Observed changes in calculated coronary risk in patients given dietary advice in primary care

BACKGROUND: Dietary advice is usually the first-line treatment for increased blood cholesterol in primary care with a reduction in levels as the expected response. In practice, the diet adopted by the patient may lead to changes in blood lipids characterised by a greater decrease in high-density lipoprotein (HDL) than total cholesterol. The ratio of total cholesterol to HDL cholesterol is an important factor in calculated coronary risk using the Framingham model, from which most risk tables currently in use have been derived. This suggests that either coronary risk may increase after dietary advice or that risk should always be assessed on measurements made before any intervention has taken place. AIM: To report observed changes in blood lipids and calculated coronary risk following dietary advice in primary care. METHOD: Subjects with at least one coronary risk factor and baseline cholesterol above 5.2 mmol/l from an inner-city general practice had cardiovascular risk factors, including fasting lipids, recorded before receiving dietary advice. At follow-up several months later, risk factor measurements were repeated. Ten-year coronary risk was calculated using the Framingham model. Lipid levels and coronary risk at baseline and follow-up were compared. RESULTS: There was a significant decrease in both total cholesterol and HDL cholesterol in both sexes. However, in 56% of subjects, HDL decreased by a greater proportion than the total cholesterol. These subjects showed a highly significant increase in the total cholesterol/HDL cholesterol ratio (median = 0.8 [semi-interquartile range = 1.5], P <0.001, which was correlated with a change in triglycerides (rs = 0.309, P <0.001). In those who had an increase in the total cholesterol/HDL cholesterol ratio, calculated coronary risk increased from 5.45% (13.2) at baseline to 7.25% (15.5) (P <0.001). In all subjects, the change in calculated coronary risk associated with dietary advice ranged from -15% to 15%. CONCLUSIONS: Low fat dietary advice in this primary care setting was frequently associated with undesirable changes in the lipid profile. The majority of subjects showed an increase in the total cholesterol/HDL cholesterol ratio, owing primarily to a decrease in HDL. Consequently, calculated coronary risk increased in over one-half of the subjects. Owing to our incomplete understanding of HDL metabolism, it is unclear whether the fall in HDL is actually detrimental; however, it seems prudent to give dietary advice to patients to avoid excess simple carbohydrate as a fat substitute. This helps avoid a rise in triglycerides, which appears to be associated with an increase in the ratio. These results confirm that coronary risk should always be calculated using measurements made before intervention.