food Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2

(Received 18 September 2008; final version received 9 March 2009)

Since the early 1980s, diverse epidemiological studies have been published with the propaganda that red meat isdeleterious to human wellbeing, and could lead to health problems such as coronary heart disease, thrombosis, andcancer. These health issues were mainly related to the presence of saturated fatty acids at high levels in some cuts of red meat. Unfortunately, lean red meat was blemished in the same way, even though it contains very low levels of fat. Studies indicated that lean red meat does not increase the plasmatic lipid levels with regard to total cholesterol

(TC), and low density lipoprotein-cholesterol (LDL-C). In addition, diets containing lean red meat and lean whitemeat presented similar patterns of TC and LDL-C during both short and long-term studies. When compared withsoy, lean red meat did not show the same levels of LDL-C reduction, but presented similar effects on the LDL-C :HDL-C ratio. Apparently, red meat fat and not meat per se is related to increased plasmatic lipid levels, and redmeat trimmed of fat can be consumed without major effects to human health. To date, epidemiological studiesrelating the consumption of red meat to cancer and thrombosis have had contradictory results and furtherstudies are needed.

Keywords: lean meat; cholesterol; fat; coronary heart disease; cancer; thrombosis

Desde principios de los ochenta, estudios epidemiologicos diversos se han publicado con la propaganda de que lacarne roja es perjudicial para el bienestar humano, y podrı á llevar a problemas de salud como cardiopatı áscoronarias, trombosis y ca ´ ncer. Estos problemas de salud se adjudicaron principalmente a la presencia de altosniveles de acidos grasos saturados en algunos cortes de carne roja. Desafortunadamente, la carne roja magra fuedesprestigiada de la misma manera aunque tuviera niveles muy bajos de grasa. Estudios han mostrado que la carneroja magra no aumenta los niveles de lı ´pidos plasma ´ ticos, que incluyen a los colesteroles totales (TC) y al colesterol-lipoproteı ńa de baja densidad (LDL-C). Adicionalmente, las dietas que contienen carne roja magra y carne blancamagra presentaron patrones similares de TC y LDL-C durante estudios de corto y largo plazo. Cuando se lecompara con la soya, la carne roja magra no mostro ´ los mismos niveles de reduccio ´ n de LDL-C, pero presento éfectos similares en la razo ´ n LDL-C:HDL-C. Aparentemente es la grasa de la carne roja y no la carne roja en sı ´misma la que se relaciona con niveles elevados de lı ´pidos plasma ´ ticos, y la carne roja magra puede ser consumida sinmayores efectos nocivos para la salud humana. Hasta la fecha, estudios epidemiologicos relacionando el consumo decarne roja con ca ´ ncer y trombosis han tenido resultados contradictorios y se requiere hacer ma ´ s estudios.

Palabras clave: carne roja magra; colesterol; grasa; cardiopatı ás coronarias; ca ´ ncer; trombosis

Introduction

The lifestyle of Westernized societies has changed in

recent centuries in such a way that foods have become

excessively caloric and people are more sedentary.

Nowadays, food products are more convenient, but at

the same time have higher amounts of fat and sugar,

while red meat is considered one of the main sources of

fat in the human diet (Hill & Melanson, 1999). The

main result of this way of life is the higher rates of

obesity in the occidental part of the globe. In the

United States alone 97 million people are considered

obese or overweight, and at least 50% of Americans

are on diets to lose weight (Kuczmarski, Flegal, &

Campbell, 1994; Mokdad et al., 1999). Issues

concerning obesity are mainly due to the high rates

of comorbidities that come along with excess of weight.

For instance, it was reported that subjects either

overweight or obese have a 72% chance of developing

diseases such as type 2 diabetes mellitus, cardiovas-

cular diseases, dyslipidemias, and some types of cancer

(Melanson et al., 2003). Obesity itself and its comor-

bidities have been related to more than 300,000 deaths

per year in the US (McGinnis & Foege, 1993).

Therefore, it is clear that the contingent of obese

subjects might be reduced through better feeding habits

accompanied by exercise.

