Onset of the Thermic Effect of Feeding (TEF): a randomized cross-over trial

Resting metabolic rate (RMR) and TEF were measured over 30-minute periods via indirect calorimetry using a ventilated hood technique. Eighteen subjects (7 men and 11 women) completed two randomized, double-blind trials. Data were collected in 1-minute measurement intervals. RMR was subtracted from TEF and the time of onset was obtained when two consecutive data points exceeded 5% and 10% of resting metabolic rate.At 5% above RMR the onset of TEF for CHO was 8.4 ± 6.2 minutes and was not different as compared to PRO, 8.6 ± 5.2 minutes (p = 0.77). Likewise, no differences were found with a 10% increase above RMR: CHO, 14.1 ± 7.5 min; PRO, 16.7 ± 6.7 min (p = 0.36). Several subjects did not show a 10% increase within 30-min.We conclude that the onset of TEF is variable among subjects but is initiated within about 5 to 20-min for most subjects after ingestion of a 1255 kJ liquid meal. No differences were found between CHO or PRO liquid meals.Antoine Lavosier (1743–1794) may have been the first to directly connect digestion with an increased heat production and oxygen consumption [1]. Later in the 20th century it was discovered that increases in energy expenditure after eating, called the thermic effect of feeding (TEF), varied depending on the composition of the meal [2]. Metabolic rate not only rises to a greater extent with an increased caloric intake [3,4] but there is a 6–8% increase in energy expenditure with carbohydrate meals, 3% increase with fat, and 25–40% with protein based meals [2]. Research tends to focus on the extent and timing of the peak TEF where measurements can go on for hours [5]. Measurement intervals too can be lengthy often occurring in 15 or 30-minute periods. Lengthy measurement intervals reduce measurement variability [6] but they also make it difficult to pinpoint precise time periods; for example, determining when TEF rises.Sports nutritionists have brought timing issues to attention where it has been recommended that nutrient ingestion pos