Are Butter and Full Fat Foods Safe?

Review

Citation: Harcombe Z, Baker JS, Cooper SM, et al: Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis. Open Heart 2015 2: doi: 10.1136/openhrt-2014-000196

This was a systemic review and meta-analysis of randomized control trials (RCTs) regarding the relationship between dietary fat consumption, serum cholesterol levels, and subsequent coronary heart disease development. All trials considered were prior to the establishment of dietary guidelines in 1977 by the United States and in 1983 by the United Kingdom regarding dietary fat and cholesterol consumption.

Study Methods

The authors underwent a systemic review and subsequent meta-analysis of randomized control trials available prior to 1983 to determine what available evidence was available regarding the influence on development of CHD and mortality from dietary fat intake and/or serum cholesterol levels.

Results and Outcomes

Six randomized control trials were identified prior to the establishment of national US and UK guidelines in 1977 and 1983 respectively. Five of the six trials did not examine either total fat consumption as < 30% of daily caloric intake or total saturated fat consumption as < 10% of daily caloric intake (the current recommendations). Four trials examined the administration of vegetable oils, 3 trials examined the substitution of saturated fates with vegetable oils, and one trial examined a 20% fat consumption diet. One trial examined a 10% saturated fat diet.

The six trials represented 7 dietary interventions including a total of 1227 intervention group subjects and 1240 control group subjects. All-cause mortality in the intervention and control groups was 30.2% in the intervention group and 29.8% in the control group (an absolute all-cause mortality of 370 in both groups) with a non-significant risk ratio of 0.996 (95% CI 0.865 to 1.147).. CHD mortality was 207 in the intervention groups and 216 in the control groups, again, with a non-significant risk ratio of 0.989 (95% CI 0.784

to 1.247). There was no statistical significance for either all-cause mortality or CHD mortality. Serum cholesterol levels fell in all groups but had a statistically larger fall in intervention groups.

Conclusions

Data from randomized control trials available prior to 1983 do not support the subsequent (and current) dietary restrictions recommending total fat consumption as < 30% of daily caloric intake or total saturated fat consumption as < 10% of daily caloric intake.

Commentary

Coronary heart disease (CHD) is a very important medical topic in the United States. According to the CDC, CHD remains as the #1 cause of death in the United States as of 2013 and has long been thought to be linked to high-fat and cholesterol diets.

The supposed link between high fat diets/high dietary cholesterol and CHD is a decades-old correlation born out of epidemiological data without subsequent randomized controlled trials (RCTs) to support it. More recent data have begun to challenge this link, throwing doubt on the relationship between high-saturated fat and high-fat diets, dietary cholesterol, and subsequent CHD(1,2). Many individuals in the scientific community now view dietary recommendations that lead to low-fat, high-carbohydrate diets as one of the major contributors to today’s obesity epidemic and argue that current

US dietary recommendations are not supported by solid scientific data.

This paper looks back in time to assess whether the current US dietary guidelines were supported by contemporary data when first enacted. The authors compiled data available at the time from randomized control trials finished before 1983 and completed a meta-analysis to look for consensus. They chose to use only randomized control trials because the authors argue epidemiological data from non-controlled studies do not produce data as reliable.

The authors analyzed six randomized control trials and found that available data did not support the subsequent US dietary recommendations. Patients randomized into low-fat diet groups or to other interventions did not have lower rates of mortality from CHD or from all causes. Patients treated with dietary interventions did have statistically significant decreases in blood cholesterol levels but no drop in mortality, thus calling the link between blood cholesterol and CHD mortality into question.

It is very important to recognize what this paper does and does not say. By analyzing these earlier randomized control trials this paper makes the argument that current US dietary recommendations were not supported by proper data before being enacted. While trials available at the time did not support lower CHD mortality in dietary intervention groups, it’s important to note that only one out of 6 analyzed trials actually set a limit on fat intake based on daily calories. It would be wrong to interpret this study as suggesting high-fat diets are safe because the majority of RCTs did not examine that component specifically. The main conclusion to be taken from this study should only be that data at that time had not reached a conclusive decision and US dietary recommendations on the subject were premature.

More recent data does suggest the link between high-fat diets and death from CHD has been misrepresented for years and the US government has taken notice. The Scientific Report of the 2015 Dietary Guidelines Advisory Committee has just been released and in a deviation from 2010 guidelines, the Committee states that, “the U.S. population should be encouraged and guided to consume dietary patterns that are rich in vegetables, fruit, whole grains, seafood, legumes, and nuts; moderate in low- and non-fat dairy products and alcohol (among adults); lower in red and processed meat; and low in sugar-sweetened foods and beverages and refined grains” and “sodium, saturated fat, and added sugars are not intended to be reduced in isolation, but as a part of a healthy dietary pattern that is balanced, as appropriate, in calories.” (3)

References

1 DiNicolantonio JJ. The cardiometabolic consequences of replacing saturated fats with carbohydrates or Ω-6 polyunsaturated fats: Do the dietary guidelines have it wrong? Open Heart 2014;1:e000032.

2 Chowdhury R, Warnakula S, Kunutsor S, et al. Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis. Ann Intern Med2014;160:398—406.

3 http://www.health.gov/dietaryguidelines/2015-scientific-report/02-executive-summary.asp