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PURPOSE OF REVIEW: Physical activity is the main determinant of variability of individual energy expenditure. Reliable assessment of the activity level of an individual provides information on energy requirement and vital health. Here, evidence is presented on the validity of methods to assess physical activity as applied in health and disease. RECENT FINDINGS: Improvement of technology has resulted in a growing number of physical activity monitors to evaluate the activity level of an individual. Outcome measures vary from raw data on body acceleration and posture to activity levels derived from proprietary algorithms based on body acceleration combined with sensor information on additional activity-induced physiological responses. Data interpretation is limited by evidence-based studies on the value of measured parameters for the assessment of physical activity. SUMMARY: The optimal tool for reliable assessment of physical activity is an accelerometer providing a valid measure of body movement. Overall validity is derived from studies using doubly labelled water-assessed activity-induced energy as a reference. Thus, out of the large range of activity monitors, three came out with a better validity. The ultimate tool is a single unobtrusive device allowing valid and long-term monitoring of activity with regard to type and intensity.

Body weight and energy balance can be maintained by adapting energy intake to changes in energy expenditure and vice versa, whereas short-term changes in energy expenditure are mainly caused by physical activity. This review investigates whether physical activity is affected by over- and undereating, whether intake is affected by an increase or a decrease in physical activity, and whether being overweight affects physical activity. The available evidence is based largely on studies that quantified physical activity with doubly labeled water. Overeating does not affect physical activity, while undereating decreases habitual or voluntary physical activity. Thus, it is easier to gain weight than to lose weight. An exercise-induced increase in energy requirement is typically compensated by increased energy intake, while a change to a more sedentary routine does not induce an equivalent reduction of intake and generally results in weight gain. Overweight and obese subjects tend to have similar activity energy expenditures to lean people despite being more sedentary. There are two ways in which the general population trend towards increasing body weight can be reversed: reduce intake or increase physical activity. The results of the present literature review indicate that eating less is the most effective method for preventing weight gain, despite the potential for a negative effect on physical activity when a negative energy balance is reached.

PURPOSE OF REVIEW: Is trafficking of dietary fat involved in the development of obesity? RECENT FINDINGS: Studies on energy expenditure and substrate utilization during overfeeding, studies on individual differences in substrate utilization between individuals fed at energy balance, and differences in responses in energy expenditure and substrate utilization in individuals after weight reduction, illustrate that the capacity of fat oxidation is a potential determinant for the development of obesity. SUMMARY: The ability to store dietary fat seems to be involved in the susceptibility to gain weight during a positive energy balance. Obese individuals show less oxidation and more storage of dietary fat as compared with the lean phenotype. Differences in fuel trafficking make individuals prone to overeating in the current obesogenic environment with a high availability of energy-dense fatty foods. It is difficult to get rid of excess body fat as energy requirement for weight maintenance after weight reduction is lower than predicted from the new body composition reached and thus, there is a high risk for weight regain.

Objective:Obesity results from protracted energy imbalance. Whether this comprises excessive energy intake, lowered physical activity or both, remains disputed.Design:Physical activity energy expenditure, evaluated in three different ways from daily energy expenditure (DEE) measured using doubly labelled water, was examined for trends over time. Data included subjects in Europe (Maastricht, the Netherlands) and North America extending back to the 1980s. These data were compared with measures from the third world, and measures made on wild terrestrial mammals.Results:Physical activity expenditure in Europe (residual of the regression of DEE on basal energy expenditure (BEE)) has slightly but significantly increased since the 1980s. There was no trend over time in physical activity level (PAL=DEE/BEE), or in the residual variance in DEE once mass, sex and age were accounted for. This latter index of physical activity expenditure also significantly increased over time in North America. DEE of individuals in Europe and North America was not significantly different from individuals measured in the third world. In wild terrestrial mammals, DEE mostly depended on body mass and ambient temperature. Predicted DEE for a 78 kg mammal living at 20 degrees C was 9.2 MJ per day (95% CI: 7.9-12.9 MJ per day), not significantly different from the measured DEE of modern humans (around 10.2-12.6 MJ per day).Conclusion:As physical activity expenditure has not declined over the same period that obesity rates have increased dramatically, and daily energy expenditure of modern man is in line with energy expenditure in wild mammals, it is unlikely that decreased expenditure has fuelled the obesity epidemic.International Journal of Obesity advance online publication, 27 May 2008; doi:10.1038/ijo.2008.74.

Inter-individual variation in energy expenditure is mainly a function of differences in body size and physical activity. Intra-individually, the energy expenditure associated with physical activity, i.e. muscular contractions to perform body postures and -movements, is the most variable component of total energy expenditure. Determinants of activity associated energy expenditure (AEE), as derived from observational and intervention studies are presented. Twin studies showed that most of the between subject variation in AEE is explained by genetic factors. AEE of subjects in the confined environment of a respiration chamber was on average halve the value as observed in the same subjects in free-living conditions with doubly labeled water. In young adults, non-training activity was not affected by exercise training. However, in elderly subjects, exercise training induced an equivalent compensatory decline in non-training activity. Similarly, AEE was reduced during energy restriction and in patients with chronic disease increasing resting energy expenditure. Studies with exercise training showed the reduction is difficult to overcome.

