• Recruitment: 1,300 runners from the greater Buffalo metropolitan area running community were sent letters requesting their participation in the study.
• Design: Non-randomized clinical trial
• Blinding used: Not used.
• Intervention: Subjects consumed diets of 16%, 31% or 44% fat for four weeks.

Statistical Analysis

• Comparisons were made using all 25 subjects between the first two diets and using 12 subjects between the last two diets
• Two-way ANOVA with repeated measures was used with diet and gender as the main factors for all performance data
• For blood measurements, a three-way ANOVA with repeated measures was done using diet, gender and time during the exercise test as the main factors
• The effects of low- to medium-fat diets were analyzed with N=25 and the medium- to high-fat diets analyzed with N=12
• Post-hoc testing to determine significant difference among the means was done using the Newman-Kuels post-hoc test (P<0.05).

Timing of Measurements

• Endurance and VO_2max tested at the end of each diet
• Blood sampled before and after the VO_2max and endurance runs.

Dependent Variables

• Endurance; run to exhaustion at 80% of VO_2max
• Wingate Anaerobic Power Test
• VO_2max measured through expired gas collection
• Plasma levels of lactate, pyruvate, glucose, glycerol and triglycerides measured by colorimetric commercial kits
• Free fatty acids assayed using spectrophotometric method
• Body weight measured on electronic scale
• Body fat percentage measured by underwater densitometry.

Independent Variables

• Isocaloric diets of 16%, 31% or 44% fat for four weeks
• Given one-week sample menus to follow, but food was self-selected
• Subjects taught how to record their food, fluid and supplement intake and returned food records weekly to dietitians for review to determine compliance 
• No washout period.

• Initial N: 45 subjects originally met the criteria to participate, but it is unclear how many enrolled.
• Attrition (final N): 25 subjects completed the study; 12 males and 13 females completed the first two diet periods and six males and six females completed all three diet periods

Age

• Females: 33±2.2 years for LF-MF, 32±3.2 for MF-HF
• Males: 37±2.0 for LF-MF, 36±2.6 for MF-HF.

Ethnicity

Not mentioned.

Anthropometrics

Males and females were significantly different from each other in terms of height, weight, body fat and VO_2max.

Location

Buffalo, New York.

Measurements During the Endurance Run

Other Findings

• Runners on the low-fat diet ate 19% fewer calories than on the medium- or high-fat diets
• Fat levels actually consumed by runners were 16% and 31% for 25 subjects used on low- to medium-fat diet comparisons and 33% and 44% for 12 subjects used for medium- and high-fat comparisons
• Body weight, body fat percentage, VO_2max and anaerobic power were not affected by the level of dietary fat
• Endurance time increased from the low-fat to medium-fat diet by 14% (increased 20% in females and 8% in males). There were no significant differences between the high- and medium-fat diets.
• No differences were seen in plasma lactate, glucose, glycerol, triglycerides and fatty acids, when comparing the low- vs. the medium-fat diet
• Subjects who increased dietary fat to 44% had higher plasma pyruvate (46%) and lower lactate levels (39%) after the endurance run.

• These data support previous studies demonstrating that increased dietary fat intake, without compromising carbohydrate intake, improves endurance performance
• If the diet is hypocaloric however, increasing fat and decreasing carbohydrates reduces glycogen stores and impairs performance
• Clearly demonstrated by the reduced running capacity on the low-fat diet, reduction in total calories or fat is not conducive to optimal exercise performance
• It is suggested that the intramuscular stores of glycogen and fats are the crucial ones as the rate of supply from the blood is too slow to meet energy requirements
• The blood substrates are important for the replenishment of intramuscular stores during recovery from exercise
• The present study extends these observations to female runners and runners of a more recreational nature
• The present study does not support the hypothesis that increasing fat to 44% of total calories improves performance to a greater extent than does 31% fat. However, further studies using more intensely trained athletes with lower body fat are needed.

• Compliance assessed by dietitian review, but subjects did not follow diets well and only half of subjects increased fat intake to 44%
• Unclear as to how many of 45 subjects asked to participate actually enrolled
• No washout period between diets.