If saturated fat isn't the problem, what is?
In this study, in which greater saturated fat intake was associated with less progression of coronary atherosclerosis, carbohydrate intake was associated with a greater progression. Carbohydrate, through its effect on insulin, is the key player. Insulin not only sweeps up glucose from the blood but it also plays air traffic controller, making the call as to whether that glucose is turned into fat or is used for energy. Most importantly, insulin determines what happens to dietary fat — whether it gets stored or oxidized for fuel. In fact, insulin has so much control over how dietary fat is metabolized that when levels of fat are measured in the blood, they are not strongly associated with a person's diet. In other words, one person who has a high intake of saturated fat may turn out to have a similar ratio of saturated to unsaturated fat in the blood as someone who consumes very little saturated fat.
A recent study by Jeff Volek at the University of Connecticut compared low-carbohydrate and low-fat diets. Even though the low-carbohydrate diet had three times as much saturated fat as the low-fat diet, levels of unhealthy fats in the blood were lower in the low-carbohydrate group. How is that possible? That is what metabolism does.
What is the best diet?
We don't know the ideal diet composition. We do know that saturated fat, unlike trans-fat, is a normal part of body chemistry and extreme avoidance is not justified by current scientific data. Removing some saturated fat to reduce calories is good, but adding back carbs appears to be deleterious. It appears that healthy, carbohydrate restriction will trump the effects of any kind of fat. For a person with diabetes, blood glucose must be the first consideration. If you have relatively tight blood sugar control, the amount of saturated fat you eat may be a non-issue. You can do what we did before the diabetes-obesity epidemic: regulate your intake by your taste and your natural appetite. No one ever did want to eat a pound of bacon.
1 - Food and Nutrition Board: Macronutrients. In: Dietary reference intake: National Academies Press; 2005, p.484.
2 - JB German, CJ Dillard: Saturated fats: what dietary intake? Am J Clin Nutr 2004, 80:550-559.
3 - MW Gillman, et al. : Inverse association of dietary fat with development of ischemic stroke in men. JAMA 1997, 278:2145-150.
4 - D Mozaffarian, EB Rimm, DM Herrington: Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women. Am J Clin Nutr 2004, 80:1175-1184.
5 - JS Volek, et al. A hypocaloric, very low carbohydrate, ketogenic diet results in a greater reduction in the percent and absolute amount of plasma triglyceride saturated fatty acids compared to a low fat diet. NAASO, Boston, MA, October, 2006.
Reviewed by Susan Weiner, R.D., M.S., C.D.E., C.D.N. 3/08
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