Low fat or low carb: Which is better for treating metabolic syndrome? Original paper

Metabolic syndrome (MetS) substantially increases the risk of type 2 diabetes and cardiovascular disease. Compared with people who don’t have the syndrome, people with MetS are at twice the risk of developing cardiovascular disease over the 5- to 10-year period following diagnosis.^[1] MetS is defined as the presence of 3 or more of the following 5 criteria:

• Waist circumference ≥40 inches for men or ≥35 inches for women
• Blood pressure ≥130/85 mm Hg
• Fasting triglycerides ≥150 milligrams per deciliter (mg/dL)
• Fasting high-density lipoprotein cholesterol (HDL-C) <40 mg/dL for men or <50 mg/dL for women
• Fasting blood glucose ≥100 mg/dL

MetS is typically treated with lifestyle changes aimed at improving insulin sensitivity and other metabolic abnormalities. Low-carbohydrate diets (LCDs) are an increasingly popular option for improving insulin sensitivity, but the macronutrient ratios vary between studies and it’s not clear whether a specific ratio is optimal. There is also concern surrounding the potentially adverse effects of a high fat intake on blood lipids.

In this 6-month, nonrandomized controlled trial, 94 adults (average age of 40) with obesity consumed either an LCD or a low-fat diet (LFD). The target macronutrient composition of the LCD was <130 g/day of carbs, while the LFD allowed a maximum of 35% of daily calories from fat. There was no calorie restriction assigned for the LCD, but participants in the LFD group were told to limit overall energy intake to 1,800 kilocalories per day. Written meal plans and the same physical activity guidelines were given to participants, who also met with the researcher weekly for weight measurements and diet consultation.

The primary outcome was the prevalence of MetS, and the secondary outcomes were BMI, waist circumference, triglycerides, HDL-C, blood pressure, and fasting blood glucose.

The prevalence of MetS at baseline was 44.4% in the LCD group and 60% in the LFD group; it decreased to 3.7% and 22.5% in the LCD and LFD groups, respectively, at 6 months. Compared with baseline, both diets improved triglycerides, HDL-C, diastolic blood pressure, fasting blood glucose, and waist circumference. The only significant difference between groups was for triglycerides, of which there were greater reductions with the LFD.

The primary limitation of this trial is its short duration, as long-term adherence is of paramount concern with any dietary intervention.

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