A review of the week’s plant-based nutrition news 29th May 2022
This week I cover dairy consumption and cancer risk, diet and COVID-19 and the latest low fat versus Mediterranean diet study. In addition, I highlight guidelines on exercise and diet during cancer therapy and dietary interventions for type 2 diabetes remission. Lastly, a new report from WWF highlighting the negative impact of food production and consumption in Europe.
DAIRY AND CANCER IN A CHINESE POPULATION: This is a useful study as most prior studies assessing the impact of dairy consumption on cancer risk are from Western populations. Dairy consumption is generally low in China although has been increasing in recent decades.
The study included 510,146 participants from the China Kadoorie Biobank who were followed for a median of 10.4 years. The aim was to assess the impact of habitual dairy consumption on the risk of total and site-specific cancers. During this time 29,277 cancers were diagnosed. Dairy consumption in this population was generally low with 20.4% of participants reporting consuming dairy products (mainly milk) regularly (i.e. ≥1 day/week), with the estimated mean consumption of 80.8 g/day among regular consumers and of 37.9 g/day among all participants. 68.5% reported never or rarely consuming dairy.
After adjusting for a number of confounders, the results showed that dairy consumption was significantly associated with an increased risk of total cancer (9%),when comparing regular consumers with non-consumers. In particular, dairy consumption was associated with an 18% higher risk of liver cancer and a 22% higher risk of breast cancer. There was also a trend for an increased risk of lymphoma, but this result was not statistically significant. There was also dose-dependent effect with 50g/day higher consumption resulting in a 7%, 12%, 19% and 17% increased risk of total, liver, lymphoma and breast cancer respectively. The observed associations were independent of other lifestyle factors, including adiposity and hepatitis B infection for liver cancer and were largely consistent across the various subgroups of participants. Unlikely in Western populations, there were no associations, positive or negative, with colorectal or prostate cancer risk, which may be because the incidence of these cancers are relatively low compared to Western populations.
This is an interesting observational study which of cause can not prove cause and effect but does provide reason for caution. There are very plausible reasons why dairy consumption could cause cancer, including the higher exposure to the growth factor IGF-1, higher concentrations of branched chain amino acids, exposure to bovine hormones, such as oestrogen, and the saturated fat content promoting insulin resistance. The high prevalence of lactose intolerance in the Chinese population may produce different breakdown products, which could also play a role.
We know that the dairy industry are trying to find new markets for their products as Western countries start to reconsider their devotion to dairy. The growing demand for plant-based milks is disrupting the industry. Sadly, China has been targeted and is now producing and consuming more dairy then ever, despite the fact that the majority of the population are unable to digest lactose. Let’s hope this paper acts as a warning.
DIET AND COVID-19: I love a good news story on veggie and vegan diets, but this has got to be one of the worst papers I have seen in a while. The study from Taiwan is a retrospective analysis of 509 patients who had been diagnosed with COVID-19 at a single medical centre between May 2021 and August 2021. Patients were divided into three groups according to disease severity. The aim of the study was to evaluate the association between self-reported dietary patterns and the severity of COVID-19 in a hospital setting.
The study reports that a vegetarian diet was associated with less severe disease. However, when you look at the numbers included, 487 (95.7%) of patients were non-vegetarian leaving only 16 vegetarians and 6 vegans in total. For the subgroup analysis of patients over the age of 65 years there were only 6 vegetarians and 3 vegans in the cohort. The authors highlight the low numbers of vegetarian as a limitation of the study ‘too few vegetarians were recruited in this study, thus limiting our study power’. Sadly, I think this study is hugely underpowered to answer the study question and the results may well have been due to chance alone.
We do however have more robust data from the Zoe symptom app study demonstrating that healthy plant-based diets are indeed associated with a lower risk of contracting COVID-19 and a significant reduction in severity. This is likely to be due to the beneficial impact of a plant-based diet on the health of the gut microbiome. You can catch up with my latest articles on diet and COVID-19 here (scroll down for the newest articles).
EXERCISE AND DIET DURING CANCER TREATMENT: We have a lot of robust data to guide recommendations for an optimal diet and lifestyle for cancer prevention and for those who have completed cancer treatment. However, we have fewer studies examining the impact of diet and lifestyle factors during cancer treatment. So it is great to have this new guideline from which to base our recommendations. The guideline specifically addresses whether interventions involving exercise, diet, and/or weight control compared with no intervention leads to meaningful improvements in outcomes related to quality of life (QoL), treatment toxicity, or cancer control in adult patients with cancer undergoing active treatment with systemic antineoplastic therapy or radiotherapy.
