A review of the week’s plant-based nutrition news 24th July 2022

This week I have a cancer-related theme. A plant-based diet, along with other healthy lifestyle habits, plays a key role in preventing cancer and surviving well after a diagnosis of cancer.

WHAT IS ALREADY KNOWN ABOUT NUTRITION AND CANCER: This is a fantastic summary of the current knowledge on diet and cancer. The following key points are highlighted.

• Plant-based diets are associated with a lower risk of developing cancer.
• Plant-based diets reduce the risk of metabolic disorders such as obesity and type 2 diabetes that increase the risk of cancer.
• Plant-based diets reduce the risk of chronic conditions after a diagnosis of cancer.
• Plant-based diets may positively impact response to anti cancer treatments, but more studies are needed.
• Mechanisms involved include reduced inflammation, insulin and insulin-like growth factor 1 levels and healthier gut microbiome.
• This is because plant-based diets are high in fibre, phytochemicals and support increased production of short chain fatty acids by gut microbes.

The article concludes: ‘The results of this review suggest that the collective evidence supports plant-enriched diets for the reduction of cancer risk and the improvement of metabolic disorders in survivors’.

Coincidentally, Dr Laura Freeman and I have published an opinion piece highlighting the importance of diet and lifestyle counselling as part of cancer care, providing both a doctor and patient perspective. We cover very similar information to the JAMA review. Find our full article here.

PLANT PROTEIN IS BEST FOR OLDER ADULTS: More evidence to support the superiority of plant sources of protein over animal sources, this time for older men. This study included 794 men in Australia with a median age of 81 years and followed for 3.7 years. During this time there were 162 deaths with 54 (33.3%) and 49 (30.2%) men dying from cancer and cardiovascular disease, respectively. Protein intake was correlated with all-cause and cause-specific mortality.

Overall, higher intakes of protein were associated with a lower risk of death, with longer life expectancy among people consuming 93–113 g/day of protein. But when the source of protein was considered it was found that each increase in serving of animal protein was significantly associated with a 12% and 23% increased risk of all-cause and cancer mortality respectively. This association was driven mainly by consumption of red meat and dairy but not other animal sources of protein. In contrast, each increase in serving of plant protein was significantly associated with a 25% and 28% reduction in risk of all-cause and cancer mortality, respectively. This association was driven by consumption of nuts and seeds but not legumes or soya. These associations remained significant even after adjustment for other lifestyle factors. There were no associations found between protein consumption and death from CVD, possibly due to the low number of CVD-related deaths. The authors conclude ‘Higher consumption of animal-derived proteins was associated with greater mortality risk, whereas this association was reversed when protein consumption was replaced with plant-derived protein’. They also make the point that ‘it is important to promote plant-based protein diets ….as being more environmentally sustainable that animal protein-rich diets’.

These results are in keeping with prior data that confirms that the source and quality of protein is key, with consumption of plant sources leading to improved health outcomes, even in older adults. An example is recent data from the Nurses’ Health Study showing that increased consumption of plant protein reduced the risk of frailty with ageing in women.

CRUCIFEROUS VEGETABLES AND RISK OF PREMATURE DEATH: I am not one for recommending a superfood, but if there is one type of vegetable to include in your diet on a daily basis, it has to be cruciferous vegetables (broccoli, cauliflower, kale, cabbage etc.). Their consumption is associated with an array of health benefits, including a reduced risk of cancer and cancer progression.

This new report from the NHANES (National Health and Nutrition Examinations Survey from the US) study, including 10,489 non-smoking participants followed for a median of 7.8 years recorded 800 deaths, 136 from cardiovascular disease (CVD). It specifically examined the association of urinary excretion of thiocyanates, a biomarker of cruciferous vegetable intake, and risk of death from CVD and all causes. The results showed a 50% lower risk of CVD mortality and 25% lower risk of all-cause mortality with higher excretion of thiocyanates. The findings are consistent with a prior large meta-analysis of 95 studies from 2017, which found a reduced risk of all-cause and cancer mortality with high intake of cruciferous vegetables, and a suggestive inverse association with CVD.

