Can a low-carbohydrate diet affect insulin-resistant lipoprotein metabolism?

This study determined the effect of varying carbohydrate and saturated fat dietary contents on cardiovascular disease (CVD) risk factors during weight-loss maintenance. The authors concluded that restriction of carbohydrates provided improved insulin resistance on lipoprotein metabolism, without unwanted side effects on low-density lipoprotein (LDL) cholesterol or inflammation.

Saturated fat is a type of dietary fat found in animal-based products and tropical oil such as coconut and palm. Saturated fats are a risk factor for the development of CVD. They are associated with an increase in LDL cholesterol (“bad cholesterol”) which can result in cholesterol buildup in arteries. LDL cholesterol levels can be lowered by dietary changes. Replacement of saturated fat with unsaturated fat (found in nuts, avocados, olive oil, and seeds) in the diet can reduce the risk of CVD and total deaths. However, the replacement of saturated fat with highly processed carbohydrates in the diet does not reduce the risk of CVD and may negatively affect LDL cholesterol.

Patients with type 2 diabetes (T2D) have insulin resistance in which body cells are unable to effectively respond to insulin. This results in high blood glucose that is associated with abnormal cholesterol levels. Although low-carbohydrate diets with saturated fat are used for T2D management, the effect of carbohydrate restrictions and variations in saturated fat on LDL cholesterol elevation and CVD risk is unclear.

This study 147 participants with diabetes and/or CVD. All patients had previously followed a diet and lost between 10 and 14% of their body weight. They were then randomly assigned to 3 groups for maintenance diets for 20 weeks.

Group 1 was the low-carbohydrate diet which consisted of 20% carbohydrates, 60% fat (21% saturated fat), and 20% protein. Group 2 was the moderate-carbohydrate diet that contained 40% carbohydrates, 40% fat (14% saturated fat), and 20% protein. Group 3 was the high-carbohydrate diet that had 60% carbohydrates, 20% fat (7% saturated fat), and 20% protein. Fasting blood samples were collected and the lipoprotein insulin resistance (LPIR) score was determined. Triglycerides, HDL cholesterol, LDL cholesterol, adiponectin, and inflammatory markers were measured. 

A decrease in LPIR score was observed with group 1 only. There was no LPIR change in group 2 and a non-significant increase in group 3. Triglycerides, HDL cholesterol, LDL cholesterol, adiponectin, and inflammatory markers were not different based on diets.

The study found that carbohydrate restriction resulted in dose-dependent benefits for insulin-resistant lipoprotein metabolism without side effects.

The study included young to middle-aged, relatively healthy adults with low LDL cholesterol so results may not apply to older populations, groups at higher risk, or those with more restrictive diets.