The guidelines summarised the findings of 52 systematic reviews (42 for exercise, nine for diet, and one for weight management), and an additional 23 randomised controlled trials. The most commonly studied types of cancer were breast, prostate, lung, and colorectal.
The following findings and recommendations are made:
- Exercise interventions during active treatment reduce fatigue; preserve cardiorespiratory fitness, physical functioning, and strength; and in some populations, improve QoL and reduce anxiety and depression. Given the low risk of adverse effects, oncologists should recommend aerobic and resistance exercise during active treatment with curative intent to mitigate side effects of cancer treatment. Insufficient evidence was was found to recommend for or against exercise during treatment to improve cancer outcomes (recurrence or survival).
- Preoperative exercise should be recommended for patients undergoing surgery for lung cancer to reduce length of hospital stay and postoperative complications.
- There is currently insufficient evidence to recommend for or against dietary interventions such as ketogenic or low-carbohydrate diets, low-fat diets, functional foods, or fasting to improve outcomes related to QoL, treatment toxicity, or cancer control. However, I am very pleased to see that neutropenic diets (specifically diets that exclude raw fruits and vegetables) are not recommended to prevent infection in patients with cancer during active treatment with data suggesting the harms outweigh any potential benefits, even in the setting of haematologist cancer (albeit with limited evidence).
- There is currently insufficient evidence to recommend for or against intentional weight loss or prevention of weight gain interventions during active treatment to improve outcomes related to QoL, treatment toxicity, or cancer control.
I am disappointed by the lack of clear dietary recommendations given what we know about the benefits of a healthy plant-predominant diet for cancer prevention and other chronic conditions. The frequent interactions with hospital staff during cancer treatment provides an ideal teachable moment to address dietary habits. Given that in the UK and other high incomes countries more than 50% of what is consumed is classified as ultra-processed, most of our patients will be on a diet that is considered unhealthy and likely nutrient-deficient, lacking sufficient fruit, vegetables and fibre. The documents states ‘The Expert Panel is not discouraging clinicians from discussing healthy diet and weight with their patients, but did refrain from making specific recommendations, given gaps in the evidence’. However, I feel the document reads as if we don’t have sufficient evidence by which to guide dietary recommendations. This could not be further from the truth. The guidelines does state this ‘Despite the significant observational data showing an association between a healthy or prudent diet and lower cancer risk and/or better outcomes in several malignancies, there are very limited data testing the impact of plant-based diet interventions during active treatment on toxicity or cancer outcomes, highlighting a critical need for further research in this area’. I suspect this will soon change as we are rapidly recognising the importance of a healthy gut microbiome on cancer outcomes.
A NEW MED VS LOW FAT STUDY: This study has already made waves. The CORDIOPREV study (Coronary Diet Intervention With Olive Oil and Cardiovascular Prevention) randomised 1002 participants who were known to have heart disease and followed them for 7 years. Participants were either assigned to a Mediterranean (Med) diet or a low fat diet. The goal in the Med diet was to consume >35% of calories from fat mainly from olive oil. In the low fat group the aim was to lower fat consumption to < 30% of calories. Protein consumption was intended to remain constant and hence fat was replaced by carbohydrates; <50% carbohydrates in the Med diet versus >55% carbohydrates in the low fat group. In the Med diet group, fat was increased by consuming more olive oil, nuts and fatty fish. In the low fat group these foods were reduced and replaced by more whole grains, legumes and low fat dairy.
The low fat group did not achieve the macronutrient goals, so this can not truly be deemed a low fat intervention. In the Med diet the goals were exceeded. On the Med diet 40% of calories came from fat versus 32% in the low fat group. In the Med group 39% of calories were from carbs versus 45% in the low fat group. The Med diet group did consume more olive oil, nuts and fatty acids. Both groups cut back on red meat and refined carbs. But there was little difference between groups in the consumption of legumes, whole grains and potatoes with the Med group ending up eating about 10% more fruit and vegetables.
Both groups had a relatively low rate of subsequent cardiovascular disease (CVD) events and death. The results showed a significant benefit for the Med diet with participants having a 26% lower overall rate of CVD events and mortality. Of note most of the participants were men (82.5%) and therefore these benefits were specific to men. Those with the greatest adherence to the Med diet had a 40% reduction in CVD events.
