The Role of Carbohydrate Restriction in Reducing Cardiac Risk Factors

One in five adults has some form of cardiovascular disease (1). A recent flood of clinical research suggests that the time for re-evaluating nutritional recommendations for bringing heart disease under control may be well overdue. It is a known fact that carbohydrates increase triglyceride levels. Triglycerides, total cholesterol, LDL ("bad") and HDL ("good") cholesterol are fats that your physician tests for when you get your blood tested.
Elevated Triglyceride Levels Are an Independent Risk Factor for Heart Disease 
Recently, 17 studies involving over 46,000 men followed over eight years and nearly 11,000 women followed over 11 years indicated that a small elevation of triglycerides led to a 32 percent increase in cardiovascular risk in men and 76 percent increased risk in women.(2) These results clearly challenge the emphasis that has been placed on total cholesterol and LDL cholesterol. One study showed that among 12,500 men in Sweden, the lower the triglyceride level, the lower the incidence of myocardial infarctions (MI). Even in the group with the highest cholesterol level, which averaged 245 mg/dl, only 11 individuals with triglyceride levels less than 100 mg/dl had MIs, compared to 97 individuals who had triglycerides greater than 184 mg/dl.(3)
All 16 of the other studies also confirmed elevated triglycerides as a major risk factor and most showed that elevated LDL cholesterol levels, when combined with triglyceride elevations, increased cardiovascular risk considerably.(2)
Perhaps the most startling study was led by J. M. Gaziano at Harvard Medical School.(4) Subjects with the highest ratio of triglyceride to HDL had a 16-fold greater incidence of coronary events than those with the lowest ratio. Gaziano's study, as well as the other studies mentioned above, lends support to the idea that elevated levels of triglycerides and low HDLs are also associated with hyperinsulinism.
Questioning the Wisdom of Low-Fat Diets for Everyone 
For those who have high triglycerides and low HDL, an appropriate question would be: Is the low-fat, high-carbohydrate diet recommended by the American Heart Association and the National Cholesterol Education Program the best option? The results from numerous clinical studies would suggest not. Studies comparing a low-fat diet that is comprised of 60 percent carbohydrate with diets based on fewer carbohydrate show that triglyceride levels rise significantly when carbohydrate content is greater. (5-6). It is unfortunate that there are no studies comparing lower levels of carbohydrate intake. It is highly likely they would show a correlation between lower carbohydrate content and lower triglyceride levels.
A 1966 study by P.K. Reissell at Harvard demonstrated that a diet containing only 26 grams of carbohydrate produced a greater than 70 percent drop in triglycerides in people whose original triglycerides count exceeded 500 mg. (7) (With such a severe restriction of carbohydrate intake, stored body fat becomes the body's primary fuel source.) In the study, triglyceride levels were dramatically lowered.
A recent study on obese adolescents comparing a low-calorie diet with an unlimited calorie, controlled carbohydrate eating plan showed a greater than 50 percent average drop in triglycerides for individuals on the controlled carb plan and a 10 percent drop for those on the control low-fat diet.(8)
A Swedish study (3) that found that triglyceride levels below 100mg/dl protected against coronary events was strongly confirmed by M. Miller's study in Baltimore showing that the lowest group, those whose triglycerides were below 100, had 2-1/2 times the protection from coronary events than did the other three groups.(9)
The Role of a Controlled Carbohydrate Program 
For years, it has been an assumption that a nutrition plan primarily composed of protein and fat has an adverse effect on blood chemistry. Amazingly, however, there have been virtually no published studies confirming such results when the diet was low enough in carbohydrate to cause the body to burn stored fat as fuel. All of the studies indicating that dietary fat creates lipid abnormalities were done with diets that also contain high amounts of carbohydrate.
All studies where carbohydrates comprise less than 20% of the calories have shown a drop in average total cholesterol and triglyceride levels. (8,10,11)
Selected References
1.    National Health and Nutrition Examination Survey (NHANES) 3, 1988-94, CDC NCHF and the American Heart Association.
2.    Austin, M.A., Hokanson, J.E., Edwards, K.L., "Hypertriglyceridemia as a Cardiovascular Risk Factor, " The American Journal of Cardiology, 81(4A), 1998, pages 7B-12B.
3.    Stavenow, L., Kjellström, T., "Influence of Serum Triglyceride Levels on the Risk for Myocardial Infarction in 12,510 Middle Aged Males: Interaction With Serum Cholesterol," Atherosclerosis, 147, 1999, pages 243-247.
4.    Gaziano, J.M., Hennekens, C.H., O'Donnell, C.J., et al., "Fasting Triglycerides, High-Density Lipoprotein, and Risk of Myocardial Infarction," Circulation, 96(8), 1997, pages 2520-2525.
5.    Abbasi, F., McLaughlin, T., Lamendola, C., et al., "High Carbohydrate Diets, Triglyceride-Rich Lipoproteins, and Coronary Heart Disease Risk," The American Journal of Cardiology, 85, 2000, pages 45-48.
6.    McLaughlin, T., Abbasi, F., Lamendola, C., et al., "Carbohydrate-Induced Hypertriglyceridemia: An Insight Into the Link Between Plasma Insulin and Triglyceride Concentrations," Journal of Clinical Endocrinology and Metabolism, 85(9), 2000, pages 3085-3088.
7.    Reissell, P.K., Mandella, P.A., Poon-King, T.M.W., et al., "Treatment of Hypertriglyceridemia," The American Journal of Clinical Nutrition, 19, 1966, pages 84-98.
8.    Sondike, S.B., Copperman, N.M., Jacobson, M.S., "Low Carbohydrate Dieting Increases Weight Loss but not Cardiovascular Risk in Obese Adolescents: A Randomized Controlled Trial," Journal of Adolescent Health, 26, 2000, page 91.
9.    Miller, M., Seidler, A., Moalemi, A., et al., "Normal Triglyceride Levels and Coronary Artery Disease Events: The Baltimore Coronary Observational Long-Term Study," Journal of the American College of Cardiology, 31(6), 1998, pages 1252-1257.
10.    Yancy, W. S., Bakst, R., Bryson, W., et al., "Effects of a Very-Low-Carbohydrate Diet Program Compared With a Low-Fat, Low-Cholesterol, Reduced Calorie Diet," October 7, 2001, Abstract of the North American Association for the Study of Obesity Annual Meeting, Quebec City, Canada.
11.    Reed, T., Shakir, K.M.M., Harari, A.E., et al., "High-Fat, Low-Carbohydrate Diet Improves Symptoms of Postprandial Hypoglycemia," June, 2000, Abstract of the 81st Annual Meeting of the Endocrine Society, Toronto, Canada.