Review of the week’s plant-based nutrition news 29th November 2020
I am back this week with important studies on bone health, supplements for vegans, negative effects of a low-carb diet and the impact of cholesterol levels in older adults.
VEGAN AND VEGETARIAN DIETS AND BONE HEALTH: For obvious reasons this study has caused waves in the media and vegan community this week. The paper brings us a new analysis from the EPIC-Oxford study, one of the longest running and largest studies investigating the health of vegetarians and vegans. There is a lot to digest in the paper with some quite complicated analysis.
This was a robust study design with rigorous analysis of the data. Two of the authors are vegan. The results showed an increased rate of fracture in those not consuming meat. This was not exclusive to vegans and includes vegetarians and fish eaters, but the effect was more pronounced in the vegan group. For vegans the impact was greatest for hip fractures with a 231% elevated risk compared to meat eaters. Vegans had a 43% increased risk of developing any fracture compared to meat eaters. In absolute terms, this amounted to 19 more cases of fractures in vegans for every 1000 people over 10 years.
The points of interest are that body mass index (BMI) had a major influence on fracture risk with a BMI less than 22.5 associated with the increased risk. For vegans with a BMI greater or equal to 22.5, this risk disappears. The fracture risk was also only increased in women (who made up more than two-thirds of the participants) and not men. Vegans in this study had a lower than recommended intake of calcium and a lower use of HRT in women compared with meat-eaters, factors that are relevant to the risk of bone fractures. The mean calcium intake for vegans was around 600mg/day, so not meeting UK recommendations for 700mg/day. Non-meat eaters also had a lower protein intake than meat-eaters, which appeared to be contribuing to the risk of fractures in the analysis. We also know from prior reports from the EPIC-Oxford cohort that the vegans had lower B12 and vitamin D intakes compared to the non-vegans. Only around 50% of vegan participants in this study were taking dietary supplements, which means that 50% were relying on food sources of vitamin B12 and vitamin D, which we know are inadequate. These participants were recruited in the 1990’s at a time when fortification of plant-based alternatives was not common.
The major limitation is that the study can not tell us the cause of the fractures i.e. are they due to poor bone health or due to accidents. There was also no determination of bone mineral density. The study did not correlate fracture rates with vitamin D status, a major factor in bone health. So, overall the study does not prove a causal relationship between diet and fractures but an association. Having said that, we need to pay attention to these results rather than discount them.
For me the take home messages are the importance of adopting a healthy vegan diet, paying attention to nutrients such as calcium, zinc, B12, vitamin D. A healthy vegan diet is one that is composed of a variety of fruits, vegetables, whole grains, beans, nuts and seeds and minimises processed/packaged foods. It’s also helpful to incorporate fortified foods and drinks such as soya milk, yogurt and calcium-set tofu. Weight bearing physical activity and muscle strengthening are vitally important for bone health and may need to be emphasised more for those on a 100% plant-based diet, along with other healthy lifestyle practice that impact bone health; avoiding alcohol and tobacco smoking, limiting caffeine and fizzy drinks. It may also be beneficial to aim for the middle of the BMI range rather than a BMI of <20.
We must not forget that the same EPIC-Oxford study has shown us that a vegan diet is associated with around a 50% reduction in risk of high blood pressure, significantly lower levels of blood cholesterol, a 25–30% reduction in ischaemic heart disease (this includes vegetarians as well), 19% reduction in cancer risk and a 30–40% reduction in risk of type 2 diabetes in those not eating meat. These are all major causes of death and disability in the UK and a far greater risk to personal and public health than bone fractures.