Usually, obesity and obesity-related diseases are

related to the dietary fat intake. Firstly, fat has a high

*Email: [email protected]

CyTA – Journal of Food

Vol. 7, No. 2, August 2009, 143–151

ISSN 1947-6337 print/ISSN 1947-6345 online

Ó 2009 Taylor & Francis

DOI: 10.1080/19476330902940523

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caloric content that facilitates the accumulation of

energy in the body. Furthermore, most of the co-

diseases are directly or indirectly caused by enhanced

quantities of fat deposited in adipocytes and augmen-

ted serum cholesterol levels (Dreon et al., 1998).

Consequently, most of the dietary regimens to loseweight are designed to reduce dietary fat intake

(Lissner, Heitman, & Bengtsson, 1997).

Among fats, the saturated form (SFA) is more

likely related to unhealthy effects, whereas some

monounsaturated (MUFA) and polyunsaturated fats

(PUFA) are more associated with beneficial health

status. Nutritionists have recommended a PUFA:SFA

ratio of 0.4 or higher in a balanced healthy diet (Wood

et al., 2004). Red meat has a PUFA:SFA ratio of 0.1

and is recognized as one the main sources of saturated

fat in the human diet, which has transformed it into

food enemy number one to human health. This

propaganda has been spread since 1984, when im-portant epidemiological studies were published sug-

gesting that red meat consumption was directly related

to augmented risk of cardiovascular diseases

(Snowdon, Phillips, & Fraser, 1984). Additionally,

long term studies such as the Nurses’ Health Study in

the US (Hu et al., 1999) and the 1984 report of the

British Government’s Committee on Medical Aspects

of Food and Nutrition (COMA, 1984) correlated the

intake of saturated fatty acids and, indirectly,

meat with coronary heart disease. Actually, they

showed that beef consumption (rich in stearic acid)

was even more deleterious than isolated fatty acids(palmitic, myristic and lauric acids) (Li, Siriamornpun,

Wahlqvist, Mann, & Sinclair, 2005). Further studies

also showed increased levels of blood low density

lipoprotein-cholesterol (LDL-C) and triacylglicerol

(TG) to be related to red meat consumption when

compared to vegetarian diets (Li et al., 2005). Although

cardiovascular diseases are often a result of diverse

factors, the image of red meat has been blemished due

to its relationship with saturated fatty acids. Since

these epidemiological studies were published, physi-

cians and nutritionists have encouraged the population

to decrease the consumption of red meat in their daily

meals (Mann, 2000).

On the other hand, some researchers and the meat

industry have pointed the fact that humankind evolved

with a meat-based diet for millions of years and it

would be unlikely that meat per se could lead to many

unhealthy conditions (Cordain, Eaton, Miller, Mann,

& Hill, 2002). In addition, red meat is an excellent

source of minerals (e.g. zinc, iron, selenium) and the

main source of vitamin B12 in the human diet

(Herbert, 1998). The reduction of red meat consump-

tion by women in Australia has been associated with

lower levels of iron dietary intake, leading to a higher

rate of anemia cases within this specific population. Itis also one of the main sources of protein and energy in

many countries around the World (Mann, 2000).

O’Dea (1984) carried out an epidemiological study,

where he observed that the reversion of the urbanized

diet of diabetic Australian Aborigines to their tradi-

tional hunter-gatherer diet enhanced their overall

health status. The subjects of the study showed

improvement on the diabetes biomarkers levels,reduction of both blood lipid levels and risk of

thrombosis, as well as better arterial pressure rates.

These positive changes occurred regardless of the

significant amount of wild animals’ meat within the

dietary regime. However, even with a substantial

content of meat, the diet had low fat intake, due to

the fact that wild game meat is very lean (1–2% of fat)

and poor in saturated fatty acids. The low fat content

of game meat has also been described by others

(Hoffman, 2000; Van Zyl, & Ferreira, 2004). This

suggests that lean red meat does not increase the levels

of blood lipids and, therefore, the risk of cardiovas-

cular diseases (Mann, 2000).This review discusses some of the statements that

relate the consumption of red meat to several human

diseases. Consumers and health professionals have

interpreted that red meat can lead to deleterious effects

to their health, but they largely get the wrong

impression that lean red meat is also unhealthy.

Diverse studies are presented here showing that rates

of cancer and cardiovascular diseases are no different

amongst individuals who consume lean red meat, lean

white meat, fish, or vegetable proteins.

