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Functional nutrition: the role of food in disease prevention and management

Woman with dark hair smiling
9 min read
AUTHOR: Anna Turns
woman's abdomen with fruits and vegetables

Few cookbooks begin with a health warning. The pages often start with an evocative introduction about when the author first learnt to cook or discovered a new hero ingredient, surrounded by deliciously-composed photos, perhaps of vibrantly coloured dishes on a rustic table.

But in his foreword of The Diabetes Weight-Loss Cookbook by Katie and Giancarlo Caldesi, Dr David Unwin writes: I believe we have eaten our way into this epidemic of diabetes and obesity and that we can eat our way out of it.” Aside from great recipes, it’s a fascinating read – about personal connection to food, positive behaviour change and the management of blood sugar levels through diet. Unwin, who has worked as a GP since 1986, aims to empower people to take control of their health by changing what they eat. And for good reason.

The link between diet and diabetes

For certain conditions like type 2 diabetes, diet can influence the ‘disease burden’, or level of impact on a person’s health. Diet can also play an instrumental role in disease remission. As Duane Mellor, Registered Dietitian and Senior Lecturer at Aston University, explains, “For some people, [changing diet] is a way of reversing the physiology to bring the glucose under control [in the case of those susceptible to type 2 diabetes].”

The Norfolk Diabetes Prevention Study found that, for people with pre-diabetes, losing just a few kilograms in weight and sustaining small lifestyle changes that included a healthy diet and regular physical activity for two years, reduced their risk of developing type 2 diabetes by up to 47%.

Unwin, an advocate for low-carb diets, has run studies that have demonstrated the reversal of diabetes in a number of his patients, while a 2014 study by the Second University of Naples showed that a low-carb Mediterranean diet (including oily fish, colourful fruit and vegetables, and olive oil) increases the rates of remission in people with type 2 diabetes. After one year of following the diet, 15% of participants achieved remission and, after six years, the percentage was 5%. At a population level, this is enormously significant because, according the charity Diabetes UK, some five million Brits are diabetic, with a further 13.6 million now at increased risk of type 2 diabetes nationally.

Prevention is better than cure

“In many conditions, you are working with someone’s medical issue to optimise their quality of life and health, so diet is a very powerful tool but not a direct, curative tool,” according to Mellor. “It’s a way of manoeuvring the situation to maximise health in people with a clinical condition.”

He explains that a varied, simple and healthy diet has a big role in reducing risk of disease: “Multiple sites of cancer are associated with dietary risk factors and other lifestyle risk factors, including higher body weight. Colon cancer links to exercise [studies have shown that those who do regular physical activities have a lower chance of developing this type of cancer] and Mediterranean diets are associated with a lower risk of cardiovascular disease.” In fact, the in-depth Lyon Diet Heart Study, carried out during the 1990s, outlined how a Mediterranean-type diet drastically cut the risk of a second heart attack.

“Reducing risk of heart disease involves lowering cholesterol and blood pressure – you can take a tablet for that,” says Mellor. “Diet is not as powerful at pushing any one of those risk buttons, but it pushes across so many different buttons, it will reduce your risk of other things as well.” So it’s about taking a holistic view, finding ways to enjoy eating a variety of healthier foods and sustaining those habits.

Immunity starts in the gut

The gut contains more than 70% of your immune cells. Registered Dietitian Lucy Kerrison explains that the trillions of bacteria within your gut microbiome affect your body’s response to disease. “The gut microbiome is part of our immune system … and your gut bacteria can rapidly change, depending on the foods you are eating, within just a few weeks,” she says, adding that the diversity and health of your gut microbiome also depends on non-food factors such as sleep and exercise. The gut acts as a barrier to pathogens that may cause infectious disease: “If you have a slightly more robust gut and a more diverse set of gut bacteria, that can strengthen the gut walls, she adds. “There’s something called ‘leaky gut’ that’s potentially linked to poor gut health, poor diet or an untreated medical condition, whereby the cells in your gut lining become slightly more leaky and you’re more likely to get pathogens entering.”

“Multiple sites of cancer are associated with dietary risk factors and other lifestyle risk factors, including higher body weight.

Duane Mellor, Registered Dietitian and Senior Lecturer at Aston University

The gut links to hormonal health, too: “Your gut bacteria change during perimenopause and menopause to a less diverse set so your risk of cardiovascular disease goes up, the way that you retain weight goes up and your metabolism changes too,” explains Kerrison, who works with clients experiencing chronic conditions including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), an autoimmune condition.