VITAMIN AND MINERAL STATUS IN A GERMAN COHORT: This is actually a timely study, albeit small. It brings us a modern day group of vegans from Germany in which vitamin and and mineral status was investigated. 36 vegans and 36 non-vegans were recruited in 2017 and their dietary macro and micronutrient intakes were assessed in this cross-sectional study. Dietary questionaires were completed and blood and urine was collected to measure various micronutrients. 97% of vegans and 33% of omnivores were taking dietary supplements. The results showed that both groups had a similar calorie intake but for macronutrients vegans were consuming significantly more fibre (46g vs 24g) and significantly less protein and fat. For micronutrients vegans were consuming significantly less vitamin B12, B2, B3, B5, vitamin D, iodine, calcium and zinc but significantly more folate, vitamin E, vitamin A and iron. The nutrients intakes that fell below recommended were vitamin B12, vitamin D (for both groups), vitamin B5 (for both groups) and iodine (for both groups). Regarding blood meaurements, vegans had significantly lower total and LDL-cholesterol levels, vitamin A, vitamin E, vitamin B2 and B3 and zinc. However, none of these levels were below the normal range. In urine measurements, vegans had significantly lower excretion of iodine and calcium.
Overall, these results show that despite lower dietary intakes of certain nutrients in a vegan diet, this group of vegans had sufficient blood/body levels of virtually all nutrients, except for iodine and calcium. This implies that they were adequately supplementing their diet, in particular with vitamin D and B12. Calcium intakes clearly need attention in a vegan diet, as highlighted by the EPIC-Oxford data, and iodine intakes need attention in both vegan and omnivorous diets.
SOYA CONSUMPTION AND HUMAN HEALTH: There remain unfounded myths around the consumption of soya, even amongst vegans. I hope this study put this discussion to rest because soya is an essential component of a healthy vegan diet.
This large study brings together all the available data on soya consumption and its impact on human health. The findings are remarkable and its worth reading the detail. To summarise, the most well-established benefits are for reducing the risk of cardiovascular disease, both stroke (18% reduction) and ischaemic heart disease (17%). This may be in part due to the ability of soya to lower cholesterol levels. For cancer, there are benefits for reducing the risk of ovarian (48% reduction), prostate (29%), breast (13%), colorectal (21%), gastric (22% for non-fermented soya), lung (17%) and endometrial (19%) cancers. The only word of caution for cancer is an increased risk of gastric cancer (17%) in men consuming 1–5 cups of miso soup per day, likely due to the high salt content. The study also showed a benefit of soya consumption for perimenopausal symptoms in women, especially in relation to hot flashes. Other benefits reported include reduced risk of kidney disease, better cognitive function, reduced risk of type 2 diabetes, healthy weight status and improve bone health in women (crucial in light of the EPIC-Oxford study). The only side-effect of soya consumption reported in studies were gastrointestinal symptoms.
It is clear that soya consumption provides many health benefits. In part due to its nutrient profile; high quality ‘complete’ protein, fibre, isoflavones, omega-3 fats. In part, the impact may also be due to what soya replaces in the diet i.e. those eating soya are likely eating less meat. The studies that try and tease out the components of soya that are beneficial e.g. isoflavones, protein, often generate mixed results and overall consuming the whole food rather than protein or isoflavone isolates is the best approach. Aiming for 2–3 portions of minimally processed soya (80g or 200mls soya milk) is certainly desirable in a healthy vegan diet.
LOW CARB DIETS ADVERSELY EFFECT HEART HEALTH: Despite the concern about bone health this week for those avoiding meat consumption, this paper reminds us of the deterimental impact of animal foods on heart health. The low-carb diet continues to be popular for weight loss and management of type 2 diabetes, but at what cost? This study investigates the impact of a low-carb diet on coronary artery calcium (CAC) scores in 2226 participants from the CARDIA study (Coronary Artery Risk Development in Young Adults), who were in their 40’s at recruitment. CAC reflects the presence of atherosclerotic plaque in the coronary arteries and is associated with the risk of cardiovascular disease. Diet was analysed and correlated with CAC scores determined by computed tomography at year 15 of follow-up and then at years 20–25 follow-up. The risk of progression of CAC was determined. The low-carb group were consuming around 40% of calories from carbohydrates versus the high-carb group consuming 60% of calories from carbohydrates. The lower carb group were also consuming more animal protein and fat. Participants with lower carbohydrate intake were more likely to be men, current smokers, to have a lower education level, to drink more alcohol, and to have higher levels of body mass index, systolic blood pressure, fasting plasma glucose, total cholesterol, LDL cholesterol, and triglycerides. The results showed an inverse relationship between carbohydrate intake and presence and progression of CAC scores. The higher carb intakes were associated with a 15–25% reduction in risk of CAC progression. When analysing the components of the diet, the results showed that those consuming a low-carb diet, in which carbs were replaced by animal protein and fat, had the greatest risk of CAC progression during the follow-up with an increased risk of 45%. However, replacing carbohydrates with plant sources of fat and protein did not have an impact on CAC progression. These findings were despite the fact that the study did not elucidate the quality of carbohydrates consumed; simple vs complex.