It is hypothesized that low dietary fat oxidation makes subjects prone to weight gain.The aim of the study was to determine dietary fat oxidation in normal, overweight, and obese subjects.The subjects were 38 women and 18 men with a mean (+/-SD) age of 30+/-12 y and a body mass index (in kg/m2) of 25+/-4 (range: 18-39). Dietary fat oxidation was measured with deuterated palmitic acid, given simultaneously with breakfast, while the subjects were fed under controlled conditions in a respiration chamber. Body composition was measured by hydrodensitometry and deuterium dilution.Dietary fat oxidation, measured over 12 h after breakfast, ranged from 4% to 28% with a mean (+/-SD) of 16+/-6%. Dietary fat oxidation was negatively related to percentage body fat, and lean subjects had the highest and obese subjects the lowest values (r=-0.65, P

Altitude exposure decreases energy intake and thus induces an energy deficit resulting in the loss of body mass. The energy deficit is worsened when energy expenditure is increased by exercise because the increase is not matched by an increased energy intake. The indicated fuel for the optimal use of the rarefied oxygen at altitude is carbohydrate. For optimal taste and maximizing energy intake, fat is the best. Protein should rather be limited because of its high thermic effect. Intestinal malabsorption probably does not play a role in the energy deficit. Even though the sensation of exertion during climbing at high altitude is intense, the actual energy expenditure is not high.

The palatability of a diet is an important determinant of energy intake. Due to a high palatability, a relatively high energy density, and a weak effect on satiation, the consumption of high-fat foods induces passive overfeeding. It is well known that a high-fat diet often leads to a loss of portion control of tasty foods. Here, studies are reviewed on the effect of overfeeding on substrate utilization and energy expenditure. It is often suggested that humans differ in the susceptibility to weight gain in response to overfeeding. Six years ago, non-exercise activity thermogenesis was presented as a new mechanism to explain differences in weight gain between subjects. Activation of non-exercise activity thermogenesis could dissipate excess energy to preserve leanness and only failure to activate non-exercise activity thermogenesis resulted in ready fat gain. However, there is still little evidence for this form of adaptive thermogenesis from additional studies. The conclusion is that the fat content has an effect on body fat as a function of the effect of dietary fat on energy intake.

Although water is an important nutrient, there are no recommended intake values. Here, water intake, energy intake, physical activity and water loss was measured over 1 week in summer and in winter. Subjects were healthy volunteers, forty-two women and ten men, mean age of 29 (SD 7) years and mean BMI 21.8 (SD 2.2) kg/m2. Water intake was measured with a 7 d food and water record. Physical activity level (PAL) was observed as the ratio of total energy expenditure, as measured with doubly labelled water, to resting energy expenditure as measured in a respiration chamber. Water loss was measured with the deuterium elimination method. Water loss was highly reproducible and ranged from 0.20 to 0.35 l/MJ, independent of season and activity level, with higher values in women. Water loss was related to water and energy intake in summer (r 0.96, P<0.0001 and r 0.68, P<0.001, respectively) as well as in winter (r 0.98, P<0.0001 and r 0.63, P<0.01, respectively). Water loss was, for men, higher in subjects with a higher physical activity in summer (r 0.94, P<0.0001) and in winter (r 0.70, P<0.05). Normalizing water loss for differences in energy expenditure by expressing water loss in litres per MJ resulted in the same value for men in summer and winter. For women, physical activity-adjusted values of water loss were higher, especially in summer. In men, water turnover was determined by energy intake and physical activity, while seasonal effects appeared through energy expenditure. Women showed a higher water turnover that was unrelated to physical activity.

OBJECTIVE: Daily energy expenditure consists of three components: basal metabolic rate, diet-induced thermogenesis and the energy cost of physical activity. Here, data on diet-induced thermogenesis are reviewed in relation to measuring conditions and characteristics of the diet. METHODS: Measuring conditions include nutritional status of the subject, physical activity and duration of the observation. Diet characteristics are energy content and macronutrient composition. RESULTS: Most studies measure diet-induced thermogenesis as the increase in energy expenditure above basal metabolic rate. Generally, the hierarchy in macronutrient oxidation in the postprandial state is reflected similarly in diet-induced thermogenesis, with the sequence alcohol, protein, carbohydrate, and fat. A mixed diet consumed at energy balance results in a diet induced energy expenditure of 5 to 15 % of daily energy expenditure. Values are higher at a relatively high protein and alcohol consumption and lower at a high fat consumption. Protein induced thermogenesis has an important effect on satiety.In conclusion, the main determinants of diet-induced thermogenesis are the energy content and the protein- and alcohol fraction of the diet. Protein plays a key role in body weight regulation through satiety related to diet-induced thermogenesis.

Alcohol forms a significant component of many diets and it supplements rather than displaces daily energy intake. Surprisingly, alcohol intake does not systematically increase body weight. The present study assessed whether a higher level of habitual physical activity in the daily environment is associated with a higher alcohol intake. Alcohol intake as part of total food intake was measured with a 7 d dietary record while at the same time physical activity was monitored with a tri-axial accelerometer for movement registration. Subjects were twenty women and twenty-four men, aged 61+/-5 years, of BMI 27.1+/-4.6 kg/m(2). Between subjects, there was a positive association between the level of habitual physical activity and alcohol intake (r 0.41; P<0.01). The subjects with higher alcohol intake had a higher activity level. On days with and days without alcohol consumption there was no difference in physical activity within subjects. In conclusion, it was shown that subjects with higher alcohol consumption are habitually more active. This may explain the lack of increasing body weight through additional energy intake from alcohol.