Review of the week’s plant-based nutrition news 15th May 2022
This week I cover protein source and risk of gestational diabetes, impact of a low-fat vegan diet on metabolic health, diet pattern and risk of diabetes, healthy lifestyles and Alzheimer’s and a new study on meat-free diets for children.
PROTEIN SOURCE AND GESTATIONAL DIABETES (GD): GD shares all the same risk factors as type 2 diabetes and is driven by underlying insulin resistance. The condition is associated with a higher risk of adverse outcomes for mother and baby and in the longer term, a significantly increased risk of developing cardiovascular disease and type 2 diabetes. Healthy diet patterns are known to reduce the risk of GD. This cross-sectional study is the first to assess the impact of dietary protein source on the risk of GD in pregnant women in China, a country where there is a rising incidence of the condition.
The study included 1014 Chinese women of whom 191 developed GD on the basis of a oral glucose tolerance test. Based on dietary questionnaires, the results showed that higher total protein and animal protein intake was associated with a 5–6 fold increase in the risk of GD. Women were further divided into three dietary protein patterns, namely, white meat, plant-dairy-eggs, and red meat protein patterns. A red meat and white meat protein pattern was associated with approximately 80% increase in the risk of GD compared to a plant protein pattern. These associations persisted even after adjusting for body weight, family history, energy intake and physical activity. Based on these results, the authors conclude ‘Pregnant women should follow a balanced diet and avoid excessive consumption of meat-based protein’.
Meat-based diets are also known to increase the risk of diabetes outside of pregnancy. A number of reasons could explain this risk, including the packaging of animal protein with saturated fat and haem iron and also the higher amounts of branched chain amino acids. All these compounds have been shown to increase insulin resistance. In addition, meat-based diets are associated with a higher body weight and negatively impacts the gut microbiome, which is crucial for glucose regulation.
The results are consistent with several previous studies showing increased GD risk with higher intake of animal protein and meat. Results of a previous prospective cohort study from China found that a plant-based dietary pattern as defined by the plant-based dietary index significantly reduced the risk of GD such that the authors of the study concluded ‘adopting a plant-based diet during pregnancy could reduce GD risk among Chinese women, which may be valuable for dietary counselling during pregnancy’.
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.
DIET, OBESITY AND TYPE 2 DIABETES: The results of this study may come as a bit of a surprise given that vegetarian and vegan diets have in general been associated with a lower risk of developing type 2 diabetes, in part due to a healthier body weight. This paper analysed data from 203,790 participants of the UK Biobank (mean age 55.2 years). Based on dietary information participants were categorized as vegetarians (n=3,237), fish eaters (n=4,405), fish & poultry eaters (n=2,217), meat eaters (n=178,004) and varied diet (participants who reported that their diets varied often n=15,927). Vegans were excluded from the analysis as there were only 57 identified.
The headline results were that after a median follow up of 5.4 years and after adjusting for other lifestyle factors (such as physical activity and smoking), fish eaters, and fish and poultry eaters had a lower risk of type 2 diabetes, in the order of 30–50% reduction, compared with meat eaters. There was no association with a vegetarian diet. Varied diet was associated with a higher risk of type 2 diabetes. Obesity partially mediated the association of fish (30.6%), fish and poultry (49.8%) and varied (55.2%) diets.
There are some reasons why vegetarians in this cohort do not have a reduced risk of type 2 diabetes. As expected from the UK, there was a higher proportion of South Asians in the vegetarian group (15.1% vs <5% in other diet patterns) who have a higher risk of type 2 diabetes than Caucasians. When you look more closely at the diet of the vegetarian group they were consuming a median of 5 portions of fruit and vegetables a day (which includes legumes as well), 25% of energy was from sugar, 12.1% from saturated fat (same as the meat and fish eating groups) and fibre consumption was 20.7 grams per day. 49.7% of the vegetarian group had a BMI >25. Thus, the only conclusion that can be reached is that these vegetarians, as is typical in the UK, were consuming a highly processed diet, low in whole plant foods and high in refined grains. Sadly, the diet pattern of South Asians in the UK reflects this way of eating too and we are also aware of the fact that the risk of diabetes in Asian population increases at lower BMI levels when compared to Caucasians given their lower ‘fat tolerance’ and propensity to lay down visceral fat.
