Randomized Controlled Trial

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POSITIVE: See Quality Criteria Checklist below.

To systematically examine the effects of low-fat diet and exercise, both individually and in combination on METS, using a randomized controlled study design and adjusting for change in body composition.

• Men between the ages of 30 to 64 years, women 45 to 64 years
• Men HDL-cholesterol less than 1.17mmol per L, LDL-cholesterol 3.26 to 4.90mmol per L and BMI 34kg/m² or less
• Post-menopausal women with HDL-cholesterol less than 1.55mmol per L, LDL-cholesterol 3.26 to 5.41mmol per L and BMI 32kg/m² or less
• Blood pressures below 160/95mm Hg, triglycerides under 5.65mmol per L, fasting glucose under 7.77mmol per L and a normal maximal exercise treadmill test
• Provided written informed consent.

• History of heart disease
• Abnormal response to symptom-limited treadmill exercise test
• Insulin-dependent diabetes mellitus
• Neuromuscular or orthopedic disability
• Use of lipid, blood pressure or insulin medication
• Non-euthyroid, low hematocrit
• Excessive smoking or alcohol consumption
• Inability to attend session by judgment of a physician.

Recruitment

Not described, but participants were part of the Diet and Exercise for Elevated Risk Trial (DEER), which began in 1992.

Design

Randomized controlled trial.

Blinding Used

Implied with measurements.

Intervention

• Low-fat diet group: Participants randomized into this group were instructed on methods to achieve the dietary goals set forth by the National Cholesterol Education Program Step II Guidelines to:
  • Reduce total fat to less than 30% of total calories
  • Reduce saturated fat to less than 7% total calories
  • Reduce dietary cholesterol to less than 200mg day
• Exercise group: Participants randomized to this group met with a member of the exercise intervention team to develop an individualized exercise prescription. The plan consisted of six weeks of one-hour supervised aerobics classes conducted three days a week. 
• Diet plus exercise group: Participants received both interventions in session separate from the diet-only and exercise only groups
• Participants randomized into the control group were asked to maintain their usual diet and exercise habits until tests were completed one year after randomization.

Statistical Analysis

• All statistical analysis were performed using SAS software version 9.1, all analyses were done separately by gender
• General linear models were used to explore potential between-group differences in demographic, physiological and behavioral variables at baseline
• Chi-squared was used to examine treatment group differences for baseline prevalence of METS
• Differences between the changes in METS between control, diet, exercise and diet plus exercise groups were assessed using general linear modeling with two separate models. Model 1 controlled for baseline METS score, cohort, age and menopausal hormonal therapy (MHT). Model 2 included covariates for baseline body fat and the change in body fat (percent).
• Change in percent body fat was calculated as the difference between follow-up and baseline. Between group was analyzed within gender using general linear modeling adjusting for
  • Baseline percent body fat
  • Age
  • Cohort
  • MHT
• Change in body fat was divided by tertiles and its association with change in METS was assessed with correlations and general linear models adjusted for
  • Age
  • Cohort
  • Baseline
  • METS score
  • MHT.

 

Timing of Measurements

Measurements made at baseline and at one year.

Dependent Variables

• Body weight was measured with a standard medical beam balance scale
• Height was measured using a Harpenden stadiometer
• BMI was calculated by dividing the participants body weight in kg by height in meters squared
• Three measures of waist circumference were taken from the narrowest circumference of the torso when viewed from the front and average
• Changes in metabolic syndrome (METS): Defined as changes in blood pressure which was measured using a mercury sphygmomanometer from the brachial artery. The average of the two readings of the first and fifth phase Korotkoff were noted as systolic and diastolic blood pressure readings.
• Changes in metabolic syndrome (METS): Also defined as changes in HDL-C, VLDL-C, LDL-C, total cholesterol and triglyceride values. These were measured by blood samples  taken in the morning on two different visits at baseline and once at follow-up. All collected blood was mixed with 1.5mg per ml of EDTA. Both baseline fasting blood samples were analyzed for lipoproteins and averaged. Total cholesterol and triglycerides were measured using standard enzymatic procedures. HDL-C, VLDL-C and LDL-C were also calculated.

Independent Variables

• Low-fat diet group: Participants randomized into this group were instructed on methods to achieve the dietary goals set forth by the National Cholesterol Education Program Step II Guidelines to:
  • Reduce total fat to less than 30% of total calories
  • Reduce saturated fat to less than 7% total calories
  • Reduce dietary cholesterol to less than 200mg per day
• Exercise group: Participants randomized to this group met with a member of the exercise intervention team to develop an individualized exercise prescription. The plan consisted of six weeks of one-hour supervised aerobics classes conducted three days a week. 
• Diet plus exercise group: Participants received both interventions in session separate from the diet-only and exercise-only groups
• Participants randomized into the control group were asked to maintain their usual diet and exercise habits until tests were completed one year after randomization.

Control Variables

• Percent body fat was determined from skinfold measurements. Gender-specific skinfold thickness were taken three times on the right side of the body and averaged.
• Body density was estimated using generalized equations.

• Initial N: 377 participants
• Attrition (final N): 328 total (179 men, 149 women)
• Age: Mean age for men 48.6±8.7, for women 57.6±5.1 years
• Ethnicity: 86% white
• Other relevant demographics: 57% men and 40% women had completed a college degree
• Anthropometrics:
  • Mean BMI (kg/m²) for men in control group 26.7±2.9, diet group 26.8 ±3.1, exercise group 26.7±2.7, diet plus exercise group 26.8±2.6. Mean BMI (kg/m²) for women in control group 25.9±3.9, diet group 26.5±2.9, exercise group 26.1±2.4, diet plus exercise group 26.5±3.4.
  • There were no significant differences between treatment groups for any of the lipid, metabolic or anthropometric variables in either men or women at baseline
• Location: Baton Rouge, Louisiana.

Key Findings

• In men, the change in METS was higher for D vs. C (P=0.04), D+E vs. C(P=0.0002) and D+E vs. E (P=0.02)
• For women, change in METS was greater for D vs. C (P=0.045), E vs. C (P=0.02) and D+E vs. C(P=0.004)
• After adjusting for change in BF, all differences between groups were attenuated and no longer significant. Change in METS were associated with change in body fat for both men (P<0.0001) and women (P=0.004)
• After adjustment for change in body fat, low-fat diet alone and in combination with exercise had no effect on METS
• Renal outcomes were not studied.

 

 

In conclusion, the results demonstrate no effect of low-fat diet alone or in combination with exercise on METS after adjusting for percent body fat loss in men and post-menopausal women. This study provides evidence that the key component for change in METS is reducing percent body fat. Future studies are needed to further elucidate biological mechanisms to explain the relationship between METS and body fat. Clinical trials are also needed which can identify the specific threshold and location of body fat loss that corresponds to a significant change in METS.

Government:

National Institutes of Health R21HL086651

The authors did note that a post-hoc analysis revealed that the sample sizes of the treatment groups in this study were not powered to detect differences using a dichotomous outcome for METS.