Grains, pulses and heart disease
There are many factors in grains and pulses which suggest that they may prevent the development of heart disease:
Cereal fibre and heart disease - the evidence
Epidemiological studies
The first indication that cereal fibre might lower the risk of heart disease
was reported in 19772. In this study of 337 English men, those who developed
heart disease after
10-20 years, consumed on average 6.7 g of cereal fibre per 1000kcal (less than
7 g cereal fibre/day) whereas those who didn't develop heart disease consumed
on average 8.9 g of dietary fibre from cereals. Interestingly, differences in
the amount of dietary fibre from fruit, vegetables, pulses and nuts consumed
did not seem to indicate who would get heart disease.
Since then, several large studies from around the world have found that consuming 25-30 g of cereal fibre a day reduces the risk of developing heart disease in both men and women.
In 1996 a large study of 43 757 men also found that men consuming the highest amounts of dietary fibre (28.9 g/day) were less likely to get heart disease after six years than those consuming lower levels of dietary fibre (12.4 g/day)3. Called the Health Professionals Follow-Up Study, the authors concluded that high intakes of dietary fibre, particularly from cereal and grain sources, can substantially reduce the risk of heart disease. Cereal fibre lowered the risk of heart disease to a greater extent than fruit and vegetable fibre. Soluble fibre was shown to be more beneficial in reducing risk of heart disease than insoluble fibre.
Another study in 21 930 Finnish men who were all smokers and aged 50-60 years also found that the men with the highest intake of cereal fibre (26.3 g/day) were least likely to develop or die from heart disease compared to those consuming the lowest level of fibre (8.8 g/day) 4. In this group of men, dietary fibre was mainly derived from cereal fibre, particularly rye products which are usually consumed as the whole grain. Again, cereal fibre was more strongly associated with reduced risk of heart disease than vegetable and fruit fibre.
Cereal fibre seems to also protect women against heart disease. In the Nurses'
Health study, the health of 68 782 female nurses has been monitored since 19745.
As in previous studies, the women who consumed the highest amount of cereal
fibre
(7.8 g/day) were less likely to get heart disease after 10 years than women
consuming the least amount of cereal fibre (1.9 g/day). As in other studies,
cereal fibre was more protective than fibre from vegetables and fruits, suggesting
other components, besides dietary fibre, may be involved in protecting against
heart disease.
These studies consistently show that cereal fibre is more protective than dietary fibre from other sources and that more than 8 g/day in women and more than 10 g/day in men of cereal fibre is required to reduce the risk of heart disease.
Randomised controlled trials
There is only one intervention trial investigating the effect of increasing
dietary fibre intake on the risk of developing heart disease6. In this study
of subjects who had recovered from a heart attack, the effect of different types
of dietary advice relating to dietary fibre, fish and fat intake was compared
to no advice. Those advised to increase dietary fibre intake consumed 17 g/day
at the end of two years compared to 9 g/day in the no advice group. However,
increasing dietary fibre intake did not reduce the risk of having another cardiac
event. It is possible that subjects did not consume adequate dietary fibre,
particularly cereal fibre, to detect a protective effect from cereal fibre.
Another possibility is that the protective effect of cereal fibre is greater
in primary prevention (i.e. before the development of the disease) rather
than in secondary prevention (i.e. preventing progression of the disease once
it
is established).
Wholegrain-based foods and heart disease - the evidence
Epidemiological studies
Several large epidemiological studies have investigated the extent to which
consumption of wholegrain foods protect against heart disease.
A study of 34 000 women aged 55-69 years, showed that the risk of dying from heart disease after 9 years was reduced by about one-third in women eating as little as one serve a day of wholegrain foods compared to women who rarely ate wholegrain foods7. The major sources of wholegrain foods for these women were dark bread and breakfast cereals. In contrast, the amount of refined cereal consumed did not seem to influence the risk of dying from heart disease. The authors concluded that there are as yet unidentified dietary factors present in wholegrain foods which together with known factors such as dietary fibre seem to provide protection against the development of heart disease. Overall death rates were lower in women consuming at least one serve of wholegrain foods a day over the 9 years of the study.
The Nurses' Health Study also looked at consumption of whole grains and found lower rates of heart disease after 10 years in the women consuming more than two serves of wholegrain foods a day8. In particular, there were less cases of heart disease in women who consumed 5-6 serves a week of each of wholegrain breakfast cereal (defined as those that contained over 25% wholegrain or bran by weight), brown rice, wheat germ and bran. The most cases of heart disease were reported in those women who almost never ate wholegrain foods. Consumption of refined grain foods such as sweet rolls, cakes, white bread, pasta and rice and refined grain breakfast cereals did not seem to increase the risk of getting heart disease or provide protection.
These studies consistently show that consumption of at least one serving per
day of whole-grain foods such as breakfast cereals, wholegrain breads and brown
rice reduces the risk of developing heart disease. Because it is difficult to
measure whole grain intake, these studies may have underestimated the effect
of wholegrain foods on risk of heart disease. For instance, the dark bread category
may have included refined-grain products such as breads with a tough crust which
may have been wrongly perceived by participants to be wholegrain foods.
Pulses and heart disease
To date, there is little evidence to show that consumption of pulses reduces the risk of coronary heart disease, possibly since pulses are consumed in such small quantities in the populations in which these studies were carried out. Further research is needed to investigate this relationship in more detail.
There is some evidence that chickpeas lower blood cholesterol levels.
References