EXPERT REACTION: Is eating meat, chicken or fish bringing us closer to death?

This study pooled dietary intake and health outcome data from 6 cohort studies in the USA. The baseline assessments were between 1985 and 2002, with about 30,000 adults followed for up to 24 years. They investigated associations between intakes of processed meat, unprocessed red meat, poultry and fish with the incidence of heart disease, stroke and death from all causes.

After adjusting for many factors that might affect risk of heart disease or death, such as age, sex, ethnicity, smoking, use of hormone therapy, physical activity, diet quality and alcohol intake, they found a small but significantly increased risk (measured by a Hazard Ratio) for heart disease, stroke or heart failure of 7 per cent for having two serves of processed meat a week compared to none.

For each additional two serves of unprocessed red meat or poultry a week the risk was increased by 3 per cent and 4 per cent respectively. For death rates, adjusting for all the potential confounders, the association were significantly increased but also small. Each additional two serves of processed meat and unprocessed red meat were each associated with a 3 per cent increased risk of death from any cause. There was no increased risk of death based on poultry or fish consumption. 

When the absolute risk (meaning the probability of having a heart disease event or dying from any cause) was evaluated over a 30 year period it equated to less than 2 per cent. In other words, the lifetime excess risk was small, although when it is applied across the whole population it still means fewer people getting heart disease or dying, very important if that life saved is yours.

This paper provides support for moderating your unprocessed and red meat intake, while eating fish more often. You can reduce your meat intake by extending or replacing it with legumes (lentils, chickpeas and dried beans).

Based on our anatomy, humans are omnivores. Due to the abundance of food, in many wealthy countries, one of our biggest dilemmas is what to eat? There are essentially three macronutrients – fat, carbohydrate and protein (while it provides energy, alcohol does not meet other criteria for being a macronutrient). Fats were demonised in the 80’s and 90’s, carbohydrates (starches and sugars) in the noughties. Now it's protein’s turn.

This latest battle in the protein wars investigates the association between eating processed meat, unprocessed red meat, poultry, or fish and the risk of developing cardiovascular disease (fatal and nonfatal coronary heart disease, fatal and nonfatal stroke, fatal and nonfatal heart failure, and other CVD deaths) in a pooled cohort of 29,682 American adults. Food frequency questionnaires were used to assess intakes of these protein sources at baseline only. Methods of preparation or cooking were not included. Participants were followed up for up to 30 years. The overarching finding was that higher consumption of processed meat, unprocessed red meat, or poultry, but not fish led to an approximately 3 per cent to 7 per cent higher relative risks and less than 2 per cent higher absolute risks of incident CVD and all-cause mortality over the 30 years of follow-up. The effect sizes of these association estimates are small, and consequently at high risk of confounding despite multiple statistical adjustments.

While the results of this pooled analysis are interesting, they do not constitute high-quality scientific evidence. Serious weaknesses include the fact that few people maintain exactly the same eating habits over a 30-year time frame due to ageing, and associated life-stage changes (e.g., rearing children). Future epidemiological research should at the very least assess dietary intakes every five years, and include cooking methods of core foods like meat, poultry, and fish.

Independent of this new research, most Australians eat more than enough protein (> 50% more than the RDI), and in particular animal protein. Like all nutrients, excess protein can lead to weight gain and associated consequences. Moderating intakes may be a worthwhile aim for many individuals and may have some environmental benefits.

Finally, we don’t just eat meat, poultry, and fish – overall dietary patterns are important and may moderate or exacerbate health risks, depending on their composition. A diet composed of minimally processed vegetables, fruits and whole grains, for example, helps reduce the risk of cardiovascular disease.

A study in the US has observed a total of 29,682 men and women with an average age of 53.7y and BMI of 26.2kg/m2 (at the low range of overweight) over a median of 19 years to see the effect of different meats on cardiovascular disease and death due to any reason.

