Low-carb Diet Without Calorie Restriction Favorable on Metabolic Syndrome

A recent study compared three equicaloric diets with varying carbohydrate intake amounts for their effect on metabolic syndrome risk factors.

A recent study found that a low-carbohydrate diet, independent of weight loss, can not only reduce patients’ risk factors for metabolic syndrome, but also can reverse the disease in previously diagnosed patients.

Metabolic syndrome is characterized by a group of risk factors that increase patients’ risk for major health problems and heart disease such as diabetes, stroke and heart failure. According to the American Heart Association, risk factors include: large waistline (>35 for women, >40 for men), high triglyceride levels (>150 mg/dL), reduced HDL cholesterol (<40 mg/dL in men and <50 mg/dL in women), elevated blood pressure (>130/85 mmHg) and elevated fasting blood glucose (>100mg/dL). To qualify for diagnosis, patients must present with three or more of the described risk factors.

Metabolic syndrome is becoming more and more common as the rate of obesity in the United States continues to rise, affecting more than 1 in 3 adults. Simple lifestyle changes, such as diet and exercise, can help patients to avoid serious illness and even death caused by heart disease. Traditionally, metabolic syndrome has been viewed as a result of excess energy intake and subsequent obesity, and treated with reduced-fat and low-calorie diets. Controversy remains regarding the role of high-carbohydrate intake in the pathogenesis of metabolic syndrome. Due to the relationship between carbohydrate intake and insulin secretion and fat storage, there is reason to believe a low-carbohydrate diet, independent of weight loss, could be a viable treatment option for patients with metabolic syndrome.

The objective of this study was to test the theory that dietary carbohydrate intake has a primary role in the development of metabolic syndrome, independent of weight loss. Researchers recruited patients with obesity (mean ± SD age 41.3 ± 10.7 years, BMI 39.3 ± 8.3 kg/m2) that had at least 3 of the 5 risk factors to be characterized as having metabolic syndrome. As a crossover design, participants were fed three 4-week weight maintenance diets, each of equal caloric intakes, but varied by low, moderate and high carbohydrate content. A 2-week washout diet separated each treatment period. Macronutrient ratios are displayed in table 1.

Table 1: Macronutrient Distribution of Three Study Diets

Each diet contained 2950 kcal/day.

After four weeks of the low carbohydrate diet, 9 of 16 participants no longer met criteria for metabolic syndrome compared to 3 of 16 within the moderate carbohydrate group, and 1 of 16 in high carbohydrate groups. Triglycerides decreased to normal levels (p = 0.006), HDL increased by an average of 3 mg/dL (p = 0.009), and fasting glucose decreased to an average of 98 mg/dL (p = 0.023). There was no significant difference in blood pressure from either of the three diets; women showed a more significant decrease in blood pressure than men after the low-carbohydrate diet.

Although there were no significant findings regarding LDL-C numbers, an interesting finding may favor the low carbohydrate diet for patients with metabolic syndrome. At baseline, all participants’ serum LDL-C was in the normal range and remained so throughout all three diets. At baseline, 13 of 16 participants displayed predominantly small, dense LDL particles, a characteristic commonly associated with dyslipidemia in metabolic syndrome. After the low-carbohydrate diet, two-thirds of participants displayed large, buoyant LDL particles, which is linked to improved cardiovascular outcomes when compared to the contrary. Therefore, a low-carbohydrate diet increases LDL size and decreases the amount of small, dense LDL particles, independent of LDL concentration, resulting in less risk for atherogenic dyslipidemia.

While this study possessed several strengths including its crossover study design and measurement of many outcome measures, the population size was very small and only included patients with obesity. Further studies would be helpful to examine the effects of the low-carbohydrate diet on patients without obesity and at risk for metabolic syndrome.

Practice Pearls:

• This study has shown that a low-carbohydrate diet, independent of caloric intake, reduces presence of risk factors for metabolic syndrome in patients with obesity.
• Metabolic syndrome is characterized by having 3 of 5 risk factors (elevated triglycerides, increased waist size, low HDL, elevated fasting blood glucose and elevated blood pressure) and puts patients at risk for type 2 diabetes and heart disease.
• A low-carbohydrate diet may be an advantageous treatment plan for patients with metabolic syndrome risks factors to prevent the development of type 2 diabetes.

References:

“Symptoms and Diagnosis of Metabolic Syndrome.” Www.heart.org, www.heart.org/en/health-topics/metabolic-syndrome/symptoms-and-diagnosis-of-metabolic-syndrome.

Hyde, Parker N., et al, “Dietary Carbohydrate Restriction Improves Metabolic Syndrome Independent of Weight Loss.” JCI Insight, vol. 4, no. 12, 2019, doi:10.1172/jci.insight.128308

Amber Satz, PharmD Candidate, LECOM School of Pharmacy