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Questions about overweight/obesity and the role of activity in weight maintenance and weight lossThis answer is brought to you by many of the Australian nutrition professionals who regularly contribute to a nutrition email discussion group. At the outset, it needs to be understood that an increase in weight does not necessarily imply an increase in fat—the additional weight could be fluid, muscle, or other non-fat tissue. But for most people, a gain in weight means that their body fat level has increased. I have heard that there has been a big increase in the number of Australians who are overweight. Is this correct, and what does being ‘overweight’ actually mean?Along with the remainder of the Western world – and now increasingly also in the developing world - Australia is undergoing an epidemic of overweight/ obesity. In the past 20 years or so the proportion of Australian adults who are ‘obese’ (see definition below) has more than doubled, and the proportion of Australians who are ‘overweight’ has also substantially increased. As an indication of the worldwide extent of the problem, the World Health Organization (WHO) believes that the rise in obesity could have "an impact on health which may prove to be as great as smoking." One important point to consider before addressing the issue of activity and body weight is ‘who needs to lose weight?’ Perhaps partly because of the number of extremely thin models whose photographs appear in fashion magazines, many normal-weight people believe (wrongly) that they are overweight. Because body fat cannot be easily measured outside a laboratory, overweight and obesity are defined by the National Health and Medical Research Council (NHMRC) in terms of weight for height, according to the ‘body mass index’ (BMI). The formula is: BMI = weight (in kilograms) divided by height-squared (where height is measured in metres). A simple example is that of a man (perhaps a rugby forward or AFL ruckman) who weighs 100 kg and is 2.00 m tall. His BMI is 100 divided by two-squared = 100/4 = 25. The classifications used by both the WHO and NHMRC can be summarised as: Underweight BMI <18.5 [Click here for more detailed information and the Aim for the Healthy Weight Range poster.] However, these definitions do not take into account body build or racial origin. During World War II, potential recruits who failed the medical examination (based on weight for height) for selection to the US Army included some professional American football players. These were among the fittest and strongest men in the country. They had large builds and so were ‘overweight’ without being overfat—their extra weight was due to muscle, not fat. However, unless you are a professional footballer, body builder or weightlifter, having a BMI greater than 30 is usually a good indication that you are carrying too much excess body fat. Having a BMI of 25–30 means that your body fat level is probably greater than recommended, but your build and racial origin should be taken into account in deciding whether or not this is true. For example, there is good evidence that most people of Asian origin may have to aim for a BMI in the low 20s for optimal health. Although a small amount of excess body fat relative to one’s best young adult (e.g., BMI of 25 or 26 in someone of European origin where previously it had been 23 or 24) is not likely to be very harmful to health for most people, having a BMI above 30 significantly increases the risks of a wide range of diseases, including heart disease, type 2 diabetes, stroke, osteoarthritis and gallbladder disease. This is especially true for people who have excess ‘abdominal’ fat (e.g., the so-called ‘beer gut’ that is developed by many Australian men). High levels of body fat in the region of the abdomen is far more strongly associated with increased risk of diseases such as diabetes and heart disease than if the fat accumulates elsewhere on the body (e.g., the hips and thighs, as happens in many overweight women). To assist in determining whether or not you are carrying excess abdominal fat, the NHMRC suggests taking waist circumference into account in addition to BMI. To measure your waist circumference, while you are standing, relaxed (i.e., without tensing the abdominal muscles) pass a tape around your waist at the narrowest point between the bottom of your ribcage and your hips. Breathe in, then out, and then measure the circumference before you commence breathing in again. If you are of European origin, have a BMI of 25 or more and a waist circumference greater than 94 cm (men), or 88 cm (women), you are at increased risk of carrying too much body fat. But if your waist circumference is greater than 102 cm (men) or 88 cm (women), it is very likely that your body fat level is too high for good health. People of Asian origin should generally subtract about 10 cm from the above cut-offs to determine how likely their body fat level is to increase their risk of ill-health. So Australia is undergoing an epidemic of overweight/obesity; what is causing so many of us to put on weight?The causes of this increase in body fat levels are not completely understood and are the subject of much scientific research. Years ago, many people were made to feel that it was gluttony and/or sloth (two of the ‘seven deadly sins’) that led to obesity; i.e., people had no-one to blame but themselves. It is now known that there are genetic differences between people that make it very easy for some individuals to maintain normal weight, while others must struggle mightily to keep their weight down. This tendency to easily put on weight had great survival value thousands of years ago, when periods of ready food availability were followed by the inevitable famine—those people whose metabolism had allowed them to store excess energy as body fat were more likely to survive the famine than those who remained slim no matter how much they ate. So in one sense it could be argued that the ability to store excess body fat during the early evolution of people represented a genetic success. Fortunately, those times of famine have been virtually banished in the Western world, where abundant food supplies mean that nutritious and palatable food is available in our supermarkets and groceries all year round. However, unfortunately, this also means that people who have a tendency to easily accumulate body fat now find themselves in an environment that