Fats and atheroma: a retrial

A network analysis of the propagation of evidence regarding the effectiveness of fat-controlled diets in the secondary prevention of coronary heart disease (CHD): Selective citation in reviews

OBJECTIVE

To examine how the first randomised controlled trials (RCTs) evaluating the efficacy of cholesterol-lowering diets in the secondary prevention of coronary heart disease were interpreted in reviews of the literature prior to the National Institutes of Health consensus conference in 1984.

DESIGN

Claim-specific citation network analysis was used to study the network of citations between reviews and RCTs over a defined period (1969-1984). RCTs were identified and classified according to whether their conclusions supported or opposed the use of dietary fat modification/restriction in the secondary prevention of coronary heart disease. Each review published in this period that cited any of the RCTs was classified as supportive, neutral, or unsupportive to the use of dietary fat modification based on a quotation analysis of its evaluation of the findings of these RCTs. Citation bias and underutilisation were detected by applying a comparative density measure, in-degree centrality, and out-degree in a series of sub-graph analyses.

RESULTS

In total, 66 unique publications were identified (four RCTs-one supportive, three unsupportive; 62 reviews-28 supportive, 17 neutral, 17 unsupportive). On average, supportive reviews underutilised the available RCTs to a greater degree than other reviews. Amongst the supportive group, citation bias was common-23 (82%) reviews cited only the one RCT that was supportive.

CONCLUSION

Most reviews that disseminated a supportive evaluation of the results of RCTs in the context of secondary prevention cited only data that supported this position.

Diet and risk of coronary heart disease and type 2 diabetes

A high intake of saturated fat is an important risk factor for coronary heart disease (CHD) and type 2 diabetes. However the declining rates of CHD in many affluent societies and the steady increase in type 2 diabetes worldwide suggest that these important causes of serious morbidity and premature mortality have differing risk or protective factors worldwide. Changed macronutrient composition, reduced cigarette smoking, and improved treatment of risk factors and acute cardiac events might explain the reduction in risk of CHD, whereas the increasing rates of obesity are probably the most important explanation for the increase in diabetes. Coronary risk factors associated with diabetes could outweigh improvements in conventional cardiovascular risk factors such that the decline in CHD could be stopped or reversed unless rates of obesity can be reduced. Reduced intake of saturated fatty acids and other lifestyle interventions aimed at lowering rates of obesity are the changes most likely to reduce the epidemic numbers of people with type 2 diabetes and CHD.

A comparison of coronary and internal mammary arteries and implications of the results in the etiology of arteriosclerosis

Comparison was made between the intimal thickening of the anterior descending branch of the left coronary artery and the internal mammary artery in 352 necropsy examinations. The coronary arteries showed severe intimal thickening, progressing in severity throughout life, whereas the internal mammary showed no more than slight changes at any age. These observations, together with the variation in severity of the changes in different portions of the same vessel, and the freedom from this disease of the smaller arteries throughout the body, strongly suggest that a local or anatomic factor is the dominant influence in coronary artery disease.

The effect of various regimens of hormone therapy on serum cholesterol and triglyceride concentrations in postmenopausal women

The serum cholesterol and triglyceride concentrations of 84 postmenopausal women both before and after 2, 6 and 12 months therapy with various regimens of hormone therapy were measured. There was little alteration in mean serum cholesterol concentration with cyclical oestrogens but both sequential mestranol and norethisterone and sequential oestradiol valerate and norgestrel significantly reduced the mean serum cholesterol concentration to a level similar to that found in age-matched premenopausal women. There was a small and sometimes significant rise in serum triglyceride concentration with cyclical oestrogens. Sequential mestranol and norethisterone significantly elevated serum triglyceride levels, but sequential oestradiol valerate and norgestrel significantly depressed them. The results suggest that the progestogenic agent norgestrel has an important role to play in reducing both serum cholesterol and triglyceride levels, and that the sequential preparations, by virtue of their greater cholesterol lowering effect, should perhaps be preferred to cyclical oestrogens.

New perspectives on the dietary management of diabetes

Some of the confusions and misconceptions surrounding the diabetic diet are discussed together with the reasons why there is controversy over its formation. Current understanding of the contribution which diet may make to the prevention of complications is outlined. A new approach to the dietary management of the diabetic is suggested.