Making Sense of Fat, Cholesterol and CHD
(continued from the front page)
What Framingham finds:
Coronary Heart Disease
Duration of follow-up
Maximum of 12 years, 10-year risk prediction
Population of interest
Individuals 30 to 74 years old and without overt CHD at the baseline examination
JNC-V blood pressure categories
NCEP total cholesterol categories
LDL cholesterol categories
Now, the review in Open Heart has found something quite different. By studying 2,467 males across six randomized control trials published prior to 1983 (the year the second of the guidelines appeared advising the population against high fat consumption), the researchers found:
“There were no differences in all-cause mortality and non-significant differences in CHD mortality, resulting from the dietary interventions. The reductions in mean serum cholesterol levels were significantly higher in the intervention groups; this did not result in significant differences in CHD or all-cause mortality.” The “intervention groups” were participants who had restricted fat intake.
Lowering dietary saturated fat intake lowers serum cholesterol. Total serum cholesterol, as well as LDL cholesterol, is correlated with increased CHD risk. So what do we make of the seeming incompatibility of this new, extensive review and studies like the decades-long Framingham results?
At the same time the Open Heart study was published, the same journal offered an editorial attempting to address the conflicts here. The author, Dr. Rahul Bahl, points out the distinction between whether enough evidence existed in 1983 to steer people away from dietary fat intake and whether changes to public health policy should actually be made. It's important to remember that the researchers analyzed only the clinical evidence base for recommendations on cutting dietary fat to lower CHD risk.
Dr. Bahl notes that just because the meta-analysis legitimately unearthed a lack of direct, clinical evidence at the time the recommendations were made does not mean all evidence of a relationship between fat intake, high serum cholesterol and CHD does not exist. Epidemiological studies like Framingham can never really prove causation, but that does not mean they should be discarded. At times circumstantial evidence can be so time-tested, abundant and consistent that practicality dictates adopting certain precautions as if direct causal evidence exists.
To quote Dr. Bahl at length:
“[T]here is a fair argument to say that there are entire fields of science where positive results, even if they were to occur, are unlikely to represent true associations. Much dietary science of the type examined here is likely to fall into this category. However, there is a body of evidence supporting a link between fat consumption and cardiovascular disease that should be considered first.
“Epidemiological and ecological evidence suggests a link between fat consumption and heart disease. The seven countries cohort study by Keys referred to by the authors did find that higher serum cholesterol tended to be related to coronary heart disease incidence and that higher saturated fat consumption tended to be related coronary heart disease incidence. These findings were consistent in long-term follow-up. Certainly, a graded relationship between serum cholesterol level and coronary heart disease is a finding in other cohorts and lowering serum cholesterol appears to improve clinical outcomes. Serum cholesterol levels therefore remain a cornerstone in the assessment of cardiovascular risk. Occasionally ‘natural experiments’ have occurred where large population-level declines in coronary heart disease were associated with changes in the supply of dietary fat available as in Eastern Europe in the 1990s.”
How should we ultimately understand fat intake, serum cholesterol, and heart-disease risk?
Let go of macronutrient focus
One very big take-home lesson from all of this is that a common-sense, balanced approach to your diet that favors certain foods and de-emphasizes others is the best approach to take.Clinical trial evidence aside, we now know what those foods are.
As Dr. Bahl notes, “There is certainly a strong argument that an overreliance in public health on saturated fat as the main dietary villain for cardiovascular disease has distracted from the risks posed by other nutrients such as carbohydrates. Yet replacing one caricature with another does not feel like a solution. It is plausible that both can be harmful or indeed that the relationship between diet and cardiovascular risk is more complex than a series of simple relationships with the proportions of individual macronutrients.”
Mind sugar and calories
Going back nearly two decades, the USDA Agriculture Fact Book has been pointing out unhealthy trends in the way we eat compared to the way previous generations did. This excerpt is from around 2000:
“Americans at the beginning of the 21st century are consuming more food and several hundred more calories per person per day than did their counterparts in the late 1950s...or even in the 1970s...The USDA’s Economic Research Service...data suggest that average daily calorie intake increased by 24.5 percent, or about 530 calories, between 1970 and 2000.”
Of that increase:
- (mainly refined) grains increased 9.5%
- fats and oils, 9.0%
- added sugars, 4.7%
The nation's waistline will benefit when we dial these percentages back by replacing much of this intake with fruits and vegetables, along with reducing overall calories.
What are the new DGAC recommendations exactly?
Setting aside that the committee unwisely opened itself up to political attack by mentioning the benefits of certain dietary changes on the environment, the new guidelines offer much good advice and common sense. Here is a summary:
- Limitations on dietary cholesterol have been removed. Previously, the group recommended no more than 300 mg per day.
- Overall, people should consume a diet rich in fruits and vegetables, whole grains, low-fat dairy, seafood, legumes, and nuts and low in red or processed meats, sugar-sweetened foods and beverages, and refined grains.
- People should limit their daily consumption of added sugars (<10% of calories), saturated fat (<10% of calories), and dietary sodium (<2300 mg).
- Half of all grain intake should come from whole grains.
- Moderate alcohol intake is fine in most adults.
- The equivalent of up to five cups of coffee daily is not associated with adverse effects in most adults.
What may have gone missing in recent decades is balance. The epidemiological evidence continues to strongly suggest that a diet that causes the build-up of serum cholesterol is a diet out of balance: a bad diet. As Dr. Bahl puts it in his Open Heart editorial, “There are disagreements in the interpretation of available data from [randomized control trials], but despite this there remain reasons to postulate a causal connection between fat consumption and coronary heart disease.”