The best studies of 2022…. so far, 3rd July 2022

Half way through the year and COVID-19 has finally come to our house. I have therefore summarised my top studies of the year so far.

NUTRIENT INTAKE IN MEAT VERSUS PLANT-BASED DIETS: This is a surprisingly useful paper given that it is written by two employees of the company Unilever. The aim of the study was to assess the nutritional adequacy of meat-based diets compared to plant-based diets (mainly vegetarian and vegan). This is a systematic review of observational and intervention studies published between 2000 and January 2020 and included a total of 141 (101 studies on meat eaters, 118 vegetarians, 63 vegans) mostly from Europe, South/East Asia, and North America.

There is a lot of detail in the text, which is well worth reading. Overall, all diet patterns were found to have nutritional inadequacies. Meat-eaters were at risk of inadequate intakes of fibre, polyunsaturated fatty acids (PUFA), alpha-linolenic acid (ALA), folate, vitamin D, E, calcium and magnesium. Vegetarian and vegans had lower intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), vitamin B12, vitamin D, iron, zinc, iodine, calcium and lower levels of bone turnover markers than meat eaters. Vegans had the lowest vitamin B12, calcium and iodine intake, and also lower iodine status and lower bone mineral density. Fibre, PUFAs, folate, vitamin C, E and magnesium intakes were high in plant-based diets. Average fibre intake amongst vegans was 44g/d compared to 28g/d in vegetarians and 21g/d in meat eaters. All diet groups met protein and energy requirements. There was no mention of saturated fat intake which I assume was high in meat eaters.

The table below summarises the findings.

The authors’ conclusion is eminently sensible. ‘There were nutrient inadequacies across all dietary patterns, including vegan, vegetarian and meat-based diets. As plant-based diets are generally better for health and the environment, public health strategies should facilitate the transition to a balanced diet with more diverse nutrient-dense plant foods through consumer education, food fortification and possibly supplementation.’ Unilever have come out as surprising leaders in supporting a transition to a plant-based diet. Whatever their underlying motivation, they have made a valuable contribution to the literature on plant-based diets.

FOOD CHOICES AND LIFE EXPECTANCY: Good news! Our food choices really can add years to life. Sadly, unhealthy diets remain the leading cause of death and disability globally, with an estimated 1 in 4 deaths due to an unhealthy diet, including a third of all premature deaths in Europe and the US. In this new study, researchers used existing meta-analyses and data from the Global Burden of Diseases study to build a model that enables the instant estimation of the effect on life expectancy (LE) of a range of dietary changes. Based on prior data, an optimal diet was considered to be higher intakes of whole grains, legumes, fish, fruit, vegetables, and included a handful of nuts, while reducing red and processed meats, sugar-sweetened beverages, and refined grains.

The optimal diet was similar to the the Eat-Lancet Planetary Health Plate and included the following quantities of various foods per day. Whole grains 225g (fresh weight) or 75g (dry weight), vegetables 400g, fruit 400g, nuts 25g, fish 200g, eggs 25g (half an egg), dairy 200g, refined grains 50g, red and processed meat 0g, white meat 50g, sugar sweetened beverages 0g, oils 25g.

The results showed that a sustained change from a typical Western diet to the optimal diet from age 20 years was estimated to increase life expectancy by 10.7 years in women and 13 years in men. The largest gains were shown to occur by eating more legumes (females: 2.2 years; males: 2.5 years), whole grains (females: 2.0; males: 2.3 years), and nuts (females: 1.7 years; males: 2.0 years) and less red meat (females: 1.6; males: 1.9 years) and processed meat (females: 1.6 years; males: 1.9 years). Changing from a typical diet to the optimal diet at age 60 years was estimated to increase LE by 8.0 years for women and 8.8 years for men, and 80-year-olds would gain 3.4 years. Even a half way transition towards an optimal diet was predicted to increase LE by 6.2 years for 20-year-old women from the United States and 7.3 years for men. Results were presented based on US data but similar trends were found when considering data from China and Europe.

The authors conclude ‘sustained change from a typical to an optimised diet from early age could translate into an increase in LE of more than 10 years’. Of note, a previous report from the Nurses’ Health Study and Health Professionals Follow-Up study has shown that the extra years derived from healthy diet and lifestyle habits are spent in good health rather than chronic ill health.