encourages them to put on weight, so yesterday’s survival mechanism has become a problem for many people today. Related to this is the tendency of many people to eat high-kilojoule, high-fat, low-fibre diets. The 'natural' diet, i.e., the one eaten by our early ancestors thousands of years ago, was almost certainly lower in fat and richer in dietary fibre than is the typical modern Australian diet. High-fat foods (especially those high in saturated fats, such as fatty meats, sausages, pastries, cakes and many takeaway foods) promote the storage of body fat, while high-fibre foods promote a feeling of fullness for relatively low kilojoule intake, and therefore help to protect against overeating. The best sources of fibre are breads and other cereal foods (preferably wholegrain), vegetables and fruits. Another problem is that most people are less active than their parents and grandparents were. Modern technology, with all its labour-saving gadgets, means that we are becoming an increasingly sedentary society. The availability of cars, remote control units, computer work-stations, television, videos, DVDs and so on means that most adults can now be seated for virtually their entire working day and again all evening (and sit in cars, trains or buses on their way to and from work). Similarly, nearly all children used to play physically active games, thereby largely balancing their desk-bound schoolwork. Now, many children watch television or sit in front of computers after school, playing computer games or ‘chatting’ to each other over the Internet. How important is activity for weight maintenance?Until fairly recently, many nutritionists and doctors considered that diet was the major key to maintaining, or regaining, appropriate body weight; if activity had a role to play, it was thought to be only a minor one. It was also thought that for activity to be of much benefit it would have to be very vigorous (e.g., running) rather than moderately vigorous (e.g., brisk walking). This is no longer the situation—nutritionists are increasingly coming to accept that the observed decrease in activity is almost certainly a major contributor to the rise in obesity. It is now generally believed that both diet and activity levels are vitally important in maintaining (or regaining) appropriate body weight. But the belief is that exercise (i.e., structured, planned physical activity), while important, is not the only way in which activity might help protect against obesity. Rather movement—incidental physical activity that we do almost unconsciously through the day—is now believed to be very important in adding to our energy output, and therefore helping to keep our weight at an appropriate level. The form this incidental activity takes is relatively unimportant. It may include (as just a few examples) parking your car at the end of the car park furthest from the office and walking the last few hundred metres to work; walking down the corridor to talk to a colleague rather than using the telephone; taking stairs rather than the lift or escalator; using non-power tools for odd jobs around the house; walking to the corner shop to buy a litre of milk or the Sunday newspaper rather than driving, and so on. Provided it is safe, children should be encouraged to participate in outdoor activities that involve movement: for example, perhaps the computer and television set can be switched off while there is still daylight (and the weather is fine). Overcoming the ‘couch potato’ syndrome may turn out to be one of the kindest things parents can do for the future health and wellbeing of their children. I understand now that ‘activity’ doesn’t necessarily mean ‘exercise’, but how much activity and how much exercise do I need if I am normal weight and don’t want to put on weight?In a companion FAQ in this series it is recommended that for general health, adults should put aside 30 minutes (or more) for moderate exercise (e.g., brisk walking and light weight-training) each day. This is in addition to any ‘incidental activity’ (see previous section). The 30+ minutes of planned activity does not have to be taken ‘all at once’. Many people would find three lots of 10 minutes of moderately vigorous exercise more convenient (and easier to complete) than one session of 30 minutes. A suitable level of intensity of exercise is one that increases your rate of breathing so that you are still be able to talk normally (just), but not to sing. If you can find the time and motivation, it is also worthwhile engaging in 20+ minutes of vigorous activity (e.g., jogging, fast swimming, fast cycling) several days per week. ‘Vigorous’ activity makes you breathe much harder than moderate activity; examples of other activities that are suitable include singles tennis, squash, aerobics, rowing (fast) and hockey. Caution should however be exercised with jogging: very large people can easily damage knees and spines that were custom-designed during adolescence for a leaner body. Of course, engaging in this level of activity doesn’t mean you can now increase your food intake and still expect to lose weight or keep your weight at an appropriate level; adhering to a health-promoting diet is also important (as discussed in greater detail later in this FAQ). In summary, for people who are not overweight/obese, the National Physical Activity Guidelines for Australians (from the Department of Health and Aged Care) are:
What if I am above the normal weight range, and it isn’t because I have a big build—how much and what sorts of activity/exercise do I need to help me lose weight?For people who need to lose some body fat, there is evidence that the intensity of activity needs to be greater than for simply maintaining weight. To assist with weight loss, a level of activity may be needed that increases your rate of breathing so that even talking is difficult. Of course, if you are well above your ‘best fighting weight’ it will be difficult and perhaps damaging to exercise vigorously at first. The exercise program you develop (preferably with a qualified person such as an exercise physiologist or fitness trainer) should allow you to start gradually, and slowly build up both the duration and intensity of exercise. To begin it might be best to do a few minutes each day of activities that ‘test’ you, but you can cope with, e.g., brisk walking for five minutes twice per day, combined with five minutes of low-level weight training. ‘Low-level’ weight training involves repeatedly