Does it work? Can almonds reduce cholesterol levels?

BACKGROUND:Cardiovascular disease remains a leading cause of death in Ireland and around the world. Diet plays an important role in preventing and treating cardiovascular disease.

Various dietary changes and food supplements are now recommended because of their impact on cholesterol lipid levels. Epidemiological studies survey people’s dietary and lifestyle habits and make correlations with various health indicators. Several such studies have found a connection between the level of nut consumption and risk of heart disease. This risk is primarily estimated using blood cholesterol levels.

Cholesterol levels can be measured in different ways because of how cholesterol connects itself to other components in the blood. Total cholesterol is measured, as well as two other types of cholesterol. These are high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C). Higher LDL-C levels put people at higher risk of heart disease, while higher HDL-C lowers this risk. This is why LDL-C is sometimes called “bad cholesterol” and HDL-C, “good cholesterol”. Interventions that lower LDL-C or increase HDL-C are seen as beneficial.

The almond tree is native to the Middle East, but now grows all along the Mediterranean. California is the leading commercial producer of almonds. Almonds have long been eaten raw or combined in various dishes. Almonds are about 50 per cent oil (consisting of various fatty acids), which can be extracted to make almond oil or butter. The nuts contain numerous other nutrients which have led to much recent interest in their potential health benefits.

EVIDENCE FROM STUDIES

Several randomised controlled studies have been conducted with almonds and most show a beneficial effect on cholesterol levels. For example, in one study eating 37g per day of almonds led to a 3 per cent reduction in total cholesterol levels and 4 per cent reduction in LDL-C. In the same study, eating 70g per day of almonds led to approximately twice the reductions in the two cholesterol levels. Other studies have shown that almonds provide additional cholesterol-lowering effects when combined with heart-healthy diets.

Interest in almonds arose initially because of their fatty acid content. They, like many nuts, contain unsaturated fatty acids. Dietary approaches to cholesterol reduction have emphasised replacement of saturated fatty acids (such as from animal foods) with unsaturated fatty acids.

When such replacements were carried out in studies, the reduction in cholesterol levels was about 25 per cent greater than expected. This suggested that almonds have cholesterol-lowering benefits beyond those of fatty acids. This has led to an examination of other components in almonds that might help reduce cholesterol.

Almonds contain a number of compounds called phytosterols, with 100g of almonds containing about 120mg phytosterols. These compounds are known to increase excretion of cholesterol from the body and slow absorption of dietary cholesterol. Almonds are also excellent sources of dietary fibre, having one of the highest proportions of fibre per gram. Increased fibre in the diet reduces risk of heart disease.

PROBLEMATIC ASPECTS

Adverse reactions to almonds are very rare. However, while almonds are high in fibre and unsaturated fatty acids, they are also very high in calories. This must be taken into account when adding almonds to the diet as weight gain would increase the risk of heart disease.

RECOMMENDATIONS

Because of this evidence, the US Food and Drug Administration permits “qualified health claims” about nuts, including almonds. Such claims are somewhat tentative because the studies conducted have had limitations. Packages may state that eating 1.5 ounces (about 40g) per day of nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease.

Earlier in 2011, the European Food Safety Authority did not allow health claims related to nuts, including almonds. However, the main reason for this decision was because the evidence presented was for several different nuts, not individual ones.

From the studies published to date on almonds, there is some evidence of a beneficial effect on cholesterol levels. A regular portion of almonds would be good to include in a heart-healthy diet – so long as their impact on overall calorie intake is taken into account.

Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University