Review of the week’s plant-based nutrition news March 28th 2021
This week I cover protein intake and kidney function, ultra-processed foods and cardiovascular disease, the impact of diet and lifestyle on dementia risk and another study on eggs.
DIETARY PROTEIN AND KIDNEY FUNCTION: Protein remains a revered macronutrients, with many trying to increase protein intake in the diet. More is not necessarily better when it comes to health outcomes. Within renal medicine, the data now suggested that high protein diets can worsen the progression of kidney failure and that low protein diets are preferred to slow the decline in kidney fucntion. However, once kidney failure is more severe, protein intakes may need to be more individualised to take account of the increased catabolic rate and potential for protein-energy wasting. We know that in general high protein diet put a strain on the kidneys as evidence by glomerular hyperfiltration, increased urinary albumin secretion and the development and progression of kidney failure. We also know that there are differences between the consumption of plant protein versus animal protein when it comes to kidney health.
This retrospective study examined the association of dietary protein intake with all-cause mortality among 27,604 adults of the NHANES (National Health and Nutrition Examination Study) study in the US between 1999–2010. Participants were also stratified based on their kidney function; GFR <60ml/min vs >60ml/min. The impact of high biological value (HBV), protein consumption which has amino acid compositions similar to human protein (i.e., containing the full spectrum of essential amino acids) and are more likely to be from animal proteins, was also examined.
The results showed that amongst participants with impaired kidney function, high protein intake (>1.4g/kg/d) was associated with a 37% increased risk of death whilst lower intakes (<1g/kg/day) did not impact the risk of death. Protein of HBV in this group was also associated with a 24% increased risk of death. In participants with normal kidney function, high protein intake did not impact the risk of death. Instead, low protein diets (<0.6g/kg/d) increased the risk of death by 18%. Of note, those consuming lower amounts of protein were consuming significantly lower amounts of calories overall (1240 to 1432 k/cal/day), raising the possibility of residual confounding. Physical inactivity also further worsened the risk of death.
The authors state that this is the first study to examine the relation between protein intake and mortality risk among participants with impaired versus normal kidney function. They conclude that the data supports recent recommendations for limiting protein intake in patients with kidney disease, although these have not been widely implemented for fear of protein-energy wasting. In people with normal renal function, we still need to understand the impact of habitual high protein intake, for example in those following an Atkins or Paleo-style diet. This study only recorded diet data at baseline and therefore does not clarify the impact of long-term intake of protein. In addition, this study suggests that protein of HBV i.e. animal protein, is even more detrimental to the kidneys and the authors state ‘our findings suggest that plant-based sources of protein may be more favorable in those with chronic kidney disease’. The authors also discuss the addition benefits of focussing on plant sources of protein including improved lipid profile, better acid-base balance, less production of toxic uraemic compounds, decrease bioavailability of phosphorus, reduced risk of CVD, cancer, hypertension and type 2 diabetes.
More and more data support choosing plant sources of protein over animal sources and there remain an open question about the threshold at which too much protein can cause harm. Here is a great review on why a patient-centered plant-dominant low-protein diet (PLADO) may be best for chronic kidney disease
ULTRAPROCESSED FOOD AND CARDIOVASCULAR DISEASE (CVD): Although we intrinisically know that processed and ultra-processed foods are less healthy than consuming mimimally processed or whole foods, there have not been many studies examining the impact of ultra-processed foods on CVD outcomes.
This new study reports data from the Framingham off-spring cohort, which includes 3003 adults followed for a mean of 20 years. The NOVA classification was used to examine food frequency questionnaires and investigate the impact of ultra-processed food consumption of CVD. On average participants were consuming 7.5 portions of ultra-processed foods/day (range 4–12 servings). Increased intake of ultra-processed foods was associated with worse CVD outcomes. Each serving of ultra-processed foods above 7.5 servings/ day resulted in increased risk of CVD, coronary heart disease, overall CVD and CVD mortality of 7%, 9%, 5%, and 9%, respectively. There was no impact on overall mortality in this study although prior studies have shown a negative impact.
There are a number of reasons why ultra-processed foods have a detrimental effect on health. They tend to be high in salt, sugar and unhealthy fats. Calorie dense yet nutrient poor and low/lacking fibre. They do not provide adequate satiety and lead to overconsumption of calories. They crowd out healthy foods from the diet such as fruits, vegetables, whole grains, beans, nuts and seeds. They contain or produce chemicals on cooking that adversely affect the body including heterocyclic amines, acrylamide, polycyclic aromatic hydrocarbons.
Unfortunately, both processed animal and plant foods have a negative impact on health, so this is a concern for vegans, vegetarians and omnivores alike. We are doing really badly in the UK, with more than 50% of foods consumed being ultra-processed. Check out my short article on ultra-processed foods and the NOVA classification.
LIFESTYLE FACTORS AND BRAIN HEALTH: The rising rate of dementia is a global problem that severely impacts quality of life and consumes vasts amounts of healthcare resource. Around 50 million people globally have dementia yet we know that 30–40% of cases could be prevented or significantly delayed by addressing socioeconomic and lifestyle factors. There are of course some genetic factors that increase the risk of dementia, but this risk can still be reduced by adopted a healthy lifestyle. The ApoE4 allele increases the risk of Alzheimer dementia (AD). Around 25% of the population have one copy of the gene which increases the risk of AD two-fold. 2% of the population have 2 copies of this gene which increases the risk of AD 3–5 fold.
