Ben Greenfield on nutrition: what the evidence says · JRE #1069
“the prevailing research and the literature suggests that you can burn about 1.0 grams of fat per minute during exercise. Like that would be about how much fat you would burn, 1.0 grams of fat per minute.”
What the evidence says
Greenfield's underlying reference is Volek et al. (2016), a cross-sectional study comparing 10 elite ultra-endurance athletes on a long-term low-carbohydrate diet to 10 on a high-carbohydrate diet, often nicknamed the FASTER study. Peak fat oxidation measured 1.54 g/min in the low-carb group during a graded maximal test, and 1.21 g/min during 180 minutes of submaximal running at 64% VO2max, figures below the 1.5 to 1.7 g/min range Greenfield cites. The high-carb comparison group's peak fat oxidation was 0.67 g/min. The general exercise-science literature does not describe a fixed 1.0 g/min "ceiling"; a 2018 review reports maximal fat oxidation across trained and untrained individuals typically spans 0.17 to 1.27 g/min, with the same Volek study cited as the source for the higher rates seen in keto-adapted athletes. Because the FASTER study was cross-sectional rather than a randomized controlled trial, and its glycogen-depletion equivalence findings applied only to prolonged submaximal running, it does not establish that fat-oxidation rates of 1.5 to 1.7 g/min are typical or that performance is preserved at race pace or higher intensities.