These data are consistent with prior observational data that show an animal-based low-carb diet is associated with an increased risk of cardiovascular disease. The authors of this paper conclude ‘Taken together, we found that low-carb diets beginning at early adulthood were associated with an increased risk of subsequent CAC progression in middle age, particularly when animal protein or fat …are increased. As a popular strategy for weight management, long-term animal-based low-carb diets should be advocated with great caution to avoid its potential impact on coronary atherosclerosis’.
ITS NEVER TOO LATE is the message of this important paper. We know that blood cholesterol, particularly LDL-cholesterol is a causal factor in atherosclerotic cardiovascular disease. However, the impact of lowering cholesterol levels in older adults has not been clear or rigorously investigated. This study included 91,131 individuals aged 40–100 years from the Copenhagen General Population Study who did not have atherosclerotic cardiovascular disease or diabetes at baseline and who were not taking statins. The results confirm that for every 1mmol/l increased in LDL-cholesterol there was a 34% and 16% increased risk of myocardial infarction and atherosclerotic heart disease, respectively. The risks were greater as age increased. It was predicted that the impact of lowering cholesterol was greatest in those aged 80–100 years. The number needed to treat (NNT) to prevent 1 myocardial infarction in the next 5 years was 80 for age 80–100 years, 145 for those aged 70–79 years, 261 for those aged 60–69 years, 439 for those aged 50–59 years, and 1107 for those aged 20–49 years. NNT in 5 years to prevent one atherosclerotic cardiovascular disease event was 42 for individuals aged 80–100 years, 88 for those aged 70–79 years, 164 for those aged 60–69 years, 345 for those aged 50–59 years, and 769 for those aged 20–49 years. The authors conclude ‘Thus, high LDL cholesterol in apparently healthy people older than 70 years is not a benign finding because it is associated with a substantially higher risk of developing myocardial infarction and atherosclerotic cardiovascular disease’.
So this brings me back to effective ways to lower blood cholesterol levels. Sadly, the paper only concentrates on statin therapy. Yet we know that diet and lifestyle can have an enormous impact on blood cholesterol with those avoiding all animal foods and eating a high fibre plant-based diet having the lowest cholesterol levels. The Portfolio diet, a plant-based dietary pattern pioneered by Dr David Jenkins, can have a similar impact on blood cholesterol levels as statin therapy. So for me, the main message is that it is never too late to advocate diet changes in our patients and in fact the impact will be greater in older adults based on the data presented. We must not assume that older people will not change habits, as there are no data to support this viewpoint.
ARE SUSTAINABLE DIETS AFFORDABLE: We know that globally a shift to a plant-predominant diet is necessary for both human and planetary health. Those that oppose this viewpoint often argue that a healthy plant-based diet can be expensive. This study from Australia put this to the test using the Eat-Lancet planetary health diet as the example diet. Encouragingly, the Planetary Health Diet was shown to be statistically less expensive and more affordable than the Typical Australian Diet nationally, in all metropolitan areas and in all socio-economic groups across Australia. The median cost of the Planetary Health Diet was AUD$188.21 versus the Typical Australian Diet at AUD$224.36 for a family of 2 adults and 2 children per week.
This study provides the first analysis of the affordability of the planetary health plate and is encouraging. However, we must not underestimate the issues around access to healthy foods in many countries including the UK. I recently highlighted a report from the UK called The Broken Plate. This showed that the poorest 20% of UK households would need to spend 39% of their disposable income on food to meet the cost of our dietary guidelines, the Eatwell Guide. This compared to just 8% for the richest 20%. We therefore need to continue to campaign for healthy foods to be made accessible and affordable through appropriate subsidies and support for farmers and consumers.
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