Lean meat and fat profile

Beef and lamb were described to reach amounts as high

as 80% of lipids in the overall meat weight (Li, Ball,

Bartlett, & Sinclair, 1999). When the fat is trimmed,

lean red meat can have amounts of SFA as low as

1.5 g/100 g, whereas a marbled meat can reach ratios

over 37 g of SFA/100 g (Li et al., 2005). Fat acid

profiles in lean meat of different animals are presented

in Table 1. Generally, the amount of fat present in lean

meat is a result of the phospholipids composition in

muscular cells’ membrane and the content of TG.

Table 1. Fatty acid profiles in lean meats (g/100 g) (adaptedfrom Hoffman and Wiklund, 2006; Li et al., 2005).

Tabla 1. P erfiles de a ´ cidos grasos en carnes magras(g/100 g) (adaptado de Li et al., 2005; Hoffman & Wiklund,2006).

SFA MUFA PUFA PUFA:SFA

Beef 0.38 0.39 0.15 0.40Lamb 1.48 1.44 0.33 0.22Chicken 0.57 0.81 0.36 0.63Turkey 0.29 0.24 0.26 0.90Pork 0.54 0.65 0.30 0.56

Duiker* 0.47 0.80 0.85 1.81Kudu* 0.57 0.32 0.69 1.21

*Game meat.

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In beef and lamb, phospholipids are rich in PUFA,

whereas TG is composed of SFA and MUFA. More-

over, it has been reported that the content of

phospholipids present in red meat is invariable,

regardless of whether it is lean or marbled meat. On

the other hand, TG levels are augmented along withincreased amounts of total lipids in the meat (Li et al.,

2005). The content of fat in meat is also dependent on

regional customs. For instance, Australian and South

American cuts are leaner than North American meats,

where marbling is a requirement for meat good quality

(Li et al., 1999).

Lean red meat and cholesterol

High levels of TG and LDL-C have been associated

with cardiovascular diseases, such as coronary heart

disease (Drexel et al., 1994; Sarret et al., 1994).

Increased concentrations of LDL-C result in a depositof this lipoprotein within the vessels’ interstitial space,

between the endothelium and the vascular smooth

muscular cells. This deposition reduces the luminal

space of veins and arteries, resulting in hypertension

and coronary heart disease. These deposited LDL-Cs

are more likely to be oxidized, which can activate

macrophages and cause an inflammatory response

resulting in a pathology called atherosclerosis. Other

diseases related to the atherosclerosis process can be

cited, such as stroke, heart attack, and ischemia

(Davidson, Hunninghake, Maki, Kwiterovich, &

Kafonek, 1999). Some researchers showed that redmeat increases the levels of LDL-C and it seems to be a

result of the meat fatty acids content (Denke, 1994;

Morgan, Sinclair, & O’Dea, 1993).

Asleanredmeathaslowlevelsoffattyacids(Table1),

it was not expected to increase serum cholesterol levels.

Trying to confirm this hypothesis, O’Dea, Trainanedes,

Chisolm, Leyden & Sinclair (1990) performed a study to

evaluate the effects of lean beef and beef fat on lipids

serum profile. Ten subjects (five men and five women)

with an average body mass index (BMI) of 23.8 + 1.0

were used, corresponding to normal-weight people.

Their age ranged between 22 and 30 years old. The

subjects were fed with an isocaloric diet for 5 weeks. In

the first week, they consumed their usual diet (30–100 g

of beef per day) with 38% of the energy derived from fat.

During the second and third week, the diet had a

significant reduction of fat content (9% of the energy

from fat) and the subjects were alimented with 500 g of

leanred meatper day.In the final2 weeks ofthe study,fat

was re-added to the diet by beef dripping in a stepwise

way (29% of the energy from fat). During the 2 weeks in

which subjects were fed with lean red meat in a low-fat

diet, total cholesterol and LDL-C dropped 17%

(5.84 + 0.36 to 4.69 + 0.38 mmol/L) and 27%

(3.88 + 0.44 to 2.82+ 0.31 mmol/L), respectively.However, levels of total cholesterol (5.39+

0.38 mmol/L) and LDL-C (3.25+ 0.44 mmol/L)

significantly increased when fat was re-included to the

diet. In addition, high density lipoprotein cholesterol

(HDL-C) was not significantly altered during this study.

With these results, the authors suggested that lean red

meat can be consumed in diets to lower the serum

cholesterol content.Following up this study, the same research group

designed a new experiment (Morgan et al., 1993) to

survey the effect of dietary saturated and poly-

unsaturated fatty acids on the serum cholesterol rates.