The model used in the study is also now available as a publicly available online tool called the Food4HealthyLife calculator (https://food4healthylife.org/).

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 suggested 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 studies the difference between diet groups was not that 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 results from the EPIC-Oxford and Adventist Health Studies that show vegetarians and vegans have a lower risk of cancer, with a greater benefit in 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.

ULTRA-PROCESSED FOOD (UPF) CONSUMPTION, MEAT AND MORTALITY: UPFs have become a centre-piece of Western diet patterns. In the UK and US more than 50% of foods consumed are classified as ultra-processed. The designation of UPF is based on the NOVA classification. UPF consumption is associated with increased calorie intake and a higher risk of various chronic conditions including cardiovascular disease, overweight/obesity, type 2 diabetes, autoimmune conditions and more.

This paper reports finding from the Adventist Health Study-2 and specifically examines the impact of both UPF and animal food consumption on the risk of mortality (death). The study included 77,437 participants who were followed for an average of 7.5 years. Around a third of participants in this cohort are vegetarian or vegan.

The median consumption of UPFs was 27.4% of energy. Comparing the 90th centile of UPF consumption ( 47.7% of dietary energy) to the 10th centile (12.1% of dietary energy) there was a 14% higher risk of total mortality. This association persisted after adjustment for a more animal-based diet suggesting that UPFs regardless of whether animal-derived or plant-based are detrimental to health. Interestingly, UPF consumption was not associated with cardiovascular disease or cancer mortality, but primarily with mortality from neurological (particularly Alzheimer disease and Parkinson disease) and respiratory causes. The association of UPF consumption with mortality appeared stronger among those with chronic diseases at baseline, suggesting the potential for greater impact among those with higher mortality risk.

There was no significant association between total animal food intake and mortality. But it should be noted that in this cohort consumption of animal foods was very low with a median of 9.8% of calories derived from animal foods. However, consuming just 6.2% of total calories from red meat compared to zero calories was associated with a 14% increase in risk of mortality.

The researchers also examined the impact of replacing UPFs with moderately processed or unprocessed foods and found that UPFs were associated with a higher risk than both moderately processed and unprocessed foods.

Overall, both higher UPF and red meat consumption adversely affected health and increased the risk of death in this population who are generally healthier than the average American.

PROTEIN INTAKE AND FRAILTY: I am very pleased to read the results of this paper as the erroneous and prevalent narrative continues to be that animal protein is superior to plant-based sources of protein for prevention of frailty in older people.

The analysis included 85,871 women aged 60 years and above from the Nurses’ Health Study. Participants were aged 30–55 years at the start of the study in the 1970’s and had been followed for 22 years. The study assessed the impact of protein intake on the risk of frailty. Frailty was defined as having at least three of the following five criteria from the Fatigue, Resistance, Ambulation, Illnesses and Loss of Weight (FRAIL) scale; fatigue, low strength, reduced aerobic capacity, 5 or more chronic conditions and loss of weight of ≥5%. The occurrence of frailty was assessed every 4 years from 1992 up to 2014 and dietary intake on at least 9 occasions. The main food sources of plant protein were bread, cereals, pasta, nuts, beans, and legumes; main food sources of animal protein included processed and unprocessed red meat, poultry, fish and seafood, eggs, and dairy products.

The results showed that comparing women consuming the most plant-based protein to the least (6.2g per day vs 3.8g per day), higher plant protein intake was associated with a 14% reduction in risk of frailty. In contrast, high animal protein intake was associated with a 7% increased risk of frailty. Replacing 5% of energy from animal protein with plant protein was associated with a 38% lower risk of frailty with a positive impact from replacing both dairy and non-dairy protein.

The authors conclude ‘among older adults, a higher intake of plant protein was associated with reduced risk of frailty. Moreover, these data suggest that replacing animal protein with plant protein might help to avoid the development of the frailty syndrome’.

Prior reports from the Nurses’ Health Study have reported that healthy dietary patterns characterised by a greater consumption of whole plant foods are associated with a lower risk of frailty, whilst red meat consumption increases the risk. So, all in all, a useful endorsement for emphasising plant sources of protein in the diet, even in older adults.

