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The doubly labelled water method for the assessment of energy expenditure was first published in 1955, application in humans started in 1982, and it has become the gold standard for human energy requirement under daily living conditions. The method involves enriching the body water of a subject with heavy hydrogen ( 2 H) and heavy oxygen ( 18 O), and then determining the difference in washout kinetics between both isotopes, being a function of carbon dioxide production. In practice, subjects get a measured amount of doubly labelled water ( 2 H 2 18 O) to increase background enrichment of body water for 18 O of 2000 ppm with at least 180 ppm and background enrichment of body water for 2 H of 150 ppm with 120 ppm. Subsequently, the difference between the apparent turnover rates of the hydrogen and oxygen of body water is assessed from blood-, saliva-, or urine samples, collected at the start and end of the observation interval of 1–3 weeks. Samples are analyzed for 18 O and 2 H with isotope ratio mass spectrometry. The doubly labelled water method is the indicated method to measure energy expenditure in any environment, especially with regard to activity energy expenditure, without interference with the behavior of the subjects. Applications include the assessment of energy requirement from total energy expenditure, validation of dietary assessment methods and validation of physical activity assessment methods with doubly labelled water measured energy expenditure as reference, and studies on body mass regulation with energy expenditure as a determinant of energy balance.

Activity-induced energy expenditure, as determined by the activity pattern including exercise, is the most variable component of daily energy expenditure. Here, the focus is on effects of exercise training on energy balance and body composition in subjects with a sedentary or light-active lifestyle. Then, exercise training induces an energy imbalance consistently lower than prescribed energy expenditure from exercise. Additionally, individual responses are highly variable and decrease in time. Combining the results from 23 exercise training studies in normal-weight, overweight, and obese subjects, varying in duration from 2 to 64 weeks, showed an average initial energy imbalance of about 2 MJ/day with an exponential decline to nearly zero after about 1 year. A compensatory increase in energy intake is the most likely explanation for the lower than expected effect of exercise on energy balance. Overall, exercise training results in a healthier body composition as reflected by a reduction of body fat, especially in overweight and obese subjects, with little or no long-term effect on body weight.

Wrist-mounted motion sensors can quantify the volume and intensity of physical activities, but little is known about their long-term validity. Our aim was to validate a wrist motion sensor in estimating daily energy expenditure, including any change induced by long-term participation in endurance and strength training. Supplemental heart rate monitoring during weekly exercise was also investigated. A 13-day doubly labeled water (DLW) measurement of total energy expenditure (TEE) was performed twice in healthy male subjects: during two last weeks of a 12-week Control period (n = 15) and during two last weeks of a 12-week combined strength and aerobic Training period (n = 13). Resting energy expenditure was estimated using two equations: one with body weight and age, and another one with fat-free mass. TEE and activity induced energy expenditure (AEE) were determined from motion sensor alone, and from motions sensor combined with heart rate monitor, the latter being worn during exercise only. When body weight and age were used in the calculation of resting energy expenditure, the motion sensor data alone explained 78% and 62% of the variation in TEE assessed by DLW at the end of Control and Training periods, respectively, with a bias of +1.75 (p <.001) and +1.19 MJ/day (p = .002). When exercise heart rate data was added to the model, the combined wearable device approach explained 85% and 70% of the variation in TEE assessed by DLW with a bias of +1.89 and +1.75 MJ/day (p <.001 for both). While significant increases in TEE and AEE were detected by all methods as a result of participation in regular training, motion sensor approach underestimated the change measured by DLW: +1.13±0.66 by DLW, +0.59±0.69 (p = .004) by motion sensor, and +0.98±0.70 MJ/day by combination of motion sensor and heart rate. Use of fat-free mass in the estimation of resting energy expenditure removed the biases between the wearable device estimations and the golden standard reference method of TEE and demonstrated a training-induced increase in resting energy expenditure by +0.18±0.13 MJ/day (p <.001). Wrist motion sensor combined with a heart rate monitor during exercise sessions, showed high agreement with the golden standard measurement of daily TEE and its change induced by participation in a long-term training protocol. The positive findings concerning the validity, especially the ability to follow-up the change associated with a lifestyle modification, can be considered significant because they partially determine the feasibility of wearable devices as quantifiers of health-related behavior.

Assessment of physical activity in a free-living environment is important for understanding relations between physical activity and health and determining the effectiveness of interventions. Techniques include behavioral observation, questionnaires in the form of diaries, recall questionnaires and interviews, and physiological markers like heart rate, calorimetry, and motion sensors. The doubly labeled water method has become the gold standard for the validation of field methods of assessing physical activity. Then, questionnaires show a low reliability and validity but can be adequately applied as an activity-ranking instrument. The heart rate requires individual calibration to be an effective method to assess physical activity only at group level. The indicated method for the assessment of habitual physical activity in daily life is a doubly labeled water validated accelerometer. Future developments are simultaneous measurement of body acceleration and heart rate for the assessment of physical fitness. A new generation of accelerometers will provide information on body posture and activity recognition to allow objective assessment of subjects’ habitual activities, options for a healthy change, and effects of the follow-up of any changes.

