Many news outlets recently reported on claims that labelling food with how much exercise is needed to ‘burn’ it off can reduce obesity. The research that prompted these articles can be read here .

The research basically suggests that food labels should display how much exercise it would take to burn off the calories. They contend that by so doing, an awareness of the energy cost of food is created, helping people to indulge less and potentially shaving a couple of hundred calories from their daily energy consumption. By educating people, they can make informed choices and choose healthier options.
Examples given by a few news outlets:

•One bowl of cereal (172 calories) – 16 minutes of running or 31 minutes of walking to burn off.
•Small chocolate bar (229 calories) – 22 minutes of running or 42 minutes of walking.
•Sugary soft drink (138 calories) – 13 minutes of running or 26 minutes of walking.
•Blueberry muffin (265 calories) – 25 minutes of running or 48 minutes of walking.
•Packet of crisps (171 calories) – 16 minutes of running or 31 minutes of walking.
•Chicken and bacon sandwich (445 calories) – 42 minutes of running or 1 hour, 22 minutes of walking (BBC)
• One can of coke (140 calories) – 22 minutes running.
• BLT sandwich (405 calories) – 48 minutes of swimming.
• Fish and chips (840 calories) – 1 hour, 20 minutes of cycling.
• One can of Pringles (980 calories) – 3 hours, 20 minutes of walking.
• Pint of Guinness (210 calories) – 1 hour of yoga (Telegraph)
• 500ml tub of Ben and Jerry’s peanut butter ice cream (1,400 calories) – 2 hours, 20 minutes of running or 4 hours, 40 minutes of walking.
• 266g milk chocolate McVitie’s (1,245 calories) – 2 hours, 4 minutes running or 4 hours, 8 minutes walking.
• 180g Doritos Chilli Heatwave (894 calories) – i hour, 30 minutes of running or 3 hours of walking.
• 110g Cadbury Dairy Milk chocolate (588 calories) – 59 minutes of running or 1 hour, 57 minutes of walking.
• 140g Haribo Tangfastics (484 calories) – 48 minutes of running or 1 hour, 37 minutes of walking (Daily Mail)

Not everyone was so enamoured by this idea, however (for example). Arguments against include the position that such labelling would act as a trigger for those with (or vulnerable to) eating disorders, and that this is just another example of the ‘nanny state’ apportioning blame to the individual for the obesity epidemic.

Whatever the eventual outcome of this research, at least the debate is under way and these news articles have hopefully helped raise awareness (or at least re-awakened it).

When I used to work with individual clients, I personally found it very useful to educate them about calorie consumption and expenditure. One tool I used to make extensive use of was Ainsworth et al’s (2000, 2011) compendium of physical activities (The Compendium of Physical Activities Tracking Guide, 2011 Compendium of Physical Activities: A Second Update of Codes and MET Values, Update of Activity Codes and MET Intensities, and Metabolic Equivalents). This is basically a list of physical activities with their MET (metabolic equivalent) value. The amount of oxygen the body consumes is directly proportional to the energy expended during physical activity. At rest, the body uses approximately 3½ ml of oxygen per kilogram of body weight per minute (3.5 ml/kg/min). This resting metabolic rate is referred to as 1 MET. All activities can be classified by intensity according to their oxygen requirements. An activity that is rated as a 2 MET activity would require 2 times the resting metabolic rate (7 ml/kg/min) and an activity that is rated at 4 MET would require approximately 14 ml/kg/min.

Resting metabolic rate is fairly close to 1 kcal per kg of body weight per hour. The energy cost of activities may be expressed as multiples of this. To work out energy expenditure, multiply your body weight in kg by the MET value and duration of the activity (as a decimal).

For example, high impact aerobics has been assigned a MET value of 7.0. A 60kg woman who participates in a high impact aerobics class for 1 hour will burn (7 METs x 60kg x 1 hour) = 420 kcals. Her friend arrives 20 minutes late and only completes 40 minutes of this class. She weighs 55 kg. Her energy expenditure will therefore be (7 METs x 55kg x 40/60 minutes) = (7 x 55 x 0.67) = 257 kcals [Please note that the minutes need to be expressed as a decimal – to do this, divide the minutes by 60 minutes].

Another example, kickboxing has been assigned a MET value of 10.0. A 95kg man performing a 90 minute class will burn (10.0 METS x 95kg x 90/60 minutes) = (10 x 95 x 1.5) = 1425 kcals. Yet another example: A 65 kg man mows his lawn (assigned value = 5.5 METs) and it takes him an hour and a quarter. His energy expenditure is (5.5 x 65 x 75/60) = (5.5 x 65 x 1.25) = 447 kcals.

It is also possible to approximate the caloric cost of physical activity and exercise by using the following equation which is based on the MET level of an activity:

Energy expenditure in kcals/min = (MET value x 3.5 x body weight in kg)/200

For example, an individual has been prescribed a net calorie expenditure of 1000 kcals a week, he weighs 75 kg and performs an activity with a MET value of 6.0. One MET of the 6 is taken off because it accounts for resting metabolism, so only 5 METs for this activity is used in the equation:

Energy expenditure in kcals/min = (5 x 3.5 x 75)/200 = 1312.5/200 = 6.6 kcals/min

To lose 1000 kcals using this one activity will take (1000/6.6) – 152 minutes, which is equivalent to (152/7) – 22 minutes a day; or (152/3) – 51 minutes three times a week.

Please note that this method will elicit ever so slightly different results to the first method.

These are only approximations because metabolic efficiency varies considerably from one person to the next, and even in the same individual. Although the MET system is useful as a guideline for training, it fails to account for changes in environmental conditions, and it does not allow for changes in physical conditioning. Also, individual differences in skill, coordination and exercise economy (their VO2 at a given submaximal work rate) and the variable intensities within each available activity strongly influence caloric expenditure during exercise.

Even so, using METs to illustrate how different everyday activities can contribute to calorie expenditure, and how making small changes can over time lead to significant differences I found invaluable as an educational tool.