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October 2

The Role of Dietary Saturated Fat on Cardiovascular Risk

 

Jeff S. Volek, PhD, RD presented his most recent abstract at our science advisory board meeting this month. Since you have asked me to blog on the subject of saturated fat , here is a description of his presentation and abstract which covers this subject very well.
 
The current rationale for decreasing saturated intake is to reduce LDL concentration in the blood. Recommendations that reduce saturated fatty acids (SFA) to levels of 10% of calories or less must take into account the likelihood of changes in dietary habits that will increase carbohydrate consumption to levels above which data no longer shows beneficial effect. Such recommendations should consider the NHANES data showing the lack of effect of reductions in saturated fat on obesity and diabetes and should consider large trials like the Women’s Health Initiative showing limited effects of recommendations to reduce dietary fat in general. Dietary carbohydrate is key element in understanding the relation of dietary SFA to risk for cardiovascular disease.
 
Carbohydrate-restricted diets, although relatively high in SFA, show effects on the fatty acid blood profile  that are very different from those seen in studies conducted in the presence of moderate to high dietary carbohydrate. A high carbohydrate diet prolongs circulatory exposure to dietary SFA, and conversely, dietary restriction of carbohydrate, via reduced secretion of insulin, allows for greater rates of fat management of the incoming fat mix. High dietary fat is thus expected to be bad for you only if there is sufficient carbohydrate to provide the hormonal state in which the fat will be stored rather than burned. 
 
The known metabolic effects of carbohydrate provide a mechanism for explaining the seemingly paradoxical finding that a low carbohydrate diet leads to significant decreases in blood levels of SFA despite increased saturated fat intake. Recent work from controlled feeding studies in the laboratory of Dr. Jeff Volek at the University of Connecticut,  indicate that altering fat quality of a very low carbohydrate diet by emphasizing monounsaturated fats( MUFA) and omega -3 fatty acids significantly decreases the plasma SFA pool and has other beneficial effects. More generally, Dr Volek has discovered that low carbohydrate diets are a preferred approach to treating metabolic syndrome. Metabolic syndrome (insulin resistance syndrome) represents a group of seemingly disparate physiologic signs that indicate a predisposition to obesity, diabetes, and cardiovascular disease.
 
 From a clinical standpoint, there are numerous pharmacologic agents that target individual markers but none treat all. Consistent with the idea that an intolerance to carbohydrate is an underlying feature of metabolic syndrome, Dr Volek’s study has shown that reduction in dietary carbohydrate results in global improvement in traditional and emerging markers associated with metabolic syndrome, particularly the cardio metabolic profile (HDL is raised, postprandial vascular function improved; small dense LDL-C, triglycerides and apoB/apoA-1 are reduced).   Control diets, restricted in fat, are shown to be less effective. 
 
The ability to target multiple markers with a single intervention provides support for the notion of a unique metabolic state that conforms to the idea of a syndrome.   The experimental results point to carbohydrate restriction as an alternative or adjunct to other approaches that generally require multiple pharmacologic interventions, and that have had only limited success. Future recommendations on dietary fat should consider underlying mechanisms and interactions of fat with other macronutrients. All points of view should be considered. The heterogeneity of the population suggests that only very broad guidelines may be possible.
Tagged: saturated fat
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