Physical activity and health: gender differences across the lifespan Kuopio, Finland, 25-28 June 2003.

This conference, attended by participants from 50 nations, began each day with outstanding lectures from international experts on big-picture issues. The first speaker, Professor Claude Bouchard from the USA drew together the issues of overfeeding, caloric deprivation, bed rest, sedentariness and exercise as befitting today's paradigm of human energy balance. Add to this the growing scientific knowledge of genetics and the situation becomes even more complex. Professor Bouchard referred to the changing biology of the gene as creating one of the greatest scientific challenges. The number of genes known to date is a poor indicator of the biological complexity of the organism. Rather an understanding of the way in which genes interact with environmental triggers is required. Referring to the issues listed above, he suggested overfeeding changes all metabolic variables, caloric deprivation reduces biological measurements, bed rest shows a whole range of changes and gene activity has been noted with sedentariness. Environmental stimuli influence gene expression and this may explain why activity, for example, is more important in some people than others in maintaining ideal body weight. There is still a long way to go, however, before this knowledge reaches substantial clinical and public health utility.

The second speaker, Dr Karl Enqvist, a cosmologist and recipient of the prestigious Finlandia Award, discussed 'man in perspective' from our position in the universe. He suggested that questions of matter could be addressed through quantum physics, motion through relativity, the universe through cosmology, life through molecular biology and consciousness through neuroscience. The universe is one of cold and hot spots where scientists are able to determine weight and the type of matter with precision. It is here that our position is noted as miniscule, with dark matter of yet unknown elementary particles dominant. This is the mystery of the universe.

Dr Enqvist described biological structures as a kind of average of observations over space and time. He suggests we are limited in our ability to perceive all things, using the term 'coarse graining' to describe the process of perception as we move for example, from thinking about atoms to molecules to biological structures. We lose information when we move from one level to another, such that fundamental theory, through coarse graining sees the weak emergence of effective theory, which is something we can work with. One can see a parallel with using levels of evidence in terms of the generation of different forms of scientific knowledge to explain health outcomes in nutrition. At this stage, the point of the final special speaker, Dr Wille Riekkinen, Bishop of Finland, on the need to protect human dignity in a consumerist society was not lost.

The scientific program leading from these lectures was comprehensive. Focussing on physical activity, sessions addressed trends across the lifespan, the impact on prevention of CVD, obesity, diabetes, and osteoporosis and the effects on body composition and functional capacity. Details of the program can be found on the web site, www.uku.fin/conf/puijo.

Within the body of the scientific program there were a number of notable presentations. In the first instance methodological issues were addressed concerning the measurement of physical activity and energy expenditure. Dr Barbara Ainsworth summarised survey methods available for assessing physical activity, contrasted in their focus on moderate and vigorous activity in a usual week, vigorous, moderate and walking activity in the previous week and examining work, leisure, transport and inactivity in a typical week day. These tools enable classification into regularly active, insufficiently active and inactive. The link between level of physical activity and energy expenditure was difficult to assess, as this was highly dependent on body composition. Dr Michael Sjostrom noted problems with existing questionnaires in their lack of attention to moderate intensity activity at work, home and associated with transport, and the impediments to international comparisons. Work on a more universal physical activity questionnaire (PAQ) was presented. This PAQ can be downloaded from the web on www.ipaq.ki.se.

Dr Rainer Rauramaa reviewed RCTs in the period 1979 2002 demonstrating the benefits of physical activity, with Professor Bouchard commenting that it would be helpful to be able to identify responders and non-responders to physical activity coupled with genetic profiling. Following this line of reasoning, in his presentation Dr Nick Wareham from Cambridge asked the questions 'what are the features of the gene environment interaction to make it causal?' and 'do studies need to be bigger or better?'. Referring to research in both diet and physical activity, he noted the methodological problems posed when there are small interactions (exposure) and small effects. He argued that in pursuing diet and physical activity links to disease, study designs need to get smarter not bigger, by using repeated measures and more accurate detection systems. Causal inference would still be required through studies of aetiology.

From a biomarker perspective there was substantial debate on the relative merits of BMI and waist circumference for determining health risk. Dr Robert Ross emphasised the impact of exercise on weight loss and strongly supported the use of waist circumference as an outcome measure. Professor Bouchard supported the continued use of BMI given that it is universally accepted and correlates with risk. He further argued that the pathology of obesity is still not well understood. More is needed to be known about ectopic fat (muscle, heart, pancreas, liver), as opposed to abdominal fat, and about the biology of fat cells, particularly the impact of cytokine secretion.

Differences between genders was a theme throughout the conference. Dr Abby King noted that exercise appears to be more important in weight loss in men and in weight maintenance in women. Professor Jaako Tuomilehto noted the greater proportion of women in the DPS study, which also had a strong focus on individualised dietary intervention. There were many other topics too numerous to summarise here, but overall the meeting was very comprehensive and enjoyable, with many opportunities to reflect on the importance of working together in diet and exercise to promote health.

Linda C Tapsell PhD APD 

Professor

National Centre of Excellence in Functional Foods

ARC Key Centre for Smart Foods

University of Wollongong, NSW