A review of the week’s plant-based nutrition news 16th January 2022

This week I cover diet and lifestyle factors related to cancer, vegetables and bone health, omega-3 fatty acids and depression and a new study showing the massive reduction in carbon emissions if we all adopted a plant-based diet.

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FINDINGS FROM THE EPIC STUDY: The European Prospective Investigation into Cancer and Nutrition (EPIC) is a one of the largest prospective cohort studies in the world. Its aim is to investigate the relationship between diet, lifestyle, and environmental factors with the risk of developing cancer (and other chronic diseases). The study comprises 519,978 participants (153,457 men and 366,521 women), mostly aged 35–70 years, who were enrolled between 1992 and 1998. The study recruitment was carried out in 23 centres in 10 European countries.

The current analysis includes 45 studies using data from the EPIC cohort and assesses the impact of diet and lifestyle factors on cancer mortality/death. The main findings are that overall dietary patterns, rather than individual foods and nutrients, are associated with a reduced risk of death from cancer. This includes the Mediterranean diet pattern and vegetarian and vegan diets In addition, poor diet quality as measured by the dietary inflammation index was associated with overall cancer mortality. Alcohol consumption, overweight and obesity, including central obesity, were associated with increased risk of cancer mortality, whereas regular physical activity reduced the risk. Adherence to the World Cancer Research Fund cancer prevention recommendations, which includes a plant-predominant diet, was shown to reduce the risk of death from cancer by 10–30%.

Regarding individual foods and nutrients, there were associations with raw vegetable consumption, fibre, lignan and vitamin D and reduced cancer mortality.

The prior summary publication analysed diet and lifestyle factors that have been found to be associated with cancer incidence. The analysis included 110 studies and reported a reduced incidence of cancer with higher intakes of fruit, vegetables and fibre. A higher consumption of fish and lower consumption of red and processed meat were associated with a lower risk of colorectal cancer and a higher consumption of fatty fish with a lower risk of breast cancer. Calcium and yogurt intake were found to protect against colorectal and prostate cancer. Alcohol consumption increased the risk of colorectal and breast cancer. Adherence to the Mediterranean diet emerged as a protective factor for colorectal and breast cancer. No data in this publication was presented on vegan diets specifically.

Overall, the data confirm the importance of a healthy diet pattern along with other healthy lifestyle habits as outlined by the 2018 World Cancer Research Fund cancer prevention guidelines. A plant-based or healthy vegan diet remains an excellent choice for reducing the risk of cancer.

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FASTING AND CANCER OUTCOMES: There is continued interest in using forms of fasting to improve health outcomes. The fasting-mimicking diet (FMD), pioneered by Dr Valter Longo, is being used in clinical trials to enhance the efficacy of cancer treatment. The premise being that fasting or reduced calorie intake is a stressor for cancer cells, enhancing cancer cell death, whereas it can protect normal cells. The FMD involves 5 days consecutive days of low calorie (around 500kcal), low protein, high fat, predominantly plant-based foods. The only study whose results have been reported so far in cancer treatment is the phase 2 trial “DIRECT”, which was prematurely interrupted because of poor patient compliance with the proposed FMD regimen and because the FMD failed to reduce chemotherapy-induced adverse events.

The current paper reports the finding of a first in human clinical trial to investigate the safety and biological effects (metabolic and immunoregulatory) of cyclic, five-day FMD in combination with standard anti-cancer therapies in 101 patients. It also reports the results of an interim analysis of the FMD-induced systemic and intra-tumour immune responses in 22 breast cancer patients enrolled in the ongoing DigesT trial.

In this study of 101 patients, a total of 440 cycles of FMD were completed with a median of 4 per patient. Only 20% of patient completed all the cycles but grade 3/4 FMD-induced toxicity only occurred in 12.9% of patients, compared to the predicted 20%.

The laboratory studies showed some positive results including reduced plasma glucose, insulin and growth hormone levels (IGF-1). These changes were independent of cancer type and treatment administered. Laboratory studies also showed a reduction in blood cells involved in immune suppression and an increase in immune active cytotoxic cells. In a subset of patients with melanoma who had repeat biopsies performed after FMD cycles, the pathological assessment showed an increase in immune cells infiltrating the tumour with additional functional changes noted suggesting an enhanced anti-tumour effect of these cells. Single cell analysis of these tumour infiltrating immune cells showed increased expression of several immune-related genes.

Overall, the study showed that the protocol was feasible and induced metabolic and immunoregulatory changes that would be predicted to lead to better anti-cancer effects of chemotherapy drugs. These results now need to be correlated with patient outcomes.