IMPACT OF A LOW-FAT VEGAN DIET: Another great paper from the research team at PCRM. They have been studying the impact of a low-fat vegan diet on health outcomes for decades with some remarkable results. This study is a secondary analysis of data from a 16-week randomised clinical trial in overweight adults with the aim of determining the effects of a low-fat vegan diet on food and nutrient intake, diet quality, and identify potential associations with changes in body weight, body composition, and insulin sensitivity. It included 244 participants, mainly female, of whom 222 completed the study and complete food records were available from 219 participants. The final results included data from 117 participants on a vegan diet and 102 in the control group. The vegan group were asked to follow a vegan diet, without calorie restriction, and to consume vegetables, whole grains, legumes, and fruits and to avoid animal products and added fats.

Participants were assessed at baseline and after 16 weeks. As expected, fruit, vegetable, legume, meat alternative, and whole grain intake significantly increased in the vegan group. The increase in each of these food groups was associated with weight loss, with legume consumption being the strongest predictor of weight loss. The lower fat intake was also associated with a reduction in fat mass after adjusting for changes in body mass index (BMI) and energy intake. Reduction in the consumption of all animal-derived foods was also associated with weight loss. The diet quality of the vegan group improved significantly as assessed by the Alternate Healthy Eating Index, which gives positive marks for the consumption of whole plant foods and negative marks for consumption of red and processed meat and processed foods in general. This overall improvement in diet quality was associated with reductions in body weight, fat mass and insulin resistance even after adjusting for energy intake.

Overall these results highlight the benefits for weight management and metabolic health of a healthy plant-based or vegan diet, which naturally results in reduced calorie intake whilst improving the overall quality of the diet compared to the conventional diet consumed in the US.

DAIRY CONSUMPTION AND PROSTATE CANCER: We have known for a while that there may be is an association between dairy consumption and an increased risk of prostate cancer. This is acknowledged by the World Cancer Research Fund but the strength of evidence is considered weak or limited given that not all studies confirm this association and a dose response is not always apparent. In their summary they state that in general, studies show that 400g (386ml milk) of total dairy consumption per day increases the risk of prostate cancer by around 7%. It has been postulated that it may be the calcium in dairy that causes this increased risk given that there are also data suggesting higher consumption of calcium from all sources increases the risk of prostate cancer. The mechanism may be that higher intakes of calcium down regulates the formation of vitamin D3, which drives cell proliferation. The other proposed mechanism is that higher exposure to the growth factor IGF-1 through dairy consumption is increasing cancer risk.

It is good to have this analysis from the Adventist Health Study-2 cohort in which researchers have assessed the contribution of both dairy consumption and calcium separately, with the inclusion of participants who are vegan and thus do not consume dairy and obtain calcium from alternate sources. The study included 28,737 Seventh-day Adventist men in the United States and Canada, of whom 6389 were of black ethnicity. 11.7% (3370 participants) had very low (≤10 g/d) or no intake (2302 participants) of dairy. In total, 1254 (190 advanced) cases of prostate cancer were diagnosed during an average 7.8 years of follow-up. Participants were analysed in quintiles of dairy consumption with comparisons made between the midpoints of the upper and lower quintiles of dairy consumers (430 versus 20.2 g/d).

The results showed that men consuming 430g/d of dairy compared to those consuming 20.2g/d had a 27% increased risk of developing prostate cancer. The association was similar for advanced and non-advanced cases of cancer, in people of black ethnicity and after excluding vegans from the analysis. The major rise in risk of prostate cancer was seen to occur between the zero intake category and second quintile of the dairy users, with the risk then remaining high but plateauing. Compared to participants consuming zero dairy, those consuming the most had a 60% increased risk. The increased risk was mainly seen with the consumption of milk with no association found for cheese and yogurt. In contrast, higher intakes of non dairy and supplemental calcium did not increase the risk of prostate cancer.

The authors conclude ‘these data from a population with a wide range of dairy and calcium exposure do not clearly support a connection between calcium intake and prostate cancer. However, they do suggest that risk of prostate cancer is causally associated with higher intake of dairy products or some unknown causal factor that is strongly associated with dairy intake’. I think its time to seriously rethink our reliance on dairy for nutrients. We can definitely do better.

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