Randomized Controlled Trial

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POSITIVE: See Quality Criteria Checklist below.

To determine the relative efficacy of reducing dietary SFA, by isoenergetic alteration of the quality and quantity of dietary fat, on risk factors associated with metabolic syndrome (MetS).

• Age: 35 to 70 years
• BMI: 20 to 40kg/m²
• TC: 8.0mmol per L or less
• Regular consumers of alcohol who did not drink excessively, as defined by elevated liver enzymes
• MetS as defined by three or more of the following:
  • Fasting plasma glucose: 5.5 to 7.0mmol per L
  • TAG: 1.5mmol per L or more
  • HDL-C: Less than 1.0mmol per L (males) or less than 1.3 (females)
  • Systolic BP (SBP): 130mm Hg or more
  • Diastolic BP (DBP): 85mm Hg or more
  • On BP-lowering medication
  • Waist circumference (WC): more than 102cm (males) or more than 88cm (females).

• Anti-inflammatory or hypolipidemic medication, nutritional supplements, medical conditions
• Fatty acid supplements including fish oils, evening primrose oil
• High doses of antioxidant vitamins
• Red rice yeast supplements
• More than two servings of oily fish per week
• Highly trained endurance athletes or more than three periods of intense exercise per week
• Planning to start a special diet or lose weight
• Weight change of 3kg or more within the last three months
• Alcohol or drug abuse
• Pregnancy, lactation or planning a pregnancy in next 12 months. 

Recruitment

Completed centrally, according to age, gender and fasting plasma glucose concentration, applying Minimisation Program for Allocating Patients to Clinical Trials, Department of Clinical Epidemiology, The London Hospital Medical College.

Design

Randomized controlled trial.

Blinding Used

Implied with measurements.

Intervention

Subjects assigned to one of four isoenergetic diets differing in fat quantity and quality:

• Two diets provided 38% energy from fat, one with high content (16% of energy) of SFA (HSFA diet) and the other with high content (20% energy) of MUFA (HMUFA diet)
• The other two diets were low-fat, high-complex carbohydrate (LFHCC) diets that contained 28% energy from fat, with diet LFHCC n -3 including 1g to 2g per day supplement of very-long-chain marine n-3 PUFA and diet LFHCC and diet LFHCCC control including a control high-oleic acid sunflower-seed oil capsule.

Statistical Analysis

• All data are presented as group means ± SE of the mean
• Repeated measures ANOVA determined the effect of dietary fat modification on metabolic markers
• Data were normalized by log, square root, inverse or sine transformation
• Analyses were adjusted for between-subject factors: Sex, center and diet group with age and change of body weight as covariates
• Significant time-diet and time x diet x gender interactions and significant main effects were investigated using Bonferroni post hoc tests
• A Bonferroni correction was applied for multiple testing
• Post hoc analysis was completed to determine whether habitual fat intake, defined as being above or below the median pre-intervention fat intake [36% of total energy intake, excluding subjects with the lowest (5%) and highest (5%) total fat intake], influenced the metabolic response. 

Timing of Measurements

Baseline and 12 weeks except for three-day food records, which were completed at six weeks.

Dependent Variables

• Body weight: Calibrated scale
• Waist circumference: Directly on skin in duplicate at the midpoint between supra iliac crest and lower rib margin at end of a normal expiration to nearest 0.1cm using a non-stretch tape measure
• Hip circumference: In duplicate in nearest 0.1cm using non-restrictive tape measure, at the level of the greater trochanter without compressing the skin
• Blood pressure: In seated position after five-minute rest, in duplicate using appropriately sized cuff before blood samples were taken
• Lipid, apolipoprotein, glucose and inflammatory markers: Standard methods
• Insulin-modified IV GTT
• Health and lifestyle questionnaire: Habitual physical activity, smoking, alcohol intake.

Independent Variables

• Subjects assigned to one of four previously described diets
• Fat-modified food products were provided to all subjects to attain dietary fat targets in conjunction with their usual foods
• A novel food exchange model was used to achieve the dietary targets
• Spreads, cooking oil, baking fats, mayonnaise and biscuits were produced with a specific fatty acid profile to be used in the HSFA and HMUFA diet groups or low-fat spread and mayonnaise for the LFHCC groups
• Volunteers were instructed to exchange any habitually used oils, fats or spreads with the study foods
• Volunteers randomized to the HFSA diet were requested to consume only full-fat dairy foods and to replace one snack product usually eaten with a study HSFA cookie daily
• This group was also asked to eat less carbohydrate
• Subjects randomized to diet HMUFA, LFHCC and LFHCC n-3 were requested to consume only low-fat dairy products
• Those on the HMUFA diet ate HMUFA mayonnaise or a handful of hazelnuts or cashews on replaced one normally eaten snack product with their choice of HMUFA biscuit
• In the LFHCC and LFHCC n-3 diets, volunteers reduced their intake of high-fat snacks, ate two extra portions of complex carbohydrate daily and took the supplied capsules daily
• They were encouraged to use cooking oil and baking fat to prepare dishes in their home
• Diet counseling was given to the subjects and frequent monitoring and reinforcement was provided
• Intervention foods were delivered to each volunteer every two weeks by their dietitian. 

