This week a government study issued a stark warning for the future: modern life has Britain sleepwalking towards an obesity crisis that could leave half the adult population and a quarter of children dangerously overweight by 2050.
Technological innovations and the way we work mean weight gain is now inevitable for most of us as we struggle with the "inherent challenge" of stopping the pounds piling on, the Foresight thinktank found.
The report's 250 expert contributors said that while hunting and gathering were crucial to survival in the prehistoric age, our sedentary jobs and reliance on cars, labour-saving devices and cheap, calorific foods means excessive weight gain should not be blamed on individuals' greed or laziness alone.
The Guardian equipped four Britons with a heart rate monitor and followed them on a typical day to find out what is going wrong - and whether the problem can be solved.
The expert: Joe Fournier is an ex-England professional basketball player with more than 10 years' experience in fitness and health training. He founded Fitness Boutique in 2005 and his clients range from celebrities to busy mothers wanting to lose baby weight
The office worker
Amisha Patel, 29, financial analyst
After a brisk 15-minute walk to the station, Amisha had tea and Shreddies in the office at 9am. A mid-morning snack of pistachio nuts kept her going at her desk until 1pm, when she went out for half an hour for a sandwich and a can of cola. After work she joined friends in a bar, where they shared spring rolls, mini sausages, hummus and chips. She drank two glasses of white wine and two of champagne. Her average heart rate was 87bpm. It peaked at 148bpm.
"I could eat better and go to the gym more often but it's hard to find time when work is busy."
Estimated calories burned: 1,850
What the expert says "Amisha is not getting much exercise at her desk and is eating too much fat. It would be much better if she had a bigger - but healthier - lunch and a smaller dinner with nothing fried. If she brought her lunch in, she could go for a 20-minute run in her break."
The manual worker
Michael Fullilove, 45, gardener
Michael had a breakfast of tea and sultana bran with muesli and was working in a client's garden by 8.10am. His first task was tackling a large, overgrown hedge, a two-hour job. He stopped for 10 minutes to eat lunch - two seeded wholemeal rolls, one egg mayonnaise and one cheddar - standing up. At home he ate dinner: spaghetti bolognese with parmesan and a raspberry pannacotta, followed by a late night treat of Maltesers. His maximum heart rate was 104bpm, and the average was 67bpm.
"I do keep myself fit - I run up to five miles three or four times a week and my work is quite physical," Michael says. "If I worked behind a desk I would definitely exercise."
Estimated calories burned: 2,900
What the expert says "Michael is in great shape. He trains regularly which increases his fitness level and could explain his very low average heart rate."
The schoolgirl
Ailish McNeela, nine
After a breakfast of cornflakes, a croissant and orange juice, Ailish was driven to school - too far away to walk - for 8.45am. At morning break she spent 20 minutes running around playing tag and snacked on a muesli bar. She had a ham sandwich and a fruit yoghurt for lunch and played rounders for 40 minutes in the afternoon. At her youth club, she sampled a chocolate crispy cake. Back at home she had an evening snack of toast and orange juice. Her maximum heart rate was 184bpm and her average over the day was 107bpm. "It's nice to eat unhealthy food like chips and pizza sometimes but I know it's bad for me so I wouldn't want to do it all the time."
Estimated calories burned: 1,500
What the expert says "Ailish's diet is fine because she is very active throughout the day, although for a child with a less active lifestyle or a lower metabolism it might create problems."
The health minister
Ben Bradshaw, 47
Out of bed by 5.30am, Ben breakfasted on grapefruit, tea and porridge with honey before cycling half an hour into Westminster, via the BBC. His day included half an hour of ashtanga yoga in his office. Lunch was a few mini-sandwiches, onion bhajis and crisps grabbed at one event. He had a pint of bitter and salted peanuts in the pub before dinner at home of roast chicken, potatoes, parsnips and carrots, and shared a bottle of red wine.
His heart rate peaked at 174 beats per minute, and averaged 102bpm over the day. "I think the most important thing for my health is building cycling into my routine. I don't eat as well as I would if I wasn't so busy."
Estimated calories burned: 3,400
What the expert says "His heart rate is higher than Michael's but you have to take his cycling into account and the amount of adrenaline in his day."
