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How much exercise to lose weight & keep it off?

By Matt O'Neill, MSc(Nut&Diet), APD

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On 18 November, I attended the UK's Association For The Study of Obesity Symposium - “Physical Activity and the prevention and treatment of obesity: How much, what and when?”

Here's a summary report that answers these key questions and provides motivation to get moving not matter what shape you're in.

Professor Wim Saris from the Netherlands opened with some interesting figures on declining human energy expenditure and the amount of exercise required to stay lean. Our Palaeolithic ancestors had a physical activity level of around 1000 calories (4200kJ) a day and they consumed about 3000 calories (12600kJ). Put another way, for every 1 calorie expended in labour, 3 calories were harvested. In contrast, sedentary humans living in affluent societies today eat and drink 2100 calories (8800kJ) with an activity level of around 300 calories (1260kJ).

In order to rebalance the modern lifestyle to the “energy in - energy out” (3:1) ratio of our leaner ancestors we'd need to burn an extra 400 calories (1690kJ) per day for a total of 700 calories (2900kJ) a day (2100:700 = 3:1). This would require around one hour of moderate intensity aerobic exercise or 35 minutes of vigorous activity every day, which can be a challenge for many people to fit into their busy lifestyle.

Professor Saris emphasised that whilst 30 minutes of activity on most days is important to limit health risks for a number of chronic diseases, including coronary heart disease and diabetes, he also stressed that the volume of exercise needs to be greater to prevent weight gain or regain after weight loss. There's also a need to reduce sedentary behaviours in an attempt to build this sort of activity level.

Professor Ken Fox from the University of Bristol followed, explaining that short bouts of activity (minimum 10 minutes) may be just as good as a single 30 minute block of exercise in terms of reducing weight and blood pressure. Shorter bouts, say 5 minutes, have not been studied yet. He suggested that `fractionising' physical activity into bite-sized chunks may be an advantage to make exercise more attractive and manageable.

Regarding total daily steps, which you can track with a pedometer, he said that very little daily movement would produce around 3000 steps. Thirty minutes of brisk walking is about 4000 steps or 630 kJ (150 Cal). And 10000 steps equals about 1260 - 1690 kJ (300-400 Cal). This is the amount Prof Saris stressed we need to add to our day.

Professor Paul Gately from Leeds Metropolitan University focused on children with his research showing that the primary reason children participate in exercise is “to have fun” followed by “improve skills” and to “learn new skills”. He also revealed that while exercise tolerance in obese adults is very low (ie. they get puffed out quickly), tolerance in obese kids is only 38% lower than normal weight kids. This means obese kids may be able to participate in activity without getting as puffed as we think.

Ashley Cooper, also from the University of Bristol showed some fascinating graphs of physical activity levels in children when tracked with accelerometers. These devices are really sophisticated pedometer-type devices that measure the rate of movement in any direction.

His research showed that:

  • Obese kids are significantly less active than non-obese kids.

  • The major differences in activity level occur at times outside work or school time, when there is choice to exercise or not. Obese kids tend to take the option to be sedentary when they can.

  • Kids who walk or ride to school are more active in addition to the “to-school” journey and that the extra exercise is from active games after school.
He suggested family-based activity after school may be the place to focus attention on to help kids become more active. It appears that girls need to aim for 12000 steps a day and boys 15000 steps to stay in shape.

The final presentation was a feisty delivery by Professor Steven Blair, CEO of the Cooper Institute in the US. Prof Blair's work clearly shows that physical activity is a powerful health promoter, irrespective of weight status. Blair described himself as a “little fat fit guy” who is healthier than a lean guy who does no exercise.

His substantial database of 30,000 individuals tracked for an average if 10 years backs up his personal claim. Blair stated, “Our data suggest that low fitness, which is caused by sedentary living habits is more important than obesity as a predictor of mortality.” In his study group there were more deaths from cardiovascular disease and other causes in the lean, unfit subjects than in the obese fit ones.

Blair said, “I couldn't believe the results when my statistician brought them to me” and “The National Institutes of Health had to put out a grant to get people to apply, perhaps to see if we were looney… I had to make a pest of myself to get the attention of authorities and the obesity cartel.”

At lunch I quizzed Blair on this cartel. He simply stated that we need to be more critical of claims that obesity is of the most concern. “Low-fitness is a far stronger predictor of all cause mortality than obesity.” Earlier he stated that doctors test for diabetes and blood cholesterol, but overlook fitness testing, which would give better guidance for boosting health.

His latest study also shows benefits from strength training. When he split his study subjects into four groups from lowest to highest muscular strength, it was the top strength group that was the healthiest. His prediction, that in the next decade we'll see more research papers and emphasis on muscular fitness.

Most memorable, was Professor Blair's strong recommendation not to treat BMI (Body Mass Index). “BMI is not a disease. Treat risk factors.”

The widom from the exercise gurus at this symposium raises some important considerations:

  • It encourages us all to enjoy the health benefits of regular physical activity at any weight.

  • It also builds the case for us to keep exercising irrespective of whether we lose weight.

  • Finally, it makes us think about how we view weight loss… for the sake of weight loss or as one of the many health-enhancing by-products of regular, fun physical activity.



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