I personally don’t think this study really tells us much about the impact of a vegetarian diet on the risk of type 2 diabetes and highlights that diet quality is key if we want to harness the power of plant-based diets. Prior studies have shown that consuming an unhealthy plant-based diet high in refined carbohydrates and processed foods is worse for diabetes risk than a meat-based diet. It’s odd that the authors do not discuss these caveats to their results.
HEALTH AND NUTRITION OF VEGETARIAN CHILDREN: It’s always useful to see papers on health outcomes of vegetarian children, given the relative paucity of data. This study included 8907 children from Canada aged 6 months to 8 years. Parents reported whether their child was consuming a vegetarian diet or not. Vegans were included in the vegetarian group and in total 248 vegetarian children were identified of which only 25 were vegan. The main outcome measure was the impact of diet on zBMI, which is calculated on the basis of World Health Organization growth standards, adjusted for sex and age. Secondary outcomes included height and weight and serum biomarkers such as iron, vitamin D and lipid profile.
After an average follow up of 2.8 years, the results showed that vegetarian children were more likely to be breastfed for longer and more likely to be of of Asian ethnicity (West Asian, South Asian, East Asian, and Southeast Asian). There was no association between diet and growth or zBMI, however, there was higher odds of vegetarian children being underweight. The children classified as underweight were more likely to be of Asian origin. Vegetarian children on average were 0.3cm shorter in height than non-vegetarian children but this finding was not statistically significant and is unlikely to be of clinical significance.
There was no impact of diet choice on blood iron or vitamin D levels. However, those children avoiding cow’s milk consumption had lower blood lipid levels that children who were consuming milk, likely due to the lower consumption of saturated fat.
Overall this study is reassuring and suggests vegetarian diets are adequate in childhood. Any differences in growth measurements were very small and unlikely to be of any clinical significance. However, it is certainly not the most robust study. The numbers of vegetarians included are small accounting for only 2.9% of the total study population. We can’t conclude anything about vegan diets as only 25 identified as vegan. The major issue is that we are not provided with dietary information i.e. what are the children actually consuming? Are they meeting their energy requirements?. We do know from previously published data that Canadian children are increasingly consuming a diet of processed and ultra-processed foods and therefore without data on diet quality, it is difficult to draw any firm conclusions about vegetarian and vegan diets.
DIET, LIFESTYLE AND ALZHEIMER’S DEMENTIA (AD): I wrote an article on this topic last week, but it is well worth highlighting once again this important paper published in the BMJ. The paper reports findings from The Chicago Health and Aging Project, a population-based cohort study in the United States, which initially included residents aged 65 years and older from a geographically defined community on the south side of Chicago. This analysis assessed the impact of 5 healthy lifestyle habits on life expectancy and the risk of AD in 2449 men and women aged 65 years and older. A healthy lifestyle score was developed based on five modifiable lifestyle factors: a diet for brain health (Mediterranean-DASH Diet Intervention for Neurodegenerative Delay — MIND diet score), late life cognitive activities, moderate or vigorous physical activity (≥150 min/week), no smoking, and light to moderate alcohol consumption (women 1–15 g/day; men 1–30 g/day). Participants most adherent to a healthy lifestyle had a longer life expectancy and were more likely to spend these extra years without AD.
For example, life expectancy at 65 was 24.2 years for women with the healthiest lifestyles and 21.1 years for those with the least healthy lifestyles. Women with healthier lifestyles spent spent 2.6 years (10.8%) of their remaining years with AD, compared with 4.1 years (19.3%) for the latter. Life expectancy at 65 was 23.1 years for men with the healthiest lifestyles and 17.4 years for those with the least healthy lifestyles. Men with healthier lifestyles spent 1.4 years with AD compared to 2.1 years for men in the least healthy lifestyle group. Thus, the proportion of remaining life spent with dementia was almost halved among participants with the healthiest versus least healthy lifestyles.
Of note, the lifestyle score without including alcohol consumption was also associated with a lower risk of AD and mortality and therefore the advice remains that people who do not consume alcohol should not be encouraged to do so.
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