In this edition of Research & Policy Update, RAC member, Dr Shireen Kassam updates us on new research studies on issues including dietary cholesterol, acid-reflux, second cancers in cancer survivors and GHG emission from organic meat production.
EGG CONSUMPTION, CARDIOVASCULAR DISEASE AND DEATH IN WOMEN: The impact of egg consumption on human health remains hotly debated. It always comes back to ‘Instead of what?’. Eggs are certainly better than eating a donut but definitely not better than eating beans. This means you can find studies that suit your own position on egg consumption. Eggs are high in cholesterol which is one of the reasons cited for the negative health outcomes, but the impact of dietary cholesterol on blood cholesterol levels also remains a topic of contention.
This new paper from the Women’s Health Initiative included 96,831 postmenopausal women from the US aged 50–79 years, followed for up to 19 years. During this time there were 9808 cases of cardiovascular disease (CVD)and 19,508 deaths. The median intake of cholesterol in participants was 120.9mg/1000kcal/day and the median egg intake 1.3/day. The results showed that dietary cholesterol, when comparing the lowest intake (73mg/1000kcal/day) to the highest intake (193.2mg/1000kcal/day), did increase the risk of CVD (12% increase), ischaemic heart disease (11%), ischaemic stroke (35%), risk of death (9%) and death from CVD (19%). There was however a reduced risk of haemorrhagic stroke (31%) and no association with risk of death from cancer, respiratory diseases or dementia.
Regarding egg intake, when comparing higher intake to lower intake (>1 egg per day versus < 1 egg/day), there was a higher risk of CVD (14%), ischaemic heart disease (11%), ischaemic stroke (40%) but not haemorrhagic stroke. These are also increased mortality from all causes (14%), CVD (23%), respiratory disease (46%), and other causes (16%), but no association with cancer or dementia mortality. For both cholesterol and egg intake, particularly for mortality outcomes, there were linear dose-response relationships. The results quoted are after adjustment for traditional risk factors and other key nutrients.
The authors conclude:
‘Our findings indicate that limiting dietary cholesterol intake while building a healthy eating pattern might be beneficial for human health’.
Although studies on egg consumption and health outcomes have been contradictory, there are some general themes emerging. The most up to date systematic review and meta-analysis of randomised clinical trials and responses of different dosages of egg consumption on blood lipid profile concluded that there is a linear correlation between consumption of greater than one egg per day and increased blood lipid levels but consuming one egg a day or less can be safe. What’s also clear is if dietary cholesterol intake is generally low i.e. in those limiting the consumption of animal foods, then adding additional amounts to the diet in the form of eggs will elevate blood cholesterol levels. However, if you are already eating a diet high in cholesterol adding a bit more is unlikely to have a significant effect as blood cholesterol levels plateau at higher intakes.
There is no doubt that a stepwise reduction in animal foods from the diet significantly lowers blood cholesterol levels, which is highly desirable. This is because a plant-based diet is low in both saturated fat and cholesterol. Those eating a 100% plant-based diet have the lowest blood cholesterol of all diet patterns. Any small increased risk of haemorrhagic stroke (which is a matter of debate and only represents 10%-15% of stroke cases) is overshadowed by the benefits for cardiovascular health such as ischaemic heart disease and stroke, a much greater personal and public health problem. In addition, the commonest cause of haemorrhagic stroke is high blood pressure, a condition that is easily prevented by adopting a healthy plant-based diet and lifestyle.
ANOTHER STUDY DEMONSTRATING A DETRIMENTAL EFFECT OF DIETARY CHOLESTEROL: We have known for decades that elevated blood lipid levels increase the risk of CVD and is a general marker of poor health. Diet choices are a major contributory factor. The dissenters are loud but a small fringe group, sadly present in most countries, including the UK. In particular, the role of dietary cholesterol is a topic of contention. So, it is always good therefore to confirm what we think we know and in diverse populations, not just caucasians.
This new study is from China and included 8952 participants between the ages of 18–60 years. It examined the relationship between dietary cholesterol, with repeated measurements over a 14-year period, and blood lipids, health outcomes and risk of death. Participants were divided into 3 groups. Those with persistantly low cholesterol intake (<150mg/day), persistently high (>300mg/day) and those with rising intake with age. During the follow up there were 399 deaths. The results showed that both increasing intake of dietary cholesterol over time and consistently high intakes compared to consistently low intakes was associated with a 2.2 to 2.3-fold increase in all-cause mortality and a 14% increase in risk of hypertension. Increased dietary cholesterol was also associated with elevated serum total:HDL cholesterol ratio and apolipoprotein B. However, associations were not significant when using only one baseline measurement for the analyses, thus demonstrating the important of measuring dietary intakes over time. This may be a reason why other studies have not been able to show an impact of dietary cholesterol on health outcomes.
So, yet another study demonstrating adverse health outcomes with high cholesterol consumption. The best way to minimise cholesterol consumption is of course a plant-based diet.
DIET, LIFESTYLE AND ACID REFLUX: Gastro-(o)esophageal reflux disease (GERD/GORD) is one of the commonest gastrointestinal disorders and affects up to 30% of adults in Western countries. Most people probably don’t even consult their doctors as anti-acid medications are readily available over the counter. Studies show that the prevalence of GERD is rising and becoming more common in younger adults. Doctors are increasingly prescribing proton pump inhibitors (PPIs), with many patients continuing long-term use. This is not without risk and chronic acid suppression can reduce absorption of nutrients such as iron and vitamin B12 and recently has been associated with an increased risk of type 2 diabetes.
