Intended for healthcare professionals

Rapid response to:

Editor's Choice

Nutrition matters

BMJ 2014; 349 doi: (Published 27 November 2014) Cite this as: BMJ 2014;349:g7255

Rapid Response:

It's linoleic acid intake that matters

"And the World Obesity Federation and UK Health Forum have joined forces to call on the World Health Organization to establish a global framework treaty similar to the treaty on tobacco control, to reduce saturated fats, added sugar, and salt in food and to control the marketing of highly processed foods."

"There is certainly a strong argument that an overreliance in public health on saturated fat as the main dietary villain for cardiovascular disease has distracted from the risks posed by other nutrients such as carbohydrates. Yet replacing one caricature with another does not feel like a solution. It is plausible that both can be harmful or indeed that the relationship between diet and cardiovascular risk is more complex than a series of simple relationships with the proportions of individual macronutrients."(1)

Having followed the saturated fat debate since the early 1980s, I find it disturbing that there is still considerable confusion regarding the nutritional roots of obesity as well as various noncommunicable diseases linked to fat intake. As far as I can tell, saturated fats appear to be benign over a wide range of intakes as long as they are consumed in the context of adequate supportive nutrition. (2)
In contrast, linoleic acid appears to be toxic when intake exceeds 1 to 2% of total energy intake.(3) Yet only an handful of scientists seem to be paying attention to the linoleic acid literature. "The incidence of obesity in the U.S. has increased from 15% to 35% in the last 40 years and is expected to rise to 42% by 2030. Paralleling this increase in obesity are a number of dietary changes, most pronounced of which is a >1000 fold increase in consumption of soybean oil from 0.01 to11.6 kg/yr/capita from 1909-1999: soybean oil consists of 50-60% linoleic acid (LA), so the energy intake from LA has increased from 2% to >7%/day.(4)

The rationale for restricting saturated fat intake is based on its cholesterol-raising effects. Myristic acid is considered the worst offender because it has the greatest impact on LDL and total cholesterol. "Bovine milk fat contains 8–14% myristic acid (14:0), and in human milk, myristic acid averages 8.6% of milk fat. As stated above, myristic acid is one of the major saturated fatty acids that have been associated with an increased risk of CAD, and human epidemiologic studies have shown that myristic acid and lauric acid are the saturated fatty acids most strongly related to average serum cholesterol concentrations. However, in healthy subjects, although myristic acid is hypercholesterolemic, it increased both LDL- and HDL-cholesterol concentrations compared with oleic acid ."(5)

Interestingly, there is research indicating that higher intakes of myristic acid may in fact be beneficial. "... dietary myristic acid, C14:0, was positively correlated with its plasma fatty acid... The saturated fat, myristic acid, was inversely related to both trunk and total body fat in the regression models."(6)

High LDL cholesterol may be important for preserving muscle mass. "Riechman and colleagues examined 52 adults from ages to 60 to 69 who were in generally good health but not physically active. The study showed that after fairly vigorous workouts, participants who had gained the most muscle mass also had the highest levels of LDL (bad) cholesterol, 'a very unexpected result and one that surprised us.'''

From what can be gleaned from linoleic acid research (8), advice to swap saturated fat and carbohydrates for linoleic acid (9) makes no sense. It's even worse to say this: "Omega-6 fatty acids lower LDL cholesterol (the 'bad' cholesterol) and reduce inflammation, and they are protective against heart disease. So both omega-6 and omega-3 fatty acids are healthy. While there is a theory that omega-3 fatty acids are better for our health than omega-6 fatty acids, this is not supported by the latest evidence. Thus the omega-3 to omega-6 ratio is basically the 'good divided by the good,' so it is of no value in evaluating diet quality or predicting disease."(10)


Competing interests: No competing interests

14 April 2015
David E. Brown
Retired carpenter
1925 Belmar Dr, Kalispell, Montana, United States