Nutrition, ageing and the gut microbiota

Research at King’s and beyond has shown that frailty – reduced resilience to bounce back after illness, an accident or stress that progresses more rapidly with age – is associated with a decrease in gut microbiota diversity. There are also specific microbial species in the gut that increase in abundance with frailty, and some that decrease.

If there are specific gut microbiota markers of frailty, could they be a target for interventions to increase health span in older people?

Looking to answer this question is Dr Mary Ni Lochlainn, NIHR Clinical Lecturer based in the Department of Twin Research and Genetic Epidemiology at King’s, and Specialist Registrar in Geriatric, Stroke, and General Internal Medicine at Guy’s and St Thomas’ Hospital. Her research focuses on the gut microbiome and ageing, and she’s particularly interested in how we can target the gut microbiome to improve age-related illness.

Meeting our nutritional needs as we age

One of the biggest ways we can influence the composition of our gut microbiota is through our diet. Probiotics (beneficial bacteria) and prebiotics (food for those bacteria), which we can get through our diet or supplementation, play an important role in our microbiota diversity, gut health and how well we process the food we eat.

Although nutrition has a significant influence on our health throughout life, there are specific factors that may influence the ability of older people to meet their nutritional needs and keep their gut microbiota healthy.

“It’s quite common for older people to have a reduced appetite. They also have slower gastric emptying, meaning that they feel full quicker. This makes it difficult for older adults to get sufficient nutrient intake,” explains Mary.

“There are also other factors that influence the ability of older people to meet their nutritional needs. For example, social isolation might mean that older people are less likely to eat good, nutritional meals. Painful teeth or ill-fitting dentures might make eating difficult, or people might be on medications for age-related conditions that cause reflux or nausea.”

A lot of evidence points towards a Mediterranean-style diet being associated with longer lifespan and healthier ageing. But in terms of specific nutritional components, Mary says that protein and vitamin D are particularly important considerations for older people. As is recommended for all adults in the UK, Mary advises that all older people should be taking supplemental vitamin D in the winter months. With regards to protein, as we get older, our bodies become less effective at harnessing the protein from our food to build and maintain muscle, in a process known as anabolic resistance.

“For most adults, guidance says that we need around 0.75g of protein per kilo of our body weight per day. But the guidance actually changes for older people to 1-1.3g per kilo of body weight per day, and a lot of people don’t know that,” says Mary.

Because older people lose muscle mass, resistance training to help maintain muscle is also important for staying healthy with age and, interestingly, Mary points out that the most successful nutritional intervention studies related to ageing tend to be those that are combined with exercise.

“If you’re looking to become healthier, switching your diet is likely to help. But what will help even more is combining that diet improvement with exercise improvement,” says Mary.

The gut-brain axis: insights from a study in older people

People often describe the gut as the second brain. That’s because the gastrointestinal (GI) tract is lined with what is known as the enteric nervous system, which works independently to our central nervous system and controls digestion. This second brain communicates with our actual brain, for example when you’re hungry or full up after a meal, or when you’re nervous and feel “butterflies” in your stomach.

This link between the gut and the brain was demonstrated earlier this year in a study by Mary and other King’s researchers. The team looked at 36 twin pairs (from TwinsUK, the UK’s largest adult twin registry based at King’s) over 60 years old and randomly assigned one of the twins to receive a placebo and the other a plant fibre supplement (a prebiotic).

After just 12 weeks, those who were taking the prebiotic performed better in memory tests used to assess brain function than those who were taking the placebo. The prebiotic led to significant changes in the participants' gut microbiome composition, including an increase in the numbers of beneficial bacteria.

“Why does giving someone a prebiotic improve their cognition? We have a hypothesis that it’s to do with the gut-brain axis, but we don't understand all the underlying mechanisms for that,” says Mary. "But having a healthier gut is also associated with reduced anxiety and depression, so these systems are all connected. The more we learn about these connections, the more likely we will be able to target them."

Although fibre supplements are safe to take and available to buy at health stores, Mary emphasises that this study alone isn’t enough evidence to definitively say that taking a fibre supplement will improve your cognition, but it will pave the way for larger studies to investigate this effect.

Looking to the future

Mary is now looking to expand her study of the fibre supplement in a larger group of healthy participants in the community, but she’s also interested in understanding how the fibre supplement could influence clinical populations. She would like to look at people undergoing orthopaedic surgery, such as a hip or knee replacement, and, because major operations can affect cognition, see if a fibre supplement could improve outcomes after surgery.

Beyond diet and nutrition, Mary is also hoping to find ways to target the gut microbiome to help older people experiencing gut symptoms as a result of heat stress.

“The gut is sensitive to heat stress,” says Mary. “Older people are much more susceptible and can become very ill because of this, and it’s one of the reasons why older people die disproportionately during heat waves.”

Mary and colleagues are exploring whether there could be ways to target the gut microbiome to increase resilience in the heat and help protect older people from becoming ill.

“We know that the gut microbiome is involved in so many different processes in the body that we’ve probably not paid that much attention to it in the past, so it’s still a huge area of learning,” says Mary. “It will be very exciting to see what the future holds.”

You can read about what Mary does to stay healthy as she ages here.