Diet, exercise and weight loss and dyslipidaemia

There is a large amount of controversy relating dietary fat intake and coronary artery disease. It has been strongly suggested that saturated fat is not harmful and that polyunsaturated fat is either not beneficial or even harmful. Given that dietary lipids and fibre can influence serum lipids which are strongly linked to the risk of coronary artery disease I have reviewed recent evidence linking diet and serum lipids to confirm a diet-heart disease link. Over 84 studies have been included in a recent meta-analysis and meta-regression which examined the effects of changes in fat type on lipid levels. An absolute 1% reduction in saturated fat or trans fat intake as a percentage of energy with replacement by n-6 polyunsaturated fat would lead to a reduction in low density lipoprotein (LDL) cholesterol of 0.05 mmol/L. In most Western countries the difference in intake between the highest quintile and the lowest quintile of saturated fat is about 7%, so moving from the highest to the lowest quintile should lower LDL cholesterol by 0.35 mmol/L or about 10%. This change should lower cardiovascular disease rates by at least 10%. Replacing this amount of saturated fat with carbohydrate of average quality would lower LDL cholesterol by 0.21 mmol/L and increase fasting triglyceride by 0.17 mmol/L. This combination of effects would have a neutral effect on cardiovascular disease rates. However, replacement of trans fat appears to reduce disease rates and total mortality. Substituting low glycaemic index carbohydrates for high glycaemic index carbohydrates will lower triglyceride by 15-25% and reduce cardiovascular risk. Large doses of fish oil will lower triglyceride with a mean lowering of 0.45 mmol/L for a 3.5 g/day amount. Large doses of soluble fibre (3.5-7.0 g/day) lower LDL cholesterol by 0.2-0.35 mmol/L with Konjac glucomannan being the most effective per gram. Plant sterols or stanols lower LDL cholesterol by about 10% for a 2 g/day dose, while exercise and weight loss lower cardiovascular risk predominantly by lowering fasting triglyceride. In conclusion, diet lowers LDL cholesterol and triglyceride and dietary changes should be ultimately linked to a reduced risk of heart disease.