Human energy expenditure (EE) is not stable over a 24 hour period, it has its own rhythm. Energy Expenditure varies depending on the time of day,  physical activity level and the exercise performed by the subject, the amount of food ingested and its composition. The human 24-hour EE is made up of several components. The different components of 24-hour EE can be measured with our indirect calorimetry (IC) equipment, such as the Room Calorimeter or the Omnical. In this web series, we will discuss and explain all EE components one by one. This time we discuss the TEF or DIT, i.e. the thermic effect of food or diet-induced thermogenesis.
What is the Thermic Effect of Food (TEF)?

The TEF is the thermic effect of food. The term TEF is also known as the meal- or diet- induced thermogenesis, abbreviated as MIT and DIT. It represents the increase in energy expenditure (EE) ensuing to the consumption of a meal or of the intravenous infusion of nutrients. The TEF can traditionally be divided into two components; the obligatory and the facultative component. The obligatory component represents the minimum energy required to convert a nutrient into the storage form that will be taken within the body. The theoretical costs of storing nutrients in the body have been known for some time. However, it is also known that the measured TEF value is always higher than the theoretically based value. This additional value is referred to as the facultative component of the TEF response. In theory, this response is thought to be a kind of flexible mechanism by which the body expended the excess of energy intake (EI). The aim of this is to maintain a stable body weight.

How to measure TEF?

In short, TEF indicates the energy requirements for processing and digesting a meal. After a large meal, processing can take up to 8-10 hours. The TEF is influenced by the size of the ingested meal and the micronutrients it contains. As a result of this association, the TEF is often expressed as percentage of the EI. This is calculated by dividing the increase in EE after the consumption of the meal by the EI. In general, of the 24hEE approximately 10% is accounted for the TEF. This percentage is close to the reality when healthy subjects are in or close to an energy balance and consuming a mixed diet. However, this value can differ between subjects or within subjects whose energy balance has changed of is changing.

Figure 1 Components of total daily energy expenditure.

Figure 2 Relationship between energy expenditure and activity. By simple regression analysis, the resting energy expenditure (REE) can be calculated as the y-intercept and the TEF of all the meals is calculated as the difference between REE and the BMR (or RMR). The energy cost of physical activity is the slope of the linear regression line.

Different study designs

In a whole-room calorimetry measurement it is difficult to discern between increases in BMR/RMR produced by TEF or by the activity thermogenesis (see Figure 1). To circumvent this problem, one of the components must be minimized as much as possible by design. This is possible with three different alternatives for the study design.

1. Have the subjects fast one day and feed them the next, while activity thermogenesis is reduced by limiting physical activity.

2. Estimating TEF by measuring the physical activity. Nevertheless, this method has been shown to have poor biological reproducibility when subjects are measured more than once, due to the analysis method. A regression graph is made with the measured physical activity data (y-axis) is against the EE (x-axis) per unit of time. Hereby, the y-intercept shows the EE of the subject in an inactive status and the
difference between the y-intercept and the BMR/RMR is considered to represent the cumulative TEF (both components) (see Figure 2). In order to measure TEF in a respiration chamber, improvements will need to be made and development are necessary in this area to make the measurement and analysis more accurate and reproducible.

3. The last method is to determine the TEF when the person is lying in a supine position. In this way neither physical activity nor movements can influence the measurement.

Measurement sensitivities

The biological reproducibility of the TEF when using a mixing chamber metabolic cart system with canopy is indicated as the day-to-day coefficient of variation (CVd-to-d). This CVd-to-d can vary from 15 to 33%. This elevation in CVd-to-d is partly due to the method of calculating the TEF, which is usually calculated as the difference between the RMR (measured before the meal) and the total post-meal EE. Because of this, the TEF can be identical from day to day. The variability in RMR prior to the meal can affect the calculation negatively. Previous studies have attempted to calculate each sequential TEF value using a fixed RMR. However, if there have been any improvements in the between day precision and CVd-to-d, these have been minimal. In order to obtain the most accurate TEF measurement possible, improvements in methodology are still a necessity when using a metabolic cart.

How can we help you with your research?

If you are interested in indirect calorimetry measurements, you have come to the right place. We have the best equipment in the field at our disposal.

“The Omnical metabolic cart seems to be the most valid system among metabolic carts for assessing both, RMR and RER.” – Juan M. Alcántara Alcántara, 2020

We provide not only our products in indirect calorimetry and accelerometry, but also an excellent service in terms of support for studies, research and measurements. You can always consult us for information and guidance on product support, software support, parameter use, measurement methods and protocols, validation options, interpretation and correct use of measurement data, complementary products, etc.

Do you plan to measure TEF/DIT/MIT?

If you are interested in measuring TEF/DIT/MIT then consult us about our indirect calorimetry metabolic cartwhole room calorimeter systems or accelerometry add-ons. Please contact us or find more information on our information pages.


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  • Alcántara Alcántara, Juan Manuel. Assessment of resting energy expenditure and nutrient oxidation by indirect calorimetry: methodological implications. Granada: Universidad de Granada, 2021.


  • Spaeth, Andrea Marie, “Consequences of Chronic Sleep Restriction on Energy Balance in Healthy Adults” (2014)
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Figure 3 The use of a metabolic hood system with canopy, here at our facilities in Maastricht.