This study examines the impact of 5 lifestyle factors on GERD in 42,955 female participants aged 42–62 years as part of the Nurse’ Health Study II between 2005 to 2017. These 5 factors were normal weight, never smoking, moderate-to-vigorous physical activity for at least 30 minutes daily, restricting coffee, tea and sodas to two cups daily, and a “prudent” diet. A prudent diet was defined as higher intakes of fruits, vegetables, legumes, fish, poultry, and whole grains and low intakes of red and processed meat and refined grains/sugar. The results showed that those women adhering to all 5 healthy lifestyle factors reduced their risk of GERD by 50% compared to those that did not follow any. The proportion of cases of GERD symptoms that may be prevented by all 5 lifestyle factors was 37% with benefits for symptom reduction shown for those already receiving anti-reflux medications.
So, lifestyle habits once again have a massive impact on symptoms such as acid reflux that can severely impact quality of life.
LIFESTYLE FACTORS CAN LEAD TO MULTIPLE CANCERS OVER A LIFETIME: I spend a lot of time talking and educating on cancer prevention. It is estimated that 40% of cancer cases could be prevented by adopting healthy lifestyle habits. These of course include a healthy plant-predominant diet, regular physical activity, avoiding alcohol, tobacco smoking, red and processed meat, maintaining a healthy body weight and safe exposure to the sun. For some cancers, such as colorectal cancer, it is estimated that more than 50% of cases could be prevented. We also know that the risk of a second cancer is further increased in those who have already had a diagnosis of cancer. Doctors often put this down to bad luck and bad genes. This new paper challenges this view.
The study examined the the risk of and mortality from second primary cancers among 1.5 million adult cancer survivors between 1992 and 2017 in the US. Compared with the general population, adult cancer survivors had a higher risk of developing a second primary cancer (11% increased risk in men and 10% in women) and an even higher risk of dying after such a diagnosis is made (45% in men and 33% in women). The risk of developing a second primary cancer among adult cancer survivors increased between 1975 to 1989 and 2000 to 2015 suggesting that environmental and lifestyle factors are having a greater impact over time.
Although it is accepted that some of this increased risk is due to underlying genetic predisposition and the cancer treatments received, the results suggest that most of this excess risk is due to host factors (aging, immunity) and to lifestyle risk factors (eg, smoking, obesity, alcohol, infection) shared by the first and subsequent cancers. Four common smoking-related cancers (lung, urinary bladder, oral cavity/pharynx, and oesophagus) accounted for 26% to 45% of the total second primary cancer incidence and mortality and 4 common obesity-related cancers (colorectal, pancreas, uterus, and liver) accounted for 22% to 26% of the total second primary cancer incidence and mortality. Lung cancer alone comprising a third of the mortality from all second primary cancers. Alcohol-related second cancers were also increased in those with alcohol-related primary cancers.
Although these are many limitations to this retrospective analysis, the take home message is a reminder of the importance of encouraging a healthy lifestyle in cancer survivors as well as in previvors (those who are at high risk of cancer but have not yet been diagnosed). This includes, avoidance of tobacco and alcohol and promoting healthy eating and regular exercise. There is still a big piece of work needed in effective public health messaging as less than 50% of people in the UK and US are even aware of the impact of lifestyle choices on cancer risk.
ORGANIC MEAT PRODUCTION JUST AS BAD AS CONVENTIONAL METHODS FOR THE CLIMATE: This paper puts to rest the false arguments for promoting organically-reared animals for food over conventional ‘factory farming’ methods. This study from Germany performs lifecycle analysis (LCA) for the production of all animal and plant foods, both organic and non-organic with particular reference to greenhouse gas emissions.
‘The LCA method examines environmental and social impacts that occur during the entire lifetime of a product…. This includes both impacts from production and impacts occurring during the usage phase of a product up to its disposal (or consumption), as well as all intermediate emissions’
The results showed that the production of meat causes the highest GHG emissions, mostly due to the high inputs required and the inefficient conversion of animal feed to food for humans. This can be as high as 43 kg of feed to produce 1 kg of beef product. This is of course lower for chicken reared for food with a conversion rate of 2.3:1. Conventional dairy production was the second highest contributor to food-related GHG emissions after beef and lamb. All plant food production has lower GHG emission than animal foods, with organic plant production being the best due to the reduced use of synthetic nitrogen-based fertilisers. Both conventional and organically produced grass-fed beef and lamb make similar contributions to GHG emissions because organic meat production requires greater land, the animals live longer and therefore are overall less ‘productive’ as a food source. Organic chicken production was slightly worse than conventional methods and organic pork slightly better. To account for the true cost of animal farming and its impact on the environment, the paper calculates that beef and lamb prices should be increased by 40% and milk prices by a third. Although the calculations are performed for the German food system, they are translatable to other European countries. The findings of the paper are nicely summarised by Damian Carrington in the Guardian.
The views expressed by our Research News contributors are not necessarily the views of The Vegan Society.
