Results undermine the never-proven hypothesis that diets high in cholesterol and saturated fat promote cardiovascular disease 09/08/2008
A new study from Britain further undermines a decades-old medical myth regarding the role of dietary cholesterol in cardiovascular disease.
And these findings add to fast-deepening doubts surrounding the broader, near century-old "lipid hypothesis” of heart disease, which is reflected in public health policies, including the USDA Food Guide Pyramid.
This increasingly discredited hypothesis holds that "excess” dietary saturated fat and cholesterol—and resulting rises in blood cholesterol and lipid (fat) levels—are major contributing factors to cardiovascular disease (atherosclerosis) and resulting coronary heart disease.
Atherosclerosis—which is the chief defining characteristic of cardiovascular disease—is the medical term for arteries lined with inflamed, unstable, plaque.
This inflammatory condition is the leading cause of heart attacks, stroke, congestive heart failure and the arrhythmias that induce sudden cardiac death.
(For a summary of the relationships and distinctions between inflammation, cardiovascular disease, atherosclerosis, and coronary heart disease, see our accompanying article, "What is Heart Disease, Exactly?”)
We covered the declining credibility of the lipid hypothesis of cardiovascular disease earlier this year: see "Cholesterol Fiasco Undermines Accepted Theory,” which contains links to several eye-opening articles in The New York Times and The Boston Globe.
Eggs and heart disease: The overdue exoneration of a scapegoat
Healthy people and heart patients alike have routinely been advised to strictly limit intake of eggs… or avoid egg yolks, where most of their fat and cholesterol reside (along with their valuable vitamin A and D).
This advice flowed from the lipid hypothesis of heart disease, which holds that foods high in cholesterol and saturated fat—such as egg yolks—promote cardiovascular disease, atherosclerosis, and resulting coronary heart disease.
Yet, misguided medical advice was never supported by a persuasive preponderance of evidence.
Indeed, with the exception of people diagnosed with diabetes—among whom high egg intake is associated with increased heart risks—none of the large epidemiological studies that looked for links between eggs and coronary heart disease or stroke have found any.
As early as 1982, researchers who examined data from the famous Framingham Heart Study found no association between eggs and heart disease: "It is concluded that … differences in egg consumption were unrelated to blood cholesterol level or to coronary heart disease incidence” (Kritchevsky SB et al. 1982).
Then, researchers from Harvard School of Public health analyzed diet and health data from two of the largest, best-controlled epidemiological studies ever conducted: the Health Professionals Follow-up Study (1986-1994) and the Nurses' Health Study (1980-1994), which together involved 37,851 male physicians and 80,082 female nurses.
The Harvard team found no evidence that eggs were risky: "These findings suggest that consumption of up to 1 egg per day is unlikely to have substantial overall impact on the risk of CHD [coronary heart disease] or stroke among healthy men and women” (Hu FB et al. 1999).
(The only exception was diagnosed diabetics, among whom a higher intake of eggs was associated with greater risk of developing heart disease. This could simply reflect the facts that diabetics are more prone to developing coronary heart disease, and that diets high in fat are associated with higher risk of CHD.)
And a study in Japan yielded more evidence exonerating eggs as risk factors for developing coronary heart disease: "In conclusion, eating eggs more frequently, up to almost daily, was not associated with an increase in CHD [coronary heart disease] incidence for middle-aged Japanese men and women” (Nakamura Y et al. 2006).
Last year, researchers at the University of Medicine and Dentistry of New Jersey came to similar conclusions after analyzing diet and health data from 9,734 adults aged 25 to 74. The title of their publication summarized their exculpatory findings: "Regular egg consumption does not increase the risk of stroke and cardiovascular diseases” (Qureshi AI et al. 2007).
Die-hard defenders of the lipid hypothesis of heart disease might say that while epidemiological studies like these reveal associations, they cannot provide final proof of a hypothesis regarding diet and disease.
However, the results of a British clinical trial should help end the debate over heart health and eggs.
British study exonerates eggs
A research team from the University of Surrey recruited 45 overweight but otherwise healthy volunteers, and divided them into two groups (Harman NL et al. 2008).
- Group A (egg group) followed a low-calorie diet that included two eggs per day for 12 weeks.
- Group B (control group) followed the same low-calorie diet for 12 weeks, but ate no eggs.
The people in both groups lost 7- 9 lbs (3 to 4 kg) and their average levels of blood cholesterol fell.
Their blood cholesterol levels were measured at six weeks and 12 weeks, and both groups showed either unchanged or reduced cholesterol levels… particularly in their LDL (bad) cholesterol levels.
This finding came despite the egg group increasing their dietary cholesterol intake to around four times that of the control group.
As the authors concluded, "An increased intake of dietary cholesterol from two eggs a day does not increase total… or LDL cholesterol when accompanied by moderate weight loss. These findings suggest that cholesterol-rich foods should not be excluded from dietary advice to lose weight on account of an unfavorable influence on… LDL cholesterol” (Harman NL et al. 2008).
Team leader Bruce Griffin, Ph.D., RPHNutr summarized their findings in a press release: "We have shown that when two eggs a day are eaten by people who are actively losing weight on a calorie-restricted diet, blood cholesterol can still be reduced.”
And Dr. Griffin's companion comment focused on the heart of the matter: "There is no convincing evidence to link an increased intake of dietary cholesterol or eggs with coronary heart disease through raised blood cholesterol.”
In fact, saturated fat—whose primary dietary sources among Americans are red meats, butter, and foods made with butter—is more responsible for raising blood cholesterol than cholesterol-rich foods, such as eggs.
However, this does not mean that saturated fat is a significant villain, either.
The available evidence shows that diets high in saturated fat are not linked much more closely to risk of heart disease than are diets high in total fat, polyunsaturated fats, or monounsaturated fats. The main exception is that younger people's risk is exacerbated more by high fat intake (Artaud-Wild SM et al. 1993; Esrey KL et al. 1996; Jakobsen MU et al. 2004; Xu J et al. 2006; Volk MG 2007).
Sadly, many doctors remain unaware that the lipid hypothesis of heart disease rests on a foundation of sand, with numerous studies proving that diets high saturated fat and cholesterol are not inherently unhealthful.
Instead, it is a lack of plant foods and exercise and an excess of refined carbohydrates (i.e., white flour products) that can make fatty diets dangerous. These contextual differences explain why people in Finland and France have widely divergent rates of heart disease despite having similar intakes of saturated fat and cholesterol (Volk MG 2007).
In other words, it appears safe to eat reasonable amounts of saturated fat and cholesterol as long as your diet meets the basic criteria outlined in our accompanying article, "What is Heart Disease, Exactly?”
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