At the beginning of the study, they documented how much processed red meat, unprocessed red meat, poultry and fish they ate. They found that a higher intake of processed meat, unprocessed red meat, or poultry, but not fish, was significantly linked to a small but higher risk of CVD. Higher intake of processed meat or unprocessed red meat, but not poultry or fish, was significantly linked to a small but higher risk of death from any cause.

This study did not look at plant sources of protein. It has to be remembered that these studies which observe people (that is, they do not make any changes to their diets) can not prove that the different type of meat is linked with death or CVD, however it indicates there is a link between the two. This is still useful for researchers as it shows what needs to be further investigated.

Along with previous research that has been done, this study adds to the evidence base that red meat is linked to a higher risk of death and chronic disease, and hence we need to swap our intake of unprocessed red meat and processed meat with fish or poultry.

Using a large sample of 29,862 US adults drawn from six cohort studies, the researchers followed their subjects for a median of 19 years, with the time extending for up to 30 years for some. During this period, there were 6,963 incident cardiovascular events (fatal and nonfatal coronary heart disease, stroke, heart failure, and other heart disease) and 8,875 deaths from all causes. 

The findings: 

• Intake of processed meat, fresh red meats or poultry were each positively associated with incident cardiovascular disease. Fish and seafood were not.
• Consumption of any kind of red meat (fresh or processed) was also significantly associated with all-cause mortality. Chicken, fish and seafood escaped this second fate.

These results are in keeping with other studies and the results grew stronger for each factor with increasing length of surveillance. However, the overall increased risks were small and in studies such as this, a single picture of what someone reports eating ignores the fact that many people change their diet over the years. Cooking methods were also ignored, a possible problem for chicken which may be fried in a variety of fats, another factor that may also change over time.

The take-home message from this large and long-term analysis is that no single food is going to determine the overall healthiness of your diet or your subsequent health. However, from this and many other analyses, it’s wise to limit consumption of red and processed meats, and probably chicken. For heart health, fish and seafood impose no apparent risk. This all fits with existing dietary guidelines.

A new, extensive, very large US study published in JAMA Internal Medicine today provides important new data on dietary choices of animal protein relevant to public health.

Researchers at Cornell University in New York followed 30,000 middle-aged adults for an average of 19 years and monitored the incidence of cardiovascular disease events (heart attack, heart failure and stroke), as well as death from all causes. The people in the study had a median intake of processed meat (bacon, ham, etc) of 1.5 servings per week, unprocessed red meat 3.0 servings per week, 2.0 for poultry, and 1.6 for fish (including shellfish). When analysing their findings, the researchers took into account an extensive range of so-called ‘confounding’ factors that might have influenced the results.

Of the almost 7,000 cardiovascular events, the researchers found that two versus zero servings of processed meat per week led to a robust significant 7 per cent increase in risk of one of these, whereas for unprocessed red meat risk increase was 3 per cent, and for poultry was 4 per cent, although whether the chicken was fried or not was not examined. The authors suggested that people who consume more than two servings per week may put themselves at higher risk. Fish did not affect risk, although it would have been interesting to compare deep-fried fish with grilled and baked fish. 

As for mortality risk, for each additional two servings of processed or unprocessed red meat there was a statistically significant 3 per cent increase in risk, whereas no increase in risk of death was seen for poultry or fish.

Interestingly, adults aged under 45 years had a 17 per cent increase in cardiovascular risk from processed meat, compared with a 12 per cent increase for those aged 45-64 years, whereas no risk increase was seen in people aged over 65 years. 

It is likely that these findings would apply to Australia.

This relatively small study of six combined US cohorts showed that both red and processed meat increased cardiovascular disease rates (as expected) while chicken did as well but fish was not protective. Only red meat increased total mortality. All effects were small with less than 2 per cent absolute increase per two serves per week over 30 years.

The study was important in that it included 30 per cent non-white participants and showed the effects were greater in younger people. Similar, but stronger results on total mortality were seen in the larger nurses and health professionals combined for red meat. Both studies would agree that substituting chicken or fish for red meat should lower total mortality.