The results of a large scale epidemiological study of risks posed by the consumption of dietary fat on total mortality and on mortality from both cardiovascular disease and cancer appeared in the August issue of the Journal of Internal Medicine. The results show that neither women nor men have increased mortality related to the consumption of total fat or saturated fat.
I did some manipulation of the data myself with some surprising results, but before looking at my work, let’s look at what the study data showed.
The authors do a good job of laying out the history of the fat or lipid hypothesis, which posits that excess intake of dietary fat, especially saturated fat, increases the risk of early death from all causes and specifically from cardiovascular disease and cancer.
From the 1950s through to the 1970s evidence accumulated from various epidemiological, ecological and clinical trials supporting the theory that diets rich in animal fats and poor in unsaturated vegetable fats produced unfavourable risk profiles for cardiovascular disease and cancer. Results from these studies founded most of the dietary guidelines by amongst others the World Health Organization and American Heart Association, the basis of which is still used in reviewed editions today.
Over the last decades evidence from large-scale epidemiological studies has been emerging, partly defying the previously believed hypotheses, with voices rejecting the fat-disease hypotheses becoming more prominent. Most researchers today agree on total fat intake not being a risk factor for cardiovascular disease or cancer. [My italics: remember this line the next time you hear or read that fat causes heart disease or cancer.] The role of dietary fat in the development and treatment of obesity has also been under question. The largest bulk of evidence still pointing towards dietary fats influencing disease development, involves increased risk of various cancers and cardiovascular disease in relation to a high intake of trans fatty acids and saturated fats, as well as lower risks with diets rich in unsaturated fats, especially polyunsaturated fats. All the same, many studies have showed negative findings or even opposite results.
In spite of conflicting evidence, most institutions and governmental authorities issuing dietary guidelines still encourage limiting the percentage of calories from total fat in the diet, usually to
What the researchers were looking for:The aim of this study was to examine whether total fat intake, saturated, monounsaturated or polyunsaturated fat intake, or the ratio between unsaturated and saturated fat intake, are independent risk factors for prospective all-cause mortality, cardiovascular mortality and cancer mortality, within a large population-based cohort.
The research team recruited 28,098 middle-aged subjects from Malmo, the third largest city in Sweden, between 1991 and 1996. After extensive evaluation the study group was divided in quartiles of fat consumption by sex. In other words, the groups of men and women were divided into four groups (quartiles) based on the amount of their fat consumption, with the group at the low end being the quarter of either the women or the men who consumed the least fat, and the quarter on the high end composed of those consuming the most fat.
Each group was then broken down further into subgroups depending upon the specific fats consumed, i.e., saturated, monounsaturated, or polyunsaturated.
As this group of subjects aged, a number of them died. The researchers compared the cause of death to fat intake. Since these people were middle-aged when the study began and only 10-14 years have passed, the people who died were not particularly aged, thus the title of the study: “Dietary fat intake and early mortality patterns.”
The data show:
Total mortality:No significant difference in RR [relative risk] was observed between quartiles of saturated fat intake, polyunsaturated fat intake, or the ratio between mono- or polyunsaturated fat and saturated fat intake for women.
For men, a significantly lower RR of total mortality was observed in the third quartile of total fat intake (RR 0.77; CI 0.62 0.95, P = 0.017), with RR for the second and fourth quartiles also
In other words no difference in total mortality as a function of overall fat intake or particular type of fat intake.
Cardiovascular mortality:For women, no significant difference was observed between quartiles of total fat or saturated fat intake.
For men, a significant trend towards lower cardiovascular mortality in upper quartiles of total fat intake was observed (P = 0.028) with the RR for men in the fourth quartile being 0.65. No difference was observed between quartiles of saturated fat intake for men.So, there was no difference in early cardiovascular mortality in women related to the consumption of total or saturated fat. In men, those who ate the most fat had a 65% lesser chance of dying than those who ate the least fat. There was no difference in early cardiovascular deaths related to the consumption of saturated fat.
Cancer mortality:Women in the fourth quartile of total fat intake (46.1% of daily energy from fat) had a significantly higher RR of dying from cancer (RR 1.46; CI 1.04 2.04, P = 0.029). This was mostly attributable to a high RR for women in the fourth quartile of monounsaturated fat intake (RR 1.47; CI 0.92 2.34, P = NS). [I don’t know how they can make that claim since P showed the finding to have not reaches statistical significance.] Saturated fat intake, and the ratio between monounsaturated or polyunsaturated fat and saturated fat, did not show any significant effect on cancer mortality for women.
For men, significant differences in cancer mortality between quartiles were not revealed for any type of fat.Women in the quartile consuming the most fat had a 1.46% greater chance of dying early from cancer as compared to those in the lowest quartile, but there was no increase in mortality from saturated fat. I find the fact that these women had greater risk of dying from cancer, yet no increased risk of dying earlier from all causes, which would imply that the increased fat decreased their chances of dying from something else not studied.
Also interesting was the fact that the authors speculated that this increased risk of early mortality was maybe related to the trans fats included in the diets of the women in the highest-fat quartile.
I found a couple of interesting items when I massaged the data myself. Both men and women the highest quartile of fat consumption consumed a greater number of calories than those in the lowest quartile—18% more in the case of the women, 16% more for men. Yet both the men and the women in the highest-fat quartile weighed the same (actually a tiny bit less, but not a statistically significant difference) as the subjects in the lowest-fat quartile.
When looking at total fat consumption the researchers looked at fat as a percentage of total calories—for what idiotic reason I don’t know; I guess because that’s what everyone else looks at. When I recalculated total fat and saturated fat in absolute amounts, the study results become even stronger as an indictment of the lipid hypothesis.
Men in the highest-fat quartile consumed 63% more fat (139 grams verses 85) than men in the lowest-fat quartile, and consumed a whopping 82% more saturated fat (62 grams vs 34) than those in the lowest quartile.
Women in the highest-fat quartile ate 76% more fat (111 grams vs 63) than those in the lowest quartile, and ate 92% more saturated fat (50 grams vs 26) than did their lowest-quartile counterparts.
And the highest-fat quartiles of both sexes consumed more protein and less carb then did those in the lowest-quartile. Maybe that’s why they ate more and weighed less.
This one statement from the discussion section of the paper should lay the lipid hypothesis of heart disease to rest:Men in the fourth quartile of total fat intake, receiving almost 50% of their total energy intake from fat, had the lowest cardiovascular mortality.
But I’m sure it won’t because the many researchers out there who have based their careers on the lipid hypothesis along with all the pharmaceutical companies that make billions of dollars on cholesterol-lowering medicines won’t let it go without a fight.