BackgroundThe most commonly used prediction models for resting energy expenditure (REE) are Harris-Benedict (1919), Schofield (1985), Owen (1986), and Mifflin-St Jeor (1990), based on height, weight, age and gender, and Cunningham (1991), based on body composition.MethodsHere, the five models are compared with reference data, consisting of individual REE measurements (n = 353) from 14 studies, covering a large range of participant characteristics.ResultsFor white adults, prediction of REE with the Harris-Benedict model approached measured REE most closely, with estimates within 10% for more than 70% of the reference population.DiscussionSources of differences between measured and predicted REE include measurement validity and measurement conditions. Importantly, a 12- to 14-h overnight fast may not be sufficient to reach post-absorptive conditions and may explain differences between predicted REE and measured REE. In both cases complete fasting REE may not have been achieved, especially in participants with high energy intake.ConclusionIn white adults, measured resting energy expenditure was closest to predicted values with the classic Harris-Benedict model. Suggestions for improving resting energy expenditure measurements, as well as prediction models, include the definition of post-absorptive conditions, representing complete fasting conditions with respiratory exchange ratio as indicator.

The doubly labelled water method for the measurement of total daily energy expenditure (TDEE) over 1–3 weeks under daily living conditions is the indicated method to study effects of exercise and extreme environments on energy balance. Subjects consume a measured amount of doubly labelled water (2H2 18O) to increase background enrichment of body water for 18O and 2H, and the subsequent difference in elimination rate between 18O and 2H, as measured in urine, saliva or blood samples, is a measure for carbon dioxide production and thus allows calculation of TDEE. The present review describes research showing that physical activity level (PAL), calculated as TDEE (assessed with doubly labelled water) divided by resting energy expenditure (REE, PAL = TDEE/REE), reaches a maximum value of 2·00–2·40 in subjects with a vigorously active lifestyle. Higher PAL values, while maintaining energy balance, are observed in professional athletes consuming additional energy dense foods to compete at top level. Exercise training can increase TDEE/REE in young adults to a value of 2·00–2·40, when energy intake is unrestricted. Furthermore, the review shows an exercise induced increase in activity energy expenditure can be compensated by a reduction in REE and by a reduction in non-exercise physical activity, especially at a negative energy balance. Additionally, in untrained subjects, an exercise-induced increase in activity energy expenditure is compensated by a training-induced increase in exercise efficiency.

Background/ObjectivesSeasonal variation in body mass is a model for the study of body mass regulation. Here a long-term study is presented on body mass, body composition, and activity-induced energy expenditure in a subject with a large seasonal variation in body mass of about 3.0 kg.Subject/MethodsBody mass was assessed daily over >20 consecutive years. Daily assessment of activity-induced energy expenditure was performed over the last 10 years. Body composition was assessed monthly for 1 year in the middle and at the end of the observation interval. Additionally, data were compared with data on body composition, resting energy expenditure, and total daily energy expenditure of the same subject as a participant in published studies.ResultsBody mass showed a pronounced seasonal variation, associated with a synchronous variation in physical activity. Body mass peaked in the cold winter months when physical activity reached the lowest annual value and decreased to the lowest value in mid-summer when daily physical activity peaked. The seasonal variation in body mass consisted mainly of body fat. Longitudinally, over the past 8 years of the observation interval, average fat-free mass showed a decrease of 1.0 kg and fat mass increased 0.8 kg.ConclusionsIn a subject with a pronounced seasonal variation in physical activity, activity-induced variation in energy requirement was covered by an annual variation in body mass, mainly as fat. Maintenance of activity-induced energy expenditure did not protect against loss of fat-free body mass with advancing age.

Obesity is a serious health problem because of its co-morbidities. The solution, implying weight loss and long-term weight maintenance, is conditional on: (i) sustained satiety despite negative energy balance, (ii) sustained basal energy expenditure despite BW loss due to (iii) a sparing of fat-free mass (FFM), being the main determinant of basal energy expenditure. Dietary protein has been shown to assist with meeting these conditions, since amino acids act on the relevant metabolic targets. This review deals with the effects of different protein diets during BW loss and BW maintenance thereafter. Potential risks of a high protein diet are dealt with. The required daily intake is 0·8–1·2 g/kg BW, implying sustaining the original absolute protein intake and carbohydrate and fat restriction during an energy-restricted diet. The intake of 1·2 g/kg BW is beneficial to body composition and improves blood pressure. A too low absolute protein content of the diet contributes to the risk of BW regain. The success of the so-called ‘low carb’ diet that is usually high in protein can be attributed to the relatively high-protein content per se and not to the relatively lower carbohydrate content. Metabolic syndrome parameters restore, mainly due to BW loss. With the indicated dosage, no kidney problems have been shown in healthy individuals. In conclusion, dietary protein contributes to the treatment of obesity and the metabolic syndrome, by acting on the relevant metabolic targets of satiety and energy expenditure in negative energy balance, thereby preventing a weight cycling effect.

The recent Covid-19 pandemic caused countries worldwide to implement measures affecting inhabitants’ freedom including a ban on travel and gatherings, instructions to work from home, and a lockdown of restaurants and nonfood shops. Consequently, there were important changes in lifestyle with regard to both, dietary habits and physical activity. Publications on lockdown induced changes in dietary habits, physical activity, and energy balance are available and show significant differences from pre-Covid values.