The original trial – double blind, randomized, 9423 participants – wanted to see if replacing saturated fat in the diet with vegetable oil (rich in linoleic acid, an omega-6 polyunsaturated fatty acid) would reduce heart disease, heart attacks, or deaths by any cause. They thought it would because this replacement typically lowers both total cholesterol and LDL. These were inpatients, so diet compliance was good.
The vegetable oil did lower cholesterol, as expected (by about 31 mg/dl). But it did not reduce deaths. That was unexpected. In fact, those eating vegetable oil had higher mortality than those eating saturated fat.
There was no evidence of benefit in the intervention group for coronary atherosclerosis or myocardial infarcts. Systematic review identified five randomized controlled trials for inclusion (n=10808). In meta-analyses, these cholesterol lowering interventions showed no evidence of benefit on mortality from coronary heart disease or all cause mortality.
These authors found the same outcome in their similar efforts a few years ago. The present study reinforces it:
Our recovery and 2013 publication of previously unpublished data from the Sydney Diet Heart Study (SDHS, 1966-73) belatedly showed that replacement of saturated fat with vegetable oil rich in linoleic acid significantly increased the risks of death from coronary heart disease and all causes, despite lowering serum cholesterol.
Here’s their prior study:
Conclusion: In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit.
Why is eating oil bad for you? Oxidation:
Increasing dietary linoleic acid has been shown to increase oxidized linoleic acid derivatives in a dose dependent manner in many tissues. These oxidized derivatives, along with other non-cholesterol lipid mediators, have been implicated in the pathogenesis of many diseases including coronary heart disease, chronic pain, and steatohepatitis [fatty liver disease]. While the biochemical and clinical consequences of high intakes are incompletely understood, there is a possibility for unintended harm.
One way to interpret the unfavorable results of the two recovered trials is that high intakes of linoleic acid could have adverse effects in people who are prone to linoleic acid oxidation (such as smokers, heavy drinkers, and older adults).
What to eat then? Here’s a clue:
Individuals eating only minimally processed whole foods — as everyone did until about 100 years ago — would have consumed about 2-3% of calories from linoleic acid. By contrast, among industrialized populations today, most linoleic acid intake is derived from highly concentrated vegetable oils, in which the fatty acids are separated from the fiber, protein, and micronutrients that are naturally present in vegetables and seeds. Because these concentrated sources of linoleic acid are used widely as cooking and frying oils and added to many processed and packaged food items, the linoleic acid content of modern industrialized diets is much higher than natural diets. For example, mean linoleic acid intake in the US of about 17 g a day (7% of calories) is much higher than the approximately 6 g of daily linoleic acid provided by natural food diets without added vegetable oils. If these concentrated sources are considered to be dietary supplements, on average Americans ingest the equivalent of 11 capsules of 1 g linoleic acid a day above and beyond intake from natural foods.
Eat foods without added oil. Bake and boil. Sauté and poach in broth. Use fat-free gravies, sauces, and salad dressings. Look at the ingredient list on processed and packaged foods and don’t buy them if they contain vegetable oils.
This is, and is going to be as history views it, an important study. It, along with its predecessor, begins the process of reversing the idea that plant fats (unsaturated) are better than animal fats (saturated).
However, and this is an equally important however, this study did not look at replacement of saturated fat with carbohydrate, that is, with less fat. Some in the medical community are saying since saturated fat is no worse and may even be better than vegetable oil, you can eat butter/cheese/eggs until your heart’s content. Well, a content heart will not be your lot if you do. Note that in the autopsy cohort, close to a quarter of people eating high saturated fat suffered a heart attack. They also had considerable plaque in their arteries. When Dr. Esselstyn cut the fat, all fat, he cut heart attack rates and lessened plaque.
Dr. McDougall, Dr. Esselstyn, Dr. Barnard, and others have for years warned against added oil. ”Vegetable oils make a bad diet worse,” says Dr. McDougall. “Carbohydrate-rich foods have nourished all large populations of people throughout all of verifiable human history.” He’s right.