The Dietary Guidelines Advisory Committee (DGAC) recently released its recommendations for the 2010 Dietary Guidelines for Americans, but some in the scientific and food communities are questioning the committee’s suggestions, particularly those regarding limiting saturated fat intake. Gerald McNeill, PhD, Vice President of Research and Development for Loders Croklaan, North America, answers Food Manufacturing’s questions about the impact these recommendations could have on public health.
Q: The DGAC recommended limiting saturated fat intake to less than seven percent of total calories. Where do nutrition experts disagree with the DGAC regarding these recommendations, and what existing data do experts have that refute the arguments of the DGAC?
A: The DGAC focused on the effect of different fats on total cholesterol and LDL (“bad”) cholesterol, while barely referring to HDL (“good”) cholesterol. When measuring any risk of heart disease, both LDL and HDL must be taken into account. A high serum HDL will cancel the effect of a high LDL level. Saturated fats not only raise LDL, but also raise HDL (more than anything else we eat). The net result is that LDL cancels HDL, suggesting that saturates have no effect on the risk of heart disease. The DGAC ignores the effect of saturates on HDL.
Very large observational studies directly measuring heart disease and trying to link it to dietary habits over many years definitively show that saturated fat neither increases nor decreases heart disease risk. Prominent researcher Dr. Robert Krauss and his co-workers studied the impact of saturated fat intake on heart disease in 340,000 people and issued this statement: “A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD (coronary heart disease)”. The DGAC sidestepped this data and talked about the benefits of polyunsaturated fat instead.
Q: Where did the DGAC go wrong in their research regarding these recommendations?
A: The idea that saturated fat is “artery clogging” started in the 1970s when there was limited understanding of causes and markers of heart disease. Various persuasive scientists of the time persuaded the government to make dietary recommendations where the centerpiece was to reduce saturated fat intake. Many scientists and nutritionists of today learned this as irrefutable fact and naturally will resist contradictory evidence as flawed or biased. However, there is so much evidence building up that saturates are neither good nor bad that we can expect a paradigm shift sooner rather than later. Already we see a shift away from “saturates are bad” to “polyunsaturates are good.”
Q: What are some possible health consequences that could result from the recommendations?
A: Continuing to demonize saturated fats will likely result in continued pressure to replace fats with carbohydrates. We know from recent research that carbohydrates increase the risk of heart disease compared to saturates. This is mainly due to a decrease in HDL caused by sugars.
The DGAC also recommended replacing saturated fat with polyunsaturated fat. While data indicates that this may reduce risk of heart disease, it may have unforeseen negative effects on other disease states. Polyunsaturates are highly reactive to air (causing off flavors in foods). Oxidative breakdown products such as free radicals and unsaturated aldehydes are known to react with DNA and protein. Damage to DNA and protein is associated with diseases of aging, including cancers and arthritis. Conversely, saturated fats are essentially inert and do not generate these oxidized products.
Another suggestion of the DGAC is to use more stearic acid, a less common saturated fat in the diet. This has a lower LDL than other saturates, and therefore is healthier. But stearic acid also has a lower HDL and overall would not be a benefit (a fact that is ignored by the committee). Early research has raised concerns that stearic acid may increase inflammation, which can also contribute to chronic diseases.
Q: The DGAC stated that individuals should substitute mono- or polyunsaturated fats for saturated fats. Is this a good solution, and why or why not?
A: Substitution of saturated fats by polyunsaturated fats is likely to provide some benefit with respect to risk of heart disease. But the benefit is much less than proponents have been claiming, as we now know that saturated fats do not increase the risk of heart disease in the first place. We have no idea what the long term effect of significantly increasing polyunsaturate intake will have. When polyunsaturates are heated in foods or used in frying, these breakdown products are pre-formed and absorbed into the body. (I banned polyunsaturated fats from cooking in my home years ago.) Apparently no one in the DGAC or anywhere else in the government is addressing this serious, unintended consequence.
Oleic acid, a monounsaturate, is not as reactive as polyunsaturated fat and shows moderately good effects on LDL and HDL cholesterol. But recent observational studies show that it only provides a small benefit on actual incidence of heart disease and would provide no significant benefit over saturates (as they are not as bad as once believed). Due to the conflicting evidence over the effects of monounsaturates, it is likely much more research will be required.
Q: What recommendations regarding saturated fat intake do nutrition experts feel should have been made in light of existing scientific evidence?
A: The unintended consequence of demonizing fats and saturated fats was a large increase in carbohydrate and trans fat consumption. This was a major contributor to an obesity epidemic, and heart disease remains the number one killer, the opposite of what previous DGAC committees had promised. As a convincing body of evidence now shows that saturated fat actually doesn’t do anything, no changes should be made to its recommended dietary intake levels. Instead the DGAC and the government should focus their resources on dietary patterns that really make a difference. These may include restriction of processed sugar intake and reduction of salt in foods.
Interview by Lindsey Coblentz, Associate Editor