Analysis: research shows how excess belly fat may have negative consequences for brain health in older adults

By Eamon Laird, TCD

Obesity is a modern day problem affecting all parts of the world's population from children to teenagers to older adults. This is of particular concern for Ireland, as over half of our over 50s are classified as centrally obese (having a high waist to hip ratio), with only 16 percent of men and 26 percent of women having a normal body mass index (BMI).

Traditionally, the concern with obesity has always been around cardiovascular disease, heart health, diabetes and joint health. However, one element often forgotten by both the public and professionals is the potential adverse effects for brain health and the risk of future disease.

Previous work by other researchers have observed that people aged 19 to 65 years who were overweight performed worse on tests of memory, visuospatial ability and executive function compared with those who were normal-weight. Furthermore, in a 27-year follow-up population study, it was reported that obesity in middle age increased the risk of future dementia independently of other pre-existing conditions. However, not much is known how this relationship continues as we age. Does it still happen in those 60 years and older?

From RTÉ Nine News, a report on global obesity trends which show that almost 25 percent of the world's population will be obese by 2045

In our research, we investigated over 4,000 older adults from the Trinity Ulster University and Department of Agriculture (TUDA) ageing cohort study. This was a large study of community-dwelling older Irish adults recruited between 2008 and 2012 from Dublin and Northern Ireland. It was designed to investigate nutrition, genes and health and lifestyle factors in the development of diseases of ageing (CVD, osteoporosis and dementia). We had a large number of tests and measures which included an in-depth battery of cognitive tests that tested memory, immediate recall, visual memory and cognitive thinking skills.

Interestingly, we found that having a bad waist to hip ratio (large amount of belly fat) was negatively associated with brain function regardless of age or other conditions or medications. Unexpectedly, a high body mass index (BMI) was found to be slightly protective. BMI cannot tell the difference between fat and fat-free mass (muscle) and having more muscle/better weight reserve could be an effective protection against loss of cognitive function.

The older overweight people who were healthy were muscular, not fat. And that’s a health advantage. A good example is to visualise an Irish rugby player. By BMI (standards), most of them would be obese, but they are mostly muscle and not fat. The opposite extreme would be, say, Santa Claus, who would have the same BMI as the rugby player, but is obviously mostly fat with a big waist belly.

From RTÉ Radio One's Morning Ireland, a report on how Ireland is becoming the fattest nation in Europe

Therefore people over age 60 with muscle and low fat may have both cognitive and metabolic advantages over someone of similar age who has belly fat or is even of normal weight. Our study wasn’t designed to answer why this would be the case, but we have evidence from other studies.

Some studies suggest that belly fat releases chemicals called pro-inflammatory cytokines that can cause inflammation in vital organs, including the brain. This can eventually cause tissue damage in the brain and may impair cognitive abilities.

Another cognitive price for belly fat is indirect. This will be surprising for the public to hear, but obese people can also be malnourished. While they often have an energy-rich diet, they could lack a number of vital vitamins and minerals, which could cause long-term organ and tissue damage, including in the brain.

With Christmas coming up we enjoy the holiday season with lots of tasty food and drink and there is nothing wrong with that. However, when reaching for that next mince pie or turkey sandwich, have a think and feel if you really are hungry and need it. You could be saving both your brain and waist line!

Dr Eamon Laird is a Nutritional researcher at the School of Medicine at Trinity College Dublin. His research involves investigating the links of nutrition with the diseases of ageing

The views expressed here are those of the author and do not represent or reflect the views of RTÉ