A dramatic rise in obesity has occurred among humans within the last several decades. Little is known about whether similar increases in obesity have occurred in animals inhabiting human-influenced environments. We examined samples collectively consisting of over 20 000 animals from 24 populations (12 divided separately into males and females) of animals representing eight species living with or around humans in industrialized societies. In all populations, the estimated coefficient for the trend of body weight over time was positive (i.e. increasing). The probability of all trends being in the same direction by chance is 1.2 Â 10 27 . Surprisingly, we find that over the past several decades, average mid-life body weights have risen among primates and rodents living in research colonies, as well as among feral rodents and domestic dogs and cats. The consistency of these findings among animals living in varying environments, suggests the intriguing possibility that the aetiology of increasing body weight may involve several as-of-yet unidentified and/or poorly understood factors (e.g. viral pathogens, epigenetic factors). This finding may eventually enhance the discovery and fuller elucidation of other factors that have contributed to the recent rise in obesity rates.

Dietary restriction (DR) is currently the only paradigm that has consistently extended maximal life span and reduced the onset of age-related chronic diseases in all of the nonprimate species tested. Although it is controversial, some investigators have suggested that the underlying mechanisms may be mediated by adaptations in energy expenditure. We evaluated the extent to which DR alters energy metabolism in a unique cohort of rhesus monkeys submitted to DR for 11 yr. Total energy expenditure (doubly labeled water), resting energy expenditure (REE; indirect calorimetry), and nonbasal energy expenditure (calculated by difference) were measured in DR (n = 12) and control (n = 11) animals. Body composition was determined by dual energy x-ray absorptiometry. Both fat mass and fat-free mass were lower in the restricted animals (56 and 12%, respectively). DR induced a 17% lower total energy expenditure that was attributable to a 20% decrease in REE without changes in the nonbasal energy expenditure. Adjusted for fat-free mass, REE was 13% lower with DR (-250 kJ/d). Taken together with a reanalysis of previous DR experiments published in humans, rodents, and monkeys, these results suggest that DR may lower REE independent of the DR-induced changes in body composition. Whether this reduction in REE contributes to the life-extending properties of DR warrants further analysis, but it suggests that the long-standing debate regarding DR effects on metabolic rates may derive from the lack of consensus on how to adjust for body size and composition.

The general public is increasingly aware of the health benefits associated with consumption of omega-3 fatty acids. While evidence of health benefits continues to mount, the underlying science is complex. Omega-3 fatty acids vary in their physiological efficacy. Consumers are typically unaware of differences in the efficacy of different omega-3 fatty acids and this lack of knowledge can result in consumers being misled within the marketplace. There is a need for consumers to be educated about the distinctions between omega-3 fatty acids. In the interim consumers remain at risk of purchasing premium fortified products and supplements that will not correspond to their desired health outcomes. This paper summarises the current understanding of fatty acid physiological metabolism and interaction for the purpose of highlighting this complex and multifaceted concern.

Caloric restriction (CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure (EE). To assess longitudinal effects of CR on EE in rhesus monkeys (Macaca mulatta), data from 41 males (M) and 26 females (F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11-28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE (24-h EE) was divided into daytime (day EE), nighttime (night EE), and daytime minus nighttime (D Ϫ N EE). M calorie-restricted monkeys showed a lower 24-h EE (means Ϯ SD ϭ 568 Ϯ 96 kcal/day, P Ͻ 0.0001) than controls (C; 630 Ϯ 129 kcal/day). Calorie-restricted M had a lower night EE (difference ϭ 36 kcal P Ͻ 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males (P ϭ 0.72). The 24-h EE decreased with age (13 kcal decrease/yr, P Ͻ 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D Ϫ N EE decreased with age (9 kcal/yr, P Ͻ 0.0001), with no interaction with age (P ϭ 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE (496 Ϯ 84 kcal/day) than M (636 Ϯ 139 kcal/day) (P Ͻ 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M (difference ϭ 18 kcal, P ϭ 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR. metabolic rate; dietary restriction; indirect calorimetry HUMAN AGING IS ASSOCIATED with morphological, physiological, and behavioral changes (31). An age-related decrease in energy expenditure (EE) is one of the measurable changes, such that total EE was shown to decrease by 1-2% with each decade increase in adult life (19). Some of this decrease was attributed to decreases in fat-free mass (FFM), but even after accounting for differences in FFM, resting metabolic rate (RMR) was significantly lower in the elderly compared with the younger individuals (24,33,34).Calorie restriction (CR) slows the aging process and extends maximal life span in multiple species (37). The physiological effects of CR in rhesus monkeys include decreased body weight, lowered body temperature (21), and a decrease in the metabolic rate (2, 8). Of particular interest, in two nonhuman primate studies, CR was associated with reductions in EE beyond those of just a smaller body size (8, 26). In one study, the reduction in total EE (24-h EE) as measured by doubly labeled water was 17% lower in the CR compared with control-fed (C) monkeys. Of this difference, ϳ90% was explained by a lower resting EE in the CR monkeys (2). In another study of CR conducted in rhesus monkeys (8), total EE normalized for differences in FFM was lower in CR compared with C monkeys. However, resting EE explained only 13% of the difference. The effect of CR on energy expenditure has also been reported in other species (2,25) . This lower EE in excess of the decr...