Dietary Interventions That May Alter Risk Factors

It is, of course, useful to know which dietary interventions affect which risk factors. The problem is that the answers are not always entirely consistent with effects on health. The reason is that altering one dietary component may affect many other dietary components and risk factors. If all of these effects worked in the same direction (to promote health), then the overall effect on health might be much greater than the estimated effect on the risk factor alone. On the other hand, if some effects on risk factors are positive and others are negative, the result might be no overall gain in health or even an overall loss of health even though the effects on the single risk factor measured looked promising. For this reason, understanding the effects of changes in diet on individual risk factors is interesting but not as helpful as understanding overall effects on health.

Unless otherwise specified, all references in this section are to systematic reviews of randomised controlled trials.

1.4.2.1 Dyslipidemia

While dietary advice has a role to play in normalizing abnormal serum lipids in people with cardiovascular disease, aspects of diet that clearly protect against death and disease should be given greater emphasis than lipid reduction in this group. Dietary changes are likely to result in reductions of total cholesterol of about 5%,25-27 while statin trials reduce total cholesterol by 18 to 28%; therefore, lipid lowering medication is more effective than dietary advice.25 Metabolic ward studies suggest that replacing 60% of saturated fats by other fats and avoiding 60% of dietary cholesterol would reduce serum total cholesterol by 0.8 mmol/L (about 13%), but it appears difficult to maintain this in a normal lifestyle.25 Replacing saturated fats with unsaturated fats leads to improved lipid levels28 and a reduction in cardiovascular events, but it is not clear whether polyunsaturated or monounsaturated fats are more cardioprotective.29

Daily use of realistic levels of soluble fiber (found in oats, pectin, psyllium, guar gum) will lower total serum cholesterol by about 2%,30,31 while large intakes of purified soy protein will lower total cholesterol levels by about 10%.32 Garlic supplements appear to lower serum cholesterol but trials are of poor quality and may have been biased.33-37

1.4.2.2 Weight

Weight can be altered by dietary change, but this appears to be difficult. Trials are often of very short duration and suffer from high drop-out rates, limiting their validity. Several good quality systematic reviews offer insights. A behavioral component improves weight loss in dietary and exercise programs (including very low calorie diets), as do written meal plans, weekly shopping lists, and group (rather than individual) therapy. Weight maintenance strategies (such as support groups) should be integral parts of all weight loss programs.38 There is little strong evidence that the proportion of dietary fat (as distinct from calories eaten) has an effect on body weight.38-40 In terms of managing cardiovascular risk, people with hyperlipidemia should receive dietary lipid lowering advice in addition to weight management advice.41

1.4.2.3 Elevated Homocysteine Levels

Elevated homocysteine levels can be reduced by supplementation with folic acid, alone or with vitamins B6 and B12,22,42,43 but it is not yet clear whether the reduction will reduce cardiovascular risk.

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