Of note, the reason for only including non-smokers is that tobacco is also a source of thiocyanate, a metabolite of cyanide. Also worth noting is that in this cohort the consumption of vegetables was not particularly high with a median of 3.4 portions per day and a median fibre intake of 17.2g per day. So even if you are not consuming a lot of plant foods, a wise choice would be to include cruciferous vegetables.

WESTERN-STYLE DIET AND COLORECTAL CANCER: We already know that a Western-style diet pattern high in red and processed meat, sugar and refined grains/carbohydrates increases the risk of colorectal cancer (CRC). This study suggests that this may be occurring through the negative impact on the gut microbiota leading to DNA damage, inflammation and altered immune surveillance.

Researchers analysed dietary data from more than 134,000 participants from two prospective cohort studies from the US; The Nurses’ Health Study and The Health Professionals Follow-up Study. During the more than 30 years of follow-up, there were 3200 cases of CRC recorded. Genetic analysis was performed on 1,175 of these tumours, specifically looking for the Escherichia coli bacterial strains carrying a distinct genetic island known as polyketide synthase (pks). Pks encodes an enzyme that has been shown to cause genetic mutations in human cells.

The results showed that a Western-style diet pattern was associated with colorectal tumours containing high amounts of pks+ E. coli but not with tumours containing little to no amount of pks+ E. coli. This provides a potential link with the Western-style diet, the gut microbiota and development of CRC.

The impact of diet on gut microbiota is implicated in a number of chronic conditions, including cancers in general. In addition, modification of the gut microbiome in those with a diagnosis of cancer, may be of benefit. This review article provides an excellent summary on the role of the gut microbiome in cancer prevention and survival. The key message is that we can modify our gut microbiome within a few days of making a beneficial dietary change. The key component of the diet to emphasise are foods rich in fibre, resistant starches, polyphenols and to include fermented foods — so all the plants!

DIET AND PHYSICAL ACTIVITY ARE IMPORTANT IN REDUCING PREMATURE DEATH: As much as I like discussing the impact of diet on health outcomes, we do also need to pay attention to other healthy lifestyle habits, including physical activity. When it comes to cancer, it is clear that regular physical activity reduces the risk of a number of cancer types and also improves survival and quality of life after a diagnosis of cancer.

This new report from the UK Biobank study finds that both diet quality and physical activity are important for reducing the risk of death from all causes, including CVD and cancer (specifically diet and obesity-related cancers; bladder, post menopausal breast, colorectal, endometrium, stomach, kidney, liver, oesophagus and pancreas cancers). The study included 346, 627 participants followed for 11.2 years. Diet quality was based on adherence to recommendations from the American Heart Association (AHA), which include consuming 4.5 or more cups of fruit and vegetables per day, 2 or more servings of fish per week, 2 or less servings of processed red meat and 5 or less servings of red meat per week.

The results showed a linear relationship between physical activity and reduction in all-cause, CVD and cancer mortality with a 13–14% reduction in mortality comparing those that did the most with those that did the least physical activity. Regarding diet quality, the association did not meet statistical significance for all-cause and CVD mortality but there was a 14% reduction in cancer mortality for those consuming the best quality diet. However, the lowest mortality was seen in those who had the best quality diet and were undertaking the most physical activity. Physical acitvity alone could not overcome the detrimental effects of a poor quality diet. Of note, the assessment of diet quality showed only 24.5% were consuming what was considered the best diet and the assessment of diet quality did not assess all food groups/nutrients due to unavailability of these data. There are more robust ways of assessing diet quality that utilise a broader range of dietary component. The AHA recommendations are rather moderate and it may be that a greater shift towards a plant-based diet is needed to improve health outcomes. This may have attenuated any potential associations between diet and mortality.

I love the conclusion as it resonates with my personal and professional experience “sensationalised headlines and misleading advertisement for exercise regimens to lure consumers into the idea of ‘working out to eat whatever they want’ have fuelled the circulation of the myth about ‘exercise outrunning a bad diet’. Our study provided important evidence for health professionals that exercise does not fully compensate for a poor diet and that we should recommend and advocate for both an active lifestyle and a healthy diet”.

I am pleased that the highly respected institution, The Mayo Clinic, also endorse plant-based diets for prevention of cancer. They state ‘Decades of research suggests that the best diet for cancer prevention is all about plants. That means lots of fruits, vegetables and legumes, and little to no meat or other animal products’.

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