To perform the experiment, 22 subjects with normal

levels of cholesterol were used (11 men and 11 women)

aged between 30 and 55 years old. As in the first study,

subjects were carried through a 5-week diet, where they

ate their usual diet in the first week. During the second

and third week, they received a low-fat diet (9% of fat)

with 500 g/day of lean red meat and subjects were fed

with lean red meat added of either safflower or olive oil

through the forth (20% of fat) and fifth week (30% of fat). The cholesterol-lowering effect was surveyed

during the second and third week, when levels of

LDL-C and HDL-C were reduced in 13–14% and 20–

25%, respectively. Interestingly, when fat was re-added

to the diet using either safflower or olive oil, LDL-C

levels were maintained low. With these results, the

authors concluded that reduction of saturated fatty

acids was more likely to be necessary to produce

cholesterol-lowering effects than the diminution of

total fat intake. Hodgson, Burke, Beilin & Puddey

(2006) also showed no significant difference on blood

cholesterol (total, LDL-C, and HDL-C) in hyperten-sive individuals consuming carbohydrates as the main

source of energy or lean red meat as a substitute. Both

diets were isoenergetic and at the end of the 8-week

study, subjects consuming lean red meat had signifi-

cantly lower rates of blood pressure.

In accordance with these studies, Morgan, O’Dea &

Sinclair (1997) showed that a low fat diet containing

lean red meat could be used to reduce levels of LDL-C

in hypercholesterolemic individuals. In this test, 24

subjects (14 male and 10 female) with total cholesterol

levels greater than 6.00 mmol/L were used. They were

on average 46 years old and had a BMI of 25.1. During

the first two weeks, subjects consumed their usual diet.

In the subsequent 6 weeks of the study, individuals

were assigned randomly one of the following isocaloric

diets: a low fat diet (10% of fat) or a diet with medium

level of fat (26%) enriched with olive oil. Subjects were

maintained for 3 weeks on each diet and received

300 g/day of lean red meat during these 6 weeks. Both

diets presented significant cholesterol-lowering effects,

but the olive oil enriched diet was more efficient to

sustain the HDL-C levels. Again, the reduction of

saturated fatty acids present in the diet, and not meat

itself, was related to lower levels of serum cholesterol.

More recently, Wagemakers, Prynne, Stephen &Wadsworth (2009) published an epidemiological study

involving 1152 subjects where they found no significant

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relationship between red meat consumption and serum

cholesterol levels or blood pressure, and therefore it

was not considered a significant risk factor in causing

coronary heart disease.

Lean white meat against lean red meat

Physicians and nutritionists usually recommend the

replacement of red meat with either poultry or fish to

patients with hypercholesterolemia due to the lower

content of saturated fatty acids present in white meat

(Beauchesne-Rondeau, Gascon, Bergerson, & Jacques,

2003). To evaluate the differences in the lipid profile of

humans after either diet rich in lean red meat or lean

white meat, Davidson et al. (1999) carried out a long-

term study starting with 191 individuals. They had a

serum LDL-C level of 3.37 to 4.92 mmol/L and TG

lower than 3.96 mmol/L. The subjects passed through

an initial 4-week period, where lipid baseline levelswere measured. Then, they were randomly included

into two diets containing 120–170 g of either lean red

meat or lean white meat per day for at least 5 days/

week. The lean red meat group consisted of 53.9% of

men and 46.1% of women, aged 56.9 years an average

(BMI ¼ 27.6 + 0.37), whereas the white meat-diet

group had 58.3% of men and 41.7% of women, aged

54.8 years on average (BMI ¼ 27.1 + 0.37). The

subjects were counseled to follow a diet based on the

National Cholesterol Education Program (NCEP)

guidelines (Krauss et al., 1996), eating at least 80%

of their daily intake of meat as lean red meat or leanwhite meat. Blood samples were taken after 4, 12, 20,

28, and 36 weeks. Both diets presented similar patterns

of lipid profile during the whole study, with a small

reduction of the LDL-C levels (1–2%), maintenance of

the TG rates and improvement of the HDL-C levels

(*2%). This study indicated that lean red meat and

lean white meat cause similar activities over plasmatic

lipid levels.

