A review of the week’s plant-based nutrition news 20th March 2022

This week is dedicated to the topic of cancer, in preparation for my talk at the Real Truth About Health Conference from 1st to 17th April 2022. You can join for free here.

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LATEST CANCER STATS: This up to date analysis reveals that cancer incidence and death and disability from cancer is increasing globally, with the greatest rise in low and low-middle income countries. In 2019, there were 23.6 million new global cancer cases, 10 million cancer deaths, and an estimated 250 million disability-adjusted life years estimated to be due to cancer. Compared to 2010, these represent increases of 26.3%, 20.9%, and 16.0%, respectively. Cancer-related disability adjusted life years were second only to cardiovascular diseases in their contribution to global disease burden, and in the high income countries, cancer overtook cardiovascular disease to become the leading cause of disability. Given that at least 4 out of 10 cases of cancer could be prevented, greater efforts are needed to control the risk of cancer globally.

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LOWER RISK OF CANCER IN THOSE AVOIDING MEAT CONSUMPTION: In case you needed anymore reasons to eliminate meat from the diet, this study will help. It included 472,377 adult participants of the UK Biobank study with a mean age in the 50’s at recruitment and followed for 11.4 years. Participants were categorised into regular meat-eaters (n = 247,571), low meat-eaters (n = 205,385), fish-eaters (n = 10,696), and vegetarians (n = 8685).Regular meat eaters consumed meat more than 5 times per week. Low meat eaters, less than 5 times per week. The vegetarian group included 466 vegans. Participants also had blood measurements of insulin-like growth factor 1 (IGF-1), testosterone and sex hormone binding globulin. During the follow-up period 54,961 cancers were diagnosed.

The data analysis showed that vegetarians and fish-eaters had a lower body mass index, were younger, more likely to be never smokers, have a university/college degree, and report consuming less alcohol at recruitment compared to regular meat-eaters

The results showed a step-wise reduction in cancer incidence as meat and fish were reduced/eliminate from the diet. Compared with regular meat eaters, vegetarians has a 14% reduction in the risk of all cancers and fish-eaters had a 10% lower risk. Low meat-eaters had an 11% reduction in the risk of colorectal cancer. There was no significant difference in risk of colorectal cancer for fish-eaters and vegetarians, potentially due to lack of power (not enough participants) as the estimates did suggest lower risks in both these non-meat-eating diet groups.

Post menopausal women who were vegetarian had an 18% lower risk of breast cancer but this was likely due to being a lower body mass index. In men, not eating meat was associated with a 20% reduction in the risk of prostate cancer and being vegetarian reduced the risk by 31%.

Regarding blood biomarkers, there did not seem to be a strong interaction between diet, IGF-1 levels and cancer risk in this cohort. Prior analysis of this cohort has shown IGF-1 levels to be slightly lower in vegetarians. In the current study, vegetarian women did have slightly lower circulating IGF-I concentrations, which may have benefited their risk of breast cancer. However, for prostate cancer the analysis did not suggest that IGF-1 levels were mediating the lower risk in vegetarians. Of note, prior studies have documented lower IGF-1 level in vegans but given the low number of vegans in this study, the difference between diet groups was not significant.

There are so many plausible reasons for these results, including reduced exposure to carcinogens in meat and increased consumption of anti-cancer compounds in plant foods. These data are in line with results from the EPIC-Oxford and Adventist Health Studies that show vegetarians and vegans have a lower risk of cancer, with a greater benefit for vegans. The current study did not have enough vegan participants to draw any conclusions but a meta-analysis from 2017 demonstrated a 15% reduction in the risk of cancer in vegans.

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NUTRITIONAL STATUS AND RISK OF CANCER DEATH: This study set out to examine the association between nutritional status and risk of dying from cancer in 12,262 participants of the National Health and Nutrition Examination Survey in the US. Nutritional status was assessed in a novel way by combining the results of 17 blood biomarkers. These biomarkers were serum vitamin D, folate (both serum and RBC), calcium, potassium, sodium, phosphorous, lead, cadmium, and mercury, total protein, albumin, triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, and HDL-cholesterol/LDL-cholesterol ratio. The results of each biomarkers were scored such that the lower the score the healthier the nutritional status with a score of “0” if the measured concentration met the recommended value; “1” if the concentration did not meet but was within 30% lower/higher than the recommended value; “2” if the concentration was more than 30% lower/higher than the recommended value. The interaction of this score with other lifestyle factors, including exercise, smoking and body weight, was also assessed.

During the 6.75 years of follow-up there were 288 deaths due to cancer. The results showed that those with the lowest and thus most favourable nutritional score had around a 45% reduction in risk of dying from cancer compared to those with the least favourable score. As expected, there was an additive effect with other healthy lifestyle factors. The healthier nutritional status reflected a dietary pattern that was higher in fruit and vegetables, total grains, dairy and nuts, but lower in processed meats, red meats, seafood, and added sugars. One interesting finding is the lower intake of seafood in participants with a higher nutritional status, which is assumed to result in lower exposure to environmental toxins such as mercury.

The authors conclude ‘our results indicated that better nutritional status plays a protective role in decreasing risk of cancer mortality’.

