The aim of this study was to examine the effects of a 7-day Zone diet compared with a normal diet on maximal oxygen uptake (V̇O2max), running time to exhaustion during endurance performance, and body composition. Eight men, with the following physical characteristics (mean ± SE), participated in this study: age, 26.1 ± 1.9 years; height, 178 ± 1.7 cm; mass, 70.7 ± 2.1 kg; and V̇O2max, 54.6 ± 3.1 ml·kg-1·min-1. All subjects undertook pretesting for V̇O2max, time to exhaustion (80% V̇O2max), and body composition (Biostat 1500) before following either the normal diet or the Zone diet for 7 days. These performance trials were performed before and after the dietary period. There was a significant (p < 0.05) decrease in total energy consumption from a mean of 2,314 ± 334 kcal on a pretest diet to 1,994 ± 438 kcal on the Zone diet. Subjects showed a significant reduction (p < 0.02) in body mass from 70.7 ± 2.1 kg to 69.8 ± 2.1 kg. In the 80% V̇O2max time to exhaustion trial, there was a significant reduction (p < 0.05) in time to exhaustion from 37.68 ± 8.6 minutes for the pretest diet to 34.11 ± 7.01 minutes for the Zone diet. In conclusion, the claim of the authors of the Zone diet that performance time and V̇O2max can be improved was not shown in this 1-week research trial. We would suggest that this is not a nutritional strategy that athletes should use until further work has been conducted.
Jarvis, M., McNaughton, L., Seddon, A., & Thompson, D. (2002). The acute 1-week effects of the zone diet on body composition, blood lipid levels, and performance in recreational endurance athletes. Journal of Strength and Conditioning Research, 16(1), 50–57. https://doi.org/10.1519/1533-4287(2002)016<0050:TAWEOT>2.0.CO;2