lifting weights that are light enough so that you can lift them comfortably 8-12 times (or, for people over ~50 years of age, 10-15 times). A range of upper and lower body weight training exercises is recommended on at least two days per week (and preferably more). Completing two sets of 8-12 (or 10-15) repetitions is better than completing just the one set. About ten different exercises are needed to condition all the major muscle groups. Weight training is recommended partly because it increases the likelihood that only fat is lost, not fat and muscle. Over time, the level of exercise can be slowly built up until a total of 30+ minutes of brisk walking, slow jogging (or similarly vigorous exercise) can be easily completed on five or more days per week, and another 20 minutes of light weight training on three days. Long, slow stretches are also appropriate, two or three days per week, to ensure that flexibility is maintained (or even enhanced) while you are losing weight. To reach this level of activity may take many months, so don’t be discouraged if you can’t maintain a high level of activity straight away. One researcher described a man he was advising who could barely walk a kilometre at the start of his weight-loss program. This man was so successful that he eventually lost 37% of his initial weight and ran a marathon in 2 hours 31 minutes. This is less than 25 minutes outside world record time! It is not suggested that this is a suitable goal for everyone who wants to lose weight! Rather it is simply mentioned as an indication that weight loss programs can sometimes be spectacularly successful. For people who do not like walking quickly or jogging, or for whom jogging is likely to be harmful (see above) suitable alternative activities include swimming and cycling (either outdoors or inside on a stationary bike) because during these activities your body weight is supported. Deep water running (e.g., running across the pool where the water is chest deep) is also good exercise. Will increased activity and exercise be enough for me to lose weight, or do I need to change other aspects of my lifestyle, e.g., the food I eat?As mentioned briefly above, although increased activity is very important, it is true that activity alone may not be enough to shed a substantial amount of unwanted body fat. A slight reduction in total kilojoule intake, and a major reduction in intake of fatty foods are also recommended if you are trying to reduce weight. Keeping alcohol consumption down to a reasonable level is also important – alcohol provides more kilojoules per gram than either protein or carbohydrate. For men, a couple of 285 mL (10 ounce) beers or two 100 mL glasses of wine a night is probably reasonable, if you want to continue to enjoy a moderate alcohol intake while losing weight. Women might be well advised to restrict their intake to one drink per day (even 'Mother Nature' is sexist sometimes: women's different body composition and metabolism means they can safely drink only about half as much alcohol as men, on average). If your aim is to lose weight, it should only be to lose it slowly: about one-half to one kilogram per month is fast enough. This will still allow you to eat enough food to obtain all the vitamins, minerals, fibre and other essential nutrients, but only if your diet is based largely on the Dietary Guidelines for Australians, available through: http://www.nhmrc.gov.au/publications/synopses/dietsyn.htm These guidelines include:
and take care to
What if I try to do all the right things and I still can’t lose weight; have I wasted my time altering my lifestyle?This question is addressed in another FAQ in this series: [Why is it that despite being active on a daily basis and having a low food intake, I have great trouble losing unwanted weight?]. Briefly, despite increasing activity levels, reducing total food intake and eating mainly low-fat foods, many people still find it hard to lose weight. The body seems to ‘defend’ a level of body fat and it is apparently much easier to reset this ‘lifestyle weight’ upwards than it is to permanently lower it. But even if there is little or no weight loss following the addition of exercise (or simply of increased movement) to your daily lifestyle, increasing activity still leads to improvements in many of the factors associated with disorders such as heart disease and diabetes. Blood pressure, blood glucose levels and blood cholesterol will all respond positively to increased activity, so you have not ‘wasted your time’ by being more active, even if the kilograms of excess body fat do not disappear as fast as you would like. It is also true that increased activity, especially moderate and vigorous exercise, helps most people to combat the stress associated with modern living. Stress is believed to have a huge negative impact on many aspects of health. Stress may even make an indirect contribution to the obesity epidemic. With increased stress also comes an indirect effect—a tendency to look to pleasurable activities, including eating fatty/sugary food and drinking alcohol. Many people increase their intake of both food and alcohol during times of stress and then find that they cannot lose the extra body weight they have acquired. So increasing physical activity may be doubly valuable—in addition to using up some of the excess kilojoules most people now eat, activity can help to reduce stress (and therefore to reduce stress-induced overeating). Many people find that taking ‘time out’ from a busy day by going for a stroll in the park, playing tennis, chopping firewood, taking the dog for a walk or digging over the vegetable garden (as just a few examples) is effective in reducing tension and helping to reduce stress-induced overeating. Exercise has even been successfully used in the treatment of mild depression. It is important to realise that many people set goals for themselves that are unachievable: getting back to the clothing size they were when teenagers, losing a kilogram of weight a week, or similar. The important thing is to achieve a weight and body shape that is healthy for you as an individual, and that can be maintained. Healthy behaviours (increased activity, lower fat diet, limiting alcohol consumption, reducing stress, quitting smoking) will all contribute to achieving this aim, and, if you persevere, to some weight loss as well. For more information Nutrition Australia recommends:Back to Frequently Asked Questions Index |