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Getting the best out of your food
By Rebecca Morelle
Health reporter, BBC News
A balanced diet is the key to a happier, healthier life, so the mantra goes.
Experts advise us to eat more fruit and veg; boost protein and fibreintake; make sure we get the optimum levels of vitamins and minerals.
But what actually happens to these nutrients once they are inside the body?
Food scientists, working in an area called bioavailability, are tryingto answer this question in a bid to discover how people can get thevery best out of what they eat.
Toni Steer, a nutritionist at the Medical Research Council HumanNutrition Research Centre in Cambridgeshire, said: "The idea that weabsorb everything we eat just isn't true.
"While you may have a certain amount of a nutrient within a food, what is actually absorbed may be less.
"Bioavailabity means how much of that nutrient within a food is usefully absorbed."
But, she says, bioavailability is not set in stone, and researchers areworking to find ways of manipulating the levels of nutrients that canbe absorbed by the body.
"If people are meeting dietary requirements, all of the nutrients they need are probably being absorbed.
"But for people who suffer vitamin or mineral deficiencies, or forthose in developing countries where nutrition is poor, research intobioavailability can be very useful."
Pop-Eye's favourite
Take iron - a lot of people are just not getting enough of it, and toolittle can lead to anaemia and increased susceptibility to infections.
But how we get our iron can impact on the amount we absorb, saysRichard Faulks, a senior researcher at the Institute of Food Researchin Norwich.
While red meat contains the type of iron - haem-iron - that is mostreadily absorbed by the body, vegetarians are pointed towards iron-richfoods like as spinach.
However, this vegetable contains the mineral in a form that is not so readily absorbed - non-haem iron.
But, explains Mr Faulks, a glass of orange juice alongside your plate of spinach can make all the difference.
"Vitamin C in orange juice changes the iron to its non-oxidised state(haem iron) - which is much more readily absorbed than the oxidisediron (non-haem iron).
"You can manipulate to some extent the gastric and small intestinal chemistry by what you eat and combine."
Conversely, explains Dr Steer, tea and coffee contain compounds calledphenols that inhibit iron absorption - so they shouldn't be consumedalongside iron-rich foods.
Raw vs cooked
Whether your food is raw or cooked can also make a difference.
Tomatoes contain lycopene, a form of antioxidant. Antioxidants havebeen hailed for their ability to neutralize free radicals, which arelinked to ageing, stroke and heart disease.
"If you have fresh tomatoes, they have a total antioxidant potential ofabout 80," explains Dr Catherine Collins, a dietician at St George'sHealthcare NHS Trust.
"But if you boil or can them the antioxidant potential goes up five or six-fold."
"This happens because the lycopene in the raw tomato has beentransformed to trans-lycopene in the cooked version, and trans-lycopeneis much more readily absorbed."
Likewise, says Dr Collins, cooking carrots makes the beta-carotene,another form of antioxidant, more available because you break down thecell wall with the cooking process.
Fat-loving
A nutrient's relationship with water and oil can also alter bioavailability.
Mr Faulks said: "To absorb fat-soluble nutrients, you have to get themout of the cellular structure, and then they have to be transferredinto lipophilic - or fat-loving - carriers in the gut to absorbed."
Lutein is one such nutrient. Present in spinach and other greenvegetables such as kale, broccoli and peas, some evidence suggests itcan protect or slow age-related macular degeneration, a leading causeof blindness.
"Lutein is actually absorbed more efficiently if it is eaten with alittle bit of fat, the oil helps it to hop onto to the fatty acids inthe gut and to be absorbed," said Dr Steer.
Mr Faulks believes bioavailability is a growing area, and somethingthat has the potential to impact on the health-food industry: "Once youbegin to understand and can manipulate how nutrients are delivered intothe body, it can help you to tailor a product that can deliver certainattributes."
However, says Dr Steer, it is a complex field, especially because different nutrients interact in different ways.
"For a long time breakfast cereals have been fortified with added iron.But they also contain phytates - a form of energy store - which arepresent in whole-grain cereals, and these actually inhibit theabsorption of iron.
"And calcium in dairy products can also inhibit iron absorption. So youhave your cereal with iron and phytates, but then you pour on your milkthat will also contribute to inhibition of the absorption of iron. Itcan get very complicated."
Jigsaw puzzle
According to researchers, there are pros and cons of combining food in this way.
By cooking tomatoes to gain antioxidants, vitamin C is degraded. Byadding fats to green vegetables, your cholesterol intake is boosted.
And, experts add, more is not always best. High intake of some vitamins and minerals has been associated with risks.
But, says Dr Steer, the more we understand about how the body absorbsnutrients, the better the dietary recommendations we can make.
"It is all about understanding how these nutrients are absorbed in thebody, and how much of them we need to reduce or even prevent certaindiseases while avoiding any adverse symptoms.
"Understanding bioavailability it is really part of the jigsaw of understanding optimum nutrition."
FOOD PREPARATIONS AND THEIR BENEFITS
Food
Nutrient
Benefit
Why it works
Spinach and orange juice
Iron
Helps prevent anaemia, energy loss, infections
Juice turns iron into more easily absorbed form
Canned or cooked tomatoes
Lycopene
Antioxidant thought to halt cell damage
Lycopene turned into more readily absorbed form
Cooked rather than raw carrots
Beta-carotene
Antioxidant
Cooking breaks down cell wall allowing easier absorption
Leafy vegetables dressed in oil
Lutein
May prevent eye disease
Lutein is fat-soluble, so oil aids absorption
Once you can manipulate how nutrients are delivered into the body,it can help you to tailor a product that can deliver certain attributes-- Richard Faulks
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/4777607.stm
Published: 2006/08/29 07:05:01 GMT
© BBC MMVI
