A review of the week’s plant-based nutrition news 3rd April 2022
This week I cover the impact of a plant-based diet on male and female fertility, the positive benefits for longevity and the potential role of flaxseeds for rheumatoid arthritis.
PLANT-BASED DIET AND MORTALITY: There has always been debate about whether a plant-based diet can positively impact life expectancy, with differing results amongst the main vegan study cohorts. This is likely to be due to the fact that not all vegan diets are created equal and a healthy vegan diet is one that is centred around fruit, vegetables, whole grains, beans, nuts and seeds. We have plenty of data now confirming that a unhealthy plant-based diet high in refined grains and sugar is no better than a meat-based diet for health outcomes.
This large analysis from the Million Veteran Program included 315,919 US veterans aged 19 to 104 (average 65.5) followed for an average of 4 years. Dietary data was analysed using the plant-based diet index (PDI) which scores plant foods positively and animal foods negatively. The healthy plant-based diet index (hPDI) scores healthy plant foods positively and both animal and less healthy plant foods (ie. sugar-sweetened beverages, refined grains, etc.) negatively.
The results showed that compared to those with the lowest PDI scores, those with the highest scores had a 25% lower risk of dying during the study after adjusting for potentially confounding variables, and each 10-point increase in PDI scores was associated with a 13% lower risk. High hPDI scores were associated with a 36% lower risk and each 10-point increase was associated with a 19% lower risk. In contrast, high uPDI scores were associated with 41% increase in risk and each 10-point increase was associated with 15% increase in mortality. The results were similar for risk of both cardiovascular and cancer mortality.
The results were consistent amongst different subgroups, including different ethnic backgrounds, smoking status, income levels, alcohol consumption, physical activity level, and weight.
This study adds to the now abundant data supporting a healthy plant-based diet for optimal health and longevity. There are no downsides with co-benefits for planetary health and the animals.
PLANT-BASED DIET AND FERTILITY: I have learnt a new word this week, fecundability ‘the probability of conception in a month or in a menstrual cycle’. This paper explores the impact of a plant-based diet on fecundability using the plant-based diet index. Participants were from the Singapore Preconception Study of Long-Term Maternal and Child Outcomes (S-PRESTO) study who were non-pregnant women of Chinese, Malay, or Indian ethnicity and who planned to conceive within 1 year from recruitment. The study included 805 women, who had 383 pregnancies confirmed by ultrasound scans during the follow up.
The results showed that greater adherence to a healthy plant-based diet increased the chances of conception, whereas an unhealthy plant-based diet, with a particularly negative impact of sugar-sweetened beverages and fast food, reduced the chances. The associations were relatively weak yet provide interesting observations given that there are very few studies examining the impact of diet pattern and on the chances of conception. It is entirely plausible that a healthy plant-based diet would be beneficial given the association with lower inflammation and improved insulin sensitivity. Similarly, there are data suggesting a healthy plant-based diet may be associated with better pregnancy outcomes such as a reduced risk of gestational diabetes.
This is an excellent article by Lisa Simon RD written for the BDA on diet and fertility.
HEALTHY PLANT-BASED DIET AND ERECTILE FUNCTION: This study, the largest to date, explores the association between adherence to the plant-based diet index and risk of erectile dysfunction in men. We know that erectile dysfunction is an early sign of cardiovascular disease, particularly atherosclerotic cardiovascular disease. Therefore, it is not surprising that a healthy plant-based diet would improve erectile dysfunction, yet, not many studies that have explored this exact question.
The current study included 2549 men with a median age of 54 years from the The National Health and Nutrition Examination Survey (NHANES) in the US. 57.4% of participant reported some type of erectile dysfunction. The results showed that higher consumption of healthy plant-based foods as defined by the healthy PDI was associated with a lower risk of erectile dysfunction after adjusting for relevant confounding factors. However, there was no association with the overall plant-based diet index, which also includes the less healthy plant-based foods such as refined grains and sugars, thus suggesting that it is the fruit, vegetables, whole grains and legumes in particularly that are key for maintaining erectile function. The results also showed that age, BMI, and African American race were associated with increased risk of erectile dysfunction across both plant-based diet indices, as were past medical history of diabetes, hypertension, stroke, and positive smoking history. Similar results have previously been reported in a smaller cohort of Chinese men in which a plant-based dietary pattern in general was associated with a lower risk of erectile dysfunction.
