High density lipoprotein cholesterol (HDL-C) is considered “good” cholesterol. This type of cholesterol has an inverse relationship to cardiovascular disease. In other words, the higher the levels of HDL-C, the lower the risk for cardiovascular disease.
Many studies have been done on lowering “bad” cholesterol levels (LDL-C) in subjects, but little research has been done regarding raising HDL-C levels. Kadir Has University in Istanbul, Turkey has done such a study, however. The Turkish population has naturally lower HDL-C levels than European and American populations. The researchers saw a need to find an effective way of increasing this good cholesterol in hopes to aid the larger population.
For the four week study, both overweight (a BMI between 25-30) and obese (a BMI over 30) subjects were assessed. A group of 43 individuals was assembled; the group contained men and women. Participants were instructed not to alter their daily physical activity level as they went about their daily lives on a low-carbohydrate diet.
Women were told to take in 1400 calories/day with a maximum of 75 grams of carbohydrates.
Their energy consumption contained 21% carbohydrates, 26% protein, and 53% fat. Men were instructed to take in 1800 calories/day with no more than 100 grams of carbohydrates. Their energy intake was 22% from carbohydrates, 29% protein, and 49% fat. The percentage of fat seems high for a weight loss plan, but this is for good reason.
It has been shown that a low-fat diet decreases HDL-C levels and increases triglyceride levels. Since the aim of this study is to raise HDL-C levels a low-carbohydrate diet that is not low in fat is most appropriate.
After four weeks of the low-carbohydrate, calorie restricted diet, all of the participants had significantly reduced their body weight, BMI, waist circumference, body fat ratio, systolic blood pressure, total cholesterol, and insulin levels. Men had a significant increase in HDL-C levels, but women did not.
While the decreased caloric intake was correlated to the decrease in body weight and total cholesterol for the whole group, it was significantly correlated to improved triglyceride levels only in men.
The decreased consumption of carbohydrates was responsible for the outcomes of this study in more instances than the decreased calorie intake. It had a significant effect on the reduction in body weight, BMI, and total cholesterol in men. In women, the decreased carbohydrates correlated with the improvements in diastolic blood pressure, insulin levels, and fasting glucose levels.
A low-carbohydrate diet has been shown to improve cardiovascular risk factors by raising good cholesterol levels. Previous research has shown that for every 100 grams of carbohydrates consumed, HDL-C levels decrease by 5.8 mg. By reducing carbohydrate intake, the levels of HDL-C actually increase.
This study was small and researchers note that more studies need to be done on a larger scale to confirm these findings. It is also noted that low-carbohydrate food is expensive which could make it difficult for people to follow this diet, especially in a developing country like Turkey.
Based on the results of this study, a low-carbohydrate diet is the best plan to follow for raising good cholesterol levels in men. The low-carbohydrate diet is not effective in increasing HDL-C levels in women; however, it has other health benefits. A low-carbohydrate, reduced calorie diet is effective for both men and women in reducing body weight, BMI, blood pressure and total cholesterol levels and is effective in raising HDL-C in men.
Reference: Ahmet Selçuk Can, Canan Uysal, K Erhan Palaoğlu. Short term effects of a low-carbohydrate diet in overweight and obese subjects with low HDL-C levels. BMC Endocrine Disorders. 2010;10:18
Study can be found at: http://www.biomedcentral.com/1472-6823/10/18