Review of the week’s plant-based nutrition news 27th November 2022
This week I bust some myths about nut consumption. Despite the well documented health benefits, there remains a lot of confusion amongst health professionals and in general, most people in the UK and globally are not consuming enough.
We have decades worth of data supporting the consumption of nuts as part of a healthy diet pattern. Nuts are full of healthy nutrients, being an excellent source of protein, unsaturated fats, fibre, tocopherols (vitamin E family of compounds), folic acid, vitamin B6, calcium, magnesium, copper, zinc, selenium, phosphorus, arginine, potassium, niacin, phytosterols and polyphenols. The most robust data support nut consumption for heart health but studies also report benefits for prevention and treatment of type 2 diabetes, cancer, weight management and more.
Nut consumption came to fame back in the early 90's with the publication of two studies from Loma Linda University. The first was from the Adventist Health Study, which included 31,2018 participants and showed that participants consuming nuts more than four times per week, when compared to those eating nuts less than once per week, had a 51% reduced risk of having a heart attack and a 48% reduction in risk of dying from heart disease. The second, a small, randomised study in 18 men who were either assigned to a standard healthy diet or one that included walnuts as 20% of energy (replacing fatty foods, meat and added fats) demonstrated a significant reduction in blood cholesterol levels in the walnut group 2. Since then, the number of studies and publications on the impact of nut consumption have risen exponentially. The findings are incredibly consistent, with the consumption of around 30g of nuts on most days of the weeks associated with a significant reduction in the risk of developing cardiovascular disease (CVD) and dying from it.
Not only are their benefits for individual health, the farming and production of nuts are associated with some of the lowest greenhouse gas emissions when compared to other food groups and producers can even be carbon negative due to the ability of nut trees to capture carbon. Thus swapping animal sources of protein for nuts is a great way to reduce your personal carbon food print
Despite these wide ranging benefits, nut consumption in the UK, according to the Global Nutrition Report, is on average 5.4g per day with only 0.34% of the population meeting recommendations to consume 30–40g per day. It is astonishing to consider that studies have suggested that an increased intake of nuts to ≥20 g/d could prevent 4.4 million deaths annually in North and South America, Europe, Southeast Asia, and the Western Pacific combined.
There is often criticism that studies on nut consumption are usually funded by the nut industry. This is true, but we need to find a way of assessing these studies, addressing any potential bias and then using the information to inform clinical practice. Without going into detail, the data on nut consumption is very consistent, be it observational or interventional studies. Inclusion in the diet, especially in place of animal-based foods, is beneficial to health with improvements in cardiovascular biomarkers, reduction in cardiovascular events and possible benefits for cancer prevention.
NUT CONSUMPTION LOWERS TOTAL AND LDL-CHOLESTEROL: The Portfolio diet or Dietary Portfolio was developed by Dr David Jenkins from the University of Toronto and nuts are a key component. It is a plant-based dietary pattern that was first devised in the early 2000s as a “portfolio” of 4 cholesterol-lowering plant foods, each of which has a Food and Drug Administration (FDA), Health Canada, and/or European Food Safety Authority (EFSA) approved health claim for cholesterol-lowering or cardiovascular disease risk reduction. The four core food components of the Portfolio dietary pattern include (based on a 2000 kcal diet): 42g nuts (tree nuts or peanuts); 50g plant protein from soya products or dietary pulses such as beans, peas, chickpeas, and lentils; 20 g viscous soluble fibre from oats, barley, psyllium, eggplant, okra, apples, oranges, or berries; and 2g plant sterols initially provided in a plant sterol-enriched margarine. An enhanced Portfolio dietary pattern has also been studied in which monounsaturated fat (MUFA) replaces carbohydrate (13% replacement providing 26% energy from MUFA) and is added to the other 4 components.
The original studies demonstrated that this dietary portfolio could lower LDL-cholesterol by around 30%, similar to the reduction achieved with the first generation statin lovastatin, whilst also reducing inflammation (C-reactive protein). The original studies provided food to participants and thus were able to ensure adherence. In free living individuals the reduction in LDL-cholesterol is less, around 15%, but still very much worthwhile.
In the study highlighted, seven randomised controlled studies of more than 3 weeks duration were included. There were 437 participants with hyperlipidaemia who adopted the portfolio dietary pattern on a background of a National Cholesterol Education Program (NCEP) Step II diet. The results showed with a high level of certainty that the portfolio dietary pattern in combination with the NCEP diet reduced LDL-cholesterol by an average of 17% whilst also showing a benefit for other CVD risk factors such as blood pressure, CRP, total cholesterol, triglycerides and apolipoprotein B. This resulted in a significant reduction in the estimated 10-year coronary heart disease (CHD) risk, compared with an NCEP Step 2 diet alone. It is expected that for every 1.0 mmol/L reduction in LDL-cholesterol there is an ~20% reduction in major cardiovascular events.
