Dietary saturated fatty acids increase cholesterol synthesis and fecal steroid excretion in healthy men and women

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Abstract
In a strictly controlled 6‐week trial with 47 healthy volunteers we have determined the effect of replacement of polyunsaturated by saturated fatty acids on the fecal steroid excretion and on the rate of whole body cholesterol synthesis, as measured both by the sterol balance method and by the concentration of the cholesterol precursor lathosterol in serum. Subjects were fed mixed natural diets, of which the total fat content was kept constant at 45% energy. Consumption of polyunsaturated fatty acids, mainly linoleic acid, was 21 % energy for the first 3‐week period (P: S ratio 1.9), and 5% of energy (P: S ratio 0.2) for the next 3‐week period, or vice versa. Cholesterol intake as determined by analysis of duplicate diets was 41 mg MJ‐1 (about 500 mg day‐1) during both periods. Feces were collected for 5 days at the end of both periods. The steroid composition of the feces was not affected by the change of diets. The fecal excretion of neutral steroids was significantly higher on the low P: S high‐saturated‐fat (2.25 ± 0.68 mmol day‐1) than on the high P:S high‐linoleic‐acid diet (2.00 ± 0.69 mmol day‐1; P < 0.01). The excretion of bile acids was similar (0.77 ± 0.40 and 0.79 ± 0.41 mmol day‐1, respectively). The cholesterol balance and the rate of cholesterol synthesis were higher during the low P:S (1.86 ± 0.83 mmol day‐1) than during the high P:S period (1.55 ± 0.85 mmol day‐1; P < 0.01). The ratio of lathosterol to cholesterol in serum was 0.86 ± 0.33 μmol mmol‐1 on the high‐and 1.07 ± 0.39 μmol mmol‐1 on the low P: S diet (P < 0.01). Thus, both the balance and the cholesterol precursor method suggested that saturated fatty acids stimulate whole‐body cholesterol synthesis.

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