While most malnourished people have an underlying medical condition, experts say the poor state of the average British diet - often high in fat, salt and calories, but low on essential vitamins and minerals _ means there are increasing numbers of people with nutritional deficiencies who may otherwise appear normal.
The Department of Health says at least 2 million Britons are likely to be malnourished. Many nutrition experts put the figure as high as 4 million, about 6 percent of Britain's population.
According to hospital admissions figures collected by the Department of Health from the past decade, up to half of all in-patients had some symptoms of malnutrition and a quarter were recognized as being malnourished.
No statistics are collected on how many obese people may be malnourished, but doctors say they are seeing more malnourished patients in hospitals, including those who are overweight. According to government statistics, 22 percent of Britons are obese and 75 percent are overweight.
"You can't always tell if a person is malnourished with your eyes," said Dr. Marinos Elia, a professor of clinical nutrition and metabolism at Southampton University. "People may be eating too much food, but they may not be eating enough fruits and vegetables."
Dr. Alastair McKinlay, a gastroenterologist and chairman of a British malnutrition action group, put it bluntly: "There's a widely held misconception that if you're fat, you can't be malnourished."
Some experts even contend that the food rationing system implemented during World War II offered Britons more nutritious food than what they're eating today. From 1939 to 1945, Britons received books of coupons, which they traded in for limited quantities of foods including flour, milk, eggs, meat, and canned fruit.
"Rationing was a huge success because it ensured that if you got your alloted amounts, you got a nutritionally reasonable diet," said Dr. Colin Waine, chairman of the National Obesity Forum. "I'm not advocating a return to rationing, but it was a more balanced diet back then."
Despite the unlimited food supply in Britain today, Waine said people don't always make the right choices.
"Under the rationing system, people got the right nutrients in the right amounts," he said. "That isn't always the case today."
In the last five years, according to the Department of Health, the number of hospital-identified malnourished patients has risen by more than 40 percent, though experts say this is largely due to heightened surveillance rather than to a dramatic jump in incidence.
While malnourished fat people are hardly in danger of starvation, other health problems are possible, in addition to the usual complications that accompany obesity, like diabetes or heart disease. Once they start losing weight, malnourished patients may actually burn through their own tissue, including muscle, rather than their fat. They may also retain water as their body burns through its lean body mass, thus providing no clues to their doctors that they actually lack certain vitamins and minerals.
Usually, people with vitamin deficiencies have skin problems, a swollen thyroid, or bleeding gums. In severe cases, malnourished people might also experience hair loss, muscle wasting, a swollen abdomen, anemia or rickets. The majority of malnutrition cases are people suffering from chronic illnesses like AIDS, cancer or tuberculosis.
In a country where it's more typical for people to be over rather than under-nourished, experts say malnutrition in Britain is rarely noticed. "You've got to have pretty severe deficiencies before this is picked up," said Waine. "But I think a lot of people are on the borderline."
Part of the blame goes to the rise of prepared and fast foods, most of which contain only trace amounts of healthy nutrients. And despite a campaign by celebrity chef Jamie Oliver to introduce nutritious food across Britain's schools, authorities recently decided to bring back foods like hamburgers, sausages and meat pies to school cafeterias, ruling that the manufactured meats could be served four times every two weeks.
The national diet is in such trouble that earlier this month, the United Kingdom's Food Standards Agency recommended that folic acid be added to the nation's flour, to compensate for the lack of folate in the population's eating habits.
Recent surveys estimate that less than 20 percent of adults eat the recommended five daily portions of fruits and vegetables. "People never think that malnutrition occurs in a place like the United Kingdom," said McKinlay. "But just because people are eating lots of food doesn't mean they're eating enough nutrients."