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VEGETABLE INTAKE AND BONE HEALTH: There are ongoing concerns about vegan diets and bone health. I have summarised the literature in this article. The main learning points are that vegans should consume enough calories, not be underweight and consume enough calcium and vitamin D, meeting country-based nutrient recommendations. In addition, adequate weight bearing and resistance exercise is crucial to bone health. What we also know is that eating a variety of fruit and vegetables promotes bone health.

This randomised study recruited 102 overweight and obese participants who were consuming 1 or less serving of vegetables per day (I know what you are thinking; how is that possible?) to a community based 8-week intervention. The intervention groups was provided with 270 g/d of extra vegetables per day. Blood and urine biomarkers of bone health were measured in the vegetable and control groups.

The results showed that blood biomarkers of vegetables consumption (such as carotenoids) increased in the intervention groups confirming that they were indeed eating the vegetables provided. In addition, the vegetable group had a higher urine pH suggesting lower renal acid load, lower urine magnesium excretion and an increase in the blood concentration of the bone resorption marker CTX (C-terminal telopeptide of type 1 collagen). However, markers of bone formation were not affected.

The classic hypothesis is that fruit and vegetable intake alters the acid–base balance toward alkaline and that the mild alkalisation decreases urinary calcium excretion and bone resorption thus positively affecting bone metabolism. This study did demonstrate reduced urine acid load and the lower magnesium excretion may have a positive impact on bone health but the study did not show reduced calcium excretion. Prior studies that have shown reduced calcium increase have used a much high dose of vegetables, >9 servings a day.

This study does provide some evidence of a beneficial impact of increasing vegetables consumption to that recommended in dietary guidelines. However, for best bone health, all aspects of diet quality need to be addressed. A whole food plant-based diet is able to meet requirements for all nutrients required for optimal bone health although vitamin B12 and D are required as supplements. In addition, it is assumed that the lower levels of inflammation and higher antioxidant capacity with a plant-based diet is also going to benefit bone health.

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OMEGA-3 FATTY ACIDS AND DEPRESSION: There is ongoing concern that vegan diets may adversely affect brain health, be it mental health or cognitive function, due to lower consumption of long-chain omega-3 fatty acids usually obtained from fish. Here is a my summary article on omega-3 fatty acids and health outcomes. There is ongoing debate about whether vegans should supplement with algae-derived DHA and EPA.

This large study adds to our knowledge on the impact of fish-derived omega-3 fatty acid supplementation on the risk of depression. The study included 18,353 participants with a median age of 67.5 years and without symptoms of depression who were randomised to 1g/d of fish oil, including 465mg of eicosapentaenoic acid and 375mg of docosahexaenoic acid. After a median follow up of 5.3 years the results showed that the supplementation group had an increased risk of depression, mainly in women. Overall, the results do not support the use of omega-3 supplements in adults to prevent depression.

It is always difficult to assess the applicability of studies such as these, especially in the context of prior studies. Results will be influenced by the background dietary consumption of omega-3 fats, the dose of the supplements, with higher doses potentially required for prevention of depression, the relative doses of EPA and DHA with EPA thought to have more of a protective effect. Nevertheless, there are currently no data to support the use of fish derived omega-3 fatty acids for prevention or treatment of depression. Instead, consuming an abundance of fruits and vegetables, concentrating on overall diet quality and consuming sufficient plant-derived short chain omega-3 fatty acids are likely to be better advice for those on a plant-based diet.

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THE CLIMATE IMPACTS OF ADOPTING A PLANT-BASED DIET: We already know that animal agriculture is a major driver of the climate and ecological crises. This study investigated how the carbon footprint of food production would change if 54 high-income countries were to shift to a more plant-based diet in line with the recommended EAT-Lancet planetary health diet. The researchers also determined how much land could be freed up by such a dietary shift and quantified how much extra carbon could be drawn down by soil and vegetation if this surplus land were allowed to revert to its natural state of mixed native grassland and forest.

The results show that high-income nations could reduce their agricultural emissions by 62% by shifting to a more plant-based diet whilst at the same time freeing up an area of land larger than the entire European Union. If this area were allowed to revert to its natural state, it would capture around 100bn tonnes of carbon — equal to 14 years of global agricultural emissions. This alone could meet the country-based carbon reduction targets for limiting global warming to less than 1.5 degrees C.

This really should come as good news as we have a relatively straightforward solution that could keep us within planetary boundaries of climate change. Yet we all know how difficult and complicated it is to change dietary norms and habits. An insightful article by Dr Marco Springmann clearly describes how farming subsidies need to move away from meat and dairy and rather be put towards supporting the production of both healthy and sustainable foods, such as fruit, vegetables and legumes. A top down and bottom up approach is required.

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