A comparable study was performed by Beauchesne-

Rondeau et al. in 2003. They used 18 hypercholester-

olemic men between 21 and 73 years old and divided

them into three groups that rotated through three

different diets. Each diet was carried through 26 days

and a 6 weeks washout period was used before

switching the diet, avoiding residual effects. Diets

were differentiated by their protein source (lean beef,

lean fish, or lean poultry) and had controlled levels of

carbohydrates, protein, total fat, cholesterol, and fibre.

Both body weight and body mass index were main-

tained within the groups to avoid any effect of these

parameters on the lipid profile. All diets showed similar

reduction on total cholesterol (TC), LDL-C and TG

(Table 2). The HDL-C concentration during the lean

beef and lean fish diet had no significant difference in

comparison with the baseline. However, it wasincreased in 5% after the poultry diet. This study

indicated that lean red and white meat have no

significant difference on cholesterol levels, which

agreed with the experiments of Davidson et al.

(1999). However, Beauchesne-Rondeau et al. (2003)

obtained substantial cholesterol reduction during their

study, even without weight loss.In 2003, Melanson et al. reported a study compar-

ing the effect of lean beef and lean chicken on

cholesterol during weight loss. Subjects were all women

between 21 and 59 years old and with 20–50% of

weight excess in comparison with BMI standards.

Moreover, participants were randomly assigned one of

three different hypocaloric diets containing 1200, 1500

or 1800 kilocalories per day, depending on their daily

energetic need. Each group was split in two sub-groups

using either lean beef or lean chicken as the main

source of protein. The tests were conducted over

12 weeks accompanied by physical activity. Some

parameters, such as body weight, serum lipid profile,

and body composition were assessed before and after

the diet period. Both lean beef and lean chicken

presented similar patterns of weight (beef ¼ 75.6% +

0.6%; chicken ¼ 76.0% + 0.5%) and body fat reduc-

tion (beef ¼73.6% + 3.3%; chicken ¼ 74.1% +

2.4%). In addition, serum lipid enhancements were

also surveyed, where TC (719 to 21%) and LDL-C

(710 to 14%) were significantly reduced along the

study, without substantial difference between the beef

and chicken groups. Moreover, HDL-C remained

practically unaltered throughout the study with both

types of meat. The authors concluded that bothlean beef and lean chicken can be used in diets

accompanied by exercise for weight loss, without

Table 2. Plasma cholesterol and triglyceride profiles of hypercholesterolemic individuals before and after threedietary treatments containing different sources of protein(adapted from Beauchesne-Rondeau et al., 2003).

Tabla 2. Perfiles de colesterol en plasma y triglice ´ ridos deindividuos hipercolesterole ´ micos antes y despue ´ s de tres

tratamientos diete ´ ticos que contenı ´an diferentes fuentes deproteı ´na (adaptado de Bauchesne-Rondeau et al., 2003).

Lean beef Lean fish Lean poultry

Total cholesterol Before (mmol/L) 5.9 5.9 6.0After (mmol/L) 5.4 5.6 5.5Difference (%) 78 75 78

Total triglyceridesBefore (mmol/L) 1.6 1.5 1.6+0.1After (mmol/L) 1.3 1.2 1.2+0.1Difference (%) 719 720 725

LDL cholesterol Before (mmol/L) 4.3 4.4 4.4

After (mmol/L) 4.0 4.2 4.0Difference (%) 77 75 79

HDL cholesterol Before (mmol/L) 0.96 0.96 0.96After (mmol/L) 0.95 0.98 1.01Difference (%) 71 2 5

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differences between each other on the improvement of

the plasma cholesterol profile.

Consumption of lean red meat and soy

Epidemiological studies have shown that Asiaticpopulations are less susceptible to suffer cardiovascular

diseases (Yusuf, Reddy, O ˆ unpuu, & Anand, 2001).

This was related to their dietary customs, with lower

amounts of fat and higher intake of vegetables when

compared with Westernized cultures. Another com-

mon practice in Asiatic countries is the consumption of

soy, which has widely been recognized for its choles-

terol-lowering effects (Anderson, Johnstone, & Cook-

Newel, 1995; Ho et al., 2000).

Ashton and Ball (2000) designed a randomized

cross-over dietary intervention study to examine the

effects of two different diets on lipid plasmatic levels.

