Why (some) slim people can eat twice as much as the rest of us

Gain six kilograms in six weeks - yes, you can! That's one cover line you won't see on the front page of any glossy magazine - at least not while so many Australians are overweight. Yet putting on weight can be as tough as losing it, as journalist Clementine Johnson discovered when she set herself the goal of gaining six kilograms in six weeks. After three weeks of eating bigger meals and increasing healthy fats such as those found in nuts, avocados and olive oil, she gained only 200 grams.

A petite runner who, before her weight-gain diet, was just 43 kilograms, Johnson is what a Sydney sports dietitian, Rebecca Hay, calls a ''burner'' - someone whose metabolism torches kilojoules so efficiently she has no chance to turn them into fat. ''If you're a burner, it can be as hard to put weight on as it is for others to lose it,'' she says.

This, along with running 11 kilometres every second day, is why Johnson can eat big meals (and demolish everyone else's leftovers) and gain grams rather than kilograms. While close friends know her tiny frame is not the result of dietary restraint, Johnson feels that others look at her and inwardly murmur ''eating disorder''.

''People who don't know you well misjudge you,'' she says. ''It surprises me how some people feel it's OK to say, 'You're skinny. You really should put on some weight,' while it's not OK to tell someone, 'You're fat and you need to lose weight.'''

In September, she starts a new job in Uganda. She wants to put on weight to mitigate the possibility of losing it from gastroenteritis. Determined to add those six kilograms, she upped her daily kilojoules to 17,000 - almost twice the average daily intake of 8700 kilojoules.

Breakfast was five Weet-Bix, half a litre of full-fat soy milk and fruit. Lunch was four thick slices of grainy bread with half an avocado, tuna, full fat ricotta, and vegetables dressed with olive oil. Dinner was three or four serves of rice, 300 grams of fish, meat or poultry, a corn cob, half an avocado, two cups of vegetables and more olive oil. Dessert was two pieces of fruit with yoghurt or ice-cream and nuts. Between meals were more nuts and homemade muffins.

After three weeks she finally gained four kilograms - but only after dramatically reducing her running. It was a difficult decision. Having come third in Tasmania's 11-kilometre City to Casino run earlier this year, Johnson was keen to improve.

Why were those four kilograms so hard to gain? Hay says burners find it difficult to gain weight without eating so much they feel like ''a Strasbourg goose''.

''Volume becomes a problem,'' she says. ''You can't fit any more in. My advice to anyone who wants to add weight is to include more liquid foods. They add kilojoules without bulk. Juices or drinks made with powdered nutrition supplements like Sustagen or Ensure are good. So is adding skim milk powder to reduced fat milk for tea or coffee or on cereal … Concentrated kilojoules in foods like honey and dried fruit help, too.

''Another tip is making main meals smaller and snacks larger. This makes it easier to fit more food in.''

Running can be another obstacle to weight gain. That's good news for anyone keen to lose kilograms, not gain them. Intense exercise that raises your heart rate can burn fat efficiently.

But for those who want to add weight and keep exercising, Hay suggests a small, easily digested snack such as a banana 20 to 30 minutes before exercise. This prevents the body from dipping into its fat stores.

Paula Goodyer blogs at smh.com.au/chewonthis

From: Spectrum