Effects of replacing saturated fat (SFA) with monounsaturated fat (MUFA) or carbohydrate (CHO) on plasma lipids and lipoproteins in individuals with markers for insulin resistance

We carried out a six-sequence crossover design study to examine the effects of replacing dietary SFA with MUFA or CHO (Step 1 diet). Three diets were fed in random order for 7 weeks each to 86 subjects ages 21 to 61 yrs. Subjects had baseline triglycerides (TG) >70th percentile, and/or HOL C <30th percentile, and/or plasma insulin >70th percentile. The average American diet (AAD) provided 36% of calories from fat (F) with 16% from SFA and 14% from MUFA. The MUFA diet had 36% F, 21% MUFA, 9% SFA. The Step 1 diet had 29% F with 8% SFA and 15% MUFA. All diets had 5-6% PUFA and 300 mgs cholesterol (C). All food was provided using a standardized metabolic diet protocol. Fasting bloods were obtained during weeks 5-7 for measurement of TC, TO and HDL C; LDL C was estimated. The means ±SEs for each variable were: AAD HighMUFA Step 1 Diet TC mg/dl 201.0 (±6.0; 192.0 (±6.0)* 192.0 (±6.0)* LDL C mg/dl 134.0 (±5.0; 126.0 (±50)* 125.0 (±5.01)* HDLC mg/dl 42.4 (±1.6) 40.8 (±1.6)* 39.3 (±1.6)*† TGs ln(mg/dl) 4.79 (+.02) 4.75 (+.02) 4.85 (+.02)*† TGs (mg/dl) 134 116 121*† *Significantly different from AAD, †Significantly different from high MUFA The MUFA and Step 1 diets decreased TC (∼5%) and LDL C (∼7%) similarly. In contrast, both the HDL C and TO response to the diets differed. The decrease in HDL C associated with a change from the AAD to the high MUFA diet (-3.8%) was only half that observed with the Step 1 diet (-7.4%). Additionally, while plasma TGs remained unchanged between the AAD and high MUFA diets, TGs were significantly increased on the Step 1 diet. These results suggest that a Step 1 and high MUFA diet are equally effective in lowering TC and LDL C. A high MUFA diet, however, may be preferable for some individuals because it lowers HDL C less and does not increase TG compared to a Step 1 diet.