How do soy foods lower cholesterol?

Scientists have already identified several factors, which may be responsible for soy's heart health benefits.

Soy Protein

The evidence highlighting soy protein as an effective cholesterol-lowering agent is extensive. Numerous studies have been conducted showing that, on average, soy protein lowers LDL cholesterol by approximately 5.0% ⁷ . The actual reduction in individuals may depend on factors such as the amount of soy protein consumed, how highly processed it is and whether it is distributed throughout the day rather than being taken on a single daily occasion ¹¹ .

Isoflavones

Soy is a naturally rich source of these phytonutrients, which are virtually absent from typical western diets. Research strongly suggests that isoflavones, in their naturally occurring combination with soy protein, play a critical role in the ability of soy foods to lower blood cholesterol levels.

A study by Dr. J Robin Crouse ¹² at Wake Forest University, USA, showed that the higher the amount of naturally present isoflavones in soy protein, the greater the cholesterol lowering ability of soy. If the isoflavones were removed from the soy protein or at very low levels, no reduction in cholesterol was observed. Many other studies have shown that soy protein and isoflavones are important components in soy foods that lower cholesterol.

Interestingly, Professor Ken Setchell and colleagues from Italy showed that consuming isoflavones in the form of an isoflavone-enriched pasta (providing 33mg per day), was effective in reducing total and LDL cholesterol, as well as markers of inflammation in people with elevated cholesterol levels. The authors' speculated that the effectiveness of the isoflavones in lowering blood cholesterol in this case may have related to the pasta being able to provide a special 'food environment' to enable the isoflavones to be more bioavailable and more readily converted to the isoflavone equol. (See 'A potential role for equol') ¹³ .

However, it is clear that isoflavone supplements on their own are not the answer for cholesterol lowering. Australian research published by Dr. Leon Simons and colleagues ¹⁴ from St. Vincent's Hospital in Sydney confirms the findings of several other studies showing soy isoflavones cannot bring about a reduction in cholesterol when consumed alone i.e. as a supplement or pill.

A potential role for equol

Equol is a type of isoflavone that is not present in soy foods, but made in the body by some people after soy foods are consumed. Exciting evidence is emerging for the potential role of equol - a more potent isoflavone - in promoting enhanced health effects, including for heart disease.

Studies have shown that daidzein (one of the isoflavones present in soy foods) is converted to equol by bacteria that live in the large intestine of some people. Not all individuals can produce equol ¹⁵ . The search is on for factors that might switch on equol production.

Many studies are now testing for equol and the results, in some cases, are showing that equol producers experience greater health effects than non-equol producers ¹⁵ .