“Eating more nuts and oats – rather than simply avoiding fatty foods – could boost efforts to reduce cholesterol,” the Daily Mail has reported.
The news comes from a six-month trial examining the impact of dietary advice specifically highlighting foods that reduce cholesterol and comparing it against a more traditional course of advice advising people to eat a low-fat diet. The two approaches were tested in 345 people who had high cholesterol levels but were otherwise not considered to be at high risk of cardiovascular disease.
Those who were randomly chosen to receive dietary counselling sessions (which were provided at two different levels of intensity) that focused on known cholesterol-lowering foods (such as soy milk, high protein foods and nuts) managed to reduced their cholesterol levels more than those in the control group advised to follow a low-fat diet. However, people in all three groups – both intensity groups advised to eat cholesterol-lowering foods and the control group – managed to lower their cholesterol, highlighting the fact that following a low-fat diet is still beneficial.
However, less than half of the participants were able to stick to the cholesterol-lowering food advice. This suggests that it takes considerable commitment to significantly change one’s diet. The low compliance level is an important limitation of the trial. It raises questions about how long the change of diet can be sustained in a real-world situation, and therefore how long any cholesterol-lowering benefits could be maintained.
Also, people taking cholesterol-lowering drugs were excluded from the study, so it is not known whether diet could produce the same level of cholesterol reduction in those on medication. Further research will also need to assess whether the reductions in cholesterol seen in this study will translate into reductions in conditions such as heart disease.
Where did the story come from?
The study was carried out by researchers from the Clinical Nutrition and Risk Factor Modification Centre in Toronto, Canada.
The study was primarily funded by the Federal Government of Canada with supplementary funding from industry sponsors, including Loblaw Brands Ltd, Solae and Unilever. The authors state that the industrial sponsors played no role in the design, conduct or analysis of the study. A number of the study’s authors declared being previously employed by or involved with commercial companies involved in selling nuts, oats and other foods, including Kellogg’s and Quaker Oats.
The study was published in the peer-reviewed Journal of the American Medical Association (JAMA).
The Daily Mail generally reported the story accurately. Its coverage included comment from the British Heart Foundation, which said that “people need to be aware that following this type of [diet] plan in the long-term takes commitment. Eating a few nuts or having the odd portion of soya beans won’t make up for an otherwise poor diet”.
What kind of research was this?
The research was a randomised control trial that aimed to assess whether two different courses of advice instructing people to eat a diet high in cholesterol-reducing foods were better at lowering cholesterol than advice that instructed people to stick to a low-fat diet.
Reducing high levels of blood cholesterol levels are known to be important in maintaining a healthy heart and cardiovascular system. One way of achieving this is through eating foods known to have cholesterol-lowering properties, singly or in combination. In this study, researchers wanted to examine whether dietary counselling sessions advising people to follow a diet high in cholesterol-reducing foods (which they termed a “diet portfolio”) were more effective than more traditional dietary advice, which emphasised fibre and whole grains but lacked specific advice on cholesterol-reducing foods.
What did the research involve?
The trial recruited 345 participants with high levels of fat in their blood (hyperlipidaemia) but who were otherwise not considered to be at high risk of cardiovascular disease. The researchers had excluded people with a history of cardiovascular disease, diabetes, or people currently taking lipid-lowering medications.
Participants were randomised to one of three treatment courses lasting six months: dietary advice on following a low-saturated fat diet (control group); a routine-intensity “dietary portfolio” involving dietary counselling that emphasised the consumption of known cholesterol-lowering foods; or a high-intensity dietary portfolio providing the same type of guidance but given over more sessions and in greater detail. The routine dietary portfolio training was given through two clinic visits of 40-60 minutes each. The intensive dietary portfolio was given through seven clinic visits of the same length.
During the six-month intervention period dieticians gave all participants similar counselling, advising them to follow weight–maintaining vegetarian diets using foods available in the supermarkets and health food stores. Further counselling and advice differed depending on which group the participants were randomised into.
