Diet and Cardiovascular Disease: Is There A Relationship?
The New York Times reported today that a new study in the Journal of the American Medical Association (JAMA) stated dietary changes had no effect on the prevention of cardiovascular disease (CVD).
This finding would (to steal Marx’s reference of Hegel) turn modern medicine on its head.
It is not uncommon for the media to incorrectly interpret and report findings found in medical journals. Medical literature is complicated and statistical analyses are often above even the most intelligent individual’s grasp. So it is unfair to blame the media’s shortcomings in reporting studies in medicine. However, the misinterpretation of studies almost always leads to the public becoming misinformed on a medical topic and questioning their physician’s knowledge.
Unfortunately, the New York Times was a recent victim of a medical study misunderstanding. In order to avoid any confusion among the five readers of this blog, one of whom is my dad who has documented coronary heart disease (CHD) – so listen up dad – I will do my best to explain this study.
As the New York Times reported, the current study was done by the Women’s Health Initiative (WHI) and followed 48,835 females, between the ages of 50 and 70 years old, for 8.1 years. There were two treatment groups, one of which – the intervention group – received dietary modifications that included reductions in total fat (below 20% of energy expenditure) and high fruit, vegetable and grain intake. The other group – the control group – did not participate in this diet. The study was randomized, controlled and double blind. The authors concluded the intervention group did not have a statistically significant reduction in the primary end-points, fatal and non-fatal CHD, fatal and non-fatal cerebrovascular accidents (CVA) and cumulative CVD (both CVA and CHD), when compared to the control group.
As the late Mr. English used to say, “I agree with everything you just said, but there’s more.”
The first issue with this report is that it was done on post-menopausal women and the primary initiative of this study was to see if the low fat/high grain, vegetable, and fruit diet would decrease the risk of colorectal cancer and breast cancer (which the authors stated it did not reduce the risk). Thus, it is difficult to assess the validity of these results because the primary objective was not the prevention of CVD.
Secondly, the authors stated one significant limitation was the generalizability of these results beyond the sample studied. The women in this study had higher income, education and lower smoking rates than that of the general population. And because this study was limited to women, it is unclear whether these results are applicable to men.
Thirdly, as the authors also stated, eight years may not be long enough to expect significant reductions in CVD. Atherosclerosis (ATH), the formation of thrombogenic plaques on the walls of arteries, begins as early in life as 18 years old. Individuals could have had significant ATH, without history of cardiovascular events, i.e., myocardial infarction, and thus, they may be out of the window for dietary modification to have any significant effects on future CVD. That is, when the study began they were already headed down a path of CVD and dietary modification would only have a minor benefit anyway. If the diet had been started earlier, before the age of 50, perhaps around 18 years old, the diet may have had more significant effects.
Moreover, as Anderson and Appel illustrated in their review of this article, there has been a significant change in the paradigm of dietary risk factors in CVD since the WHI began in 1991. For instance, the literature now suggests modifying fat intake to protect against CVD. This study simple decreased total fat and some types of fats may be protective against CVD.
Finally, to fully asses the effect of diet on CVD, studies should include diets directed against known CVD risk factors, hypertension, hypercholesterolemia, diabetes and weight as well as diets high in fish and fish oils. Anderson and Appel stated, “…the trial did not test current dietary guidelines for CVD prevention, none of which includes reducing total fat intake as a means to prevent CVD,” (pg. 695).
Although this study (which was a very well done study) concluded low fat/high fruit, vegetable and grain diets do not reduce the risk of CVD, this should not be thought of as support against healthy diets to control CVD. To fully reduce the risk of CVD individuals should stop abusing tobacco, regularly participate in physical activity and eat a diet consistent with the updated food pyramid.
As an interesting side-note, the authors of this study did find that increased carbohydrate intake had no long-term effects on LDL (bad cholesterol), glucose or insulin and thus did not increase the risk for CVD. This finding, along with several others similar to it, illustrated that the popular Atkins Diet is not effective in reducing the risk of CVD.
This finding would (to steal Marx’s reference of Hegel) turn modern medicine on its head.