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PLANT-BASED DIETS AND PROSTATE CANCER: Over the last few year we have seen more and more data supporting plant-based, lifestyle interventions for the prevention of prostate cancer. The seminal study by Dr Dean Ornish published in 2005 demonstrated that an intensive lifestyle intervention, which included a plant-based diet, could halt the progression of early-stage prostate cancer. He was able to show potential mechanisms at play, including changes in gene expression favouring cancer suppression and lengthening of telomeres. More recently, a study published in JAMA showed the efficacy of an exercise intervention in men with early stage prostate cancer. In addition, it has been consistently shown that a diet pattern centred around healthy plant foods is associated with a lower risk of prostate cancer, whilst dairy consumption may increase the risk.

The current study uses the plant-based diet index (PBDI) to analyse dietary data. Developed by researchers at Harvard University, the PBDI, is a way of scoring food frequency questionnaire data to assess the impact of a plant-based dietary pattern without necessarily including vegan or vegetarian participants. The overall PBDI gives a positive score to all plant foods and a negative score all animal foods. The healthy PBDI scores only healthy whole plant foods positively but unhealthy plant foods such as refined grains and sugar, negatively, thus being able to tease out the impact of a healthy or unhealthy plant-based diet. We now have quite a lot data demonstrating that adherence to a healthy plant-based diet can reduce the risk of a number of chronic conditions, with any incremental shift towards a plant based diet being beneficial. You can read my previous summary here.

This study, for the first time, assesses the impact of adherence to the PBDI on the risk of prostate cancer in 47,239 men participating in the the Health Professionals Follow-up Study. During the 20.7 years of follow up, 6,655 men were diagnosed with prostate cancer, including 515 men with advanced stage at diagnosis, 956 with lethal disease (metastasis or death) and 806 prostate cancer deaths (fatal). Greater adherence to an overall plant-based diet was associated with a 19% significantly lower risk of fatal prostate cancer. In men age <65 years, greater adherence to a healthy plant-based diet was associated with a 16% lower risk of total prostate cancer and a 44% reduction in lethal prostate cancer (prostate cancer death or distant metastasis) and 38% reduction in fatal prostate cancer (prostate cancer death). However, there were no associations between overall or healthy PBDI and prostate cancer in men ≥65 years. Surprisingly, more unhealthful plant-based foods were associated with a lower risk of lethal and fatal prostate cancer in men over age 65 years. This suggests that so called unhealthy plant foods may not be detrimental as such in the context of prostate cancer, but this would need confirmation in future studies.

There are several proposed reasons for these finding, including the anti-inflammatory potential of plant-based diets, the avoidance/limitation of dietary carcinogens and lower levels of IGF-1 when avoiding meat and dairy.

Of course, this study can not be extrapolated to make conclusions about vegetarian or vegan diet as <1% of participants followed such a diet pattern with the rest still consuming animal foods. However, the data do support the international cancer prevention guidelines which state ‘Make wholegrains, vegetables, fruit and pulses (legumes) such as beans and lentils a major part of your usual daily diet’. Read my article on diet and prostate cancer here.

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THE GUT MICROBIOME AND CANCER OUTCOMES: This open access paper is an essential read for all healthcare providers, especially those working with people with cancer. The impact of the health of the gut microbiome on cancer development and the response to treatment is for me one of the most exciting areas of research. In part, because we have the ability to make changes to the gut microbiome through dietary intervention in a very short space of time.

The review summarises what we have learnt to date. The gut microbiome refers to the approximately 100 trillion microorganisms (bacteria, viruses, yeast, protozoa) and their more than 300 million genes producing thousands of metabolites, which reside in the gut but have a profound impact on all aspects of our body’s function. We understand most about the bacteria that live in our gut and the most abundant species are Bacteroidetes and Firmicutes. A healthy gut microbiome is one which has a high diversity of bacteria and an abundance of bacteria that ferment fibre to produce short chain fatty acids (SCFA). These fatty acids provide energy to the intestinal cells, impact the health of the local immune environment and also the immune system more broadly. The SCFA’s also communicate with and signal to a number of other organs and impact their health. Alterations in the gut microbiome have been implicated in the pathogenesis of a number of chronic condition, including overweight/obesity, cardiovascular disease, type 2 diabetes, autoimmune conditions, dementia and mental health conditions.

When it comes to cancer, the bacterial composition has been implicated in the risk of developing colorectal cancer and also other gatrointestinal tract cancers such as pancreatic, oesophageal and liver cancer. More recently, it has become clear that the composition of the gut microbiome can influence response to certain types of anti-cancer treatments, namely those that target the immune system (immunotherapy). This includes outcomes from stem cell transplantation and with treatments that reactivate host T cells to recognise and kill cancer cells. Small studies have shown that a fibre-rich diet, abundant in whole plant foods, result in higher levels of SCFAs and can predict for a better outcome to immunotherapy. Researchers have tried to manipulate the gut microbiome using faecal transplants with promising results.

