plant protein dec cardiovasc and all-cause mortality

 A meta-analysis found decreased cardiovascular and all-cause mortality with increased consumption of plant-based protein (see diet high plant protein dec CV and total mortal bmj2020 in dropbox, or doi.org/10.1136 bmj.m2412 

 

Details: 

-- 31 prospective cohort studies with 715,128 participants were included in a meta-analysis, with follow-up period of 3.5 to 32 years 

-- age ranged from 19 to 101 years 

-- 11 publications used dietary records or recalls, 19 used a food frequency questionnaire. A few studies measured urinary urea nitrogen levels to estimate total protein intake 

-- almost all studies used only baseline data of protein intake in their analysis and then reported on future outcomes

-- total of 113,039 deaths (16,429 from cardiovascular disease and 22,303 from cancer) 

 

Results: 

-- total protein intake (plant and animal) was associated with: 

    -- all-cause mortality: lower risk by 6%, with pooled effect size of 0.94 (0.89-0.99), p=0.02; 180,003 participants, 72,261 deaths 

    -- cardiovascular disease: no significant difference

    -- cancer mortality: no significant difference 

-- animal-based protein intake is associated with: 

    -- all-cause mortality: no significant difference, pooled effect size 1.00 (0.94 -1.05); 304,100 participants, 60,495 deaths 

        -- some of the studies found increased all-cause mortality

    -- cardiovascular mortality: no significant difference; 427,005 participants, 15,518 deaths 

-- plant protein intake is associated with: 

    -- all-cause mortality: lower risk by 8%, with pooled effect size of 0.92 (0.87-0.97), p=0.003; 139,399 participants, 95,892 deaths 

    -- cardiovascular disease mortality: lower risk by 12%, with pooled effect size of 0.88 (0.80-0.96), p=0.001; 425,781 participants and 14,021 deaths 

    -- cancer mortality: no significant difference; 292,629 participants, 22,118 deaths 

--plant protein intake had a dose-response effect: each additional 3% of energy from plant proteins a day was associated with the 5% lower risk of all-cause mortality 

-- the inverse association between plant protein intake and all-cause as well as cardiovascular mortality remained significant in those studies controlled for energy, BMI, and macronutrient intake, as well as in studies with follow-up less than 15 years 

 

Commentary: 

-- there has been a growing awareness that a high protein diet may be important for its positive effects on weight loss, preservation of muscle mass, and increased strength 

    -- a literature review suggested that 1.2 to 1.6 g of protein per kilogram per day (or, meal-specific protein quantities of at least 25 to 30 g per meal) decreased appetite, was associated with weight loss, and improved cardiometabolic risk factors, both in diabetics and nondiabetics. One analysis, for example, found protein-based improvement in increasing satiety, weight loss, fat mass loss, and the preservation of lean mass (Clifton PM. Long-term effects of a high-protein weight-loss diet. Am J Clin Nutr 2008;87:23–9). high-protein diets are associated with improved blood glucose and blood pressure levels

--there are several potential mechanisms by which meat-based protein is less healthy than nonmeat protein: 

    -- there are increased insulin-like growth factor 1 levels (associated with cancers) in those consuming animal protein but not plant protein 

    -- substitution of nonmeat proteins for meat-based proteins has been associated with improvements in fasting insulin levels and reduced insulin resistance in 489 overweight or obese participants in 8 European countries (see https://www.mdpi.com/2072-6643/9/12/1326/htm ). This was specifically true for higher plant protein from non-cereal products 

    --studies have also found that plant proteins have antioxidative, anti-inflammatory, antihypertensive, and antimicrobial activities, and lower cholesterol levels (some studies have found plant-based protein decreases LDL levels vs animal-based protein : eg see diet protein plant vs animal jnutr2017 in dropbox or doi:10.3945/jn.116.239574 )

 

Limitations of the study: 

-- as a meta-analysis, it is combining several very different studies with different patient populations and different criteria for inclusion as well as measured outcomes, thereby limiting generalizability of the results 

-- these are all observational studies, and we really need RCTs to establish causality in these outcomes 

-- increasing protein leads to other associated changes in the diet, such as decreasing carbohydrates. It is difficult to know what the appropriate attribution of the high protein diet itself is for outcomes (ie, these studies were not RCTs where people had protein vs placebo supplements, maintaining their regular diets) 

-- almost all the studies used only initial dietary intake: especially for studies lasting for years, the diet could change over time and distort the results 

-- there is no systematic assessment in these studies of exercise, or the array of psychosocial factors that might affect outcomes. For example, there are significant differences between foods eaten across socioeconomic classes as well as by people from different cultures, but there are also many other differences in these groups (stress, living conditions, etc); so only looking at foods consumed may completely miss out on other very important health-related factors

-- there may be systematic differences in those people choosing plant- vs animal-based protein: are those who are more vegetarian in their diets also doing other things that are likely more healthful (and it is really these other things that produce the better health outcomes??)

-- there is also no information about other aspects of the diet other than reported protein content, and many macronutrients or micronutrients might also affect the results. In fact, animal meat contains fat, sodium, iron, and B vitamins, so it is hard to isolate the specific contribution of the protein itself 

-- there is no assessment of the ancillaries associated with the different proteins: eg the use of hormones or antibiotics in raising future consumable animal-based protein; of the use of pesticides or fertilizers for future consumable plant-based protein

-- there was no differentiation of types of meat protein: it may well be that fish-based protein is healthier than that from red meat (eg see http://gmodestmedblogs.blogspot.com/2014/04/soluble-fiber-microbiome-and-asthma.html ), which documents the likely very harmful effects of red meat consumption on heart disease)

-- it is also possible that different cooking or processing methods are associated with different health outcomes 

-- and, one specific concern in observational nutrition studies is reductionism: it is likely erroneous to consider single nutrients by themselves and draw conclusions based on that, since there is likely a strong interplay between the different components of diet on health  

 

So, this study adds to a pretty consistent literature that plant-based protein is overall healthier, with a clear caveat that these are observational studies with very large risk for bias, including many potential unassessed confounders (the litany of limitations noted above make it very hard to draw definitive conclusions)

-- a huge plus of this meta-analysis is that it reveals pretty consistent results across the different studies, despite their different methodologies, and that a large number of people were involved and followed for a long time

-- and, the smaller studies noted above assessing the likely mechanisms of benefit from plant-based protein are impressive and add to the likely health benefits of these diets

 

--so, based on this analysis, it appears that switching from animal-based to plant-based protein might be associated with increased longevity...

geoff

 

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