I care about my health. And one important consideration when discussing health is death; dying really puts a damper on good health. So when I go to the grocery store and see a bottle of vegetable oil proudly stamped with a sticker about how healthy it is I wonder “Is that true?”. And when I read in a magazine about evil saturated fats I sometimes ask myself “Would replacing my butter and beef fat with corn and soybean oil reduce my chances of dying?”
Of course, extensive personal experience tells me that I would feel much crappier consuming the vegetable oils, but hey, maybe I would live longer?
I decided to examine long term controlled trials who’s only variable was pitting saturated fat against polyunsaturated fat (primarily the omega-6 variety found in vegetable oils). Let’s see what happened to mortality rates, shall we?
1. The Minnesota Coronary Survey was a 4.5 year long double blind study conducted on 9057 institutionalized men and women. Both groups consumed about 38-39% of their calories as fat. Monounsaturated fat content of the diets was about the same, but the experimental group (of 4541 people) consumed 15% of their calories as polyunsaturated fats and 9% as saturated fat, while the control group consumed 18% of their calories as saturated fat and 5% as polyunsaturated fat. By the end of the study there were 267 deaths in experimental and 248 in the control. Not only that, an apparent trend was developing for more dying in the experimental group:
2. The Sydney Diet Heart Study compared the outcomes of 2 groups of males (221 experimental and 237 control) following a heart attack. The control group obtained 13.5% of energy from SFA and 9.5% of energy from PUFA , while the intervention group obtained 9.8% energy from SFA and 15.1% from PUFA. After 5 years, more subjects in the PUFA group (16.7% or 37) had died than in the SAFA group (11.8% or 28).
3. The Saint Vincent’s hospital study is fairly small and a bit different because it took 100 men with a history of heart disease and separated them into 2 groups. Both groups were given 28% of their calories as fat. Group 1 was given supplemental fat as an equal mixture of corn and safflower oil, while group 2 was given supplemental fat as equal parts peanut and coconut oil. Group 1 ended up getting 5.5% of their calories from saturated fat and 14.1% from PUFA. Meanwhile, group 2 got 9.6% of calories as saturated fat and 3.3% from PUFA. 5 years later there were 5 deaths in group 1 and 4 in group 2.
4. The British Medical Research Council Soybean Oil Trial involved 393 males following a heart attack who were an randomly allocated into 2 groups, 194 men in the control group consumed their normal diet while 199 men in the experimental group ate a low saturated fat diet and consumed 85 grams of soybean oil daily (an oil high in polyunsaturated fat). After almost 7 years there were 28 total deaths in the experimental group and 31 in the control. One question raised about this study was whether the effect of cooking/frying had an effect, since the experimental group was consuming 960 calories of uncooked oils while the control group had no such prohibitions on heating their fat.
5. The LA veterans was a double blind trial performed on 846 men. 424 of the men were put in the experimental group and replaced saturated fats in their diet with PUFA rich vegetable oils. After 8 years the mortality rates were almost equal (174 experimental v. 178 control). Worth noting is the disparity in smoking rates between the groups: there were about twice as many heavy smokers and 60 percent more moderate smokers in the control group than the experimental group. I shouldn’t have to explain that smoking tends to increase risk of death and as such, the experimental group should have had a big advantage.
6. In well known DART trial, 2033 men who had suffered a heart attack were allocated into different groups. 1018 men were instructed to reduce total fat and replace saturated fat (SFA) with polyunsaturated fat (PUFA). The fat group reduced their total fat intake from 35.0 to 32.3% of calories, while doubling the ratio of PUFA to SFA (to 0.78). After two years, there was no change in all-cause or cardiac mortality. In the 1015 men given no fat advice, 113 died. In the fat advice group, 111 died.
7. The little known Rose corn oil trial is worth mentioning. In it, heart disease patients either kept eating their regular diet or avoided saturated fat sources like eggs and butter and added 80 grams of oil to their diet. By the end of two years, 5 people in the corn oil (out of 28) group had died of heart disease and only 1 (of 26) had in the control group (total deaths were not reported, but it is assumed that heart disease deaths were the only cause of death).
8. The Anti-Coronary Trial was a study in which investigators attempted to reduce heart disease rates in people without prior history of heart disease by fat modification. Saturated fat sources were replaced primarily with vegetable oils to achieve an increased ratio of polyunsaturated to saturated fat. By the end of the several year trial, 27 of the 814 people in the vegetable oil group had died, while only 6 of the 463 in the control group.
9. The MRFIT was a primary prevention trial on men at high risk of heart disease which randomized subjects into two groups; one that ate their typical diet and one that reduced saturated fat sources and increased vegetable oil consumption. There was a 6 year follow up. Smoking cessation was promoted in the vegetable oil group and as such there was significantly less smokers in this group, a large confounding variable, as discussed in trial 5. By the end of the study 260 of the 6438 people in the control group had died compared to 265 of the 6428 people in the vegetable oil group.
Replacing saturated fat sources with vegetable oils increased risk of death in trials 2, 3, 7, and 8. Death was increased in trial 1, though statistical significance wasn’t reached.
Replacing saturated fat sources with vegetable oils produced no significant difference in deaths in trials 4, 5, 6, and 9, despite the saturated fat group’s greater rates of smoking in trial 5 and 9 and greater use of high heat cooking in trial 4.
These combined studies suggest replacing saturated fats with mostly omega-6 polyunsaturated fats from vegetable oils may increase risk of death.
Mainstream nutrition advice is weird.
*Worth noting is that some of these studies (e.g. DART) were on people who had previously had heart attacks. Obviously the risk of death would have been heavily influenced by which type of fat was more beneficial to heart disease since the subjects were statistically much more likely to die from a heart attack than the general population.