• Initial N: 486 subjects
• Attrition (final N): 417 (185 males, 232 females)
• Age:
  • HSFA: 54.9 years
  • HMUFA: 54.62 years
  • LFHCC: 54.7 years
  • LFHCC: 55.39 years
• Ethnicity: White Europeans
• Anthropometrics:  Age, body weight, blood pressure, insulin and glucose levels were not different between dietary groups before intervention
• Location: Eight European countries:
  • Ireland
  • UK
  • Norway
  • France
  • Netherlands
  • Spain
  • Poland
  • Sweden.

Key Findings

• Dietary targets were largely achieved with significant isoenergetic reduction in dietary SFA, with replacement of MUFA or complex carbohydrates. Plasma oleic acid showed significant diet x time interaction (P=0.0005); levels increased following the HMUFA diet (P=0.033) and were lower after the HSFA and LFHCC n-3 diets (P=0.005). Enrichment of plasma EPA and DHA levels followed the LFHCC n-3 diet (P=0.005). Plasma n-6 PUFA levels were not changed. 
• Reducing x diet interaction dietary SFA had no effect on insulin sensitivity, fasting insulin, glucose concentrations or HOMA-IR. A significant within-subject time (P=0.001) showed a small (less than 0.84kg or 1% body weight) but significant reduction in body weight following the LFHCC and LFHCC n-3 diets; therefore, change in body weight was controlled for in all analysis.  
• Waist circumference, BMI and blood pressure were not significantly altered. Reducing dietary SFA had no effect on biomarkers of inflammation: Plasma CRP, IL-6, TNF_x, sICAM-1, sVCAM-1, resistin, adiponectin, leptin, PAI-1 and tPA concentrations
• Plasma TAG concentrations showed a significant diet x time interaction (P=0.006) whereby plasma TAG concentrations were lower after the HSFA and LFHCC n-3 diets (P=0.018 and P=0.005, respectively). Triglyceride-rich lipoprotein (TRL) TAG concentrations showed a diet x time interaction (P=0.049), with lower levels following the LFHCC n-3 diet only (P=0.032). TAG and TRL TAG showed a time x gender x diet interaction (P=0.017 and P=0.039, respectively). TAG and TRL TAG were reduced only in men after the HSFA and LFHCC n-3 diets (P=0.039 and P=0.02 (TAG), P=0.013 and P=0.008 (TRL TAG),  respectively).
• Plasma NEFA showed a diet x time interaction approaching significance (P=0.061); post hoc analysis showed lower NEFA levels following the LFHCC n-3 diet (P=0.006). Plasma apo CIII showed a significant time x diet interaction (P=0.034); levels were reduced after the HSFA and LFHCC n-3 diets (P=0.014 and P=0.008, respectively). Neither plasma apo A1 nor apo B, apo B48, TRL apo B, apo CII or apo E were significantly altered by dietary fat modification. 
• HDL-C but not TC or LDL-C showed a diet x time interaction (P=0.005). HDL-C was increased after both high-fat diets, HSFA and HMUFA (P<0.0005 and P=0.006, respectively), which improved the TC:HDL-C ratio (P=0.005  diet x time interaction). This ration was significantly improved after the LFHCC n-3 diet (P<0.005), mainly explained by lower TC levels.

There was no effect of reducing SFA on insulin sensitivity in weight-stable obese metabolic syndrome subjects. Long-chain n-3 PUFA supplementation, in association with a low-fat diet, improved plasma triacylglycerol (TAG)-related metabolic syndrome profiles. 

Government:	EU 6 Framework Food Safety & Quality Programme, Norwegian Regional Health Authority
Not-for-profit	Norwegian Foundation for Health and Rehabilitation, Johan Throne Holst Foundation for Nutrition Research, Freia Medical Research Foundation Other non-profit:
In-Kind support reported by Industry:	Yes