Headlines continue to raise concerns over the health effects of excessive meat consumption, a situation that is boosting consumer interest in meat substitutes. But what does the science say about meat and health?
In the second part of our focus on meat substitutes, FoodNavigator looks at the risks and benefits of excessive meat consumption. In recent years, high profile studies have linked meat consumption, be it red or processed meats, to increased risks of various diseases, including cancer, diabetes, and heart disease.
The most attention – and headlines – has focussed on the link between meat intake and cancer. The World Cancer Research Fund published a report in 2007 that directly linked diet to cancer, with alcohol and red and processed meats posing particular risks.
The WCR report echoes studies from the US National Cancer Institute (NCI), which found that high intakes of red and processed meats may raise the risk of lung and colorectal cancer by up to 20 per cent.
The NCI scientists have also reported findings from a study with half a million people, noting that that increased consumption of red and processed meat may have a modestly increased risk of death from cancer or heart disease (Archives of Internal Medicine, Vol 169, pp. 562-571).
The Archives study was described by Barry Popkin from the University of North Carolina as “excellent” in an accompanying editorial. Popkin added that the results “reiterate the concerns echoed in other major reviews and studies on the adverse effects of excessive meat intake”.
Hearts and eyes
Only yesterday we reported on new data from Boston-based scientists that linked red meat to an increased risk of heart failure. According to findings published in Nutrition, Metabolism and Cardiovascular Diseases, an average of 9.5 servings of red meat per week was associated with a 24 per cent increase in heart failure risk, compared with only 1.5 servings per week. The study was claimed to be the first to evaluate the relationship between red meat consumption and heart failure risk in a large cohort.
A significant body of science also supports a potential link between meat consumption and the risk of type-2 diabetes. Indeed, a meta-analysis from Norway and the US last year found that high intakes of all types of meat were associated with a 17 per cent increase in the risk of type-2 diabetes, while similar risk increases were also noted for high intakes of red meat.
Writing in the journal Diabetologia (2009, Vol. 52, pp. 2277-2287), scientists led by Dagfinn Aune from the University of Oslo also reported that high intake of processed meat may increase the risk of developing type-2 diabetes by 40 per cent, based on data from 12 cohort studies.
Australian scientists have also reported links between red meat consumption and age-related macular degeneration (AMD), the leading cause of blindness in people over 50.
According to findings published in the American Journal of Epidemiology (doi:10.1093/aje/kwn393), two portions of red meat a day were linked to a 50 per cent increase in the risk of AMD. On the flip side, the researchers found that consumption of white meat may offer some protection.
Additives or other?
In an attempt to explain the observations and associations, scientists have pointed the accusatory finger at a range of meat constituents and additives. The salt/sodium content of processed meats has also been identified as a potential contributing factor.
In terms of heart health, scientists have proposed that the saturated fat and cholesterol content of red meat may increase the risks of both high blood pressure (hypertension) and coronary heart disease, both of which are risk factors for heart failure.
Another suspect is nitrite and nitrate additives. Nitrites are added to meat to retard rancidity, stabilise flavour, and establish the characteristic pink colour of cured meat. However, about 80 per cent of nitrates in the diet come from vegetables, while nitrites sources include vegetables, fruit, and processed meats.
Observational studies, including data from the third National Health and Nutritional Examination Survey (NHANES) on 7,352 subjects over the age of 45, have suggested that increased consumption of nitrites from cured meat could increase the risk of lung disease.
But the topic of nitrites and nitrates is controversial. Scientists from the University of Texas Health Science Center at Houston reported in the Proceedings of the National Academy of Sciences the researchers report that the compounds, also found in vegetables and drinking water, reduced heart cell death in the mice following a heart attack by 48 per cent (Vol. 104, pp. 19144-19149).
A recent study from researchers at Michigan State University went as far as to suggest that the compounds may actually be nutritious (American Journal of Clinical Nutrition, doi:10.3945/ajcn.2008.27131).
The majority of the science has focussed on relatively excessive intakes of meat. A balanced diet is promoted by all public health agencies, and that should include meat.
The World Wildlife Fund (WWF) suggested last year that red meat packs should carry labels advising people to consume no more than three portions a week.
The WWF says it is not telling people to stop eating meat altogether – rather that they should reduce portions or eat it less often.