This study examined the impact of healthy lifestyle factors in people with the ApoE4 allele who are part of the Chicago Health and Aging Project (CHAP), a longitudinal, population-based epidemiological study of AD and other health conditions in older adults aged 65 years and older. 3886 people were included in the study. 5 healthy lifestyle factors were assessed; alcohol consumption (1 drink a day for women, 2 for men), physical activity (150 minutes per week), not smoking, overall diet quality (in the top 40% of distribution), cognitively stimulating activities (in the top 40% of distrivution). Diet quality was assessed by calculating the Mediterranean-DASH Diet Intervention for Neurodegenerative Delay (MIND) diet score that summarizes information on 10 brain-healthy food groups (green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, seafood, poultry, olive oil, and wine) and five unhealthy food groups (red meats, butter and stick margarine, cheese, pastries and sweets, and fried/fast food). These healthy lifestyle factors were then correlated with scores relating to cognitive function testing.
1,269 (32.7%) of the cohort carried one or 2 apoE4 alleles. The presence of the apoE allele and lifestyle factors were independently correlated with cognitive decline. ApoE4 carriers were at higher risk of faster cognitive decline but adherence to a healthy lifestyle was associated with a slower cognitive decline during the follow-up. In ApoE4 carriers and non-carriers, a healthy lifestyle was associated with slower cognitive decline. The authors conclude ‘Our study suggests that a healthy lifestyle is associated with a slower cognitive decline in older adults, including individuals with a genetic predisposition for Alzheimer’s dementia’.
A number of studies have now shown similar results. Healthy lifestyle factors reduce the risk of cognitive decline and dementia, even if you have an underlying higher genetic risk. What’s good for prevention of heart disease, type 2 diabetes and cancer is also good for brain health. It’s also never too late to start a healthy lifestyle.
MEAT CONSUMPTION AND DEMENTIA: This study focuses on meat consumption and risk of dementia in almost 500,000 men and women aged 40–69 years (median 56.5 years) at recruitment to the UK biobank study. 23.5% of participants were known to be carriers of the ApoE4 allele. During the 8 years of follow up, 2896 cases of all cause dementia occurred, of which 1006 were ADand 490 were vascular dementia (VD). The impact of processed and unprocessed meat, poultry and total meat consumption was investigated. Overall those consuming the most meat were were more likely to be men, less educated, smokers, and overweight or obese, and had lower intakes of vegetables and fruits and higher intakes of energy, protein, and fat (including saturated fat).
The results showed a significant linear association between consumption of processed red meat and risk of dementia. Each 25g (equivalent to 1 slice of bacon) consumed per day increased the risk by 44%. However, there was a protective effect for the consumption of unprocessed red meat. Carriers of ApoE4 allele had a 3 times increased risk of developing dementia (6 times increase for AD and 5 times for VD) and it was mainly in the ApoE allele group that unprocessed red meat consumption appeared to be protective.
These data appear rather contradictory and at odds with other studies that have shown that all types of red meat adversely impact brain health. It may be that processed red meat is so bad because of the saturated fat, nitrates/nitrites and salt, that consuming unprocessed meat is somehow better. This does not give a green light to red meat consumption as the consistency of data for diets high in animal protein and saturated fat and increased risks of heart disease, type 2 diabetes and certain cancers is undeniable.
International guidelines, including the WHO, recommend a Mediterranean-style diet for prevention of dementia with a focus on consumption of high amounts of minimally processed whole plant foods and limiting red and processed meat and saturated fat in general. Food and nutrients associated with better brain health include leafy green vegetables, berries and diets high in flavonoids and carotenoids (from plant foods!) and low in saturated fat (from animal foods).
THE IMPACT OF EGG CONUSMPTION ON THE RISK OF DEATH: There have been a number of studies on egg consumption and health outcomes recently with data stacking up to suggest eggs are best left off the plate. This study from Italy included 20562 men and women aged 35+ years who were followed for 8.2 years with 838 deaths were documented (including 271 circulatory, 153 cardiovascular disease, and 334 cancer deaths). Mean consumption was 1.8 eggs per week and overall mean dietary cholesterol intake was 322 mg/d. Eggs contributed to 14.6% of total cholesterol intake.
There was a dose-response relationship between increasing egg consumption and adverse health outcomes. Compared to people consuming <1 egg per week, those consuming >4/week had a 50% increased risk of dying from any cause, 75% increased risk fo dying from CVD and 52% increased risk of dying from cancer. Each extra 1 egg per week increased risk of death by 6% and CVD mortality by 10%. Increased risk of death was also observed at lower intakes, namely 2–4 servings per week. Both dietary cholesterol and saturated fat was associated with this increased risk of all-cause and CVD mortality. The association between egg consumption and CVD mortality was much stronger among subjects with hyperlipidaemia and hypertension. The observed associations were independent of other risk factors and the overall dietary quality. The authors conclude that these data should lead to reconsideration of recommendation for egg consumption within dietary guidelines, especially in people with high blood lipids and high blood pressure.
There remains inconsistency in the data on egg consumption and health outcomes. There are many reasons for this, mainly related to the methodologies used in observational studies and industry-related funding bias. In case you missed this article last week, I reported on an excellent review on the topic by Dr David Jenkins and colleagues. Well worth reading.
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