The reconciliation of these two so-called opposites is that low-calorie intake and very low weight aren't the same things. As anyone who is in their 60s or 70s and trying to lose weight can tell you....
People who are underweight in middle-age – or even on the low side of normal weight – run a significantly higher risk of dementia as they get older, according to new research that contradicts current thinking.
The results of the large study, involving health records from 2 million people in the UK, have surprised the authors and other experts. It has been wrongly claimed that obese people have a higher risk of dementia, say the authors from the London School of Hygiene and Tropical Medicine. In fact, the numbers appear to show that increased weight is protective.
At highest risk, says the study, are middle-aged people with a BMI [body mass index] lower than 20 – which includes many in the “normal weight” category, since underweight is usually classified as lower than a BMI of 18.5.
These people have a 34% higher chance of dementia as they age than those with a BMI of 20 to just below 25, which this study classes as healthy weight. The heavier people become, the more their risk declines. Very obese people, with a BMI over 40, were 29% less likely to get dementia 15 years later than those in the normal weight category.