Of note, prior reports from this study cohort have shown reduction in plaque size, improvement in endothelial function and reduction in inflammation as measured by hsCRP on the Med diet only. No difference in body weight, triglycerides, cholesterol or fasting glucose were found between the groups by the end of the study. It seems the main difference in biomarkers between the groups was change in CRP levels (marker of inflammation), which reduced on the Med diet but increased on low fat diet.
Overall this study did achieve its aim of investigating different macronutrient combinations in two dietary patterns, however, the low fat group was not what we would typically call low fat. Although definitions vary, a low fat diet is typically < 30% of calories from fat if not < 20%. Nonetheless, the study adds to the evidence-base which supports the Med diet as a healthy diet pattern. We can not be sure which food or component was responsible for the benefits in this study but in general the Med diet group was following a healthier diet pattern. The study also confirms what we have known for a while, that diet quality matters most and macronutrient ratios are less important.
DIETARY INTERVENTIONS FOR TYPE 2 DIABETES REMISSION: The narrative around type 2 diabetes (T2D) has changed considerably over the last few decades. Rather than being a chronic, progressive condition, the aim of treatment should now be to achieve remission. The most effective way to achieve remission is an intensive dietary approach. But which dietary approach should we recommend? This much needed consensus statement has been endorsed by a number of American healthcare organisation (American Association of Clinical Endocrinology (AACE), supported by the Academy of Nutrition and Dietetics (AND) and co-sponsored by the Endocrine Society) and provides much needed clarity. There is a lot of detail in this paper and it is well work reading.
The key take away messages include;
- Remission of disease, such as T2D, is broadly defined as the disappearance of related signs and symptoms for a specified minimum time but does not exclude the possibility of recurrence.
- Remission of T2D should be defined as HbA1c <6.5% for at least 3 months with no surgery, devices, or active pharmacologic therapy for the specific purpose of lowering blood glucose.
- The ability of dietary interventions to produce remission is related to its intensity, defined by dietary restrictions and degree of patient–practitioner interactions, with high fibre content being an essential component.
- Likelihood of remission is greatest when the dietary intervention is accompanied by other lifestyle changes and the patient’s T2D is of short-term duration (4 years or under).
- There was consensus that dietary intervention should include primarily whole, plant foods (whole grains, vegetables, legumes, fruits, nuts, and seeds) while avoiding or minimising meat (and other animal products), refined foods, ultra-processed foods, and foods with added fats.
- The panel agreed that food-based dietary interventions (e.g., Mediterranean, DASH, whole food, plant-based diets) are preferred for long-term (sustained) remission of T2D.
- A very-low-carbohydrate diet can be associated with significant adverse events and cardiovascular risk that make this diet inadvisable for long-term remission of T2D.
- The panel recognised the positive data supporting calorie restriction and agreed dietary intervention for T2D may include some liquid meal replacements to facilitate patient adherence to a calorie-restricted diet
Overall, the experts agreed that a diet centred around whole plant-foods was an essential component of an intervention for diabetes remission.
AN ALARMING NEW REPORT: This new report from WWF should serve as a call to action. The report clearly finds that the production and consumption of food in Europe is hugely inefficient, wasteful and is contributing to environmental degradation, fuelling climate change, biodiversity loss, whilst contributing to social injustice. At the core, it finds that we need to vastly reduce our consumption of food from animals. It states, ‘We produce more animal products than we consume, and we consume more than is good for us. To sustain this oversized livestock sector, we feed half the grain crops we grow to animals, while our intensive agricultural practices damage biodiversity, soil health, and the climate. Vast quantities of food are also wasted, including on farms — which, contrary to popular belief, is a greater problem in Europe than in low-income countries’. It’s clear that the farming system needs to change drastically and quickly. This is required not only to support planetary health but would have co-benefits for our personal health too.
There is good news too. We produce enough crops to feed not just today’s global population, but the projected 9.7 billion people in 2050. But ‘the most drastic transformation lies with shifting diets, with intensively raised meat and dairy being replaced with plant-based foods’. We need to make these changes now. It starts with consumers eliminating the demand for animal foods and switching to a plant-based diet. In high income countries like the UK, most of us can do this now, and studies have shown that this would reduce our food bills by 30%. Please read the full report and share widely.