An article in dLife, written by Richard Feinman, PhD:
Here’s an idea to chew on: The carbs in your diet tell your body what to do with the fat you eat, so it’s the type and amount of carbohydrates that matter when it comes to your weight and health.
Virtually every bit of health information today includes the advice to avoid saturated fat — the so-called evil stuff that lurks in animal foods like steak and eggs. The basis for this recommendation is that research has shown a correlation between saturated fat intake and total cholesterol and LDL (“bad cholesterol”). The problem with these studies is that the effects are not large, there is wide variation among individuals and, in most of these studies, the predicted benefit in incidence of cardiovascular disease did not materialize. In addition, we now know much more about risk factors for cardiovascular disease (CVD) beyond LDL. No assessment of CVD risk can be made without considering HDL (“good cholesterol”), triglycerides, and the size of the LDL particle. Plenty of research shows that these markers can worsen when people reduce their intake of saturated fat and that they can improve by reducing the intake of carbohydrates.
You don’t have to be a medical researcher to recognize that this is a politically charged issue. The thing that is missing for the public is an impartial evaluation of all the data on saturated fat. My personal opinion is that there is much contradictory data and a recent review of the situation suggests that there is not sufficient evidence to make any recommendations.
There is a sense that, in the absence of definitive evidence, lowering saturated fat will at least do no harm. This is not right. The problem for people with diabetes is what happens when saturated fat is replaced with carbohydrate, and research has repeatedly shown that this may actually be harmful. Consider that, according to the Centers for Disease Control and Prevention, during the onset of the current epidemic of obesity and diabetes, almost all of the increase in calories in the American diet has been due to carbohydrate. The percent of total fat and saturated fat in our diet decreased. In men, the absolute amount of saturated fat consumed decreased by 14 percent!
One of the most striking reasons to doubt the across-the-board proscriptions against saturated fat is the report from the large scale Framingham study in the Journal of the American Medical Association, titled “Inverse association of dietary fat with development of ischemic stroke in men.” You read that right: The more saturated fat in the diet, the lower the incidence of stroke.
Perhaps the most compelling research was published in a 2004 issue of the American Journal of Clinical Nutrition by researchers from the Harvard School of Public Health. Their study showed that, in postmenopausal women with heart disease, a higher saturated fat intake was associated with less narrowing of the coronary artery and a reduced progression of disease. Even with similar levels of LDL cholesterol, women with lower saturated fat intake had much higher rates of disease progression. Higher saturated fat intake was also associated with higher HDL (the “good” cholesterol) and lower triglycerides.
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, the fat profile in the blood (cholesterol and triglycerides) is not strongly tied to diet.
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.