Participants of the study were men, aged 35–62 yearsold and had normal initial serum lipid levels. Firstly,

they were conducted over 1 week through their usual

diet for measuring baseline lipid levels. Secondly, the

42 subjects were randomly divided into two groups

receiving an isocaloric and isoproteic diet containing

either lean red meat or tofu as the main source of

protein. After a 4-week period, blood samples were

surveyed to determine lipid serum profile. After a 2-

week washout diet to avoid residual effects of the

anterior diet, the groups switched the experimental

regimens for another 4-week period. Once more,

blood samples were analyzed. In this study, both dietssignificantly decreased both LDL-C and TC levels.

However, the soy-based diet had a significantly higher

reduction of LDL-C, TC, and HDL-C. Actually, the

lean meat-based diet had a positive HDL-increasing

effect. Overall, even with significant lower rate of TC,

the soy diet had a similar LDL:HDL ratio in

comparison with the lean red meat regimen. In

conclusion, soy-based diet can indeed decrease serum

cholesterol rates, but this reduction is likely to be

better noticed when the soy-based diet is replacing a

regimen with high content of saturated fatty acids.

A longer study regarding serum lipid levels was

carried out by Yamashita, Sasahara, Pomeroy, Collier,

& Nestel (1998). They used overweight and obese

subjects to compare a soy-based diet and a lean red

meat diet during weight loss, with regard to serum lipid

levels. Participants were all women with an average

BMI ¼ 32.4 + 5.2 and aged 30 to 61 years. They

were randomly split with either a red meat or a tofu

diet (isocaloric and isoproteic) for 16 weeks accom-

panied by regular physical exercise. During the study,

both diets resulted in similar weight loss (9%) and

nearly the same rates of TC (12%), LDL-C (14%), and

TG (17%) reduction. In addition, arterial pressure was

also diminished with both diets. These results indicatethat weight loss has beneficial effects on serum lipid

profiles and, therefore, on overall health status

regardless of whether the protein is from soy or lean

red meat.

In summary, these studies revealed that vegetarians

using soy as their main source of protein can achieve

better lipid profiles when compared with diets rich in

saturated fatty acids but not necessarily when com-pared against non-vegetarian diets. Actually, vegetar-

ian and non-vegetarian diets can have similar beneficial

results, once the fat intake is controlled (Yamashita

et al., 1998).

Red meat and thrombosis

Besides the fact that red meat is related to augmented

cholesterol levels, it has also been indicated that red

meat possibly enhances the risk of thrombosis (Li

et al., 2005). One of the first steps of the thrombotic

pathways is the activation of platelets by tromboxane

A2 (TXA2), which is a proinflammatory eicosanoiclipid. During TXA2 synthesis, arachidonic acid is

released from the cell’s membrane and is cycled by a

dual enzyme called cyclooxygenase (COX), which has

reductase and peroxidase activity. This enzyme is

responsible for the production of prostaglandins and

also TXA2. Red meat has considerable amounts of

arachidonic acid (AA) that could stimulate the TXA2

synthesis and, therefore, increase the risk of thrombo-

sis. Once a clot is formed, it can occlude vessels,

causing a stroke or a heart attack (Moncada & Vane,

1979). On the other hand, red meat and fish supply

important amounts of poly-unsaturated fatty acidswith recognized anti-platelet aggregation activity, such

as docosahexaenoic acid (DHA), eicosapentaenoic acid

(EPA), and docosapentaenoic acid (DPA) from the n-3

PUFA family (Howe, Meyer, Record & Baghurst,

2006; Sinclair, Johnson, O’Dea & Holman, 1994).

In 1997, Mann et al. performed a study to analyze

the production of prostacyclin (PGI2) and TXA2 in 29

participants (14 men and 15 women) after consumption

of considerable amounts of AA. The subjects were

aged between 22 and 52 years old and were divided into

three diets, where they received fish, turkey, or lean red

meat as the main source of AA. The diets were

calculated to supply double the amount of the usual

daily intake of AA. Subjects were assigned to a 3-week

diet: in the first week they replaced their usual diet for a

vegetarian regimen, followed by a 2-week period

receiving one of the meat diets. Participants rotated

through the diets, but were taken through a 3-week

washout period in between the red meat and tofu diets.