Of course, the main predictor of the health of the gut microbiome is our diet. Therefore, we can hypothesise that a healthy plant-based diet might positively impact response to cancer treatments. The review highlights the key elements of the diet that are important. First, a diversity of whole plant foods, as we know from the results of the American Gut Project that participants who consume more than 30 different plant types a week have a more diverse gut microbiome. Second, consuming polyphenol-rich plant foods. Third, increasing the intake of dietary fibre (AKA plant foods) to at least the recommended intake of 30g per day. Fourth, to include fermented foods in the diet. In addition, limiting or avoiding processed foods, including processed meat and artificial sweeteners is also beneficial to gut health.

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GUT MICROBIOME IN MELANOMA TREATMENT: Much of the data on gut microbiome and response to cancer treatment is in people with melanoma. This latest study is the largest ever to assess the association between the composition and function of the gut microbiome and response to immunotherapy in people with melanoma. Participants were recruited from five clinical centres in the UK, the Netherlands, and Spain.

The results showed that the association between the different gut bacteria in and how well they responded to treatment is complex. There was no single type of gut bacteria identified that predicted for a better outcomes. Overall, there were three particular types of bacteria (Bifidobacterium pseudocatenulatum, Roseburia sp., and Akkermansia muciniphila) that seemed to be associated with a better immune response. As might have been predicted, the study found that the composition of the gut was influenced by performance status, use of proton pump inhibitors and diet.

Although there was an association between the gut microbiome and response rate, this was not reproducible across the different cohorts. Nonetheless, the the findings could have important implications for the more than 50% of patients with advanced melanoma who don’t respond to immunotherapy.

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HEALTHY LIFESTYLES, CANCER AND CARDIOMETABOLIC DISEASE: Not only does underlying chronic illness increase the risk of cancer, but there is an increased risk of cardiometabolic disease after a diagnosis of cancer. This makes lifestyle interventions for cancer survivorship increasingly important.

This paper reports finding from the UK biobank study and examines the impact of a healthy lifestyle on the risk for cardiovascular disease (CVD) and type 2 diabetes (T2D) before and after the onset of cancer. Two sub-groups were included. A cancer-free cohort of 397,136 individuals in the general population and a cancer-prevalent cohort of 35,564 individuals with cancer. All participants were aged 40 to 70 years, free of CVD and T2D at recruitment and then followed for median of 14 years. The healthy lifestyle index (HLI) was made up of 5 cardiometabolic disease–related healthy behaviours (smoking status, physical activity, diet, alcohol consumption, and sleep duration). If participants met the criteria for each healthy habit they received a score of 1 and if not a score of 0, so a maximum score of 5 could be obtained. A healthy diet was high in fruits, vegetables, whole grains, refined grains, fish and low in unprocessed meat and processed meat.

In the cancer-free cohort 40,097 individuals (10.1%) developed cancer during follow-up. Each 1-point increment in HLI was associated with an 8% lower risk of developing cancer. A 1-point increment in HLI was also significantly associated with a 10% lower risk for developing CVD in patients diagnosed with cancer and a 12% lower risk in those free of cancer. Each additional healthy lifestyle factor had a 17%-26% reduction in risk of death during follow up, with smoking having the strongest negative impact. A 1-point increment in HLI was also associated with a 19% reduction in risk of T2D and a 16% reduction in T2D following a cancer diagnosis.

In the cancer cohort, cancer survivors with 5 healthy lifestyle factors had a 44% reduction in the risk of developing CVD and 38% reduction in the risk of T2D. A 1-point increment in HLI was associated with risk reductions of 10% and 13% in developing CVD and T2D, respectively.

Overall the finding confirm the importance of healthy lifestyle habits for prevention of cancer, CVD and T2D and also the benefits of these healthy habits after a diagnosis of cancer when the risk of chronic conditions is even higher.

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PHYSICAL ACTIVITY AND COGNITIVE FUNCTION: Many of my patient report problems with cognitive and executive function during and after chemotherapy. ‘Chemo brain’ is an actual syndrome, but we don’t fully understand the pathogenesis or how to prevent and manage the condition.

This study provides one of the largest assessments of physical and cognitive function before and after chemotherapy in patients with breast cancer. Researchers prospectively compared 580 individuals who were being treated for breast cancer with 363 normal controls with a median age of 53 years and assessed cognitive function over time and their level of physical activity. With the use of objective testing, there was a fall in cognitive function in the patients who received chemotherapy, although over time, that began to improve.

In the patients with breast cancer who started chemotherapy with a high level of physical activity, there was less of a decline in cognitive function and individuals who maintained their physical activity during chemotherapy did not experience the decline seen in others.

The level of physical activity that was considered adequate was that recommended by international guidelines; 150 minutes of moderately vigorous activity per week. Of note, more then two-thirds of the patients were not meeting these recommendations

The researchers conclude ‘This nationwide study demonstrates that physical activity maintenance before and during chemotherapy is associated with better cognitive function immediately and 6 months after chemotherapy completion’.

In a large analysis of 1535 cancer survivors in the US followed for 4.5 years, it was found that prolonged sitting (more than 8 hours per day) and lack of physical activity was associated with an increased risk of death, in the order of 80–400% increase, from cancer and non-cancer causes.

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