- Click here for explanation of classification scheme.

To determine whether altered meal timing patterns affected:

1) weight and body composition changes during a weight loss intervention that combined regular exercise with a controlled, moderately energy restricted diet , and

2) energy utilization under standardized conditions of rest, exercise, following meals and following exercise to determine whether altering meal patterns would affect the metabolic fate of energy-yielding nutrients.

• women
• 20-40 years of age
• healthy
• premenopausal with normal menstrual cycles
• body fat > 30%

• self-reported tobacco use
• positive urine test for nicotine, narcotics, or mood-altering drugs
• history of orthopedic injury
• medical contraindication for partipation in the exercise program

Recruitment Not specified        

Design 15- week metabolic unit study, consisting of a 3-week stabilization period for weight maintenance, followed by 2 consecutive 6-week experimental periods for weight loss. The macronutrient composition of the intake was kept constant throughout the study at 60% carbohydrate, 18% protein, and 22% fat. Energy intake restriction and exercise was used for weight  loss.  Each subject was assigned to one of 2 groups such that mean values for body weight and composition, physical fitness, and history of dietary restraint were similar between groups. For the 1st experimental period, group A ingested 70% of the daily energy intake in the AM and group B ingested 70% of their energy intake in the PM. For both conditions, the 70% was broken down into 4 meals - the AM with 35% at breakfast, 35% at lunch, 15% at dinner and 15% at evening snack, with the PM being 15% at breakfast, 15% at lunch, 35% at dinner, and 35% at evening snack. The mean energy intake was 107 ±6 kJ/kg.  For the 2nd experimental period, the groups switched to the alternate energy intake pattern.  For both groups, the time of the exercise sessions remained constant through both experimental periods.

Blinding used (if applicable) Not used.

Intervention (if applicable) Energy intake was individually prescribed to be 2 MJ/day below stabilization energy intake.  Exercise involved aerobic activity and weight training and was individualized depending on the subjects' ability and VO2max. Subjects lived on the metabolic ward during study.

Statistical Analysis ANOVA was used to test the effects of order, meal pattern, and period on change in weight and body composition and energy utilization.  If a significant order effect was found, the meal pattern effect was examined for each period using Student's t test.  Probability was set at < 0.05.

Timing of Measurements  Dietary intake was measured daily, subjects were weighed daily, body composition was determined twice weekly, and energy expenditure and utilization was measured using 2 protocols, one conducted twice during the last 2 weeks of both experimental periods, and one conducted twice during weeks 2-4 of each experiemental period.

Dependent Variables  For each 6 week experimental period: weight loss, fat-free mass loss,% fat; also energy expenditure and utilization.

Independent Variables meal pattern assignment

Control Variables none mentioned

Initial N: 12 females    

Attrition (final N): 10 females

Age: group A mean = 29.8 ± 7.6 years, group B mean = 29.2 ±4.2 years.

Ethnicity: 8 Caucasian, 1 Asian, 1 Black

Other relevant demographics: No other demographics included

Anthropometrics  weight, height, FFM, body fat, RMR, and RER prior to weight loss are reported - although means are close, it does not appear they were tested for between group differences.

Location: Western Human Nutrition Research Center at UC-Davis

Effect of AM pattern vs. PM pattern on changes in weight and body composition during weight reduction

	AM pattern	PM pattern
Weight, kg/6 wk	-3.90 ± 0.19	-3.27±0.26**
Fat-free mass, kg/6 wk	-1.28± 0.14	-0.25±0.16*
Fat percentage, %/6 wk	-1.83±0.22	-2.52±0.29***

*P<0.001, **P<0.01, ***P<0.05

 

Effect of AM pattern vs. PM pattern on changes in fat mass and body energy stores during the first 6 wk of weight loss (period 1) and the second 6 wk of weight loss (period 2)

	AM pattern	PM pattern
Fat mass, kg/6 wk
Period 1	-2.91±0.08	-3.69±0.15*
Period 2	-2.57±0.28	-2.02±0.20
Energy content, MJ/6 wk
Period 1	-116.7±3.6	-144.0±6.0*
Period 2	-105.0±10.8	-80.4±8.1

*P<0.01

• Large AM meals resulted in greater loss of weight and FFM compared to large PM meals (p < 0.01 and < 0.001, respectively).
• Large PM meal pattern resulted in a greater decrement in body fat % (p < 0.05).
• Significantly greater loss of fat mass with the PM pattern in period 1, but not 2.
• More body energy stores were lost with the PM pattern during period 1 (p < 0.05), but not 2.
• The effects on energy expenditure and utilization with each pattern were as expected.
• Meal pattern did not affect AM RMR, pre-exercise, exercise, or post-exercise metabolic rate.

 

While weight loss was greater with the AM large meal pattern, there was greater loss of FFM with this pattern.  The authors suggest that this may be due to the lack of precision in their method for measuring body composition which was not able to quantify the specific components of FFM, but conclude that their results suggest that large PM meals may be effective in maintaining FFM. They also conclude that they found little evidence of consistent changes in energy utilization associated with meal pattern and that period effects may be due to greater weight loss during initial weight loss efforts.

Government:

USDA

This was a sophisticated, well-designed study. Inclusionary and exclusionary criteria ensured a homogeneous sample, eliminating many factors that might have affected results.  The cross-over design provides a more stable estimate of true effects and the authors provide a thoughtful discussion of their findings and future research questions.