Results from a new study conclude that there was no evidence to support the 1977 national dietary guidelines aiming to reduce the incidence of coronary heart disease (CHD) by limiting overall fat consumption. At the time of the release of the guidelines, the United States Senate Select Committee on Nutrition and Human Needs report included data from a non-randomized, cross-over trial but no randomized controlled studies (RCTs).

Because the guidelines have remained unchanged over the past 30+ years, a systematic review and meta-analysis sought to assess published RCTs available at the time of the committee recommendations for support of the guidelines on dietary fat (reducing overall fat consumption to 30% of total energy intake and reducing saturated fat consumption to 10% of total energy intake). Six RCTs examining the relationship between dietary fat, serum cholesterol, and mortality were identified and outcome data was pooled. In the studies containing a total of seven dietary interventions involving 1,227 people in the intervention groups and 1,240 in the control groups, all-cause mortality was identical in both groups. No statistically significant difference in deaths due to CHD was observed; while the reductions in mean serum cholesterol levels were significantly greater in the intervention groups, this did not result in significant differences in CHD or all-cause mortality.

The lack of RCT evidence supporting the introduction of these dietary fat guidelines is likely to lead clinicians and patients to question the benefits of a low-fat diet, particularly when fat is replaced with carbohydrates. Lifestyle modification that include diet and exercise have shown to produce numerous benefits in other studies, so healthcare professionals may wish to emphasize a balanced diet that includes fruits, vegetables, whole grains, and even fats like olive oil.