One of the mechanisms by which a plant-based diet is likely to benefit erectile function is through the higher consumption of nitrate-rich foods, which generate the vasodilating compound, nitric oxide. Higher intakes of nitrate-rich plant foods are known to benefit cardiovascular health in general. Men often worry that a plant-based diet will adversely affect testosterone levels, given the prevailing myth that meat consumption is synonymous with masculinity. However, the data does not support this theory and a plant-based diet does not impact testosterone levels in the small studies that have examined this.
You can find a great review paper on the topic here and the finding are summarised in the talk by Dr Robert Ostfeld below.
VEGAN DIET AND SPERM QUALITY: There has always been a stigma around vegan diets for men with entrenched beliefs that vegan men are less masculine. This in part may explain why three-quarters of vegans identify as women. This preliminary study add to the evidence to the contrary.
This small study compared sperm quality, oxidative stress values, presence of DNA damage and sperm acrosome reaction (a measure of the sperms ability to fertilise an egg) in 10 men who had been on a vegan diet for more than a year with 10 men on an omnivorous diet who consumed animal-derived foods daily.
The results showed that there was no difference between groups in sample volume, sperm viability, and morphology. However, total sperm count and motility was higher in the vegan group with non‑vegans having a lower percentage of rapid motile sperm. There was also evidence of less DNA damage and oxidative stress in the vegan group although there was no difference in the acrosome reaction.
These data are hypothesis generating rather than definitive given the very small study size. However, there are plausible reasons why a plant-based diet may be better for male reproductive health. High levels of reactive oxygen species that cause oxidative stress are associated with damage to sperm DNA and function. Prior studies have reported lower levels of antioxidants in the sperm of subfertile men. Thus, in theory, a diet high in antioxidants found in healthy plant foods may be beneficial. Small studies have shown that antioxidant supplementation may improve sperm health. Studies also suggest that a healthy plant-predominant diet pattern such as the Mediterranean diet may be associated with better sperm quality.
A plant-based diet has also previously been shown the to improve a number of aspect of men’s health included a reduced risk of coronary heart disease, type 2 diabetes, and lower risk of prostate cancer.
DIET, FLAXSEED AND RHEUMATOID ATHRITIS (RA): There is some, albeit weak, evidence that dietary patterns impact the clinical course of rheumatoid arthritis. In general, a diet that emphasises anti-inflammatory foods i.e.a variety of whole plant foods, and minimises inflammatory foods i.e. meat, processed foods, refined grains and sugars, is termed an anti-inflammatory diet. A plant-based diet or healthy vegan diet is also anti-inflammatory and there is certainly suggestive data that a healthy plant-based diet is a good approach for people living with rheumatoid arthritis. In addition, a plant-based diet helps address the higher risk of heart disease and cancer in the setting of autoimmune and inflammatory conditions and can help maintain a healthy weight.
It’s great to see a randomised study that can inform our clinical practice. 120 patients with RA who were randomised to three groups; flaxseed (30g/day) plus anti-inflammatory diet (AIF group), flaxseed (30g/day) plus regular diet (RF group), and roasted wheat (30g/day) plus regular diet (RW group). Wheat was used as the control. Principles of the anti-inflammatory diet were 2–3 servings of fish per week, 5–6 servings of vegetables, and 3–4 servings of fruits per day, emphasis on the ingestion of whole grains and legumes, the use of olive (preferably virgin and extra virgin types) and canola oil in cooking, restricting red meat to a maximum of 3 times a week, and reducing consumption of saturated fats and refined carbohydrates were recommended. The intervention was for 12 weeks and the outcome measures included disease activity, including disease activity score, physical disability, pain, and morning stiffness, changes in inflammatory markers and quality of life.
Overall, the main findings were in favour of the 30g of flaxseed per day, which had a significant beneficial impact on pain, disease activity and quality of life although did not result in significant changes to the inflammatory proteins. The anti-inflammatory diet did not appear to add additional benefits. However, from the dietary assessments, its apparent that the participants did not make big changes to their diet with vegetable intake going from 196.5g/day to 251g/day and fruit consumption 304g/d to 312g/d. From the available data it is likely that a greater change to the diet is required for clinical benefit in the setting of active inflammatory joint disease.
All in all, there is certainly no harm in adding 30g of flaxseeds a day to the diet and should be actively encouraged due to the wide ranging beneficial impacts including anti-hypertensive properties and potential anti-cancer properties. Flaxseeds are high in lignans, a polyphenol that is a precursor to phyto oestrogens, and lignan consumption has been associated with a lower risk of heart disease.