There is no doubt that regular consumption of nuts can have a cholesterol-lowering effect. Check out this great factsheet from Heart UK on maximising your vegan diet to lower cholesterol.
NUTS AND BODY WEIGHT: There has always been an assumption that the consumption of nuts contributes to weight grain given the high fat (40–70% fat) content and hence higher energy density. However, clinical studies do not support this assumption. The current systematic review and meta-analysis strengthens the evidence for a lack of association.
This analysis included data from 6 prospective cohort studies and 86 randomised controlled studies (RCTs) and assessed the association of nut consumption with global and abdominal measures of obesity. The prospective cohort studies were from USA and Europe, included participants with a median age of 48 years, with a median follow up of 18 years. The median nut intake in the highest quintile of intake was 7g/day ranging from 3 to 28 or more g/day. The RCTs were mainly from USA and included predominantly participants who were overweight or obese. These RCTs examined a wide range of different nuts with a median dose of 45.5g per day (range 5–100g) and a median follow up of 8 weeks.
The results showed that nut consumption was associated with a decrease in the risk of overweight or obesity (7% reduction) and higher nut consumption was associated with weight loss and reduced risk of weight gain. Nut consumption was also associated with a lower risk of elevated waist circumference. Measures of adiposity were lower with doses of >45.5g per day with a dose-response relationship between nut consumption and lower body weight and body fat. For body mass index, waist circumference, and waist-to-hip ratio, the maximum protective dose appeared to be around 50 g/day.
These results are in line with those from prior meta-analyses. There are a number of reasons why despite the high energy density, nut consumption is not associated with weight gain. These included the high mono- and polyunsaturated fat content which may have a greater thermic effect compared to saturated fat, the satiating effect of protein and fibre and the physical structure of nuts such that not all the fat is absorbed. Based on these data, a daily 40–45g portion of nuts per day would be a good addition to global diets, which are in general quite low in nut consumption, at around 16g per day, mostly from peanuts. The authors conclude ‘Current evidence demonstrates the concern that nut consumption contributes to increased adiposity appears unwarranted’.
Just this week a new paper further supports the evidence discussed. In a randomised study of 140 adults, a snack of 30–50 grams of almonds lowered their energy intake by 300 kilojoules at the subsequent meal. This was associated with beneficial changes in appetite regulating hormones.
NUT CONSUMPTION AND HYPERTENSION: High blood pressure, or hypertension, is a leading risk factor for disease and disability globally. Diet and lifestyle factors are key drivers of hypertension. Once again, nut consumption can reduce the risk of developing the condition. In this large prospective study of 10,347 adults from Korea, 2047 participants developed hypertension during the 4.3 years of follow-up. Nut consumption was low at around 0.3-.0.4 servings/week. The results showed that higher average nut consumption of at least 15 g per week, was significantly associated with a 26–28% lower risk of hypertension in both men and women, irrespective of potential confounders. The exact mechanism by which this may occur is not clear, but it is thought to be due to the positive impact that nuts have on vascular endothelial health and functioning.
Prior data support these findings. A meta-analysis of prospective studies from 2014 showed that 1 serving (28 g) of nuts per day was associated with a 34% lower risk of hypertension.
NUT CONSUMPTION AND IMPACT ON HEALTH OUTCOMES: So far I have discussed the impact of nut consumption on risk factors for cardiovascular disease, including body weight, blood pressure and blood lipids. This huge study examined the impact on a range of health outcomes and confirms a wide range of health benefits
The study extracted evidence from 89 articles on the consumption of nuts and relevant health outcomes, including 23 articles with meta-analysis on disease and mortality, 66 articles on biomarkers for disease, and 9 articles on allergy/adverse outcomes. The results showed that nut consumption was associated with reduced risk of cardiovascular diseases and related risk factors. For example, an intake of 28 g/day compared with not eating nuts was associated with a 21% reduction in cardiovascular disease (including coronary heart disease incidence and mortality, atrial fibrillation, and stroke mortality), an 11% risk reduction of cancer deaths, and 22% reduction in all-cause mortality. Nut consumption was also inversely associated with mortality from respiratory diseases, infectious diseases, and diabetes; however, associations between nut consumption and diabetes incidence were mixed.
Dose–response analysis suggested optimal intake levels of 15–40 g/d with generally limited benefits in increasing intake beyond 28 g/day. Allergy and adverse reactions to nuts were observed in only 1–2% of adult populations. The authors conclude that ‘Overall, the current evidence supports dietary recommendations to consume a handful of nuts and seeds per day for people without allergies to these foods.
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