The Evidence
Harcombe, Z., Baker, J. S., Cooper, S. M., Davies, B., Sculthorpe, N., DiNicolantonio, J. J., & Grace, F. (2015). 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, 2:e000196. doi: 10.1136/openhrt-2014-000196
What did the meta-analysis look into?
The meta-analysis investigated whether the low-fat recommendations were supported by evidence when they were issued (back in 1977 in the USA, and in 1983 in the UK). Today, dietary recommendations restrict “all-fat” consumption to 30% of daily food calorie intake, and “saturated fat” to 10%. This was based on the assumption that fat restriction would reduce coronary heart disease (CHD) and related deaths.
Specifically, the meta-analysis looked at:
(1) The benefits of vegetable oil consumption and fat restriction on people with CHD.
(2) The benefits of replacing saturated fats (those that are solid in room temperature and typically found in red & deli meats, dairy, baked goods) with vegetable oils, in people with CHD.
The meta-analysis synthesized evidence from 6 experimental studies, including a total 2467 male participants, out of which 740 had died from a variety of reasons, and 423 had died from CHD.
What did the evidence suggest about the relationship between fat restriction and “all-cause” deaths?
Reducing fat consumption and replacing saturated fats with vegetable oils did not substantially decrease death from “all causes”.
What did the evidence suggest about the relationship between fat restriction and deaths from CHD?
Reducing fat consumption and replacing saturated fats with vegetable oils did not substantially decrease death from CHD.
What did the evidence suggest about the relationship between fat restriction and cholesterol levels in the body?
Cholesterol levels dropped regardless of the type and amount of fats consumed, but dropped more in those who restricted their (saturated) fat consumption.
The take-home message
Reducing of “all fat” and especially saturated fat consumption does not appear to protect from CHD, death from CHD, or “all-cause” deaths. While cholesterol dropped more in those who restricted (saturated) fat consumption, this did not also lower CHD or “all-cause” deaths. High cholesterol may not be the cause of CHD. Dietary recommendations (restricting “all-fat” consumption to 30% of daily food calorie intake, and “saturated fat” to 10%) were not based on the evidence when issued. Broadly speaking, claims about the dangers of fat consumption on CHD and death may not be warranted.
