Studies prove the benefits of nuts
There is now a number of extensive evidence from a number of large population studies that nut consumption is protective against Cardiovascular Disease.
The Adventist Health Study, published in 1992, was the first to generate interest in nut consumption and coronary heart disease (CHD), showing that eating 1 ounce (28g) of nuts five or more times per week could halve the risk of both Myocardial Infraction (heart attack) and death from CHD.
While there was some question about whether these results could apply to other populations (due to the large number of vegetarians and frequent nut consumers in this study), other studies looking at nut consumption in a variety of groups has confirmed these findings.
Both the Nurses’ Health Study and the Physicians’s Health Study found a relationship between nut consumption and fatal CHD. The most frequent nut consumers in these studies had a 30-40% lower risk of dying from CHD.
The Physicians’ Health Study found the greatest benefit for the prevention of sudden cardiac death, which was almost halved in those who had the highest nut intake.
The Iowa Women’s Health Study reported a 19% reduction in risk of death from CHD in those who consumed two or more servings (57g or more) of nuts per week compared to those who ate nuts less than once a month.In a more recent follow-up of only postmenopausal women who were free of diabetes or heart disease 15 years earlier, they found strong and consistent reductions in death attributed to CVD and CHD with increasing intake of nuts and peanut butter.
Those consuming nuts plus peanut butter (28.5g of nuts or 1 tablespoon of peanut butter) 5 or more times per week had almost a 30% reduction in risk of death from both CVD and CHD.
Clinical Studies
A large number of clinical studies have been conducted looking at the beneficial effects of nuts on cardiovascular risk factors, in particular blood fats.
The results of a number of these studies are summarised in two recent reviews, showing that the regular inclusion of nuts in the diet can lower both total and LDL cholesterol.
Despite many different study designs, diverse population groups, variations in the length of the studies and the quantity of nuts consumed, the research has consistently shown that the inclusion of nuts in a diet low in saturated fat and cholesterol has benefits on blood fats when compared to a low fat or typical Western diet.
Studies have also looked at the effects of nut consumption on oxidative stress, a key factor in atherosclerosis, and endothelial function – the health of blood vessel walls.
The effect of nut consumption on blood fat profiles
A raised blood LDL cholesterol level is a risk factor for heart disease. A recent review of 25 studies found that diets containing nuts reduce LDL cholesterol by 3-19% compared with Western and lower fat diets.
An earlier review found that the cholesterol reduction observed in clinical studies of nuts is about 25% greater than would be expected based on blood cholesterol predictive calculations so the effect of nuts is greater than expected.
A number of these studies have also demonstrated an increase in HDL (good) cholesterol. The quantity of nuts consumed ranged between 40 and 100g per day.
Studies of almonds and walnuts have had the most research to date, clinical studies have also shown benefits for other nuts, including hazelnuts, macadamias, pecans and pistachios. The result of these studies suggest that all types of nuts are likely to benefit heart health.
The effect of nut consumption on oxidative stress
Oxidation of LDL cholesterol is a key step in atherosclerosis – the blocking and hardening of arteries. One study found a significant reduction in oxidised LDL following the consumption of almonds (providing 22.2% of total energy, average 73g almonds/day) for one month.
While a traditional Mediterranean diet, including nuts (30g of almonds, hazelnuts and walnuts per day) was found to reduce oxidised LDL over three months, the findings did not reach significance.
Other studies, however, have failed to show such an effect suggesting that further research is needed. Nuts contain a range of antioxidants including vitamin E, selenium, copper and zinc among others, with almond skins being found to contain about 30 different antioxidant compounds.
An experimental feeding study found a reduction in protein thiol concentration (a maker of oxidative stress) following a meal containing 60g of almonds.
Another study using macadamias found a reduction in markers of oxidative stress following the consumption of 40-90g/day of macadamias (15% of total energy) for four weeks.
The effect of nut consumption on endothelial function
Endothelial dysfunction of the normal biochemical process carried out by the endothelium (cells lining the inner surface of blood vessels) is believed to be a key event in the development of atherosclerosis and is associated with an increased risk of stroke and heart attack.
Nuts may influence endothelial function in a number of ways, including nitric oxide production, endothelin-1 production and involvement in cell adhesion and inflammatory processes.
One study found that consumption of 40-65g of walnuts as part of a low fat, plant-based diet significantly improved endothelium-dependant vasodilation (relaxation of blood vessel walls) and reduced levels of vascular cell adhesion molecule-1, or VCAM-1 (a human gene which is thought to play a role in the development of atherosclerosis).
Another study observed improvements in flow-mediated dilation (a measure of endothelial function) with the addition of walnuts to a high fat favourably improved markers of blood clotting and inflammation. Nuts are a good source of arginine, the precursor of nitric oxide, which causes relaxation of blood vessels walls and may partly explain their benefits on endothelial function.
The effect of nut consumption on postprandial glycemia
Postprandial glycemia (high blood glucose levels following a meal) are now recognised as an important risk factor for CVD and a meta-analysis of 38 studies found a positive relationship between postprandial glycemia and cardiovascular disease risk, even in the normal range (below the level at which diabetes is diagnosed).
One study has found that the addition of almonds to a meal and that these changes were associated with less markers of oxidative damage. Unlike other nuts chestnuts contain low glycaemic index carbohydrates, which also help control blood glucose levels.
These provide other possible mechanisms by which nuts may reduce the risk of CHD.
The effects of nut consumption within a cholesterol lowering diet
While diets containing nuts have been clearly shown to reduce blood cholesteroi levels, maximums dietary cholesterol reductions are likely to be achieved as part of a whole diet approach.
Jenkins and colleagues (2003,2005) found that a vegetarian diet, very low in saturated fat and cholesterol and high in plant sterols, soy protein, soluble fibre and almonds (14g/1000kcals) reduced LDL cholesterol by about 30%, similar to that seen with low dose cholesterol lowering statin drugs (20mg/day).
Nuts in a healthy diet
Nuts not only offer many healthy benefits, but also provide flavour, texture and variety to any healthy eating plan.
Here are 10 ways to incorporate nuts into your healthy diet:
- Sprinkle chopped almonds and walnuts on breakfast cereals or muesli.
- Use a pure nut spread (e.g. almond or brazil nut spread) on toast in place of a butter or margarine.
- Toss some macadamias or pine nuts into a salad.
- Make pesto for pasta using pistachios or pine nuts ground up with fresh basil, garlic and olive oil.
- Add cashew nuts to stir-fries.
- Make a crust for fish by combining breadcrumbs with crushed macadamias or pistachios.
- Mix chopped hazelnuts or pecans in muffins or cakes
- Add extra crunch to dips with macadamias or walnut pieces.
- Use roasted chestnuts in place of potato at evening meals.
- Snacks on a handful of mixed nuts.
