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Podcast TranscriptThe Naked Scientists: Science Radio & Science Podcasts |
| 25th Oct 2003 | < Previous Show | Next Show > | |||||||||||
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Why Is The Sea Salty, But Not Rivers And Lakes?
It all comes down to a thing called the water cycle. Rain, which is fresh water, falls from clouds onto the land and finds its way into lakes and rivers, and also through the ground, back to the sea, picking up salts and minerals as it goes. Once it reaches the sea, the water can be evaporated again to form new clouds containing fresh water, and the salt is left behind, so over millions of years the oceans have slowly been accumulating salt washed off the land by fresh water. So is the sea becoming more salty ? Probably not because if the level of salt rises any further the extra is removed by various processes, including chemical reactions, so the sea is now about as salty as it is going to get. That’s not to say you can’t get saltier seas – like the Dead Sea – these are just bodies of water cut off from the main ocean and in which more water is evaporating than being returned by rivers, so the water becomes more concentrated.
25th Oct 2003
Fast Food Makes You Fat - it's Official
The Medical Research council has released a study concluding what many of us have probably suspected already: regularly eating junk food can increase your risk of weight gain and obesity. It’s all about the energy density of the meal, apparently. Junk food has a high energy density, meaning that it contains a lot of calories for its weight. This is often due to the presence of high levels of fat and sugar in the meal, with a corresponding low level of fibre and protein. For example, a fast food meal has an energy density one and a half times greater than that of a normal British meal, and a staggering two and a half times greater than an African meal. When people eat foods with a high energy density, they may not realise exactly how many calories they are eating, as the body is tricked by the relatively small size of the portions. This also makes it hard for people to make informed diet choices, especially in the case of children. The MRC team tested this by asking groups of volunteers to eat apparently identical meals. But the meals had been secretly altered to have a variety of energy densities, although the volunteers believed they were all eating normally. The scientists found that the group fed the high energy density diet put on fat at an alarming rate, while those eating the low energy density foods actually lost body fat. More research on people living in the UK and in Africa, as well as analysis of the composition of junk food, confirmed that fast food meals are a fast track to lardiness. But it’s not just junk food that is energy dense- the researchers warn about the perils of energy-dense supermarket readymeals and convenience foods, saying it’s important not to just swap one unhealthy meal with another. Obesity related problems are thought to cost the UK more than 2.5 billion pounds annually so the government are very keen to find ways to stop us eating all the pies. This new research lays some of the blame firmly at the door of the fast food merchants, so perhaps we will finally see health warnings on the sides of burger cartons.
25th Oct 2003
The Best Way To Cook your Vegetables
Steaming produces the healthiest cooked vegetables, and microwaving produces the least healthy vegetables, according to Spanish researchers. Cristina Garcia-Viguera and her team looked at how the way in which vegetables were cooked affected the levels of anti-oxidant substances called flavonoids in vegetables like broccoli. Flavonoids are important because they can mop up harmful chemicals called free radicals which, left unchecked, can damage your DNA and cause cancer. The team found that microwaved vegetables lost almost all their healthy antioxidants. The researchers think this is because microwaves produce hotspots inside the food which cause the antioxidants to break down. Boiled vegetables were not much better, losing 80% of their flavonoids by the time they were cooked, with most of the healthy antioxidants leaching out into the water. But steamed vegetables lost only 10% of their flavonoids making steaming the healthiest way to cook your veggies !
25th Oct 2003
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