March 27, 2017 1238 GMT
And millions of older people could be putting their health at risk by ignoring the fact they are losing weight without trying, express.co.uk reported.
In a survey of 855 people aged 60 or over, 36 percent thought it was fine to lose weight with age, with three-quarters never having worried about doing so.
But the researchers said getting thinner can be an early warning sign of malnutrition or other serious conditions, such as cancer, dementia and liver disease.
Signs and symptoms of malnutrition include tiredness, low energy levels, dizziness and repeated infections.
The survey was carried out by the Malnutrition Task Force, an independent group of experts from the health, social care and local government sectors.
Leading the task force, Lesley Carter said: “We wrongly assume that malnutrition and dehydration belong to the past.
“But the reality is that poor nutrition and hydration are often not recognized by older people, families or healthcare professionals.
“The risk of becoming undernourished increases significantly as people age and it is further complicated by the incorrect assumption within society that losing weight is a normal part of the aging process. In fact it should raise alarm bells.
“We all know that obesity causes serious health problems but there are also serious health consequences for older people who are at the other end of the scale and don’t eat enough.
“Many may ignore the warning signs — rings may fall off, dentures could become loose or clothes become too baggy.
“Some people may start to find it hard to stand or carry objects, making preparing meals more difficult, or some may just show a general lack of appetite.
“Even the need to tighten your belt can be a clear indication that you’re not eating enough.”
One in 10 people over the age of 65 are thought to be malnourished or at risk. Those most at risk have lost their appetite, often because they are lonely or have had to cope with the death of a loved one.
Malnourished people are also twice as likely to visit a GP and end up in hospital more often.
The task force advises anyone who is struggling with appetite loss to eat smaller, more frequent meals, and to try milky drinks, milky puddings, cakes and full-fat foods.