According to the passage, some overweight people ----.

People may be overweight, not because they eat
too much, but because they spend too little
energy. More than one - third of the overweight
population report no physical activity at al during
their leisure time. Some overweight people are so
extraordinarily inactive that even when they eat
less than thin people, they still have an energy
surplus. Reducing their food intake further would
be a threat to their health. Physical activity, then,
is a necessary component of nutritional health.
People must be physically active if they are to eat
enough food to deliver all the nutrients they need
without unhealthy weight gain. One hundred years
ago, 30 per cent of the energy used in farm and
factory work came from muscle power; today only
1 per cent does. Modern technology, resulting in
such things as computers and washing -
machines, has replaced physical activity at home,
at work, and in transportation. Underactivity is
probably the single most important contributor to
overweight. And in most cases, television
watching makes the biggest contribution to
physical inactivity.