- The control group advice focused on consuming low-fat dairy and wholegrain cereals together with fruit and vegetables. It avoided mentioning the foods recommended to the dietary portfolio group.
- The dietary portfolio groups were advised to eat foods high in plant sterols, soy protein, fibre and nuts. Consumption of peas, beans and lentils was also encouraged.
Participants visited a clinic before the intervention, then at week three and then six months after starting the trial. At each visit the participants’ diet over the previous seven-day period was assessed and discussed with a dietician. Body weight and blood pressure were measured and a blood sample taken was obtained to determine blood cholesterol level.
The dietician and participants knew which diet had been assigned, but other researchers and the study’s statistician were blinded to the treatment allocation.
What were the basic results?
The main results of the study are as follows:
- Adherence to the two dietary portfolio interventions was similar - 46.4% in the intensive group and 40.6% in the routine dietary portfolio group.
- Although the interventions were not specifically geared towards weight loss, participants lost a similar amount of weight across all three treatments, ranging from 1.2 to 1.7 kg over the six-month period.
- During the six-month period, participants in the control diet decreased their LDL cholesterol by 8 mg/dl (95% confidence interval [CI] 13 to 3mg/dl). This represented a decrease of 3%, which was a significant decrease from their baseline (start) level.
- Both intervention groups showed significantly larger reductions in LDL cholesterol level compared to the control group, but did not differ significantly from one another.
- Participants assigned the routine portfolio diet had a significantly larger decrease in their LDL cholesterol (24mg/dl; 95% CI 30 to 19mg/dl) compared to the control group. This represented a 13.1% decrease in their LDL cholesterol level.
- A similar level of decrease was seen in the intensive portfolio intervention group (26mg/dl; 95% CI 31 to 21mg/dl), which represented a 13.8% decrease in their LDL cholesterol level.
- Blood pressure did not differ significantly between either of the intervention groups and the control groups.
- The extent to which participants stuck to the dietary advice was significantly associated with the percentage reduction in LDL cholesterol. This suggests that the intervention was the cause of the reduction.
How did the researchers interpret the results?
The researchers interpreted their results as showing the “cholesterol lowering potential of a dietary intervention that counsels participants to increase consumption of cholesterol-lowering foods”.
They say that the reductions in LDL cholesterol levels seen in their study were approximately half those observed in early trials of statin drugs – the main drugs currently used to lower cholesterol levels.
They state that further study is needed to determine whether cholesterol reduction using this dietary intervention is associated with lower rates of cardiovascular disease.
This study demonstrates that giving people counselling about eating a diet high in cholesterol-reducing foods can lead to significant reductions in LDL cholesterol after the six-month follow-up. However, people in the control group who were only given standard advice to avoid foods high in saturated fats decreased their cholesterol level, so following a low-fat diet was still seen to be beneficial.
A strength of this trial is that the participants selected the diets for themselves in a real-world situation, based on the advice they were given. Adopting a flexible, participant-determined approach makes the trial more realistic than other trials which provide participants a set diet and ensure that they eat little else.
The following points need to be considered when interpreting these results:
- Less than half of those advised to incorporate low-cholesterol foods were able to adhere to the diets. The low compliance level is a limitation of the trial. It suggests that the diet is relatively hard to stick to. Hence, it may be difficult to maintain the diet for longer than six months and maintain the reduced cholesterol levels.
- Other factors that influence cholesterol level were not measured, including physical activity level. This could have influenced the level of cholesterol reduction due to the dietary intervention.
- Participants on cholesterol-lowering drugs were excluded from the study. Therefore it is not known whether the same level of cholesterol reduction would be seen in people currently being treated. Also, the effectiveness of dietary change cannot be compared to that of cholesterol-lowering medications based on this particular study.
Further study will be needed to assess whether the reductions in cholesterol level seen in this study will lead to reductions in the level of cardiovascular disease, or other disease, in these participants.