It is not uncommon for the media to incorrectly interpret and report findings found in medical journals. Medical literature is complicated and statistical analyses are often above even the most intelligent individual’s grasp. So it is unfair to blame the media’s shortcomings in reporting studies in medicine. However, the misinterpretation of studies almost always leads to the public becoming misinformed on a medical topic and questioning their physician’s knowledge.
Unfortunately, the New York Times was a recent victim of a medical study misunderstanding. In order to avoid any confusion among the five readers of this blog, one of whom is my dad who has documented coronary heart disease (CHD) – so listen up dad – I will do my best to explain this study.
As the New York Times reported, the current study was done by the Women’s Health Initiative (WHI) and followed 48,835 females, between the ages of 50 and 70 years old, for 8.1 years. There were two treatment groups, one of which – the intervention group – received dietary modifications that included reductions in total fat (below 20% of energy expenditure) and high fruit, vegetable and grain intake. The other group – the control group – did not participate in this diet. The study was randomized, controlled and double blind. The authors concluded the intervention group did not have a statistically significant reduction in the primary end-points, fatal and non-fatal CHD, fatal and non-fatal cerebrovascular accidents (CVA) and cumulative CVD (both CVA and CHD), when compared to the control group.
As the late Mr. English used to say, “I agree with everything you just said, but there’s more.”
The first issue with this report is that it was done on post-menopausal women and the primary initiative of this study was to see if the low fat/high grain, vegetable, and fruit diet would decrease the risk of colorectal cancer and breast cancer (which the authors stated it did not reduce the risk). Thus, it is difficult to assess the validity of these results because the primary objective was not the prevention of CVD.
Secondly, the authors stated one significant limitation was the generalizability of these results beyond the sample studied. The women in this study had higher income, education and lower smoking rates than that of the general population. And because this study was limited to women, it is unclear whether these results are applicable to men.
Thirdly, as the authors also stated, eight years may not be long enough to expect significant reductions in CVD. Atherosclerosis (ATH), the formation of thrombogenic plaques on the walls of arteries, begins as early in life as 18 years old. Individuals could have had significant ATH, without history of cardiovascular events, i.e., myocardial infarction, and thus, they may be out of the window for dietary modification to have any significant effects on future CVD. That is, when the study began they were already headed down a path of CVD and dietary modification would only have a minor benefit anyway. If the diet had been started earlier, before the age of 50, perhaps around 18 years old, the diet may have had more significant effects.
Moreover, as Anderson and Appel illustrated in their review of this article, there has been a significant change in the paradigm of dietary risk factors in CVD since the WHI began in 1991. For instance, the literature now suggests modifying fat intake to protect against CVD. This study simple decreased total fat and some types of fats may be protective against CVD.
Finally, to fully asses the effect of diet on CVD, studies should include diets directed against known CVD risk factors, hypertension, hypercholesterolemia, diabetes and weight as well as diets high in fish and fish oils. Anderson and Appel stated, “…the trial did not test current dietary guidelines for CVD prevention, none of which includes reducing total fat intake as a means to prevent CVD,” (pg. 695).
Although this study (which was a very well done study) concluded low fat/high fruit, vegetable and grain diets do not reduce the risk of CVD, this should not be thought of as support against healthy diets to control CVD. To fully reduce the risk of CVD individuals should stop abusing tobacco, regularly participate in physical activity and eat a diet consistent with the updated food pyramid.
As an interesting side-note, the authors of this study did find that increased carbohydrate intake had no long-term effects on LDL (bad cholesterol), glucose or insulin and thus did not increase the risk for CVD. This finding, along with several others similar to it, illustrated that the popular Atkins Diet is not effective in reducing the risk of CVD.
posted by az at 7:27 PM
3 Comments:
Oh.
Funny you should write this, I was just wondering if dietary changes had any effect on the prevention of cardiovascular disease (CVD). Thanks for the timely blog. And, by the way, I understand most of the statistics.
i figured you would. hazard ratios are always used in medical literature. anyhoo, the taco bell tonight probably wasn't a good choice, but it was tasty....even if they screwed up my order
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