All regimens contained similar levels of arachidonic

acid. However, EPA was present in different amounts,

where the turkey diet supplied 1 mg/day, red meat

offered 70 mg/day, and fish 847 mg/day. Blood sam-

ples were surveyed, and the fish diet (2:1) was the more

effective in improving the plasmatic AA:EPA ratiocompared with the vegetarian diet (11:1) followed by

the lean red meat diet (8:1), while turkey increased this


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ratio (15:1). Even though, none of the diets increased

platelet AA levels, platelet aggregation or the TXA2

and PGI2 serum rates. The fish diet also reduced the

TXA2 production when the platelets were artificially

stimulated. These results suggest that red meat, at least

when consumed during the short-term, is not asso-ciated with increased levels of TXA2. Therefore, it is

unlikely that lean red meat enhance the risk of

thrombosis due its high AA content.

Relationship of meat and cancer

The World Cancer Research Fund (1997) and the

British Government’s Committee on Medical Aspects

of Food and Nutrition (1984) published reports

relating diet with cancer. Even without robust evi-

dence, these reports associated the consumption of red

meat with diverse types of cancer, particularly colo-

rectal cancer. These organizations recommended amaximum 80–90 g/day intake of red meat and their

reports resulted in bad propaganda surrounding red

meat consumption (Higgs, 2000).

Theoretically, the iron and fat content, besides the

production of heterocyclic amines and N -nitrosamines

are the main components in regards the red meat

carcinogenic effects. The iron present within the heme

group can catalyze oxidative reactions. These reactions

can produce reactive oxygen species (ROS), which can

damage the DNA, lipids, and proteins (e.g. enzymes).

Once the DNA is damaged, mutations can lead to the

development of cancer. On the other hand, thepresence of iron in the diet is necessary because it is

the major oxygen carrier in the human blood stream

and muscles (Tappel, 2007). Hodgson, Ward, Burke,

Beilin & Puddey (2007) showed in a clinical study that

iron from a lean meat diet did not increase oxidative

stress or form inflammatory biomarkers in comparison

to an isocaloric carbohydrate based diet. Moreover,

levels of anemia have increased in specific populations

that reduced or eliminated red meat consumption.

Hence, the role of meat iron on the development of

cancer is controversial and further research is needed.

Furthermore, it has been reported that heterocyclic

amines formed after meat cooking can lead to cancer in

animal models. However, the levels of meat doneness

in these studies were very high and decreased cooking

time may produce lower and probably inoffensive

levels of heterocyclic amines (Higgs, 2000). In addition,

epidemiological studies showed that there was no

significant higher intake of heterocyclic amines by

subjects that had cancer and healthy individuals

(Augustsson, Skog, Jagerstad, Dickman, & Steineck,

1999; van den Brant, Botterweck, & Goldbohm, 2003).

Nevertheless, the addition of nitrate as a meat

preservative has been linked with the formation of N -

nitrosamines after meat consumption (Theiler, Sato,Aspelund, & Miller, 1981). However, nitrate is added

in meat at low levels, which would improbably result in

cancer (Knekt, Ja ¨ rvinen, Dich, & Hakulinen 1999).

Further studies concerning the minimal levels of nitrate

required to produce deleterious health conditions are

needed.

Many of the epidemiological studies relating meat

to cancer published to date are conflicting. Recently,the European Prospective Investigation Into Cancer

and Nutrition published a study (Norat et al., 2005)

where 478,040 men and women from 10 European

countries were studied for 5 years. During this period,

1329 cases of colorectal cancers were reported. Diverse

parameters were taken into account in this study, and

among them the researchers surveyed the association

of red meat, white meat, and fish intake with colorectal

cancer. Results confirmed higher rates of colorectal

cancer among subjects with higher intake of red meat

when compared to participants with a diet rich in fish.

Even being a significant divergence, the percentile

among groups was not so different, where meat eaters(5160 g/day) and fish eaters (580 g/day) presented

colorectal cancer in 1.71% and 1.28% of the subjects,

respectively. However, Key, Fraser, Thorogood &

Appleby (1998) found no significant differences in the

mortality ratio caused by cancer between vegetarians

and non vegetarians. During this study, 8330 deaths

occurring within a 10-year period were surveyed.

Moreover, Sanjoaquin, Appleby, Thorogood, Mann

& Key (2004) found similar rates of colorectal cancer

(total of 95 cases) between vegetarians and non-

vegetarians within 10,998 subjects during a period of

17 years. Furthermore, no increased risk of colorectalcancer was seen with higher meat consumption among

non-vegetarians. On the other hand, during an

investigation of Seventh-day Adventists (Singh &

Fraser, 1998), cancer of the colon was significantly

more common in non-vegetarians than in vegetarians.