“My work often involves looking at symptom management and then improving gut health and gut bacteria,” she adds. “In IBD essentially the gut is attacking its own tissue, and the flares happen for different reasons so it’s impossible to tie them down to particular foods.” She highlights that there is some evidence that probiotics can help ulcerative colitis, a form of IBD, and she adapts advice depending on where the gut is damaged. If the flare is in the lower gut, she might recommend a lower fibre diet, for example. “Once that condition is in remission, usually with medication, then we’d look at expanding the diet, improving gut bacteria, working towards an anti-inflammatory diet, introducing more omega 3s, fewer omega 6s and improving gut health.”

Kerrison adds that clients with IBS won’t be able to tolerate all the foods that she’d love to add in to improve their gut health. “So it’s about working towards a diet that suits them and optimises as much as possible within their personal limits, and that might look slightly different for every person.”

Improving gut health with food

When Kerrison first considers improving gut health, she looks at the diversity of plant-based foods. “We know that diversity of plant-based products is really important, so if you are eating more than 30 plant-based products a week, which isn’t just fruit and vegetables but also beans and pulses, nuts and seeds, herbs and spices, you’ll have a more diverse set of gut bacteria than those eating less than 10,” she says. “That diversity is key in terms of improving your gut health generally, but also that is linked to your immune health and chronic conditions such as diabetes and cardiovascular disease.” Essentially, many plant-based fibres (e.g. garlic, onion, pulses, stone fruits) contain prebiotics that feed the gut good bacteria, and Kerrison also suggests adding in fermented foods such as kefir and kombucha to help those healthy bacteria grow in your gut.

“Exercise can independently change your gut microbiome and make it more diverse. We know that good sleep and keeping low levels of stress can improve diversity of gut bacteria.”Put simply, across the food system sustainability data is missing. Literally. This puts trillions of investment dollars at risk. It prevents consumers from their human right under the Aarhus Convention to participate in environmental justice – because they have no credible data or information to work with.”

Lucy Kerrison, Registered Dietitian

Another important dietary factor is the total level of fibre. Government guidelines recommend 30g of fibre per day, but Kerrison explains that “If we’re looking at chronic diseases and prevention, we know that you can gain even more benefit for aiming for a slightly higher fibre diet, more like 50g fibre per day. With diabetes, a higher fibre diet means your absorption of carbs is a little steadier, so you’re less likely to get those spikes in drops in blood glucose levels, [plus] your gut bacteria play a role in blood sugar control too.” For a pre-diabetic client, Kerrison would look at the order of the foods they are eating: “Having veggies first, then protein, then carbs within a meal, means they’ll be absorbing fibre and protein first – that slows down carb absorption [reducing] those spikes and dips in blood sugar levels.”

Kerrison also takes non-diet factors into consideration: “Exercise can independently change your gut microbiome and make it more diverse. We know that good sleep and keeping low levels of stress can improve diversity of gut bacteria.”

The link between gut and liver

There’s also a strong link between the gut and the liver, an organ that acts as the body’s metabolic hub. “Your liver is where you store your glucose. It’s involved in your circadian rhythm and bile acid release, which helps digest fats, so it’s really involved with digestion,” says Kerrison. Some of her clients have a fatty liver or might be moving towards the stages of longer-term liver disease or cirrhosis. “If I was seeing a client for fatty liver, the first steps would be to look at an overall balanced diet, the types of fat, then the types of carbohydrates – looking to wholegrain carbohydrates – then we’d look at diversifying your diet in terms of gut health. So looking at fats, then types of carbs, then improving overall gut health.” Because fat adaptation is important, she’d aim to increase omega 3s (oily fish, olive oil, nuts and seeds) and reduce omega 6s (vegetable oils, coconut oils, saturated animal fats) to help the liver and the gut. “Omega 3s and oily fish are also prebiotic so they feed your gut bacteria too.”

Food as medicine?

Of course, food is never a replacement for professional medical advice or prescribed drugs, and registered dietitians always adapt any recommendations on a case-by-case basis, taking any contraindications into account. “For every chronic condition, the advice differs, and then it would be slightly different depending on that person,” summarises Kerrison.

To complicate matters, gene expression can change depending on environmental circumstances through what’s known as ‘epigenetics’. Scientists are still unravelling exactly how genetic makeup influences susceptibility to disease, and how nutrition might interact that. “We’re not yet clear about how adult genes are switched on and off in various cell types because that’s complicated to measure,” says Duane Mellor.

Over the course of a lifetime, the food that we eat impacts our susceptibility to certain conditions and infectious diseases and healthy-eating patterns have multiple positive impacts, some of which go beyond the nutrients. As Mellor summarises, focusing on single superfoods is never a good idea, it’s about looking at a person’s whole dietary pattern and social connectivity is also really important in terms of disease prevention. “It’s not just the food on the plate, it’s how you interact over it,” he concludes.


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