The science of weight loss is straightforward. If you eat fewer calories than you need to power your daily activities, your body will make up the deficit by drawing on stored energy. As you force your body to use the energy that was stored as fat, you lose weight. How you create that calorie deficit depends on the food you choose to eat, and those choices impact your health in other ways. Studies have linked cholesterol levels to dietary choices, so if you decide on a diet plan that features low or no carbohydrates, you should be aware of the effect that may have on your cholesterol levels.
High-density Lipoprotein
Cholesterol doesn't dissolve in the blood so it is transported by lipoproteins. High-density lipoprotein, or HDL, is considered "good" cholesterol because it helps to transport excess cholesterol to the liver where it can be processed and excreted.
Both low-fat and low-carbohydrate diets reduced overall cholesterol in a 2005 Duke University study conducted by Eric Westman, M.D., but only the low-carbohydrate diet actually raised "good" cholesterol levels. According to researchers, the low-carb group in the study ate unlimited amounts of animal protein, including fatty meats, and there were no restrictions on calories. They supplemented with multivitamins and ate two cups of salad vegetables and two cups of nonstarchy vegetables per day.
Low-density Lipoprotein
"Bad" cholesterol binds to low-density lipoproteins, or LDL. These molecules are responsible for arterial buildup that leads to arteriosclerosis and heart attacks.
Low-carbohydrate diets are often criticized because they can be excessively fatty, which research indicates is correlated with high LDL levels in the blood. Studies have determined that, although low-carb diets tend to reduce triglycerides and raise "good" cholesterol levels, the benefits are negated by a concurrent rise in LDL. According to a 2006 study by A.J. Nordman, et al, published in the "Archives of Internal Medicine," low-fat dieters saw favorable changes in LDL while low-carbohydrate dieters saw unfavorable changes in LDL statistically significant enough to cause concern.
HDL Ratio
The ratio of HDL to total cholesterol can be more telling than the total cholesterol reading alone. For example, if the HDL reading is 60 mg/dL and the total cholesterol is 200 mg/dL, the ratio of HDL to the total is 3.3 which indicates that the patient is at half the average risk for heart disease, according to the Harvard Medical School. Higher ratios imply increased risk. In the Nordman study, low-carb dieters realized an increase in HDL but there was a concurrent increase in LDL, leaving the HDL ratio statistically unchanged.
Triglycerides
Any complete lipoprotein panel includes four results; total cholesterol, LDL, HDL and triglycerides. High levels of triglycerides, or fat in the blood, are a significant indicator of heart disease risk and should be a part of any discussion on the effects of your chosen diet on cholesterol. Low-carbohydrate diets, regardless of the fat intake associated with them, consistently demonstrate favorable changes in triglyceride levels at 6-month and 12-month measures.
Studies published in "The Archives of Internal Medicine," "The American Journal of Clinical Nutrition," and "The International Journal of Cardiology" confirm causation and note beneficial decreases in triglycerides of up to 75 points in low-carbohydrate study groups.
References
- "American Journal of Clinical Nutrition"; Long-term Effects of a Very Low-carbohydrate Diet ...; Grant D. Brinkworth, et al; July 2009
- "Archives of Internal Medicine"; Effects of Low-carbohydrate vs. Low-fat Diets ...; A.J. Nordman, et al; April 2006
- Eurekalert: Plant-based, Low-carb Diet May Promote Weight Loss and Lower Cholesterol
- Duke Health: Study Shows Low-carb Diet Improves Cholesterol
- Harvard Medical School: Which Cholesterol Test Should You Get?
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