More recently, the Fukuoka Colorectal Cancer Study

published an epidemiological report that did not

support the theory that red meat intake enhances

colorectal cancer levels (Kimura, Kono, Toyomura,

Nagano, & Mizoue, 2007).

To date, the relationship of red meat consumption

and cancer is still controversial, as studies have

reported contrary results. Moreover, vegetarians have

better health practices, eating higher amounts of fibre

and practicing more physical exercises, and this makes

it difficult to compare a single dietary difference rather

than a different life style (Li et al., 2005).

Meat aspect on human nutrition

Meat is an important source of a wide range of

micronutrients. As mentioned before, red meat is an

excellent source of iron, where 50–60% is in the easily

absorbed heme form. The presence of iron within the

proteic heme structure makes it more readily availableand in higher amounts (15–25%) when compared with

plant source (1–7%) (Fairweather-Tait, 1989). Plants

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have some chelators that reduce iron absorption, such as

phytic acid. In addition, meat contributes about 14% of

the daily total iron intake in the UK (Higgs, 2000).

Red meat, poultry, and seafood are important

sources of zinc. Similar to iron, zinc absorption is

inhibited by the presence of chelators, such as phyticacid and oxalic acid, found in high concentrations in

vegetarian diets (Freeland-Graves, 1988). It is speculated

that 20–40% of zinc intake comes from meat, and this

classifies meat as the major source of zinc inthe diet. Zinc

is an important metal present in a variety of enzymes,

being an essential component of diverse metabolic

pathways (Johnson & Walker, 1992). Lean red meat is

also a source of important antioxidants such as selenium

and glutathione, which play important roles in metabo-

lism andhomeostasis in the body (Shi & Spallholz, 1994).

Other important minerals present in significant amounts

in meat are copper, magnesium, cobalt, phosphorus,

chromium, and nickel (Higgs, 2000).Aside from minerals, meat is also an important

source of vitamins. Firstly, it supplies significant

amounts of thiamin, riboflavin, niacin, and vitamin

B6. Moreover, foods of animal origin provide the only

dietary source of vitamin B12. Vegetarians are usually

deficient in this type of vitamin, and supplementation

has been necessary (Draper, 1991). In addition, Mann

et al. (1999) reported a study showing that meat-eaters

have significantly higher plasma levels of vitamin B12

and lower homocysteine levels than vegetarians. Meat

is also one of the most important sources of protein in

the human diet, which has all the essential amino acidsand high bioavailability (Givens, Kliem, & Gibbs,

2006).

Conclusions

Typical Western omnivorous diets have increased the

consumption of fat over the last 50 years, whereas the

dietary intake of fibre has been reduced. These changes

of dietary behavior have led to enhanced rates of

pathologies, such as atherosclerosis, coronary heart

disease, hypertension and cancer. Because of its high

amount of fat, red meat has been considered a villain in

the human diet. However, lean red meat does not

appear to increase the levels of biomarkers of such

diseases, suggesting that red meat consumption is not a

bad alimentary habit, but saturated fat consumption is.

Nevertheless, nutritionists and physicians are still

recommending the replacement of red meat by lean

white meat. This practice is equivocal, because both

lean red meat and lean white meat have shown similar

action over plasmatic serum lipids.

Moreover, cancer epidemiological studies compar-

ing vegetarians and non-vegetarians remain controver-

sial. It is not clear if the rates of cancer were reduced in

vegetarian individuals due to the absence of meatconsumption or to the higher intake of fruits and

vegetables and a healthier life style. Undoubtedly,

more epidemiological and clinical studies are needed to

understand the relationship between cancer and red

meat consumption. It is also very unlikely that red

meat consumption per se leads to the development of

thrombosis and indeed more research is needed to

prove this assumption. More importantly, red meat isone of the main sources of vitamins, minerals, and

protein in the human diet, and its nutritious value

cannot be ignored. In conclusion, the human diet

cannot be typified between vegetarians and non-

vegetarians as good and bad diets, respectively. It is

more likely that a balanced diet accompanied by

exercise is the main point for a healthy life, indepen-

dent of the consumption or not of red meat.

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